HEAVY LIFT INSTALLATION STUDY

OF

OFFSHORE STRUCTURES

LI LIANG (MS. Eng, NUS)

A THESIS SUBMITTED

FOR THE DEGREE OF MASTER OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

NATIOANL UNIVERSITY OF SINGAPORE

2004

ii

HEAVY LIFT INSTALLATION STUDY

OF

OFFSHORE STRUCTURES

LI LIANG (MS. Eng, NUS)

A THESIS SUBMITTED

FOR THE DEGREE OF MASTER OF ENGINEERING

DEPARTMENT OF CIVIL ENGINEERING

NATIOANL UNIVERSITY OF SINGAPORE

ACKNOWLEDGMENTS

The author would like to express his sincere appreciation to his supervisor Associate

Professor Choo Yoo Sang. The author is deeply indebted to his most valuable guidance,

constructive criticism and kind understanding. Appreciation is extended to Associate

Professor Richard Liew and Dr. Ju Feng for their assistance and encouragement.

In addition, the author would like to thank the National University of Singapore for

offering the opportunity for this research project.

Finally, the author is grateful to his family, the one he loves, and all his friends, whose

encouragement, love and friendship have always been the major motivation for his study.

i

TABLE OF CONTENTS

CHAPTER 1 INTRODUCTION ...................................................................................... 1 1.1 Background 1.2 Objectives and Scope of Present Study 1.3 Organisation of Thesis

CHAPTER 2 REVIEW OF LIFTING DESIGN CRITERIA.......................................... 10 2.1 Review of Various Lifting Criteria 2.2 Practical Considerations for Standard Rigging Design

2.2.1 Sling Design Loads (SDL) 2.2.2 Shackle Design Loads 2.2.3 Lift Point Design Loads 2.2.4 Shackle Sizing 2.2.5 Tilt during Lifting 2.2.6 COG Shift Factor

2.3 Summary CHAPTER 3 HEAVY LIFTING EQUIPMENT AND COMPONENTS....................... 24

3.1 Introduction 3.2 Heavy Lift Cranes 3.2.1 Crane Vessel Types 3.2.2 Frequently Used Crane Vessels 3.3 Heavy Lift Shackles 3.4 Heavy Lift Slings 3.4.1 Sling properties 3.4.2 Grommets versus Slings 3.4.3 Sling and Grommet Properties 3.5 Lift Points 3.6 Summary

CHAPTER 4 RIGGING THEORY AND FORMULATION ......................................... 57

4.1 Introduction 4.2 Rigging Sling System with Four Lift Points 4.2.1 Using Main or Jib Hook without Spreader Structure 4.2.2 Using Main or Jib Hook with Spreader Structure 4.2.3 Using Main and Jib Hooks at the Same Time 4.3 Rigging Sling System with Six Lift Points 4.3.1 Using Main or Jib Hook with Spreader Frame 4.3.2 Using Main and Jib Hooks without Spreader Structure 4.4 Rigging Sling System with Eight Lift Points 4.4.1 Using Main or Jib Hook with/without Spreader Structure 4.4.2 Using Main and Jib Hooks without Spreader Structure 4.5 Summary

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CHAPTER 5 JACKET LIFTING.................................................................................... 78 5.1 Introduction 5.2 Vertical Lift of Jackets 5.3 Horizontal Lift of Jackets 5.4 Summary

CHAPTER 6 MODULE LIFTING.................................................................................. 88

6.1 Introduction 6.2 Vertical Module Lift and Installation 6.3 Deck Panel Flip-Over 6.4 Summary

CHAPTER 7 FPSO STRUCTURE LIFTING............................................................... 102

7.1 Introduction 7.2 Lift Procedures and Considerations for FPSO Modules 7.3 Rigging Systems with Multiple Spreader Bars 7.4 Lifting of Lower Turret 7.5 Lifting of Gas Recompression Module 7.6 Lifting of Flare Tower 7.7 Summary

CHAPTER 8 SPECIAL LIFTING FRAME DESIGN .................................................. 121

8.1 General Discussion 8.2 Effect of the Shift of the Centre of Gravity 8.3 Lift Point Forces 8.4 Padeye Checking 8.5 Trunnion Checking 8.6 Summary

CHAPTER 9 FINITE ELEMET ANALYSIS FOR LIFTING DESIGN ....................... 139 9.1 Introduction 9.2 Finite Element Analysis for Module Lifts

9.2.1 Structural and Material Details 9.2.2 Finite Element Modelling and Analysis 9.2.3 Discussions

9.3 Finite Element Analysis for Lifting Padeye Connection 9.3.1 Structural Details 9.3.2 Loading Cases 9.3.3 Finite Element Modelling 9.3.4 Result Analysis

9.4 Summary CHAPTER 10 CONCLUSIONS AND FUTURE WORKS.......................................... 170

10.1 Conclusions 10.2 Recommendation for Future Work

BIOBLIOGRAPHY ....................................................................................................... 174 APPENDIX A FEM ANALYSIS FOR JACKET UPENDING PADEYE.................... 181

iii

Summary Successful lift installations of heavy offshore structures require comprehensive and

detailed studies involving many engineering and geometrical constraints including

geometric configuration of the structure, its weight and centre of gravity, member

strength, rigging details, lifting crane vessel and other construction constraints. These

constraints need to be resolved efficiently in order to arrive at a cost-effective solution.

This thesis summarises the results of detailed investigations by the author involving

actual offshore engineering projects. The thesis first reviews the lift criteria adopted in

the offshore industry. The key practical considerations for selection of appropriate

crane barges, rigging components are discussed. The algorithms and formulations for

rigging systems with various number of lift points are then presented.

Practical considerations for module and jacket lifts are investigated. For deck panel

flip-over operation, the force distribution between two hooks which varies with

changing module inclined angle, is calculated consistently. Lifting procedures and

rigging systems with multiple spreader bars for Floating Production Storage &

Offloading (FPSO) modules are also studied. Emphasis is given to the design and

analysis of lifting unique components to meet the stringent installation requirements.

The thesis is reports on a versatile spreader frame design which incorporates a

combination of padeye and lifting trunnions. Detailed finite element modelling and

analysis are conducted to analyze the lifting module and padeye connection. It is found

that finite element analysis can provide important detailed stress distributions and

limits for safety verification of lift components.

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Nomenclature/Abbreviation

A - Cross Sectional Area

AISC - American Institute Steel Construction

API - American Petroleum Institute

CoG - Centre of Gravity

CRBL - Calculated Rope Breaking Load

CGBL - Calculated Grommet Breaking Load

D - Pin Hole Diameter of Padeye

DAF - Dynamic Amplification Factors

DB - Derrick crane Barge

Dh - Pin Diameter of Shackle

DNV - Det Norske Veritas

E - Modulus of elasticity of Steel

Eb - the sling bend efficiency (reduction) factor

Et - Efficiency of termination method

FEM - Finite Element Method

FEA - Finite Element Analysis

FPSO - Floating Production Storage and Offloading

Fb - Allowable bending stress

Ft - Allowable Tensile stress

Fy - Material Yield stress

Fu - Steel Tensile strength

Fv - Allowable shear Stress

G - Shear Modulus of elasticity of Steel

v

H4 - height of hook block above module (without spreader structure), or

height of spreader above module (with spreader)

H5 - height of hook block above spreader (with spreader), or,

=0 (without spreader)

HSE - Health and Safety Executive

Ix, Iy - Moment of Inertia

Lh - Inside Length of Shackle

Li - length of ith sling

MBL - Minimum Breaking Load

MWS - Marine Warranty Surveyor

Rai - ith Cheek plate Radius of Padeye

Rm - Main plate Radius of Padeye

SACS - Structural Analysis Computer System

SDL - Sling Design Load

SSCVs - Semi-Submersible Crane Vessels

Sx, Sy - Sectional Modulars

SWL - Safe Working Load

T - Static Sling Load

Tci - ith Cheek plate thichness of Padeye

Th - Crane Hook Load

Tm - Main plate thichness of Padeye

Wh - Jaw width of shackle

Wh, Lh - the width and length of hook block

Wm, Lm, Hm - the width, length and height of module, respectively

Wsp, Lsp - width and length of spreader

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WLL - Shackle Working Load Limit

d - Sling rope diameter

fb - Actual bending stress

fc - Actual Combined stress

fcog - COG shift factor

ft - Actual Tensile stress

fv - Actual shear Stress

xc, yc - location of the centre of gravity of module in local coordinate system

θi - angle of sling with respect to the horizontal plane

τg - Punching strength

vii

List of Tables

Table 2.1 Lifting Criteria comparison - Single Crane Lift

Table 2.2 Lifting Criteria comparison - Double hook Lift

Table 2.3 Dynamic Amplification Factors

Table 3.1 Some of Heavy Lifting Crane Vessels in the World

Table 3.2 Shackle Side Loading Reduction For Screw Pin and Safety Shackles Only

Table 4.1 Formulations for rigging configurations with four lift points (using main or jib hook block without spreader)

Table 4.2 Formulations for rigging configurations with four lift points (using main or jib hook block with spreader structure)

Table 4.3 Formulations for rigging configurations with four lift points (using main and jib hook blocks at the same time )

Table 4.4 Formulations for rigging configurations with six lift points (using main or jib hook block )

Table 4.5 Formulations for rigging configurations with six lift points (using main and jib hook blocks at the same time)

Table 4.6 Formulations for the rigging configurations with eight lift points (using main or jib hook block at a time )

Table 4.7 Formulations for rigging configurations with eight lift points (using main and jib hook blocks at the same time )

Table 7.1 Lifting Operation Summary for Laminaria FPSO

Table 7.2 Contingency Actions Plan / Procedure

Table 7.3 Preparation Check List

Table 7.4 Loadout Check List

Table 7.5 Installation Check List

Table 8.1 Weight and COG data

Table 8.2 Total Weight and COG

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Table 8.3 Member Analysis Result Summary

Table 9.1 Load factor used for lifting analysis

Table 9.2 Design value of material parameter

Table 9.3 Sample of Member Group Properties

Table 9.4 Sample of SACS Section Properties

Table 9.5 Sample of SACS Plate Group Properties

Table 9.6 Sample of SACS Plate Stiffener Properties

Table 9.7 SACS Loading Summary

Table 9.8 Sample of SACS Loading ID and Description Table 9.9 Type of Support Constraints and Member Releases Table 9.10 SACS Load Combinations Table 9.11 Sample of 75% Lifting Weight Factor Table 9.12 SACS Combined Load Summation Table 9.13 Support Reactions Table 9.14 Spring Reaction Table 9.15 Sample of SACS Member Stress Listing Table 9.16 Joint Stress Ratio Listing Table 9.17 Sling Force Summary Table 9.18 Dimensions and length of each tubular member

Table 9.19 Maximum stress (MPa) of each case

Table 9.20 Maximum stress (MPa) for braces

Table A.1 Member forces coming out from SACS analysis

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List of Figures

Figure 1.1 Thesis Organizations Vs Contents of Study

Figure 2.1 Centre of gravity (COG) shift

Figure 3.1 Lifting Equipment and Components

Figure 3.2 Saipem S7000 SSCV 14000 ton Capacity

Figure 3.3 Sheerleg Crane Vessel – Asian Hercules II : 3200 ton Capacity

Figure 3.4 Derrick Barge Crane – Thialf : 14200 ton Capacity

Figure 3.5 Derrick Lifting Barge DB101: 3150 ton Capacity

Figure 3.6 Samples of Some Shackles (Green Pin and Crosby)

Figure 3.7 Sling Forming & Cross Section

Figure 3.8 Sling Configuration

Figure 3.9 Actual usage of Slings

Figure 3.10 Lift point connections- Padeye and Trunnion

Figure 3.11 Fabricated Lifting Padeye

Figure 3.12 Actual fabricated Lifting Trunnion

Figure 3.13 Details of a Typical Padeye

Figure 4.1 Determination of rigging configuration: tasks, inputs and outputs

Figure 4.2 Rigging configuration for four-lift-point sling systems - using main or jib hook block without spreader

Figure 4.3 Rigging configurations for four-lift-point sling systems - using main or jib hook block and spreaders

Figure 4.4a Rigging configuration for four-lift-point sling systems - using main and jib hook blocks and spreader bars

Figure 4.4b Hook load distribution for four-lift-point sling systems - using both main and jib hook blocks

Figure 4.5a Rigging configuration for six-lift-point sling system - using main or jib hook block with spreader frame

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Figure 4.5b Sling tensions for six-lift-point sling system - using main or jib hook block with spreader frame

Figure 4.6a Rigging configuration for six-lift-point sling system - using both main and jib hook blocks

Figure 4.6b Hook load distribution for six-lift-point sling systems - using both main and jib hook blocks

Figure 4.7a Rigging configuration for eight-lift-point sling system - using main or jib hook block without spreader frame

Figure 4.7b Rigging configuration for eight-lift-point sling system - using main or jib hook block with two parallel spreader bars

Figure 4.7c Rigging configuration for eight-lift-point sling system - using main or jib hook block with spreader frame

Figure 4.8a Rigging configuration for eight-lift-point sling system - using both main and jib hook blocks

Figure 4.8b Hook load distribution for eight-lift-point sling systems - using both main and jib hook blocks

Figure 5.1 Vertical Lifting of Jacket

Figure 5.2a Horizontal Lifting of Jacket Loadout operation at Fabrication Yard (2800ton)

Figure 5.2b Horizontal Lifting of Jacket

Dual Crane Lifting a Tripod Jacket (6200 ton) Figure 5.2c Horizontal Lifting of Jacket

Dual lift of a Jacket from transportation barge Figure 5.3 ISO View of lifting horizontal Jacket (3150ton) Figure 6.1 Deck Panel Stacking in progress

Figure 6.2 Computer Model for Deck Panel Flip-over

Figure 6.3 Deck Panel – 180 Degree Flip Over

Figure 6.4 Module Lifting – Four Sling Arrangement

Figure 6.5 Module Installation – One Lifting Bar Arrangement

Figure 6.6 Module Lifting – Two Bars System

Figure 6.7 Module Lifting – Three Bars System

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Figure 6.8 Lifting with a spreader frame

Figure 6.9 Multi-Tier Rigging System

Figure 6.10 Tendem Lift of a Module

Figure 7.1 Rigging arrangement for lifting FPSO modules with spreader bars

Figure 7.2 Lifting of Lower Turret (680 ton)

Figure 7.3 Lifting of Upper Turret - Manifold Deck Structure with Three Spreader Bars

Figure 7.4 Lifting of Upper Turret – Gantry Structure

Figure 7.5 Lifting of Swivel Stack – Bottom Assembly

Figure 7.6 Lifting of Gas Recompression Module

Figure 7.7 Upending and Lifting of 92-metre Flare Tower

Figure 8.1 Lifting Frame Details Figure 9.1 Computer Lifting Model Plot

Figure 9.2 COG Shift of Module during Lifting Figure 9.3 Jacket Loadout arrangement Figure 9.4 Upending process of Jacket

Figure 9.5 Jacket positions for the four load cases

Figure 9.6 Configuration of Joint 164

Figure 9.7 Boundary conditions for the FE model

Figure 9.8 Finite element mesh

Figure 9.9 1st-principal stress contour of load case D

Figure 9.10 Local view of Von Mises stress contour of load case D

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Figure A.1 Load conditions

Figure A.2 Stress distribution for the braces of load case A

Figure A.3 Stress distribution for the braces of load case B

Figure A.4 Stress distribution for the braces of load case C

Figure A.5 Stress distribution for the braces of load case D

1

CHAPTER 1 INTRODUCTION

1.1 Background

Heavy lifts are frequently carried out during the fabrication and/or installation of major

offshore components and structures, such as welded girder beams, tubular columns,

deck panels, sub-assemblies, flares, bridges and completed jackets / modules. Without

heavy lifting equipment, offshore steel platforms cannot be built effectively.

For an offshore platform, the issue of final installation of the completed jacket /

topside is considered as early as the conceptual study stage. The major determining

factor is availability of heavy lift crane vessel around the region. Heavier structures

can be fabricated if a lager crane vessel is selected for the project. Many topside

structures are split into several modules instead of an integrated deck structure due to

non-availability of sufficient lifting capacity of heavy offshore crane barge in the

region or at required time window schedule.

Offshore hook-up and commissioning costs are very high as compared to those for the

same work performed onshore. This has led to the fabrication of very large modules,

where the intention is to minimize hook-up associated with connecting modules

together offshore.

The great advancement of offshore technology during the last 30 years was largely due

to the development of very heavy lift equipment. Thirty years ago, a 1000 ton module

would be considered a very heavy lift, while the biggest crane barge in the world at

that time could hardly lift 2000 tons at the required lifting radius. In South East Asia,

the biggest crane barge available in the region at the time was only around 600 tons.

2

Nowadays, a semi-submersible derrick barge can lift a structure up to 12,000 tons.

In the recent past, a 10,000 ton jacket in the North Sea would have to be launched.

Using present day equipment, the same jacket can now be lift-installed by a semi-

submersible crane barge which has two cranes. In most cases, lift-installed jacket is

more cost-effective. In South East Asia, jackets and decks are getting larger and

heavier, with the largest jacket to-date around 10,000 tons and the largest deck around

11,500 tons. Single lift installation can be a very attractive cost alternative. For

platform decommissioning or removal, it may be possible to use a crane barge to pick

up the old deck and old jacket. It may be appropriate to mention that the Offshore

Industry would not have developed to what it is today without all the heavy lift

equipment developed over the last 30 years.

For fabrication of offshore structures, the method which was first developed in the

United States more than 40 year ago is quite different from other industries. Offshore

structures are usually first fabricated in small units. After fabrication, these will be

moved to an open area for assembly. Offshore contractors tend to do as much work as

possible on the ground to minimize work in the air. This method is productivity driven.

In fabrication, one can do a much better and faster job on the ground and in a weather

protected workshop. This fabrication technique means that there are a lot of heavy

lifting operations in the yard as compared to typical onshore building construction.

Before all the sub-units are assembled, these may need to go through many lifting

operations, such as, roll up, stacking, flipping, etc. Each lift by itself could be more

than one thousand tons. In this type of fabrication technique, there are a lot of

3

opportunities for errors. Safety and accident prevention should thus be considered in

the design stage.

For offshore installation, major cost savings can be achieved if the structure can be

installed in one piece. For integration of topside modules, it can save significant

offshore hook-up time. For jacket, the cost of fabricating launch trusses can be

eliminated. A heavier lift requires a larger crane barge. It is a very high premium to

pay for the rental of a big derrick barge, especially if none is available in the area and it

has to be mobilized from elsewhere. A large capacity crane is an expensive equipment

and crane usage is normally considered as part of the overhead cost for fabrication

yards. Usually the cost is included in the fabrication tonnage rate. It will normally

involve fewer people to operate a crane onshore. For offshore installation, a crane

barge usually has only one big crane, except for larger semi-submersible derrick

barges which can accommodate two cranes side-by-side. When a derrick crane barge is

mobilized for an offshore installation project which includes hook-up and

commissioning, it will have 200 to 300 workers/engineers on board. The cost is

extremely high. Some of the semi-submersible derrick barges have accommodation

capacity for more than 700 men. In addition, the client will also need to pay for

mobilization and demobilization costs. Depending on location, these costs could be

millions of dollars. To design a structure to suit the installation contractor is certainly

an excellent way to minimise cost.

For a typical project, the offshore portion accounts for around 30% of the total project

cost. The question that comes to everyone's mind is how to reduce this number and be

more competitive. One of the solutions is to reduce offshore hook-up time. This means

4

that one should make the lift of a structure as heavy as possible and with few lifts as

necessary. However, one should be extremely careful in interpreting this statement.

The project may not be cheap if one has to mobilize a big derrick barge from far away

supply base. It could also be expensive if it requires two barges to do the lift and the

other barge has to be mobilized from elsewhere. Making a single heavy lift to

minimize hook up time or to eliminate the launch trusses is an excellent idea provided

we have the right equipment at a reasonable price and at the right time.

For FPSO module installation, there are normally 20 to 30 heavy lifts. The need to

design a common rigging system to suit different configurations, weights and centres

of gravity is a challenge to all designers. Since it is usually impossible to have a

common rigging system for all lifts, the designer needs to minimize the number of

rigging changes to reduce the schedule associated with heavy lifts for the planned

installation sequence.

5

1.2 Objectives and Scope of Present Study

As indicated in Section 1.1, heavy lifts in major offshore projects are required to be

conducted safely and cost-effectively. It is always a challenge for a structural design

engineer to produce an optimized design for both the lifted structure and lifting rigging

system for use with the selected crane barge that will lead to cost savings. The author

has been involved in some major offshore projects which required considerations for

alternative designs and detailed analysis for different structural schemes for heavy lift.

The author is thus motivated to investigate the inter-related engineering and fabrication

issues and to document the findings in this thesis.

The two key objectives of the research study are:

• Investigate lifting schemes which can provide cost-effective solutions and safe

operations for heavy lift installation of structures, and

• Evaluate selected rigging systems with different spreader and lift point

arrangements to provide guidelines for heavy lift design.

The scope of the present study can be summarized as follows:

• To study the current design codes for lift design and highlight key

considerations for heavy lift;

• To evaluate heavy lift rigging systems which involve different crane barges and

lifted structures with associated spreader arrangement and consistent lift point

combinations. Practical issues involved in actual projects, especially for lift

installation of jackets, offshore decks and modules for FPSO (Floating

Production Storage and Offloading) vessel will be investigated.

• To investigate global structural responses of lifted structures and detailed stress

6

conditions of the lift point through finite element analyses.

• To document the findings on heavy lift in the thesis for future reference by

designers and engineers.

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1.3 Organisation of Thesis

Figure 1.1 summarises the organisation and contents of the thesis.

Following the introduction, Chapter 1 and Chapter 2 provide a thorough review and

discussion of current design codes and standards used in heavy lift. The discussion

covers the codes and recommendations from API - RP2A (2000), DNV Marine

Operations Part 2 - Recommended Practice RP5 Lifting (1996), Phillips Petroleum

(1989), Heerema (1991), Noble Denton & Associates (NDA) (1996), Health and

Safety Executive (HSE) (1992) and Shell (1990).

Lifting equipment and components, including details on crane vessel/barge, slings,

shackles and lift points are discussed in Chapter 3. Lift points are the locations where

large sling tensions are transmitted to the lifted module structure. Lift points should be

properly selected to allow sling tensions to smoothly transfer to strong structural

members. Two common types of lift points which connect rigging systems to module

structures are padeyes and trunnions. With appropriate factored sling tensions, slings

and shackles can be selected from available sling and shackle lists (inventories) or

ordered from suppliers. It has always been the focus of the design codes to provide

consistent safety factors for the lift components within a rigging system for heavy lift.

An appropriate rigging system includes available lift points (strong points in the

module structure), available slings in inventory, spreader structure (bar or frame) and

hook block(s) of the crane barge. In actual rigging arrangement, the sling system can

involve four, six, eight or more lift points, and spreader bar or frame may be used to

8

protect the module from significant compressive forces or possible damage. Chapter 4

summarises the investigation into the algorithms and formulations to determine the

configurations of rigging sling systems, which are affected by the location of lift

points, length of slings and geometry of spreader and hook block. The hook block(s)

involved in a particular rigging system can be one (main or jib hook) or two (both

main and jib) at a time. Emphasis is placed on the determination of the critical

geometrical quantities of the rigging system including the sling angles with respect to

the horizontal plane and the distances between the module, spreader structure and hook

blocks. This chapter also serves as a theoretical basis of the following three chapters

which focus on practical issues in lift design of real projects, of which author was

involved as project manager or engineer.

Chapters 5, 6, and 7 discuss the practical considerations in lift design and operations

for jacket, modules and modules for FPSO (Floating Production Storage and

Offloading). A special design for a lifting frame is proposed and analyzed in Chapter

8.

Finite Element Analysis (FEA) is widely accepted in almost all engineering

disciplines. A finite element model can represent and analyse a detailed structural

component with greater precision than conventional simplified hand calculations. This

is because the actual shape, load and constraints, as well as material property can be

specified with much greater accuracy than that used in hand calculations. Chapter 9

discusses finite element approaches in heavy lift design and analysis. Two important

lift applications, for living quarter module lifting and padeye connection for heavy lift,

are investigated and reported in this chapter.

9

Finally, conclusions and general discussions are given in Chapter 10.

Structures to Be Lifted

Evaluation of Design Criteria

(Chapter 2)

Equipment Selection and Component Design (Chapter 3)

Rigging Theory and Formulations

(Chapter 4)

Theory and Knowledge

Scopes for Design and Analysis

Rigging System Lift Points Lift Operation

Jacket Lifting

(Chapter 5)

Module Lifting

(Chapter 6)

FPSO Structure Lifting

(Chapter 7)

Applications

Lifting Frame Design

(Chapter 8)

FEM Analysis for Lifting System

(Chapter 9)

Special Case Considerations

Figure 1.1 Thesis organization and contents of the thesis

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CHAPTER 2 LIFTING CRITERIA

2.1 Review of Various Lifting Criteria

There are several lifting criteria and specifications written specifically for offshore

heavy lift, including API-RP2A (2000), DNV Marine Operation Part 2 Recommended

Practice RP5 (1996), Phillips Petroleum (1989), Heerema (1991), Noble Denton &

Associates (NDA) (1996), Health and Safety Executive UK (HSE) (1992) and Shell

(1990). Amongst these criteria, some of these are either not updated or strictly for in-

house use. Only the API, DNV and HSE codes are easily available to the general

public. The API codes are the oldest and the most well established in the Offshore

Industry. The HSE recommendation deals with cable laid slings and grommets in

detail, but it does not address other lifting system or factors such as dynamic

amplification, weight growth, etc. This recommendation should be used in conjunction

with other codes. The DNV code is the most comprehensive and is widely used in the

North Sea.

For South-East Asia, the most commonly accepted criterion is still the API-RP2A

(2000) with a number of modifications to cater for weight inaccuracy etc. The original

lifting criterion in the API RP2A (2000) was written mostly by engineers working in

the Gulf of Mexico. The document was intended for those lifts performed in the area.

Over the years, the code expanded and received acceptance as a worldwide standard.

Although these criteria are written primarily for offshore lift, they can also be adopted

for onshore lift with minor modifications. In fact, this has been done for many years.

11

During the performance of the lift, there will be dynamic loads induced by the action

of the waves on the crane vessel and the cargo barge. These loads are conventionally

allowed for by the application of Dynamic Amplification Factors (DAF) to the static

load in the hooks and slings. Typical value of DAF, as used at present in relation to

Semi-Submersible Crane Vessels (SSCVs), is about 1.10 for slings in offshore

operations. This will be in addition to any quasi-static changes in the hook and sling

loads associated with the load transfer.

A second category of dynamic loads exists. This is associated with the action of

slewing the crane or of starting or stopping the hook as it is being raised or lowered.

These loads are normally allowed for in the specification of the safe working load

(SWL) of the crane. It should be recognized that the skill of the crane operator can

have a significant effect in reducing these forces. Also, but to a lesser extent, his

expertise will help to prevent the build-up of dynamic oscillations induced by the

waves.

Some extensive analyses of the dynamics of the lift have been carried out by using

SSCVs. In most cases, actual SSCV /module/ cargo barge combinations and rigging

geometries with predicted COG (Centre of Gravity) positions have been used. The

dynamic analyses drew attention to a number of interesting results as follows:

• It was found that increasing the barge draught tended to decrease the DAF in

short period sea states.

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• When the module was on the barge with the slings tensioned, there was a

spread of natural periods from 3-8 s. Hence, there were both significant

dynamic effects and considerable scatter in the results.

• The DAFs were generally worse in beam seas (i.e., beam onto the barge).

• The DAFs were less for the heavier modules.

• The sling load DAFs were in general larger than the hook load DAFs.

• The DAFs were quite low, while the module was freely suspended. There

would be some advantage in picking a module off the crane vessel's own deck

rather than off a cargo barge.

The distinction between beam and head sea DAF was sufficiently marked to allow

recommended DAFs for head seas to be significantly less than for beam seas.

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2.2 Practical Considerations for Standard Rigging Design

This section discusses the design requirements for the selection and design of heavy

lift rigging as given by Shell.

2.2.1. Sling Design Loads (SDL)

Standard 4 point Lifts for the Jacket or Deck

The sling design load (SDL) is based on the factored lift weight, with the individual

sling loads being determined from DNV Marine Operation, Part 2 Recommended

Practice RP5 Lifting. The procedure to be used is summarized below:

a) Distribute the lift weight to the lifting points, adopting the factored lift weight

based on the factors presented in the weight control engineering.

b) Increase each individual lifting point load by 10% to account for inaccuracy in

the calculation of the centre of gravity.

c) Further increase each individual lifting point load to account for the Dynamic

Amplification Factors given in “Cable Laid and grommets” Guidance Note PM

20, Health and Safety Executive - see Table 2.3.

d) Further increase each individual lifting point load by the skew load distribution

factor of 1.25 as recommended in DNV RP5, which primarily accounts for

different sling stiffness and lengths than theoretically assumed.

14

e) Calculate the sling load accounting for the angle the sling makes with the

horizontal, including allowance for component tilt. This sling angle should not

be below 55° at any point for level lifts.

As an example, the SDL for a 500 tonne (factored) lift, evenly distributed to 4 points,

offshore, with a 60° sling angle would be:

tonnesSDL 2.23860sin4

25.12.11.1500=

°××××

= (2.1)

2.2.2 Shackle Design Loads

These loads may be calculated as for the slings, but can be decreased by the sling

factored weight above the shackle point.

2.2.3 Lift Point Design Loads

This is primarily to determine adequate rigging sizes. For the design of the structure

and lift points (padeyes), design loads should be based on the structural analysis

requirements.

SDL is used to determine the sling, or grommet size. The governing design criteria is

given in HSE, which sets out the basis for the design criteria listed below and has been

developed for heavy lift slings of diameter 100mm and above, where the rope is not

usually tested to destruction, and which would normally be required for deck, module

and jacket lifts.

15

Individual Slings (Single Slings)

a) At the sling eye,

Minimum Calculated Rope Breaking Load,

CRBL = bE

SDL 55.025.2 ×× (2.2)

Note: the 0.55 factor allows for uneven distribution of the sling load to each leg of the sling

eye due to friction.

CRBL = the sum of the individual minimum breaking loads of the core and outer unit

ropes of the sling multiplied by a 0.85 spinning loss factor (HSE).

Eb = the sling bend efficiency (reduction) factor

= 1- 5.0)D/d(5.0 (2.2a)

D = minimum diameter around which the sling is bent

d = cable laid rope diameter

Note: D should preferably always exceed d to avoid sling load de-rating.

b) At the sling termination,

Minimum CRBL = tE

SDL 25.2× (2.3)

Where, Et = Efficiency of termination method = 0.75 for hand splices, 0.95 for

mechanical, or swaged splices and 1.0 for resin poured sockets.

Doubled slings

Where slings are doubled around the shackle and/or the lifting hook of the crane,

effectively halving the sling length, the equations given in a), b), are modified as

follows:

16

c) At the sling eye,

Minimum CRBL =bE

SDL 55.025.2 ×× (2.4)

d) At the sling termination,

Minimum CRBL =tE

SDL 55.025.2 ×× (2.5)

e) At the sling bend,

Minimum CRBL =tE

SDL 55.025.2 ×× (2.6)

Individual Grommets

Grommets sling may be sized as follows:

f) Minimum Calculated Grommet Breaking Load,

Minimum CGBL =bE

SDL 1.125.2 ×× (2.7)

Doubled Grommets

g) Minimum Calculated Grommet Breaking Load,

Minimum CGBL =bxE

SDL2

1.125.2 ×× (2.8)

17

2.2.4 Shackle Sizing

The sizing of shackles is much simpler than slings and can be based on the following:

Minimum Shackle Working Load Limit, WLL = Sling Design Load, SDL

Note: The WLL is usually quoted by the major shackle Manufacturers, e.g. Crosby

Group, and should be taken as analogous to the safe working load. The WLL is usually

based on a ratio of ultimate strength to WLL of not less than 4 for shackles above 200

tonnes WLL. Should any Manufacturer quote WLL's based on a lower factor, the WLL

should be derated accordingly. Higher ratios between ultimate strength and WLL are

normally adopted for shackles below 200 tonnes capacity, however in these cases the

WLL must not be increased above the Manufacturer's quoted values.

Shackle to Shackle Connection

It is often necessary to make up long sling lengths using 2 slings joined together with a

shackle/shackle connection, usually by joining pin/pin. This is acceptable and no

derating of the shackle is required.

Side Loads on Shackles

Shackle WLL's are quoted for sling loads in line with the shackle i.e. at right angles to

the pin. Should the lift configuration result in side loading, not perpendicular to the pin

shackle, de-rating as recommended by the Manufacturer is necessary. To avoid side

18

loading during the lifting, it is necessary to ensure a close fit-up between the inside of

the shackle jaws and the padeye main, or cheek plates. The width of the main/cheek

plate combination should preferably exceed 0.8 times of the jaw width.

In certain circumstances, the shackle available far exceeds the design requirement for

the width of the main/cheek plate combination. In such cases, this width can be

reduced to one half of the jaw width by adopting non-load bearing centralisers between

the padeye and shackle jaw to ensure an in-line lift.

2.2.5 Tilt during Lifting

Decks and modules

Matched sling pairs should be used to limit the tilt of the module, or deck, to less than

2° in either the transverse or longitudinal direction, or less than 3° in diagonal

direction, whichever is less. Where, due to excessive eccentricity of the package

centroid, the tilt exceeds this value, the lengths of the sling pairs should be altered

accordingly.

Lifting of the jacket off the barge

Sling lengths for side lifting of the jacket off the barge deck, at the offshore location,

should preferably be selected so that the barge deck and the jacket framing interface

remain parallel during the lift off. This avoids possible damage due to the jacket being

19

impacted as it is raised off the barge sea-fastenings and it also provides more clearance

between the hook and the boom sheave.

FPSO Module Lifts

For installation of fabricated modules onto FPSO, in most cases, there will be a

specific requirement in which one of the support legs is required to be settled down

first. This will require the detailed sling calculation to ensure module tilt to the touch-

down corner.

Other Lifts

For certain operations, specific tilt angles may be required to allow safe

lifting/installation as would apply when installing a bridge between two platforms.

2.2.6 COG Shift Factor

Possible Centre of Gravity (COG) shift shall be accounted for by applying a COG shift

factor (fcog) to all assigned weights in the load combinations. fcog is calculated for the

support point most sensitive to shift in COG, and applied equally for the whole

structure.

The COG from the analyses shall be used in the calculations of the COG shift.

20

fcog factor shall be calculated as follows:

05.1≥+

×+

=b

bdb

adf yxcog (2.9)

where, as shown in Figure 2.1, a and b are the distances between analysis COG and

nearest footing in x and y directions and dx and dy are the distances between the

position of maximum shifted COG and analysis COG in x and y direction,

respectively.

21

2.3 Summary

Lifting criteria and sling specifications in practice are first reviewed in this chapter.

These codes include API-RP2A (2000), Det Norske Veritas (DNV) RP-5, Phillips

Petroleum, Heerema, Noble Denton & Associates (NDA), HSE and Shell. API, DNV

and HSE codes are easily available to the general public. The API codes are the oldest

and the most well established in the offshore industry.

Practical considerations for standard rigging design are discussed in detail. The

practical and important considerations in rigging design are

• Sling Design Loads (SDL),

• Shackle Design Loads,

• Lift Point Design Loads,

• Shackle Sizing,

• Tilt during Lifting and

• COG Shift Factor.

22

Table 2.2 Lifting Criteria comparison - Double hook Lift

Noble LOC Heerema Chevron BP AmocoDenton

Range of Module Weight >2500 >1000 >2500 >2500 >8000 >2500

1 A. Weight Factor (Pre-AFC) 1.125 1.15 1.15 1.25 1.15 1.152 B. DAF (Slings) 1.10 1.10 1.10 1.10 1.10 1.103 C. CG Shift factor 1.03 1.05 1.05 1.05 1.08 1.054 D. Tilt factor 1.03 1.03 1.03 1.03 1.03 1.035 E. Yaw factor 1.05 1.05 1.05 1.00 1.00 1.056 F. Torsion factor 1.00 1.00 1.00 1.00 1.00 1.107 G. Skew factor 1.00 1.10 1.00 1.10 1.10 1.008 H = A x B x C x D x E x F x G 1.38 1.58 1.44 1.64 1.55 1.58

9 I. Rigging weight factor 1.03 1.03 1.03 1.03 1.03 1.0010 J. Lift point design factor 1.35 1.00 1.10 1.30 1.25 1.3511 K. Load member design factor 1.15 1.00 1.10 1.15 1.10 1.15

12 L. Sling Design = (H x I) 1.42 1.63 1.48 1.68 1.59 1.5813 M. Lift point Design = (H x J) 1.86 1.58 1.58 2.13 1.93 2.1314 N. Load member design = (H x K) 1.59 1.58 1.58 1.88 1.70 1.82

The overall lift point design factor (K) from API RP 2A (2000) is 2.00.

Table 2.1 Lifting Criteria comparison - Single Crane LiftNoble DnV Heerama Shell BP Oxy Amoco ChevronDenton

Range of Module Weight >2500 >2500 >2500 >1000 >2500 >2500 >2500 >2500

1 A. Weight Factor (Pre-AFC) 1.125 1.10 1.15 1.15 1.15 1.15 1.15 1.152 B. DAF (Slings) 1.10 1.10 1.10 1.10 1.10 1.10 1.10 1.103 C. Skew load factor 1.25 1.25 1.50 1.50 1.50 1.50 1.25 1.504 D. CG Shift factor 1.05 1.00 1.00 1.05 1.00 1.00 1.05 1.005 E. Tilt factor 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.056 F = A x B x C x D x E 1.62 1.51 1.90 1.99 1.90 1.90 1.66 1.99

7 G. Rigging weight factor 1.03 1.03 1.03 1.03 1.03 1.03 1.03 1.038 H. Lift point design factor 1.35 1.35 1.00 1.00 1.25 1.30 1.30 1.309 I. Load member design factor 1.15 1.15 1.00 1.00 1.10 1.15 1.15 1.15

10 J. Sling Design = (F x G) 1.67 1.56 1.95 2.05 1.95 1.95 1.71 2.0511 K. Lift point Design = (F x H) 2.19 2.04 1.90 1.99 2.37 2.47 2.16 2.5912 L. Load member design = (F x I) 1.87 1.74 1.90 1.99 2.09 2.18 1.91 2.29

The overall lift point design factor (K) from API RP 2A (2000) is 2.00.

Table 2.3 Dynamic Amplification Factors (DAF)

Design (factored) Lift Weight (tonne)

<100 100 to 1000 >1000

DAF Offshore 1.30 1.20 1.10 DAF Inshore 1.15 1.10 1.05

23

X

Y

b

dx

dy

a

Design envelope

Max. COG shift

Analysis COG

Support location

Figure 2.1 : Centre of Gravity (COG) Shift

24

CHAPTER 3 HEAVY LIFTING EQUIPMENT AND COMPONENTS

3.1 Introduction

As shown in Figure 3.1, crane vessel, rigging components including shackles, slings

and grommets and lift point connections (including padeyes and trunnions) are basic

considerations in heavy lift design.

The crane barge is the most expensive piece of equipment and the most important

member in lift operation as well. The safety of the crane barge during lift operations is

the first consideration for both crane barge owner and client. The characteristics of the

crane barge also constrain the rigging arrangement and necessary reinforcement of the

module structure.

To safely pick up and install the module is the ultimate objective of carrying out a lift

operation. The module cannot be damaged or overstressed or distorted during lift.

Reinforcement is needed when the module is too flexible to withstand the load during

lift.

The rigging system is the only connection of module to crane vessel. The rigging

components include slings, spreader structure, shackles, padeyes (or trunnions) and

their arrangement. The selection or design of a rigging arrangement is dependent on

the barge characteristics, module structural pattern and behaviour during lift, and the

site parameters.

25

3.2 Heavy Lift Cranes

In the mid 1980s, the available lifting capacity was increased dramatically with the

introduction of the latest generation of Semi Submersible Crane Vessels (SSCVs):

S7000 (with up to 14000 ton capacity) in Figure 3.2 and DB102 (with up to 12000 ton

capacity). Coupled with the upgrading of the Heerema SSCVs, Balder and Hermod,

the availability of these vessels has led to development of lifted jacket concepts for

medium and deeper water and modules over 10000 ton in weight. Table 3.1 lists some

of heavy lifting crane vessels in the world.

Nowadays it is generally recognized that the application of large SSCVs, such as

McDermott's DB102 (12000 ton capacity) and Saipem’s S7000 (14000 ton capacity),

may reduce the costs of offshore installation work significantly, especially for large

integrated topsides and liftable jacket structures. The dynamic aspects of heavy lift

installations are to some extent yet unknown. However, the knowledge of these aspects

is essential to properly assess the feasibility and safety of heavy lift operations.

Both the lifting capacity and the installed lift weights have increased dramatically

during the past two decades. For a long time the available offshore crane capacity used

to be well ahead of the demand and did not impose any significant restrictions on the

weight and dimensions of lift-installed offshore platforms. In recent years, however,

the maximum available crane capacity of large SSCV's has become a limiting factor in

the design of integrated topsides and liftable jackets.

For example, the maximum dimensions of liftable jackets are effectively constrained

by the crane capacity and outreach of large SSCV's, as well as by minimum clearance

26

requirements between the jacket legs and the crane booms. In addition it has become

apparent that the dynamic aspects of large offshore installations should not be ignored

as these may seriously impact the feasibility, safety and schedule of lift operations.

In recognition of these tendencies, many experts has been active from an early stage

onwards in promoting the theoretical and practical development of offshore heavy lift

analyses as an integral consideration in the design of large liftable offshore structures.

The objectives of such analyses are three folds: firstly, given the large weights and

sizes of present day integrated topsides and liftable jackets, the extrapolation on the

basis of past experience is often not possible and unreliable, and therefore one wants to

be reassured beforehand that a proposed lift installation is technically feasible.

Secondly, it should be verified that a lift operation can be performed in a safe manner

without unacceptable risk to personnel involved or to the structure or the crane vessel.

Thirdly, an assessment of the workability (or weather downtime) of a lift operation is

required by project management when deciding on the installation time in relation to

the fabrication schedule. Moreover it may be of interest to establish whether the

workability is determined by factors under the control of the engineering design

project team or of the installation contractor.

In an actual project, the choice between an integrated deck or split modules can be

difficult. The split module concept is to separate the integrated deck into smaller

pieces called modules, by splitting the integrated deck in vertical or horizontal

directions, which can be easily lifted by smaller crane vessel (with lower cost), but

result in higher offshore hook-up cost. Besides using a larger crane vessel to install

the integrated deck, “Float-over” method is also used for installation of heavy deck

without weight limitation. The float-over method will not be discussed in this thesis.

27

3.2.1 Crane Vessel Types In general, the floating crane lift vessel can be classified into two main groups:

A) Sheer Leg Crane, like Asian Hercules II in Figure 3.3.

Advantages

- Less draft for access in-shore shallow water area

- Smaller in barge size, easy maneuvers

- Economic saving

Disadvantages

- Non swivel of crane boom

- Offshore lifting limitation

B) Derrick Crane Barge (or SSCVs)

This group can be further classified into two types:

Type I – Facilitated with dual crane booms, such as S7000 in Figure 3.2 & Thialf

in Figure 3.4.

Type II – Single crane boom, like DB30, DB50 & DB101 as shown in Figure 3.5

Advantages of Derrick Barge

- Swivel of crane boom, more lifting flexibility

- More suitable to offshore lifting operation

- Bigger barge size, more stability

Disadvantages

- Deep draft for not able to access in-shore shallow water area

- Big barge size, not easy maneuvers

28

3.2.2 Frequently Used Crane Vessels

Sheer Leg Floating Crane – Asian Hercules II

Asian Hercules II, as shown in Figure 3.3, is a self-propelled lifting vessel that

has a maximum hoisting capacity of 3200 ton. The crane structure comprises

mainly an A-frame and jib.

The A-Frame can be skidded along fixed tracks on deck into three different

working positions:

Position 1 : Located at 5.2 m from forward of vessel

Position 2 : Located at 33.0 m from forward of vessel

Position 3 : Located at 59.0 m from forward of vessel

The general specifications are as below:

Length (overall) : 91.00 m

Breadth moulded : 43.00 m

Depth moulded : 8.50 m

Max. /Min draft : 5.00/2.40 m

Gross tonnage : 10560 tons

Net tonnage : 3168 tons

Displacement : 16500 tons (even keel)

Speed : 7 knots (12.97 km/hr)

Deck loading : 15 ton/m²

The crane structure has been designed based on the following criteria:

Harbour condition:

• Wind speed : 20 m/s

• Current : 3 Knots

Offshore condition:

• Wind speed : 20 m/s

• Current : 5 Knots

• Max. sig. wave height : Hs = 1m

29

Derrick Barge – Thialf

Thialf, as shown in Figure 3.4, is the largest Deepwater Construction Vessel

(DCV) operated by Heerema Marine Contractors and is capable of a tandem lift

of 14,200 ton. The dual cranes provide for depth reach lowering capability as

well as heavy lift capacity to set topsides. This multi-functional dynamic

positioned DCV is tailored for the installation of foundations, moorings,

SPAR's, Tension Leg Platforms (TLPs) and integrated topsides, as well as

pipelines and flowlines.

Main dimensions as below,

Length overall 201.6m

Length of vessel 165.3m

Breadth 88.4m

Depth to work deck 49.5m

Draught 11.8-31.6m

GRT 136,709 ton

NRT 41,012 ton

Deck load capacity 15 mT/square metre

Total deck load capacity 12,000 mT

Transit speed with 12,000 tons deck load 6 knots at 12.5 metres (43.6 ft) draft.

Ballast pump capacity 20,800 cubic metre/hour

PORTSIDE or STARBOARD CRANE

Main hoist revolving 7,043 ton up to 31.2 m (102 ft)

Auxiliary hoist 900 ton at 36.0 - 79.2 m (120 - 260 ft)

Whip hoist 198 ton at 41.0 - 129.5 m (134 - 425 ft)

30

Derrick Barge – DB101

DB101, as shown in Figure 3.5, has the following details:

Main Dimensions:

LOA 146.3 m (480 ft)

Beam 51.9 m (170.3 ft)

Depth 36.6 m (120 ft)

Working Draft Min. 7.5m (24.6 ft), 23.5m (Max. 77 ft)

Clear Deck: 43,000 sq. ft.

Tonnage: Gross 52,313, Net 15,693

Cranes

Main Crane: IHC E-3500

Boom Length:

Main 67.0m (219.75 ft)

Aux. 97.33m (319.33 ft)

Whip 104.2m (341.75 ft)

Hook Capacity:

Main 2,430 ton (2,700 stons) @ 66 - 78 ft. (Revolving),

3,150 ton (3,500 stons) @ 66 - 78 ft. (Tied Back),

540 ton (600 stons) @ 115 - 279 ft. (Aux.) &

135 ton (150 stons) @ 350.0 ft. (Whip)

Deck Cranes: 83 ton (92 stons) @ 25 ft.

31

3.3 Heavy Lift Shackles Shackles are used in lifting and static systems as removable links to connect wire rope,

chain and other fittings. The shackles used most commonly in industry are

manufactured by two groups, namely Green Pin and Crosby as shown in Figure 3.6.

The wide range of shackle sizes provides choices to designer, with the working load

limit from 0.5 ton to 1200 ton. The shackles are mostly used to connect sling to padeye

on the lifting components. However, the shackles can also be utilized to adjust

(increase) a particular sling length in a set of slings.

Design

The theoretical reserve capability of carbon / alloy shackles should be as a minimum 5

to 1. Known as the DESIGN FACTOR, it is usually computed by dividing the catalog

ultimate load by the working load limit. The ultimate load is the average load or force

at which the product fails or no longer supports the load. The working load limit is the

maximum force which the product is authorized to support in general service. The

design factor is generally expressed as a ratio such as 5 to 1. Also important to the

design of shackles is the selection of proper steel to support fatigue, ductility and

impact properties.

Type & Applications

- Screw pin shackles are mainly used for non-permanent applications.

- Bolt-type shackles are preferably used for long term or permanent

applications and in circumstances where the pin of the shackle may

rotate during loading.

32

- Chain shackles are used mainly on one-leg systems.

- Anchor shackles on multi-leg systems.

Shackle Material

The following are the common materials used for shackle manufacturing:

Mild steel, untreated, which is comparable to ISO Grade 3;

High tensile steel, untreated or normalized, which is comparable to ISO Grade 4;

High tensile steel, quenched and tempered, which is comparable to ISO Grade 6;

Alloy steel, quenched and tempered, which is comparable to ISO Grade 8;

All shackles are upset-forged, on special requirement drop-forged shackles can be

obtained.

The proper performance of premium shackles depends on good manufacturing

techniques that include proper forging and accurate machining. Closed die forging of

shackles assures clear lettering, superior grain flow, and consistent dimensional

accuracy. A closed die forged bow allows for an increased cross section that, when

coupled with quench and tempering, enhances strength and ductility. Closed forging

combined with close tolerance pin hole assures good fatigue life, particularly with

screw pin shackle.

Quench and tempering assures the uniformity of performance and maximizes the

properties of the steel. This means that each shackle meets its rated strength and has

required ductility, toughness, impact and fatigue properties. The job requirements

demand this reliability and consistency.

33

The quench and tempering process develops a tough material that reduces the risk of

brittle, catastrophic failure. The shackle bow will deform if overloading occurs, giving

warning before ultimate failure.

The proper application of shackles requires that the correct type and size of shackle be

used. The shackle's working load limit, its size, a traceability code and the

manufacturer’s name should be clearly and boldly marked in the bow. Traceability of

the material chemistry and properties is essential for confidence in the product.

Material chemistry should be independently verified prior to manufacturing.

For example, a Green Pin standard shackle has following technical indications:

WLL 125 T - Working Load Limit 125 tons

Bs - the manufacturer's symbol

H - Traceability code

6 - Grade

CE - Conformity European.

Documentation

Shackles can be supplied from vendors with the following documents:

• a work certificate;

• a certificate of basic raw material;

• an inspection certificate DIN 50049 - 3.1.B or 3.1.C.;

• a proof-load test certificate;

• a certificate with the actual breaking load found on the tested samples;

• a test report of Magnetic Particle Examination and

• a test report of Ultrasonic Examination.

34

Usage

The correct type of shackle should be selected for a particular application. The

Working Load Limit (WLL) should be applied in a straight pull and overloads must

not be made. Side-loads should be avoided as the products are not designed for this

purpose.

If side-loads are required, as shown in Table 3.2, shackles should be fitted to the load

in a manner that allows the shackle body to take the load in a true line along its centre-

line; and not in such a way that bending loads are induced, other than those for which

the shackle is designed.

When using shackles in conjunction with multi-leg slings, due consideration should be

given to the effect of the angle between the legs of the sling. As the angle increases so

does the load in the sling leg and consequently in any shackle attached to that leg.

To avoid eccentric loading of the shackle, a loose spacer may be used on either end of

the shackle pin or a shackle with a smaller jaw width should be used. Welding

washers or spacers to the inside faces of shackles or closing shackle jaws shall not be

used to reduce the width between the shackle jaws, as this will have adverse effects on

the mechanical properties of shackles. Extreme circumstances or shock loadings must

be well taken into account on selecting the products.

The applications, where the shackle pin can rotate and possibly be unscrewed due to

movement (e.g. of the load or rope), must be avoided.

35

Finished shackles may not be heat-treated because this may affect the Working Load

Limit and the material structure.

Shackles in use should be subject to thorough examination by a competent person at

least every 6 months. In practice, re-certificate is carried out by mechanical

Professional Engineer. This is necessary because the product in use may be affected by

wear, misuse, overloading with consequent deformation of the steel structure.

Shackles should be inspected before use to ensure that:

• the body of the shackle and pin are both identifiable as being of the same

quality grade;

• all markings are readable;

• the pin is of the correct type;

• the threads of the pin and the body are undamaged;

• the body and pin are not distorted and unduly worn;

• the body and pin are free from nicks, gouges and cracks.

Also, the pin should be correctly screwed into the shackle eye, i.e. tighten finger tight,

then lock using a small tommy bar or suitable tool so that the collar of the pin is fully

seated on the shackle eye. The pin needs to be the correct length so that it penetrates

the full depth of the screwed eye and allows the collar of the pin to bed on the surface

of the shackle eye. Incorrect seating of the pin may be due to a bent pin, too tight

fitting thread or misalignment of pin holes.

36

It is important not to replace a shackle pin with a bolt, other than one designed for the

purpose, as it may not be suitable for the loads imposed.

It is important in the case of shackles fitted with a bolt, nut and split cotter pin that the

length of the plain portion of the bolt is such that the nut will jam on the inner end of

the thread or on the eyes of the shackle, and that the rivet on the bolt is cross drilled for

a split cotter pin. A bolt type shackle in operation without using a split cotter pin

should not be used.

37

3.4 Heavy Lift Slings As an important lifting component, the sling is limited in design not only by the lifted

weight and also by the factors listed below:

• Being pre-rigged on the structure;

• Diameter - the largest slings to date have been about 400 mm, though currently

available machinery can build slings 475 mm in diameter;

• Weight of the slings - the sling making machinery has an upper weight limit,

about 80 ton, for any individual sling. Thus large diameter slings are restricted

by the length in which they can be manufactured;

• An installation contractor may wish to lay the slings down on the module after

lifting so that they can be removed individually. This is to avoid the slings

moving towards each other, hence limiting possible damage on the module.

In actual lift projects, sling retention devices (keepers plates) must be fitted to the

trunnions to keep the slings in place during transportation and sling connection. Slings

need to be tied down to the lay-down platform using soft ropes, to prevent movement

during transportation. For a module, sling slashing may be required to prevent

damage to module equipment.

3.4.1 Sling properties

The cable laid slings and grommets are most commonly used in heavy lift operation.

The term "cable laid" indicates wire rope constructed from six smaller diameter ropes

laid up in a helical manner about a single core rope. A hand-spliced soft eye is placed

at each end of the rope section to form a "cable laid sling". The term "grommet" refers

38

to a continuous sling made up in the form of a rubber band. Eyes are formed by

securing the two parts of the grommet together with seizing to produce a loop at each

end.

A common trait of these systems is that they require an element with high tensile

stiffness and relatively low bending stiffness. Selection rules for wire ropes are rooted

in history, of which the purpose or derivation is not easily traced. Most

implementations are the result of the design engineers' biases and experiences, based

on many years of practical use of cables and wire ropes.

The task of designing a wire-rope-based system follows the basic description of the

design process. In addition, each step may be decomposed into several inter-related

subtasks. For instance, system definition subtasks include the selection of a drum,

selection of the appropriate number and sizes of sheaves, selection of wire rope end

fittings, and design of the wire rope itself.

The design of a typical wire rope involves the selection of the following geometrical

and material parameters as shown in Figure 3.7.

• Numbers of wire lays in each strand, wires in each wire lay, and strand lays in

the rope

• Diameters of the individual wires and strands as well as the total rope diameter

• Lay lengths (pitches) of the wire lays within the strands and the strands within

the rope

• Configuration of the strands and total rope (i.e., lay directions, etc.)

• Individual wire cross sections

39

• Core type

• Wire and core materials (including treatment, etc.).

Conventional wire rope slings are limited to diameters of about 4 inches. Braided

slings and several other types of multipart slings have also been used for heavy lifts,

but cable laid slings have proven their superiority and are presently the standard for the

industry. The generally recognized authority for the design and construction of cable

laid slings and grommets is Guidance Note PM 20, “Cable Laid Slings and Grommets”

issued by U.K. Health and Safety Executive. The guidance note was prepared by a

working group of experts primarily from the offshore construction and wire rope

manufacturing industries. The note covers construction procedures and prescribes how

safe working loads are to be established.

One of the problems encountered in the construction of cable laid or any large

diameter slings is the maintenance of an acceptable tolerance on differential length.

Three factors involved in the minimization of the tolerances are:

• Control of the production of the unit ropes from which the slings are

constructed.

• Accurate measurement and marking of rope during construction.

• Mechanical control of splicing tensions to achieve a balanced termination.

Some measurable length differential will be present at the end of construction and the

magnitude can be expected to increase due to differential permanent elongation under

load. A reasonable tolerance on length for the life of the slings is ±0.25 percent of the

length. The length differential for a matched set of 100 foot slings constructed under

ideal conditions may be as much as 6 inches.

40

Heavy lift slings are made of machine spun cable laid rope and usually terminated by

hand made eyes and splices. The eye and splice sections are softer than the cable

section. These are up to 40 rope diameters in length and significantly affect the overall

sling characteristics. Sling splices can slip during load take up and some allowance

should be made in the sling load calculations for this effect. The characteristics

become stiffer and more linear with repeated use.

Grommets are made out of a single length of wire rope which is spun into a continuous

multi-strand loop of wire. They generally have softer characteristics than slings of

similar minimum breaking load (MBL). The single grommet is softer than the

equivalent double sling with two spliced eyes. No slippage allowance is necessary in

grommet design.

3.4.2. Grommets versus Slings

In one major offshore lift project, dual crane lifts with doubled grommets were used to

provide four parts per lifting point. These proved to be lighter as a percentage of the

module weight than doubled slings and resulted in rigging weights approximating to

2% of the lift weight. For the single crane lifts doubled slings were used and resulted in

rigging weights between 3 and 3.5% of the lifted weight.

The grommet lengths were adjusted to permit the centre of lift to be matched to the

centre of gravity. This was achieved by means of intentionally scheduled late

manufacture of a pair of grommets. However, this resulted in potential for late delivery

41

of rigging and therefore careful integration of grommet and module fabrication

scheduling was required. In spite of the rigging being a low percentage of overall

module weight, the individual rigging components still weighed approximately 50 ton

each and rigging installation in the module fabrication yard, at the lift height required,

presented some difficulty and necessitated the preparation of detailed handling

procedures.

An allowance should be made in the design for differential tension across the hook or

padeye. This is due to friction preventing the full load equalization in the rope or

spliced eyes. The tension ratio between the two parts is usually taken as 45:55. This

corresponds to a coefficient of friction of 6.4% around a 180 degree bend.

Slings apply a torque to the crane hook and lifting padeyes. This causes a 2% increase

in sling loads for single hook lifts, increasing to 4% in long and slender modules. Sling

torque has a negligibly small effect on sling loads in double hook lifts.

3.4.3. Sling and Grommet Properties

A. Properties of rope and splice

A1. New rope (1st load cycle)

mr

nr

dLoCrT ×

= (3.1)

Where,

T = Load in % MBL

Lo = Extension in % of original length

d = Sling rope diameter (mm)

Cr = 132.8 ± 25%

nr = 1.75

mr = 0.3807

42

Used rope (2nd cycle onwards)

Elastic modulus E = 2533 ± 25% kg/mm²

A2. New eye/splice (1st load cycle)

me

ne

dLoCeT ×

= (3.2)

Where,

Ce = 16.48 ± 30%

ne = 3.5

me = 0.6286

Used eye/splice (2nd load cycle onwards)

Elastic modulus E = 1357 ± 25% kg/mm²

B. Grommet properties

These properties are for a simple continuous two-part grommet, i.e. having two ropes

connecting the padeye to the hook.

B1. New grommet (1st load cycle)

mg

ngg

dLoC

T×

= (3.3)

Where,

T = Load in % MBL of tow ropes

Lo = Extension in % of original length between hook and padeye

d = grommet rope diameter (mm)

Cg = 69.0 ± 25%

ng = 1.80

mg = 0.4618

43

3.5 Lift Points Lift points are the locations where intensive sling tensions meet with module structure.

Lift points should be properly designed to allow sling tensions smoothly transfer to

other strong structural members. Depending on the factored lift loads, slings and

shackles can be selected from available sling and shackle lists (inventories) or ordered

from suppliers. How to get safe enough and yet reasonably factored lift point loads has

been the focus of all industry design codes.

There are basically two types of lift points which connect rigging systems to module

structures: Padeye and trunnion, as shown in Figure 3.10.

Padeyes are important lift components, which link module structure and shackles. In

lift arrangement, a shackle locks up a padeye by inserting shackle pin through padeye

hole, while the shackle bow connects to a sling.

The design of padeye requires special attention and detailing. It is recommended that

padeyes to be designed with the main connections in shear rather than in tension. High

tension loads in the thickness direction of steel material should be avoided. Padeyes

should be also dimensioned to properly fit up with shackles and avoid uneven contact

areas, which is usually resolved by using cheek plate and spacer plates.

Although the padeyes themselves are usually adequately designed for vertical and

horizontal loads, the structure to which the padeyes connect must be able to accept and

transmit the total vertical and horizontal forces back into structure.

Trunnions are normally used to lift very heavy modules. The advantages of trunnions

44

are their simplicity in rigging connections where slings or grommets are looped over

the braces without the use of shackles, and the freedom for a sling or a grommet to

rotate around the trunnion brace. The latter may be beneficial for module upending,

overturning or rotating.

Trunnions can be either cast or fabricated. Ideally the diameter of the trunnion should

be four times the sling diameter. The use of cast trunnions means that early design is

required because castings have a long lead time. The fabricated trunnions are

frequently used in the offshore industry.

45

3.6 Summary

Crane barges, rigging components including shackles, slings and grommets, and lift

point connections (including padeyes and trunnions) are discussed based on practical

considerations in heavy lift design.

The barge is the most expensive piece of equipment and the most important member in

lift operation as well. The safety of the barge during a lift operation is the first

consideration for both barge owner and client. The characteristics of the barge also

constrain the rigging arrangement and necessary reinforcement of the module

structure.

The rigging system is the only connection for the module to the crane barge. The

rigging components include slings, spreader structure, shackles, padeyes (or trunnions)

and their arrangement. The selection or design of a rigging arrangement is dependent

on the barge characteristics, module structural pattern and behaviour during lift, and

the site parameters.

Sling retention devices (keepers plates) must be fitted to the trunnions to keep the

slings in place during transportation and sling connection. Slings need to be lashed

down to the lay-down platform using soft ropes, to prevent movement during

transportation. For a module, sling slashing may be required to prevent damage to

module equipment.

46

Table 3.1 Some of Heavy Lifting Crane Vessels in the World

Crane Vessel

Name

Contractor

Nominal Lift

Capacity (Ton)

Vessel Type

Location

Asian Hercules II Asian Lift 3200 Sheer Leg Singapore

Asian Hercules Asian lift 1600 Sheer Leg Singapore

Semco L1501 Semco Salvage 1500 Sheer Leg Singapore

Crane 5000 McDermott 4500 Sheer Leg Gulf of Mexico

DB 50 McDermott 3960 Derrick Gulf of Mexico

DB 101 McDermott 3150 Derrick Gulf of Mexico

DB 102 McDermott 12000 Derrick Gulf of Mexico

DB 30 McDermott 2790 Derrick South Asia

DB 27 McDermott 2160 Derrick Arabian Gulf

Muashi-3600 Fukada Salvage & Marine 3600 Derrick Tokyo Bay

Suruga-2200 Fukada 2200 Derrick Japan

Kongo Fukada 2050 Derrick Hiroshima,Japan

Rambiz 3000 - 3300 Derrick Europe

Samsung 3000 Samsung Heavy Industry 3000 Derrick Korea

Thialf Heerema 14200 Derrick North Sea

Hermod Heerema 8100 Derrick Gulf of Mexico

Balder Heerema 5670 Derrick Gulf of Mexico

M7000 Saipem 14000 Derrick North Sea

Castoro Otto Saipem 2160 Derrick W. Hemisphere

S 3000 Saipem 2250 Derrick South Asia

Kurushio Nippon Steel 2250 Derrick South Asia

HD2500 Hyundai 2250 Derrick Arabian Gulf

Stanislav Yudin Seaway Heavy Lift 2250 Derrick Dubai

HLS 2000 NPCC 2160 Derrick Arabian Gulf.

Lan Jiang Hao COOEC 3420 Derrick China

Da Li Hao Shanghai Salvage 2500 Derrick China

Nian Tian Long Guangzhou Salvage 1500 Derrick China

47

Table 3.2 Shackle Side Loading Reduction For Screw Pin and Safety Shackles Only

Angle of Side Load

from Vertical In-Use of Shackle

Adjusted Working Load Limit

0° In-line* 100% of Rated Working Load Limit

45° from In-line 70% of Rated Working Load Limit

90° from In-line 50% of Rated Working Load Limit

* In-Line load is applied vertical to the pin.

Figure 3.1 Lifting Equipment and Components

Crane Vessel

SiteModule

Rigging

Spreader bar

Lift point

48

Figure 3.2 Saipem S7000 SSCV with maximum of 14000 ton Capacity

49

Figure 3.3 Sheerleg Crane Vessel – Asian Herlues II : with maximum of 3200 ton Capacity

50

Figure 3.4 Derrick Barge Crane – Thialf : 14200 ton Capacity

51

Figure 3.5 Derrick Lifting Barge DB101: 3150 ton Capacity

52

Figure 3.6 Samples of Some Shackles (GreenPin and Crosby)

53

Figure 3.7 Sling Forming & Cross Section

54

Figure 3.8 Sling Configuration

Figure 3.9 Actual Usage of Slings Left: Sling being attached to Crane hook Right: Sling being laid on platform and ready to sail for offshore hook-up

55

Figure 3.10 Lift point connections- Padeye and Trunnion

Padeye

Shackle

Sling

Pipe Trunnion

Plate Trunnion

56

Figure 3.11 Fabricated Lifting Padeye

Figure 3.12 Actual fabricated Lifting Trunnion

Left: Plate Type – Trunnion joining to Centre plate

Right: Tubular Type – Trunnion joining to Centre Tubular

Figure 3.13 Details of A Typical Padeye

57

CHAPTER 4 RIGGING THEORY AND FORMULATION

4.1. Introduction

The design of rigging sling systems involves the available lift points (strong points in

module), the available slings in inventory, the spreader structure and the hook blocks

of the barge. In other words, all the components from the lift points at the module to

the hook block should be considered. In actual rigging arrangement, the sling system

can be with four, six, eight or more lift points, and spreader bar or frame may be used

to protect the module from extensive compressive forces or any possible

clashing/damage to other equipment. Rigging sling systems with more than eight lift

points are used to lift large and flexible modules. It can be seen that the configuration

of the rigging sling system determines the forces in all the components of the rigging

system including padeyes, shackles, slings and spreader structures (if any), and thus

affects the selection and design of these members. Moreover, the configuration of the

rigging sling system is one of the most critical factors that should be considered in the

analysis of stresses in the module and in the determination of the barge gesture

including the angles of crane boom and jib.

The objective of this section is, as shown in Figure 4.1, to investigate the algorithms

and formulations to determine the configurations of rigging sling systems, which are

affected by the location of lift points, length of rigging slings and geometry of spreader

and hook block. The hook block(s) involved in a particular rigging system can be one

(main or jib hook) or two (both main and jib hooks) at a time. Emphasis is placed on

the determination of the critical geometrical quantities of the rigging sling system

including the sling angles with respect to the horizontal plane and the distances

between the module, spreader structure and hook blocks.

58

Accurate sling tensions can be computed using the methods presented in Chapters 2

and 3. Some practical methods, however, are also presented in this chapter due to the

specific nature of individual problems.

In this chapter, useful formulations and procedures for determining sling angles, hook

height above module, spreader height above module, and hook height above spreader

are derived based on the selected slings from the sling inventory and the geometrical

dimensions of spreader structures. The established formulations can also be used to

design new slings and spreaders by applying them appropriately.

For the convenience of discussion, the geometrical parameters are defined as follows:

H4 - height of hook block above module (without spreader structure), or

height of spreader above module (with spreader),

H5 - height of hook block above spreader (with spreader), or,

=0 (without spreader)

Li - length of ith sling,

θi - angle of sling with respect to the horizontal plane,

(xc, yc) - location of the centre of gravity of module in local coordinate system,

Wm, Lm, Hm - the width, length and height of module, respectively,

Wh, Lh - the width and length of hook block, and

Wsp, Lsp - width and length of spreader.

The superscripts (B) and (J) used in this chapter denote parameters related to the boom

(main frame) and jib hook, respectively, while the subscripts m and h are related to

59

module and hook. For example, L(B) and L(J) represent the lengths of boom and jib,

while Wh and Wm the widths of hook block and module, respectively.

4.2 Rigging Sling System with Four Lift Points

Rigging sling systems with four lift points are frequently used in offshore and marine

module installation where lift points can be located at the legs of the jacket or strong

structural components.

4.2.1. Using Main or Jib Hook without Spreader Structure

Three typical rigging arrangements in terms of the hook position with respect to the

Centre of Gravity (CG) are shown in Figure 4.2. These are configurations with (1)

four-equal slings, (2) two-matched-pair slings and (3) four-unequal slings. The

formulations for the geometrical parameters of the three rigging configurations are

summarised in Table 4.1.

4.2.2. Using Main or Jib Hook with Spreader Structure

As mentioned in the above section, spreaders are used to avoid extensive compressive

forces in modules to protect modules or equipment from damage. In actual

applications, a spreader structure can consist of simple spreader bar or a spreader

frame. Figure 4.3 shows three typical rigging arrangements with spreader structures: (i)

one spreader bar, (ii) two parallel spreader bars, and (iii) a spreader frame. To simplify

the discussion, module geometry, lift points, spreaders are assumed to be symmetric

about geometrical axes.

The formulations for the geometrical parameters of the three rigging configurations are

60

summarised in Table 4.2, where θ and γ are the angles of the sling below and above the

spreader with respect to the horizontal plane, respectively, φ is the angle between the

real plane of the slings and the horizontal plane, Dsp is the distance between two

spreader bars and L′ and L" are the lengths of the slings below and above the

spreader, respectively.

4.2.3 Using Main and Jib Hooks at the Same Time

In the case of using both main and jib hook blocks at the same time as shown in Figure

4.4a, the distance between the main and jib hook is normally made equal to the

distance Dx between lift points, and the real planes of the main hook slings and jib

hook slings are thus perpendicular to the horizontal plane. The formulations to

determine the geometrical parameters of rigging configurations are given in Table 4.3.

The loads taken by the main hook and jib hook are dependent on the lift points and CG

positions as shown in Figure 4.4b.

4.3 Rigging Sling System with Six Lift Points

Due to the constraint of structural patterns of modules, rigging systems with six lift

points may be used in certain cases. Modules with six lift points can be lifted up by

single (main or jib) hook block or by two (both main and jib) hook blocks due to

various practical considerations.

4.3.1 Using Main or Jib Hook with Spreader Frame

If only the main or jib hook block is used, a spreader structure is normally needed to

accommodate the force distribution in the slings above and below it. Figure 4.5a shows

a typical rigging arrangement for using a single hook block to lift up a module with six

61

lift points, where a planar frame is used to protect the module from intensive

compression and to effectively transfer the forces from the lower slings to the upper

slings. The span of the spreader frame can be designed equal to the distance Dx

between lift points to minimise the horizontal compressive forces (in the x-direction)

on the module. The formulations for determining the geometrical parameters of this

rigging configuration are summarised in Table 4.4.

Attention should be paid to the tensions of individual slings as well as the forces at

individual lift points, as the forces may be significantly unevenly distributed depending

on the global stiffness of the module structure and sling system, as discussed in

Chapter 2. It is known from Chapter 2 that the sling tensions are evenly distributed if

the module is very stiff compared to the slings. However, if the module structure is

very flexible, or, in other words, the slings are comparatively very stiff, the tensions of

the two middle slings can be much larger than the tensions of other slings. In this case,

two big slings are required for the middle positions. Since the sling tensions are

transferred to the lift points, the corresponding lift point loads at the two middle

positions are also much larger than those at the two ends. Thus, bigger shackles and

stronger padeyes or trunnions should be designed for the lift points at the middle

locations. Furthermore, as the forces finally find their paths in the structure, local over-

stressing and excessive deformation of the module may occur since the forces during

the lifting operation may be significantly different from the actual working loads

assumed during the design of the module.

To obtain accurate sling tensions and structural performance during the lift, a

comprehensive structural analysis, as proposed in Chapter 3 should be conducted on

the rigging configuration including the actual stiffness of the slings and the module.

62

The design of the spreader frame should be also based on the consistent load condition

of the rigging system.

4.3.2 Using Main and Jib Hooks without Spreader Structure

If both the main and jib hook blocks are used at the same time as shown in Figure 4.6a,

the distance between the main and jib hook is normally designed to be equal to the

distance Dx between lift points, as discussed in the previous section. The formulations

for determining the geometrical parameters of this rigging configuration are

summarised in Table 4.5. Figure 4.6b gives the loads taken by the main and jib hooks

which depend on the lift points and CoG positions.

If two doubled slings, instead of four single slings, are used for those slings at the main

hook block, the formulations provided in Table 4.5 are still valid except that the length

of the slings L(B) should be changed to half the length of the corresponding doubled

slings.

4.4 Rigging Sling System with Eight Lift Points

Rigging sling systems with eight lift points are often used in shipbuilding and offshore

structural installations. The lift points in a ship block may be the cross points of

bulkheads or strong points at hull structures. In this section, some practical rigging

configurations are discussed. In the case of doubled slings, the force split ratio of the

two arms of a doubled sling (α), as discussed in Chapters 3, should be applied

appropriately.

63

4.4.1 Using Main or Jib Hook with/without Spreader Structure

Figure 4.7a shows an eight-point rigging sling configuration without any spreader

structure where four doubled slings with the same length L are used. Figures 4.7b and

4.7c show rigging sling systems with two parallel spreader bars and a spreader frame,

and the lengths of the doubled slings below the spreader structures and single sling

above the spreader structures are denoted Ld and Ls, respectively.

The formulations for determining the geometrical parameters of the rigging

configurations are summarised in Table 4.6.

4.4.2 Using Main and Jib Hooks without Spreader Structure

As will be discussed in Sections 6.2.3 and 6.3.2, when both the main and jib hook

blocks are used at the same time as shown in Figure 4.8a, the distance between the

main and jib hook is normally made equal to the distance Dx between the lift points.

The formulations for determining the geometrical parameters of this rigging

configuration are summarised in Table 4.7. Figure 4.8b gives the loads taken by the

main and jib hooks, which depend on the locations of lift points and CoG positions.

4.5 Summary

The determination of the configuration of rigging sling systems is an important step in

heavy lift design, since the configuration affects the tensions in rigging slings, loads in

lift points and forces in shackles and link plates, and thus affects the design of those lift

components. Furthermore, it also affects the selection of the boom and jib angles of a

barge to fulfil lift requirements.

64

The geometrical configurations of rigging sling systems are dependent on the location

of lift points, available rigging slings and the details of the spreader geometry and hook

blocks. The algorithms and formulations for the determination of configurations of

rigging sling systems with four, six and eight lift points, which cover the majority of

heavy lifts in offshore and marine industries, are presented in this chapter. The sling

arrangements can be with single slings, doubled slings or doubled make-up slings. The

type of spreader structures included in the discussion can be a simple spreader bar, two

parallel spreader bars or a spreader frame. The hook block(s) involved in a particular

rigging system can be one (main or jib hook) or two (both main and jib hooks) at a

time. Emphasis is placed on the determination of the critical geometrical quantities of

the rigging sling systems. These include the sling angles with respect to the horizontal

plane, hook height above the module or spreader structure, and spreader structure

above lift points. The algorithms and formulations presented in this chapter can be

applied both for selecting slings from the inventory and for ordering new slings.

65

Type of

rigging

configuration

Parameters and formulations Approximate

tilt angle

four-equal slings

L1= L2=

L3 =L4

θ1=θ2=θ3=θ4 =1

2hy

2hx1

L

)2/L2/D()2/W2/D((cos

−+−−

)2/L2/D()2/W2/D()L(H hy2

hx2

14 −−−−=

)H

)y()x((tg

4

2c

2c1 +

≈γ

−

2-matched-

pair slings

L1= L2,

L3 =L4

θ1=θ2=1

2hy

2chx1

L

)2/L2/D()x2/W2/D((cos

−+−−−

θ3=θ4=3

2hy

2chx1

L

)2/L2/D()x2/W2/D((cos

−++−−

2hy

2chx

214 )2/L2/D()x2/W2/D()L(H −−−−−=

)Hy

(tg4

c1−≈γ

four-unequal

slings

L1≠L2≠

L3≠L4

θi=i

2ihy

2ihx1

L

)y2/L2/D()x2/W2/D((cos

+−++−−

(i=1,2,3,4)

where c43c21 xxxxxx −==== ,

c32c41 yxxyyy ==−== ,

2chy

2chx

214 )y2/L2/D()x2/W2/D()L(H +−−−−−=

0≈γ

Table 4.1 Formulations for rigging configurations with four lift points (using main or jib hook block without spreader)

66

Type of rigging

configuration

Parameters and formulations

One spreader bar

)L

)2/L2/D()2/D((cos

2spy

2x1

′

−+=θ − 2

spy2

x2

4 )2/L2/D()2/D()L(H −−−′=

)L

)2/L2/L((cos

2hsp1

′′

−=γ − 2

hsp2

5 )2/L2/L()L(H −−′′=

Two parallel spreader bars

))2/W2/W()L()2/W2/D()L(

2/)LD((cos

2hsp

22spx

2

hy1

−−′′+−−′

−=φ −

)sin()2/W2/D()L(H 2spx

24 φ−−′= )sin()2/W2/W()L(H 2

hsp2

5 φ−−′′=

)cos()2/W2/D()L(2DD 2spx

2xsp φ−−′−=

)L

)2/D2/D()2/W2/D((cos

2spy

2spx1

′

−+−=θ −

)L

)2/L2/D()2/W2/W((cos

2hsp

2hsp1

′′

−+−=γ −

Spreader frame

)L

)2/L2/D()2/W2/D((cos

2spy

2spx1

′

−+−=θ −

2spy

2spx

24 )2/L2/D()2/W2/D()L(H −−−−′=

)L

)2/L2/L()2/W2/W((cos

2hsp

2hsp1

′′

−+−=γ −

2hsp

2hsp

25 )2/L2/L()2/W2/W()L(H −−−−′′=

Table 4.2 Formulations for rigging configurations with four lift points (using main or jib hook block with spreader structure)

67

Type of rigging configuration

Parameters and formulations

Without Spreader bars

)L2

LD(cos

)B(h

)B(y1)B( −

=θ − 2)B(h

)B(y

2)B(4 )2/L2/D(LH −−=

(similar for )J(4

)J( Hand θ )

With spreader bars

)L2

LD(cos

)B(sp

)B(y1)B(

′−

=θ − 2)B(sp

)B(y

2)B(4 )2/L2/D()L(H −−′=

)L2

LL(cos

)B(h

)B(sp1)B(

′′−

=γ − 2)B(h

)B(sp

2)B(5 )2/L2/L()L(H −−′′=

(similar for (J)5

(J))J(4

)J( H andH , , γθ )

Type of rigging configuration

Parameters and formulations

With spreader

frame

)L2

D(cos y1

′=θ − 2)B(

y2

4 )2/D()L(H −′=

)L2

WW(cos hsp1

′′

−=γ − 2

hsp2

5 )2/W2/W()L(H −−′′=

Table 4.3 Formulations for rigging configurations with four lift points (using main and jib hook blocks at the same time )

Table 4.4 Formulations for rigging configurations with six lift points (using main or jib hook block )

68

Type of rigging configuration Parameters and formulations

Without

spreader

frame

)L

]2/L2/D[]2/D[(cos )B(

2)B(h

)B(y

2)B(x1)B(

−+=θ −

2)B(h

)B(y

2)B(x

2)B()B(4 ]L2/D[]2/D[]L[H +−−=

)L2

LD(cos )J(

)J(h

)J(y1)J( −

=θ −

2)J(h

)J(y

2)J()J(4 ]L2/D[]L[H +−=

Table 4.5 Formulations for rigging configurations with six lift points (using main and jib hook blocks at the same time)

69

Type of rigging

configuration

Parameters and formulations

Without Spreader Structure

)babLaL(2baLL21H 222222444

4 ++−++=

)a

H(tg 41

1−=θ , )

bH

(tg 412

−=θ

where L is the length of doubled slings,

2hy2h)1(

x ]2

L2

D[]

2W

2D

[a −+−= and 2hy2h)2(

x ]2

L2

D[]

2W

2D

[b −+−=

With Two

Parallel Spreader

Bars

21

hy1

dd2/L2/D

(cos+

−=φ − )

)sin(dH 14 φ= , )sin(dH 25 φ=

)a

H(tg 41

1−=θ , )

bH

(tg 412

−=θ , )c

H(tg 51−=γ

where φ is the angle between the real plane of sling and horizontal plane.

)qpqLpL(2qpLL21d 2222

d22

d444

dd

1 ++−++= , 2hsp2s2 )

2W

2W

(Ld −−= ,

2spy2sp)1(

x ]2

D2

D[]

2W

2D

[a −+−= , 2spy2sp)2(

x ]2

D2

D[]

2W

2D

[b −+−= ,

2hsp2hsp )2

L2

D()

2W

2W

(c −+−=

with Ld being the length of doubled slings below spreader, Ls being the length of single

sling above the spreader, 2

W2

Dp sp

)1(x −= and

2W

2D

q sp)2(

x −=

With Spreader

Frame

)babLaL(2baLL21H 2222

d22

d444

dd

4 ++−++= , 22s5 c)L(H −=

)a

H(tg 41

1−=θ , )

bH

(tg 412

−=θ , )c

H(tg 51−=γ

where Ld is the length of doubled slings below spreader, Ls is the length of single sling above the spreader,

2spy2sp)1(

x ]2

L2

D[]

2W

2D

[a −+−= , 2spy2sp)2(

x ]2

L2

D[]

2W

2D

[b −+−= and

2hsp2hsp )2

L2

L()

2W

2W

(c −+−=

Table 4.6 Formulations for the rigging configurations with eight lift points (using main or jib hook block at a time )

70

Type of rigging configuration Parameters and formulations

Without spreader

frame

)L

]2/L2/D[]W2/D[(cos

)B(

2)B(h

)B(y

2)B(h

)B(x1)B(

−+−=θ −

2)B(h

)B(y

2)B(h

)B(x

2)B()B(4 ]L2/D[]W2/D[]L[H +−−−=

)L

]2/L2/D[]W2/D[(cos

)J(

2)J(h

)J(y

2)J(h

)J(x1)J(

−+−=θ −

2)J(h

)J(y

2)J(h

)J(x

2)J()J(4 ]L2/D[]W2/D[]L[H +−−−=

Table 4.7 Formulations for rigging configurations with eight lift points (using main and jib hook blocks at the same time )

71

TASKS Determination of rigging

configuration

• Algorithms • Formulations

Inputs • Hook block info. • Sling info.

(from inventory) • Lift point info. • Spreader info.

Outputs

• Sling angles

• Heights of 1. hook above module 2. hook above spreader 3. spreader above module

Figure 4.1 Determination of rigging configuration: tasks, inputs and outputs

x Barge Direction

θ3 θ2

θ1

ISO View

θ4

Hm (H3)

H4

xyz

LPT 4

LPT 3 LPT 2

LPT 1 Wh

Lh

Dx

Lm Dy

y

x

Wm

)y,CG cc(x

Rigging configuration with four equal slings

LPT 4

LPT 3 LPT 2

LPT 1

Dx

Lm Dy

Wm

)y,CG cc(x

Rigging configuration with matched-pair slings

LPT 4

LPT 3 LPT 2

LPT 1

Dx

Lm Dy

Wm

)y,CG cc(x

Rigging configuration with unequal slings

Figure 4.2 Rigging configuration for four-lift-point sling systems using main or jib hook block without spreader

1L 2L3L4L

72

Figure 4.3 Rigging configurations for four-lift-point sling systems using main or jib hook block and spreaders

Wm

φ

φ

Lh Lsp Lm Dy

Dx

Wm γ

γ

θ θ

θ θ

H5

H4

Hm

Rigging configuration with one transverse spreader bar

γ

θ

H5

H4

Lh

Wh

Dsp

Wsp

Lm Dy

Dx

Rigging configuration with two parallel spreader bars

Hm

γ

θ H4

Hm

Lh

Wh

Lsp Dy

Wsp

Dx

Wm

Lm

H5

Rigging configuration with a spreader frame

''L

'L

'L

'L

''L

''L

x

yz

xyz

x

yz

73

jib hook

main hook

)B(4H

)B(5H

mH

)J(4H

)J(5H

mW

xD

)J(yD mL)B(

hL )B(spL

)J(hL)J(

spL

Figure 4.4a Rigging configuration for four-lift-point sling systems using main and jib hook blocks and spreader bars

)B(θ

)B(γ

)J(θ

)J(γ

)B(yD

'L

''L

xyz

W

CG

)1(xD )2(

xD

)B(W)J(W

WDD

DW )2(x

)1(x

)2(x)B(

+=

WDD

DW )2(x

)1(x

)1(x)J(

+=

Figure 4.4b Hook load distribution for four-lift-point sling systems using both main and jib hook blocks

74

W

mH

4H

spH

5HspW ′′

spW′

mL

mW

yD

xD

hW

θ θ

γ

θhW

'L

''L

T′ T′

T′ T′

W

where α is dependent on the stiffness of module structure and sling system

12 TT α=

x

y z

θ θ θ

1T

1T

1T

2T

2T

1T

1T

1T

1T

1T2T2T

W)sin(2

1Tγ

=′

Figure 4.5a Rigging configuration for six-lift-point sling system using main or jib hook block with spreader frame

Figure 4.5b Sling tensions for six-lift-point sling system using main or jib hook block with spreader frame

75

W

CG

x

yz

)B(4H )J(

4H

mH

)B(θ)J(θ

mW

xD

)J(yD mL)B(

HL)J(

HL)J(spL)B(

yD

)B(xD

main hook jib hook

)B(L)J(L

Figure 4.6a Rigging configuration for six-lift-point sling system using both main and jib hook blocks

)1(xD )2(

xD

)B(W)J(W

WDD

DW )2(x

)1(x

)2(x)B(

+=

WDD

DW )2(x

)1(x

)1(x)J(

+=

Figure 4.6b Hook load distribution for six-lift-point sling systems using both main and jib hook blocks

76

Figure 4.7a Rigging configuration for eight-lift-point sling system using main or jib hook block without spreader frame

mL yD

4H

mH

mW

mL yD

hW

hL

)1(xD

4H

mH

5H

hW

hLspD

spW

4H

mH

5H

mL yD

hW

hLspL

spW

L

Figure 4.7b Rigging configuration for eight-lift-point sling system using main or jib hook block with two parallel spreader bars

Figure 4.7c Rigging configuration for eight-lift-point sling system using main or jib hook block with spreader frame

1θ2θ

1θ2θ

1θ2θ

)2(xD

mW

)1(xD

)2(xD

mW

)1(xD

)2(xDγ

dL

sL

77

)J(hW

)B(θ )J(θ

)B(4H

)J(4H

mH

x

yz

mW

xD

)J(yD mL)B(

hL)B(

yD

)B(hW

)B(xD

)B(hL

)J(xD

W

CG

Figure 4.8a Rigging configuration for eight-lift-point sling system using both main and jib hook blocks

)1(xD )2(

xD

)B(W)J(W

WDD

DW )2(x

)1(x

)2(x)B(

+=

WDD

DW )2(x

)1(x

)1(x)J(

+=

Figure 4.8b Hook load distribution for eight-lift-point sling systems using both main and jib hook blocks

)B(L)J(L

78

CHAPTER 5 JACKET LIFTING

5.1 Introduction

The fixed steel jacket is the most common type of structure used for supporting facilities

for the offshore production of oil and gas. A few of jackets have been built with sufficient

buoyancy to enable them to self-float, but the majorities have been transported from

fabrication yard to offshore site on aboard of an ocean-going cargo barge.

The following steps should be taken during the conceptual design of a jacket.

The capacity of the lift cranes falls off dramatically with increasing radius. It is, therefore,

essential to take all possible steps to minimize the operating radius. The smaller the cross

section of the jacket is, the smaller the crane radius is. Therefore limiting both top and

bottom plan dimensions of a horizontally lifted jacket, will give improved liftability.

Smaller plan dimensions cause more piles and higher dynamic amplification in the in-

place condition.

If the jacket is not square in plan then a clearance and radius study should be carried out to

determine which way round the jacket should be on the barge to give maximum hook

capacity. Selection of barge width may also be critical in determining the optimum crane

radius.

79

In determining the crane radius, the clearance between the barge and the crane vessel hull,

the jacket and the hull, and the jacket and the crane boom or crane cabs must not be less

than 3m during lifting.

The common offshore installation method of barge transported jackets is directly by

lifting, using a heavy lift vessel (HLV) or a semi-submersible crane vessel (SSCV). While

another method is to lunch jacket from cargo barge and then upending by using crane

vessel. The main differences between lifted and launched jackets are that the latter have

launch frames and auxiliary buoyancy tanker. Launch frames have also another function,

serving as supporting framework during jacket construction and for skidding the jacket

onto the launch barge during loadout. Some form of auxiliary buoyancy is necessary on

launched jackets to arrest the jacket during launch, and as an aid during upending and

installing the jacket on the seabed.

Lifted jackets without the requirement for launch frames and the auxiliary buoyancy

tankers needed to achieve a safe launch, which will give quite saving of steel materials.

Lifting slings and lifting trunnions (installed on the jacket) are required to lift the jacket

from the cargo barge into the water.

There are a variety of ways by which a jacket may be lifted and installed into position on

the seabed. Each depends on the characteristics of the jacket. The first method is the

vertical lift whereby the jacket is vertically transported on and lifted vertically off the

barge and placed on the seabed.

80

In the situations where the jacket is too tall for vertical lifting it can be lifted horizontally

from the barge using slings attached close to the top and base of the jacket. Installation

follows by lowering the jacket base and raising the top of the jacket. This method is

inappropriate for longer jackets as the lifting capacities of the cranes reduce with

increasing crane boom radius. Such circumstances will probably result in a two-stage

installation. Firstly the jacket is lifted from the barge and lowered into the water until it

floats. This requires the use of auxiliary buoyancy. The main lifting slings are then

removed and the prerigged upending slings attached to the crane hook. The jacket is then

upended and positioned on the seabed.

It is relevant to point out that the configuration and sling tensions for lifting jackets

vertically or horizontally are discussed in the previous chapter.

5.2 Vertical Lift of Jackets

The majority of shallow water jackets are constructed, loaded out and transported with the

jacket in its vertical position. The jacket is installed by lifting it clear of the cargo barge by

either a single or dual lift, removing the barge, and then lowering the jacket into place on

the seabed as shown in Figure 5.1.

The advantages of this method of lifted jacket installation with respect to other methods

are: the jacket is vertical during all phases of installation: no re-rigging of lift slings is

required during installation (which means that offshore installation time/cost is reduced

significantly); and only a minimum ballasting system (if any) is necessary. The

81

disadvantages are that the jacket height is limited by the available boom height capacity of

the crane vessel and the vertical construction of the jacket. For jacket installation of this

sort a submersible cargo barge is required to meet hook height requirement.

However, the influence of the new generation SSCVs is illustrated by the comparatively

large weight of the 8400t Gyda jacket in North Sea, which was installed in a water depth

of approximately 65m in 1989 by Saipem S7000.

5.3 Horizontal Lift of Jackets

In the case of jackets in greater water depth, the height of the jacket prohibits vertical

lifting. Consequently, the jacket is constructed horizontally at the fabrication yard and

loaded out onto the cargo barge in a similar manner to the launched jackets. For horizontal

jacket, there will involve number of lifting operations: 1) Lifted loadout horizontally

onto the transportation barge in fabrication yard, see Figure 5.2a , 2) Lifted up from

transportation barge offshore, see Figure 5.2b, 3) upending jacket from horizontal position

into vertical position, 4) Lift jacket vertically for final installation. Also refer to Chapter

9.3 for more details.

Two upending methods are used for installation of horizontal jackets:

• Upending in air, which requires a larger SSCV with two hooks working

independently, like S7000. Refer to Figure 5.3 and Figure 9.4. This can also be

achieved by two Crane vessels, see Figure 5.2.

82

• Upending in water, which is commonly used as less SSCV requirement. This may

further be divided into two categories: those installed with the rigging always

attached (these jackets invariably have no auxiliary buoyancy) and those installed

using a re-rigging method while the jacket is free floating (such jackets may

require auxiliary buoyancy).

The former category of installation is best suited to medium water depth jackets. When

partially supported by buoyancy, the load was transferred to the auxiliary hook. The main

hook was re-rigged at the top of the jacket, which was then upended.

For short jackets the lifting points are close to the top and the base of the jacket. Such

positioning facilitates the upending of the jacket, where one crane is used to hold the top

of the jacket vertical while the other lowers the base.

The jacket size is restricted by the various factors. At the lower lift point, the main crane

hook typically only has enough wire to go to the same level as the SSCV pontoons. The

vessel operator prefers that the crane hooks do not go underwater. The upper lift slings

need to pass over the top of the jacket. Both this and the restrictions on lowering the crane

hooks result in long slings attached to the jacket. But the length of these slings is limited

by the maximum allowable hook heights when lifting the jacket off the barge. The crane

vessel draught may be limited to only a few positions because of stability and motions

restrictions.

83

The typical sequence for the lifting of deep water jackets is as following:

Step 1: Jacket lifted horizontally from the cargo barge after removing seafastening,

Jacket lowered into the water, where it floats horizontally. The jacket may require

auxiliary buoyancy.

Step 2: Slings and spreader beams are removed. The derigging of the jacket included:

• lay down of slings on the rigging platforms;

• release and removal of slings one at a time;

• removal of end shims on the spreader beam;

• removal of the spreader beams.

This operation took usually about 24hrs.

Step 3: The pre-rigged upending rigging, at the top of the jacket is attached to the crane

Step 4: The jacket is upended by a combination of ballasting and raising the crane hook

It should be noted that the large jackets have required substantial loadout frames. If they

had been built as launched jackets, the equivalent weight would have been built into the

structure as launch frames and load out rails. This in turn would have attracted higher

wave loadings in the in-place condition. Additional anodes and/or painting would have

been needed. These extra weights on a launched jacket hence require temporary buoyancy

to be fitted.

84

5.4 Summary

Jackets which are built and transported vertically offer significant savings over jackets

built on their side. These include:

• Loadout and transportation forces are carried efficiently by the legs and vertical

face braces. Plan bracing sizes reduce and there is a minimum of temporary steel

that becomes redundant when the jacket is in place;

• No ballasting/upending system is required and the legs are free flooding;

• The jacket is not required to float or to have submerged, remote, sling release

systems;

• The same slings are used for lift and placement. No separate upend slings are

required;

• The water depth for this type of lift installation is limited by the available hook

height of the SSCV to around 65-70m. If built vertically, jackets are limited by the

height of the cranes in the fabrication yard.

85

Considerations for lift jacket structures horizontally and vertically are discussed in this

chapter. Lifting large jackets have required substantial loadout frames.

Figure 5.1 Vertical Lifting of Jacket

86

Figure 5.2a Horizontal Lifting of Jacket-Loadout operation at Fabrication Yard (2800ton)

Figure 5.2b Horizontal Lifting of Jacket-Dual Crane Lifting a Tripod Jacket (6200 ton)

87

Figure 5.2c Horizontal Lifting of Jacket-Dual lift of a Jacket from transportation barge

Figure 5.3 ISO View of lifting horizontal Jacket (3150ton)

88

CHAPTER 6 MODULE LIFTING

6.1 Introduction

Normally, deck structures are broken to several modules and fabricated on the ground

block by block. After fabrication, they will be assembled together by lifting. If the

deck is a truss deck, the obvious problem is that during fabrication, we do not have

truss action in the deck, so the deflection of the deck may be very large such that final

fit-up could pose major problem. For opened deck, the deflection will not pose a

problem, but we have to make sure the deck leg work points do not shift during

assembly. It is obvious that opened deck is cheaper to fabricate than a truss deck

provided the plate girders in the opened deck are not too expensive. When a deck is

fabricated, we usually turn it upside down to facilitate downhand welding position.

After the deck plate is welded to all the deck beams. It will be turned over 180 degrees

to a correct position. For this operation, simple temporary padeyes will be provided at

the edge of the deck. The only difficulty in this operation is that the deck is half-

finished, so it is still very flexible.

With the DB102 and the S7000, modules of up to 10 000t can be lifted using cranes in

tandem. The full capacity of the crane vessels is not available as they normally operate

at radii greater than that which gives the maximum lift capacity. In addition,

allowances need to be made for weight growth, COG shift and module tilt. Lifts of up

to 8 000t can be lifted using a single crane. Chapter 9.2 presents the detailed analysis

for the completed module.

89

6.2 Vertical Module Lift and Installation

For the design of the deck padeyes, there are few problems that we should be aware of.

First, the confirmation of the deck lift weight and the exact centre of gravity location

will usually come very late during fabrication. So an economic design should be such

that it will not have major impact on the fabrication schedule even though they may be

the last item to be fabricated and installed. The padeye together with the pipe can be

fabricated separately, it then can be easily installed after the centre of gravity is

confirmed. Installation only involves one girth weld. This type of detail will have least

impact on the fabrication schedule if the equipment vendor data is late. For a deck with

a lot of equipment on the main deck, a spreader frame or a spreader bar may be

needed. In this case, the padeye main plate should line up with the adjacent webs of the

primary girders.

In terms of fabrication cost, the cost for fabricating a padeye is extremely small

compared with the overall project cost. It is therefore unwise not to be conservative in

the design, after all, the weight and centre of gravity information would normally not

be available until the end of the job. After fabrication, all primary welds in a padeye

should be l00% NDT (Non Destructive Test). In certain critical locations, a simple

MPI (Magnet Particle Inspection or DPI (Dye Penetrant Inspection) is unlikely to yield

meaningful result, So Ultrasonic Test (UT), Radiography Test (RT) or other NDT

technique may be required.

The choice of material and the design of bumper guide are also very important to

heavy lift. However, these items are the outside scope of this paper.

90

The advantages of lifting the modules in one piece are:

• Increased hook-up, in particular all piping, electrical, instrumentation and

telecommunications cables can be run without spliced connections;

• Higher percentage of commissioning the module onshore;

• No need for bumpers and guides for offshore lifting of individual modules and

• Offshore hook-up rates are approximately five times onshore rates.

The disadvantages of very large modules are:

• Modules have a high concentration of weight over a small area. This may result

in fabrication pads and loadout quay walls needing substantial strengthening of

their foundations;

• Cargo barges and perhaps even the large launch barges may require

strengthening to take the concentrated loads, during transportation;

• If large launch barges are used, then their depth may require substantial

dredging to be carried out at the fabrication yard;

• If the module is built with the drilling derrick or flare, the module may be

higher than overhead obstructions between the yard and sea. Obstructions

include power cables. Thus the module would need to be completed down river

from the main construction yard;

• The preferred load out method for modules is by using trailers. With the very

large modules, there may not be enough trailers available. For a 10 000t

module, the trailers from all owners needed to be combined to perform the

loadout. Joint venturing of trailer owner is quite common and, for example,

91

80% of Europe's trailers were needed for loading out the recent integrated deck

for Gannet;

A most important aspect of the design of large lifts is the control of weight and its

CoG. The typical sequence of weight control includes:

1. During detailed design, a monthly weight report is produced by the

designer.

2. During fabrication the responsibility for the detailed weight report passes to

the fabricator.

3. The designer produces an independent weight report less frequently during

this period.

4. Two weighings are usually required, the first of a partially complete

module and the second just before loadout (normally one week).

5. The installation contractor is able to reduce the lift tolerances on the basis

of the weighing, which in turn gave greater confidence to the offshore lift

To handle a big sling, such as one with 150mm in diameter, is not an easy task. Doing

it onshore is much easier than offshore. For this reason, all the rigging equipment

should be rigged up in the yard before loadout. One of the common mistakes in deck

padeye design is the failure of the design engineer to appreciate the difficulty in

installing the slings and shackles. In many instances, the eye of the padeye is located

below deck. This will make it difficult for the workers to line up the padeye and the

shackle to push in the pin, because there is no platform for them to stand on. In some

cases, the design engineer forgot to cater for the need for link plates to do a level lift. A

good design will make sure that the shackle can be installed on top of the deck where

people can have space to work. Another common mistake is that there must be enough

92

space to physically position the pin and push it through the pin hole. There have been

many cases that an access hole has to be cut in the web of the intersecting girder in

order to install the pin. When a spreader frame is used, it too has to be rigged up in the

yard. Design engineers should remember that the weight of the rigging is heavy. It

could be 100 tons or more. This weight has to be supported on the deck and enough

protection bumpers will have to be installed to keep the sling from damaging any deck

equipment.

When we lift a deck, the maximum out-of-level across a diagonal should be limited to

300mm to 600mm. This means that if we want to achieve almost level lift, we have to

use link plate to bring the CoG directly under the hook. If the sling capacity is not big

enough, we may have to use double slings. This can be accomplished by using sister

plates.

In certain lifting arrangement, contractor uses trunnion or padeye details. This is to

remove the requirement for very large shackles for the lift and allow the sling to turn.

For sling or cable laid sling, the sling capacity may be de-rated if it is bent around a

small object, etc. If the cable laid sling is already 300mmφ, say, we may not be able to

find a big enough wide-body shackle to go with the sling without derating the sling

capacity. In this case, a trunnion detail is an attractive alternative. For very heavy lift,

some engineers specify precast lifting eye. This is not a cheap solution. Since this is a

proprietary detail, it will not be discussed here.

Before we do the lift, we should also check the strength as well as the eccentricity on

the prongs of the hook. Using double slings at the deck level is acceptable, but at the

93

prong location, one sling will take more load than the other, because the first sling will

have already taken up a lot of space. This eccentric load may cause eccentricity

moment at the prong which may not have been designed for. If this moment causes the

prong to twist or rotate, we have to make sure the lines on the crane hook will not jump

out of the sheave. This will have to rely on the experience of the barge superintendent.

Before the deck is lifted, the derrick barge is set up some distance away from the

platform with perhaps 8 point mooring arrangement. When the deck is picked up from

the material barge, we have to walk the barge forward for setting the deck. However,

enough bumper guides will have to be provided to make sure the package will not be

damaged during setting. For dual barge or dual crane lift, we have to pay attention to

the relatively crane tip movement. This may change the load distribution of the

structure. It will be very critical if it is a marginal lift.

94

6.3 Deck Panel Flip-Over

To fabricate a topside module structure, the most common method is to sub-assembly

each deck panel on ground level, and stack them one level by another. Most of topside

modules are consist of three, or four deck levels. The lifting weight of a single deck

panel structure can go as heavy as 1,200 ton, like Malampaya project shown Figure

6.1.

To ease the fabrication work, some of deck panels are built upside down. A typical

erection sequence is as below:

• Lay the completed flat steel deck plate on temporary support,

• Weld main beams onto the deck plate,

• Secondary beams join to the main beams and

• Fit-up vertical column and braces.

The great advantage for the above fabrication method is to change welding process

from top welding into bottom welding, which leads into the benefit for welders and

time saving for the project.

It is required lots of detailed engineering to flip over the completed deck panel. As it is

involved many different steps, engineers must perform structural stress analysis for

each step as shown Figure 6.2. Temporary strengthening may be required for certain

area in case of over stress occurred. Spreader bars are utilized to facilitate the rotation.

Two or three lifting cranes may be mobilized to complete the flip-over operation as

shown in Figure 6.3.

95

6.4 Summary

Practical considerations for module lifts, which include vertical lifts and flip-over are

discussed in this chapter.

One of the most important aspects of the design of large lifts is the control of weight

and the CoG of the module. This requires a proper sequence of weighing scheme to

ensure the accuracy of these parameters. The locations of padeyes and arrangement of

slings are also to be considered properly. Link-plates or additional shackles are

frequently used in lift design to ensure level installations.

For deck panel flip-over operation, force distribution between two cranes or two

hooks should be calculated precisely. The forces at two hooks vary with the change of

the module incline angle during flip-over.

96

Figure 6.1 Deck Panel Stacking in progress (Panel lifting weight: 1,200 ton)

97

Figure 6.2 Computer Model for Deck Panel Flip-over

98

Figure 6.3 Deck Panel – 180 Degree Flip-Over

99

Figure 6.4 Module Lifting – Four Sling Arrangement

100

Figure 6.5 Module Installation – One Lifting Bar Arrangement

Figure 6.6 Module Lifting - Figure 6.7 Module Lifting - Two Bars System Three Bars System

101

Figure 6.8 lifting with a spreader frame Figure 6.9 Multi-Tier Rigging System

Figure 6.10 Tendem Lift of a Module

102

CHAPTER 7 FPSO STRUCTURE LIFTING 7.1 Introduction

The lifting operation for FPSO (Floating Production Storage and Offloading) project

involves the loadout from fabrication site, transportation to integration yard and

installation onto FPSO Hull deck. The topside modules can be fabricated in various

locations. The module size and weight are engineered to the certain lifting vessel

during the detailed design stage.

The followings are the lifting operation carried out in Sembawang Yard for Laminaria

& Corallina Development Project.

The sheerleg crane vessel namely Asian Hercules II was used for the operation. Most

of modules were directly lifted up at the Erection yard, transported to the Hookup yard

on crane hook for a distance of approximately 2.2km, and then installed onto FPSO. In

General, it took one day to complete one module lifting operation from preparation,

loadout and installation. However, there were cases that two modules were installed

onto FPSO within a day.

7.2 Lift Procedures and Considerations for FPSO Modules

GENERAL

• The communication channels were set-up for all the parties, such as Owner

(WOS), Lifting contactor (ALPL), fabricator (SME), Marine Warranty

Surveyor (LOC) etc, for different stages as below:

• during the preparation works

• during the Loadout

• during the Transportation

• during the installation operation:

103

• A flowchart showing the relationship of all parties along with responsibilities

for the operation covered under the operation.

• The estimated operating schedule for the lifting operation must be agreed prior

to the operation

• For each module, a specific procedure was prepared with all the necessary

calculation and detailed drawings.

PREPARATION FOR LOADOUT

General Preparation

The Erection site of module must be cleared from all obstructions such as

temporary supports, construction equipment, movement of crane etc.

Temporary scaffolds or other facilities shall be in place at the designated lifting

padeyes to facilitate installation and remove of rigging system.

It is crane operator’s responsibility to provide and handle the tag lines. Four tag

lines will be attached to each of modules during lifting. The minimum length

shall be 15 meters.

Environmental Criteria

The module lifting/installation was carried out in sheltered water.

Wave and Swell

No relative movements of the vessel anticipated due to lifting/installation

carried out in sheltered harbour. Any vessel movement was monitored closely.

Water depth

The water depth charts for the quay of both loadout and installation yard were

surveyed prior to crane vessel arrival to ensure sufficient water depth.

104

Wind

Hercules II can be operated at wind speed of 20 m/s during hoisting in harbour

condition. However for lifting operation, a wind speed of 5m/s is the limitation.

If higher wind occurs, a decision shall be made by agreement of all parties both

prior to the commencement of lifting and during the operation itself.

Consensus

Lifting operation was not initiated unless the Mater of Asian Hercules II Crane

vessel and representatives from all parties (owner, SME and LOC) agreed that

the lifting conditions were safe. Information regarding to wind, wave and swell

of Singapore at the time of the operation was obtained from the weather station.

Lifting Crane

For the detail of Lifting crane Asian Hercules II, refer to Chapter 3.2.1a.

LOADOUT • On the day of the lifting operation, the floating crane was moored into

position. Lower the hook and connect to rigging system as shown on

detailed drawing.

• Hook blocks were then raised until the slings are just taut. At this point,

slings/shackles and spreader bar was inspected. Prior to the lifting, the LOC

certificate shall be provided and checked off on the checklist.

• Lift-up the module until it is well clear from temporary support and other

obstacle. At the point of lifting clear of temporary support, checks should

be carried out to allow the two fixed points touching footing pads on hull

deck first, otherwise adjustment shall be made.

105

• Hercules II then raise boom to the maximum, i.e., enough gap between

crane boom and module.

• De-mooring all the mooring lines.

• Hercules II is ready for sail to Berth 8 – Installation yard.

TRANSFER OF Module

The module will be transported to Berth 8 for installation on the Hook of

Hercules II for a distance of approximately 2.2km per the transportation routine

drawing.

INSTALLATION

Asian Hercules II will lay two stern anchors. Hercules II will be moored

perpendicular to FPSO. The port and starboard forward moorings are to be tied

with bollards on the FPSO. Two fenders (1.2m OD x 1.5m in length) will be

utilized in front of Hercules II.

FPSO shall be moored at Berth 8 with adequate mooring lines. The mooring

calculation shall be approved by Client & surveyor. For installation of module,

the FPSO will be trimmed to even keel position. The pre-installed footing on

hull deck should be checked for their condition and dimensions. The

temporary scaffoldings shall be provided to access module for derigging

purpose.

Two pre-slings for mooring of the lift vessel to the Hull, will be attached to the

hull own bollards rigged down along the hull side and the ends with soft eyes are

located approximately 1m above sea water line.

106

• Final check on the mooring conditions of Hercules II.

• Hercules II manoeuver herself to slowly lower the module slowly onto Hull

deck to match with pre-installed footings. Prior to lowering, a check shall be

completed of barge/vessel moorings to confirm the continuation of operation.

• Client (WOS) /Marine Warranty surveyor (LOC) to check, confirm and accept

that module is properly installed.

• Starting minimum bolting with the approval of LOC prior derigging.

• The crane barge is ready for de-mooring for next lifting.

SAFETY ANALYSIS

The Job Safety Analysis (JSA) was conducted together with Client, Marine

warranty surveyor, Lifting contractor. The critical points and caution area

during the operation will be highlighted.

CHECK LIST

Prior to each lift, the check lists in Table 7.3 to 7.5 were checked and signed by all three parties.

7.3 Rigging Systems with Multiple Spreader Bars

Rigging systems with one, two and spreader bars, as shown in Figure 7.1, are

extensively use in the lifting and installation of FPSO modules. The configuration

and force distribution in the rigging system have been discussed in Chapter 4.

7.4 Lifting of Lower Turret

The 680ton Turret shown in Figure 7.2 was built at Noell Imac’s yard in

Mussafah, Abu Dhabi. The turret was transported to Singapore on Ocean going

heavy lift ship “Happy Buccaneer”. The turret was offloaded by Asian

Hercules and stored at Berth 8 of Sembawang yard until installation onto FPSO

for a period of three months.

107

For installation of the Lower Turrent into FPSO Moon pool, the following

challenges were faced:

Crane Selection Choose a right crane which is able to lift the Turret across over FPSO

(50m wide and 22 m height above sea water). Or else to shift FPSO is a costly operation.

Crane selected: ASIAN HERCULES II 3200Mton Floating Crane Crane Boom : A-Frame And JIB in 0 degree

Max. dry weight of Turret = 680.0 Mton Weight of lifting rigging system = 24.0 Mton ( Sling 19mton + Shackle 5mton = 24Mton ) ______________________________ Total Lifting Loadings: 704.0 Mton

Considering Dynamic Factor of 1.05, lifting weight: 739.2 Mton

Lifting Requirement: Minimum out-reach = 87.00M

Turret to Ship: 20.35 m Ship width: 50.00 m Clearance 16.65 m

Minimum hook height = 62.5 M

From crane chart: At out reach of = 87.0m Hook height = 70.0 m > 62.5 m Ok! Lifting capacity = 900 Mton > 739.2 Mton Ok!

Sling Selection

Due to a small clearance (169mm) between turret and moonpool, the tilt angle must be as minimum as possible.

As only three padeyes are installed, two grommet slings were used as the balance slings to crane hook via single Shackle.

Turret Installation For installation of Lower Turret, the FPSO was trimmed to even keel position,

and the watertight moon pool closing plate was in place with the lugs on the

closing plate welded. Three vertical support jacks installed on the moon pool

108

closing plate and set to the theoretical elevation. Three horizontal jacks were

also in position. Pumps necessary to activate the jacks was ready and tested.

Video Cameras installed inside moon pool and working properly. Gear for

rotating chain guides was in place. All the scaffoldings and other temporary

equipment inside the moon pool shall be removed to avoid any clashing with

turret during lowering operation.

Due to a small clearance (169mm) between turret and moonpool, six nos of old

ropes or cables (appr. φ50mm) as guide protections were evenly installed inside

the moon pool (against the moon pool circular wall) to protect the paint during

the turret lowering operation. Three nos of spot lights were installed in the

Turret to illuminate area where the video cameras are looking at. These lights

were facilitated with cables and end sockets for connecting the power lines at

hull deck.

The closing plate seal pressurization system as installed earlier must be

disconnected and the water filled seals must be drained and inflated with

compressed air to a pressure of 2.5 bars one by one such that one seal system

remains active at any time.

The floating crane was moored into its position. Lower the hook and connect to

the turret rigging system. Raise Hook block until the slings are just taut. At this

point, slings and shackles were thoroughly inspected. Lift-up to well clear any

obstacle, i.e. two meters between lowest point of the Turret and highest point of

109

obstacles on berth site. Rotate the Turret 90 degree clockwise by using folk lift.

Hercules II continues raise A-Frame to a boom angle of 61 degree. Retrieve

forward anchor. Move backward with the assistance of anchor lines until the

center line of turret is in line of moon pool. Release the mooring line on

starboard side. Hercules II moves sideward until the turret is on top of moon

pool. Drop the forward anchor. Tie the starboard mooring line onto a new

bollard of Hull.

Start to lower the Turret slowly into the moon pool. When chain cable is at the

level of the vessel deck, connect the chain stopper rotating slings to the main

deck. Check alignment at this stage and make adjustment when necessary.

Stop at the level where the guide wires start being functioning to check equal

activating. Video cameras will be used to monitor clearance between the

chainstoppers and the closing plate. The clearance will be adjusted by means of

the hoists fitted on vessel deck. Continue to lower the turret into the moon pool

until it is in contact with the 3 supporting jacks. WOS/Marine Warranty surveyor

(LOC) to check, confirm and accept that turret is properly supported by the 3

jacks prior to derigging - completion of lifting operation.

Figures 7.3, 7.4 and 7.5 show design details of lifting and installation of other

parts of the turret.

110

7.5 Lifting of Gas Recompression Module

For each lifting, lifting crane capacity was studied. The following is the details

of lifting of Module PX04, the gas recompression module, as shown in Figure

7.6.

The estimated lifting weight for each PX04 is 1001.0 ton

The lifting weight of PX04: 1001.0 Mton

Adding the weight of slings, shackles and Spreader bars: 78.0 Mton

Total: 1079.0 Mton

Considering Dynamic Factor of 1.05, lifting weight: 1133.0 Mton

Crane Type: ASIAN HERCULES II, 3200Mton Floating Sheerleg Crane

Crane Boom: A-Frame in Position I with JIB (0°)

Lifting Requirement:

Minimum out-reach = 70.0m

Minimum hook height = 86.0m (5m clearance)

From crane chart:

At out reach of = 70.0m

Hook height = 87.4m > 86.0m ok!

Lifting capacity = 1500Mton > 1133.0Mton Ok!

111

7.6 Lifting of Flare Tower The installation of the 92m of Flare Tower onto FPSO, as shown in Figure 7.7 was

studied during detailed design stage of Flare Tower. In general, two methods were

discussed as below:

Method A: To install the Flare Tower in two pieces, ie, to cut flare tower at mid

section.

Method B: To install the Flare Tower in one complete piece.

Advantages:

Method A:

- The Flare Tower weight can be reduced

- No any technical issue during lifting/installation

Method B:

- Time saving for both heavy lifting crane and fabrication

Disadvantages:

Method A:

- Required two separate lifts

- As the lifting height limitation of Hercules II JibII, the fly Jib is

required for installation the upper part. This would lead into

time/money costing for the boom changing.

- Safety issue. To connect the upper part onto the lower part, the welding

must be carried out up the height of 62m above the sea level. This must

be avoided to reduce any potential risk.

Method B:

- The steel weight increased slightly

112

- Required lot of detailed engineering study to ensure safety, clashing

free and cost saving

Method A was not chosen due to high risk up in the air.

For method B, following critical issues were studied carefully:

a) The flare Tower was fabricated on ground. Both main hook and Jib hook were

utilized to upbend as shown in Figure 7.6. Additional padeye was designed.

Updending structural analysis was performed with the modification of upper

leg.

b) After releasing the main hook, the flare tower was lifted by Jib hook only.

Hercules then carried the flare for about 2.2 km from fabrication site to

integration site. Dynamic analysis was done to ensure the completed system is

safe.

c) Prior to installation, the dimension of stab-in guide and Flare leg was checked.

Special guide system was designed to receive the tower.

d) The upper leg of Flare was protected with the mooring rope.

113

7.7 Summary

Design and operation for lifting FPSO modules are discussed in this chapter. Lift

procedures and considerations for FPSO modules are indicated and rigging systems

with multiple spreader bars are highlighted. Practical design and analysis

considerations for lifting lower turret, gas recompression module and flare tower,

which are unique for stingy requirement of installation accuracy, heavy load and

geometry, are discussed based on real projects.

114

Table 7.1 Lifting Operation Summary for Laminaria FPSO

LIFT NO.

AREA CODE

AREA DESCRIPTION

WEIGHING

SPREADER BAR LENGTH (M) (Eye to Eye)

M O B

LIFT WT

(TON) 1ST

Final BOTTOM

2 NOS TOP

1 NOS

NOS OF SLINGS REQ’D

1 HU10 TURRET ( LOWER ) 1ST 680 - - - - 3 2 PF00 FLARE TOWER 1ST 228 Yes Yes - - 2 3 PX20 LAYDOWN AREA FWD TURRET 1ST 46 Yes Yes - - 4 4 PX19 FLARE EQUIPMENT SUPPORT 1ST 70 Yes Yes - 14.080 6 5 PR05 PROCESS PIPERACK 5 1ST 71 Yes Yes - 2.92 6 6 PR03 PROCESS PIPERACK 3 1ST 26 Yes Yes - 4.72 6 7 PR04 PROCESS PIPERACK 4 1ST 25 Yes Yes - 4.72 6 8 PR01 PROCESS PIPERACK 1 1ST 76 Yes Yes - 2.92 6 9 PX18 CHEMICAL INJECTION 1ST 154 Yes Yes 11.565 16.720 10 10 PX01 LAYDOWN AND STORAGE AREA 1ST 212 Yes Yes - 15.840 6 11 PX02 UTILITY AREA 1ST 345 Yes Yes - 18.480 6 12 PX04 POWER GENERATION 1ST 1,120 Yes Yes 13.545 18.480 10 13 PX03 POWER GENERATION 1ST 589 Yes Yes 13.545 18.480 10 14 PM05/ ACCESS / TRANSPORT ROUTE 1ST 45 Yes Yes - 4.72 6 15 HD20 PEDESTAL CRANE X-1402 1ST 92 - - - - 4 16 HD70 PEDESTAL CRANE X-1401 2ND 92 - - - - 4 17 TX00 TURRET – MANIFOLD STRUCTURE 2ND 697 Yes Yes - 4.100 6 18 TX00 TURRET – GANTRY STRUCTURE 2ND 372 Yes Yes - - 4 19 TX00 TURRET – SWIVEL STACK 2ND 50 - - - - 4 20 PX12 PRODUCED WATER 2ND 411 Yes Yes 13.545 18.480 10 21 PX14 CORALLINA SEPARATION 2ND 780 Yes Yes 19.775 18.480 10 22 PX16 LAMINARIA SEPARATION 2ND 700 Yes Yes 19.775 18.480 10 23 PX17 DEBUTANIZER 2ND 307 Yes Yes 11.565 16.720 10 24 PX09 GAS RECOMPRESSION 3RD 875 Yes Yes 19.775 18.480 10 25 PX11 GAS LIFT 3RD 906 Yes Yes 19.775 18.480 10 26 PX13 GAS LIFT 3RD 967 Yes Yes 19.775 18.480 10 27 PX15 GAS INJECTION 3RD 1,066 Yes Yes 19.775 18.480 10 28 HU90 DEBUTANIZER COLUMN 3RD 95 - - - - 4

Table 7.2 Contingency Actions Plan / Procedure

SCENARIO

PRIMARY CONTINGENCY

SECONDARY CONTINGENCY

Breaking/parting of either shear leg or FPSO mooring line

Standby mooring rope

Tug's assist

Failure of shear leg to lower load

Lower boom Maintain crew to repair

Power failure on shear leg crane

start emergency generator automatically

None

Bad weather The lifting operation will be postponed

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Table 7.3 Preparation Check List

DESCRIPTION WOS LOC SME Asian Hercules vessel in position at Erection yard, ready for lifting operation.

Slings, shackles and spreader bar are ready Certificate for sling, shackle and cranes LOC to have checked the lifting gears Certificate for Spreader bars Qualified rigging supervisor and safety officer are present Shiploosed items removed from module and list prepared Bearing Pads and connecting bolts are ready Erection area cleared of temporary equipment and obstructions.

Temporary access way to the lifting trunnions Movable crane standby

Table 7.4 Loadout Check List

DESCRIPTION WOS LOC SME Hercules II is proper anchored and moored in its lifting position

Check mooring line conditions Shackle and slings are in good condition and attached on module

loadout area is clear of any obstruction This procedure reviewed by all the parties Agreement to commence lifting operations. Certificate of Approval for Lift issued by LOC.

Table 7.5 Installation Check List DESCRIPTION WOS LOC SME

Hercules II mooring its designed position with two mooring lines tie on FPSO, two aft anchors dropped

Set-down area on FPSO is clear of obstacles, ready to receive it.

Footing level/location survey done, trimmed if necessary Bearing Pads and connecting bolts are ready on FPSO Hull deck

LOC certificate provided to commence lifting Agreement to lower down module Module leveled and proper installed Minimum bolt connection approved by LOC Agreement to release crane hook

116

θ2

θ1

CG

θ4

θ3

Fig. 7.1 Rigging arrangement for lifting FPSO modules with spreader bars

One spreader bar

Two spreader bars

3 spreader Bars

θ2

θ1

CG

θ3

θ

θ2

θ

θ3

θ1

CG

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Figure 7.2 Lifting of Lower Turret (680 ton)

Figure 7.3 Lifting of Upper Turret – Manifold Deck Structure with Three Spreader Bars

118

• As the Gantry Structure is transported to installation yard on Barge “Sea

Prosper”, proper seafastening removal procedure was established prior to lifting; • The four slings are also very carefully selected due to COG eccentricity

Figure 7.4 Lifting of Upper Turret – Gantry Structure

Single sling is attached to Swivel Stack with the balanced system to crane hook.

Figure 7.5 Lifting of Swivel Stack – Bottom Assembly

119

Figure 7.6 Lifting of Gas Recompression Module

120

Figure 7.7 Upending and Lifting of 92-metre Flare Tower

121

CHAPTER 8 SPECIAL LIFTING FRAME DESIGN

8.1 Introduction

A versatile lifting frame is designed for the loadout / installation of six pallets (topside

structures) onto Shell EA FPSO at Sembawang Yard.

The weight and COG of six pallets used for the lifting frame design is listed in Table 8.1.

As we can see from Table 10.1, the COG for each pallet is different from other. Also, the

lifting point distances in Y-direction for Separation Pallet port and Power Generation

port are not the same as others. It is a challenge to make an uni-frame used for 6 lifts.

The final design weight is based on the pallet self-weight with 15% contingency plus

lifting frame weight and rigging weight. Dynamic factor of 1.5 is considered at the same

time. The design is performed in accordance with API RP2A and AISC (American

Institute Steel Construction) Allowable Stress Design 9th Edition. The lifting frame

analysis is performed by the software SACS (Structural Analysis Computer System).

With the lifting frame weight and rigging weight, the total weight used in analysis is

listed in table 8.2.

The hook point is 26 meters high from the lifting frame for all pallets except the pallet

Power Generation Port, in which the hook point is 16 meters considered due to hook

height limitation. Tube check and joint/overlapping check against API RP 2A are made

and the dynamic factor of 1.50 is considered. It is found that all members and joints are

sufficient. The maximum stress ratio for member check is 0.86 on the member 2-4 when

pallet Power Generation Port is lifted in Table 8.3.

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8.2. Effect of the Shift of the Centre of Gravity Lifting Point Location Coordinates (MM) Point No X Y

1 0.0 18480 2 18060 18480 3 0 0 4 18060 0

Reaction loads without COG shifting

WT COG (mm) Base Reaction (ton) Pallet (ton) X Y 1 2 3 4

Cooler 998.0 9465 8640 222.1 244.5 252.9 278.5 Utility 1088.8 8120 9340 302.9 247.4 296.4 242.1 Separation (Port)

860.0 9830 10710 227.2 271.3 164.8 196.8

Separation (Starboard)

680.4 9330 9240 164.4 175.8 164.4 175.8

Compression (Port)

594.7 9840 6740 98.7 118.2 172.0 205.8

Compression (Starboard)

618.7 8840 9240 158.0 151.4 158.0 151.4

Power (Port) 1063.4 13040 9073 145.1 376.9 150.5 390.8 Power (Starboard)

780.2 12640 9840 124.7 290.8 109.5 255.3

Reaction loads with COG 500mm shifted towards –ve X-direction

WT COG (mm) Reaction (ton) Pallet (ton) X Y 1 2 3 4

Cooler 998.0 8965 8640 235.0 231.6 267.6 263.8 Utility 1088.8 7620 9340 318.1 232.2 311.3 227.2 Separation (Port)

860.0 9330 10710 240.9 257.5 174.8 186.8

Separation (Starboard)

680.4 8830 9240 173.9 166.3 173.9 166.3

Compression (Port)

594.7 9340 6740 104.7 112.2 182.4 195.4

Compression (Starboard)

618.7 8340 9240 166.5 142.9 166.5 142.9

Power (Port) 1063.4 12540 9073 159.6 362.5 165.5 375.9 Power (Starboard)

780.2 12140 9840 136.2 279.3 119.6 245.2

y

x

1 2

4 3

123

Reaction loads with COG 500mm shifted towards +ve X-direction WT COG (mm) Reaction (ton) Pallet

(ton) X Y 1 2 3 4

Cooler 998.0 9965 8640 209.1 257.5 238.2 293.2 Utility 1088.8 8620 9340 287.6 262.6 281.5 257.0 Separation (Port)

860.0 10330 10710 213.3 285.1 154.8 206.8

Separation (Starboard)

680.4 9830 9240 155.0 185.2 155.0 185.2

Compression (Port)

594.7 10340 6740 92.7 124.2 161.5 216.3

Compression (Starboard)

618.7 9340 9240 149.4 159.9 149.4 159.9

Power (Port) 1063.4 13540 9073 130.7 391.4 135.5 405.9 Power (Starboard)

780.2 13140 9840 113.2 302.3 99.4 265.4

Reaction loads with COG 500mm shifted towards –ve Y-direction

WT COG (mm) Reaction (ton) Pallet (ton) X Y 1 2 3 4

Cooler 998.0 9465 8140 209.2 230.4 265.8 292.7 Utility 1088.8 8120 8840 286.7 234.2 312.6 255.4 Separation (Port)

860.0 9830 10210 216.5 258.6 175.4 209.5

Separation (Starboard)

680.4 9330 8740 155.6 166.2 173.3 185.3

Compression (Port)

594.7 9840 6240 91.4 109.4 179.3 214.6

Compression (Starboard)

618.7 8840 8740 149.4 143.2 166.5 159.6

Power (Port) 1063.4 13040 8573 137.1 356.2 158.5 411.6 Power (Starboard)

780.2 12640 9340 118.3 275.9 115.8 270.1

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Reaction loads with COG 500mm shifted towards +ve Y-direction

WT COG (mm) Reaction (ton) Pallet (ton) X Y 1 2 3 4

Cooler 998.0 9465 9140 234.9 258.7 240.1 264.3 Utility 1088.8 8120 9840 319.1 260.7 280.2 228.9 Separation (Port)

860.0 9830 11210 237.7 283.9 154.2 184.1

Separation (Starboard)

680.4 9330 9740 173.3 185.3 155.6 166.2

Compression (Port)

594.7 9840 7240 106.1 126.9 164.6 197.1

Compression (Starboard)

618.7 8840 9740 166.5 159.6 149.4 143.2

Power (Port) 1063.4 13040 9573 153.1 397.7 142.5 370.9 Power (Starboard)

780.2 12640 10340 131.0 305.5 103.1 240.5

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8.3. Sling Forces Unit : kN

SACS MEMBER NO.

18-22 17-22 20-22 19-22 16-22 15-22 13-22 14-22

Power Generation Starboard 869.00 957.68 2145.91 1649.33 1525.19 1844.42 815.80 833.53

Separation Pallet Starboard 1276.90 1028.62 1596.13 851.27 851.27 1596.13 1028.62 1294.64

Separation Pallet Port 1560.66 1525.19 2358.72 1241.43 1046.35 1667.07 993.15 1347.84

Compression Pallet Starboard 1259.17 957.68 1436.52 709.39 709.39 1436.52 957.66 1259.17

Compression Pallet Port 904.47 602.98 1064.08 656.19 904.47 1879.88 1223.70 1152.76

Power Generation Port 1294.64 1294.64 2908.50 2553.81 2571.54 3032.64 1365.58 1294.64

126

8.4 Padeye Checking Also refer to the typical padeye in Figure 3.13.

SHACKLE SELECTION

Required SWL (SWL = SLt) SWL 480.00 tons ( As per lifting analysis ref: section 2)

PROPOSED SHACKLE PROPERTIESType 500 M.T. Green Pin Anchor Shackle (model P-6036)Shackle I.D.Safe Working Load SWLh = 500 tons Safety Factor for Shackle SF = 4Minimum Breaking Strength MBS = 2000 tonsFactor of Safety MBS/SWL = 4.17 > 4.0. O.K!Pin Diameter Dh = 185.00 mmJaw Width Wh = 250.00 mmInside Length Lh = 700.00 mm

PADEYE GEOMETRYMain Plate : No. Nm = 1 nos

Thickness Tm = 80.00 mmRadius Rm = 381.00 mm

Cheek Plate 1 : No. Nc1 = 2 nosThickness Tc1 = 50.00 mmRadius Ra1 = 305.00 mm

Cheek Plate 2 : No. Nc2 = 0 nosThickness Tc2 = 0.00 mmRadius Ra2 = 0.00 mm

1. Check Pin Hole Diameter :Pin Dia. + 6mm Allowance = Dh + 6 mm = 191.00 mmPin Hole Dia. Provided D = 190.000 mm

2. Check Main Plate Radius :Minimum Radius = 1.25*D = 237.50 mm

or = D/2 + 3" = 171.20 mmRadius Provided Rm = 381.00 mm O.K!

3. Check Shackle Inside Length :Minimum Inside Length = (Ds + Rm- D/2+6mm) = 407.00 mmInside Length Provided Lh = 700.00 mm O.K!

( where assuming sling diameter Ds = 115mm )4. Check Shackle Jaw Clearance :

Minimum Clearance Clr = 6.00 mmRequired Centraliser plate thickness = (Wh-Nm*Tm-Nc1*Tc1-Nc2*Tc2-2*Clr)/2

= 29.000 mmProvide Centraliser Plate = 25.000 mm

127

PADEYE STRENGTH CHECKS

Padeye Des. Load Pd = SWL * 1.50 = 720.00 tons (Dynamic Fac. = 1.5) ( where SWL = SLt )

MATERIAL : Type GRADE -50Yield Strength Fy = 345.00 MPa

1. CHECK BEARINGAllow. Bearing Stress Fp = 0.9 * Fy = 310.50 MPaBearing Area Ap = Dh*(Nm*Tm+Nc1*Tc1+Nc2*Tc2)

= 33300.00 mm^2Actual Bearing Stress fp = Pd / Ap = 212.11 MPa O.K!

Stress Ratio = 0.68

2. CHECK PULLOUT SHEARAllow. Shear Stress Fv = 0.4 * Fy = 138.00 MPaShear Area :Length : Main Plate Lm = Rm - D/2 = 286.000 mm

Cheek Plate 1 Lc1 = Ra1 - D/2 = 210.000 mmCheek Plate 2 Lc2 = Ra2 - D/2 = 0.000 mm

Area : Av = (Nm*Tm*Lm +Nc1*Tc1*Lc1+Nc2*Tc2*Lc2)*2 = 87760.00 mm^2

Actual Shear Stress fv = Pd / Av = 80.48 MPa O.K!Stress Ratio = 0.58

3. CHECK TENSION FAILURE AT 3.1 SECTION THROUGH PINHOLE

Allow Tensile Stress Ft = 0.45 * Fy = 155.25 MPaTensile Failure Area At = Nm*Tm*(2*Rm-D)+Nc1*Tc1*(2*Ra1-D)+Nc2*Tc2*(2*Ra2-D)

= 87760.00 mm^2Actual Tensile Stress ft = Pd / At = 80.48 MPa O.K!

Stress Ratio = 0.52

3.2 SECTION AROUND UNDERSIDE OF CHEEK PLATE 1Allow Tensile Stress Ft = 0.60 * Fy = 207.00 MPaLength of Section Lt = approx 1.5*pi*Ra1 = 1437.28 mmArea of Section At = Tm*Lt = 114982.29 mm^2Actual Tensile Stress ft = Pd / At = 61.43 MPa O.K!

Stress Ratio = 0.30

4. CHECK ATTACHMENT FOR CHEEK PLATES

CHECK CIRCUMFERENTIAL WELD BETWEEN CHEEK PLATE & MAIN PLATEE70XX ElectrodeWeld Strength Ftw = 70 ksi = 483.00 MPaAllow. Shear Stress Fsw = 0.3 * Ftw = 144.90 MPaLoad in Cheek Plate Pcd = Pd*(Tc1)/(Nm*Tm+Nc1*Tc1) = 1962.00 kNWeld Size Req'd Lg = Pcd / (Fsw*Ra*π*0.707) = 19.99 mmMinimum (AISC) : For Main Plate thk. > 3/4" = 8.000 mmWeld Size Provided : Fillet Weld = = 35.00 mm O.K!

128

CHECK ATTACHMENTS OF PADEYES

A. SECTION PROPERTIES Y

'a'

'b' 5

'a' 'a' 'a'

'b' 2 3

4 'b'

Location 2

'b' 1 --- bottom flange X'a'

Location 1

129

CHECK ATTACHMENTS OF PADEYES (CONT'D)

A. SECTION PROPERTIES

About X-X axis

S/no Description Dimension Dimension Y Area AY AY*Y I x-x ownof 'a' 'b' (mm) A (mm^3) (mm^4) (mm^4)

Elements (mm) (mm) (mm^2)

1 NIL 0.00 0.00 0.000 0.00 0.000E+0 0.00E+00 0.000E+02 NIL 0.00 0.00 0.000 0.00 0.000E+0 0.00E+00 0.000E+03 NIL 0.00 0.00 0.000 0.00 0.000E+0 0.00E+00 0.000E+04 80 x 1312 80.00 1312.00 656.000 104960.00 6.885E+7 4.52E+10 1.506E+105 NIL 0.00 0.00 1312.000 0.00 0.000E+0 0.00E+00 0.000E+02a NIL 0.00 0.00 0.000 0.00 0.000E+0 0.00E+00 0.000E+03a NIL 0.00 0.00 0.000 0.00 0.000E+0 0.00E+00 0.000E+0

Summation 104960.00 6.885E+7 4.52E+10 1.506E+10

Yc , Distance to centroid of section measured from bottom flange = summation(AY)/summation(A)Yc = 656.00 mm

I x-x = summation(I x-x own) + summation(AY*Y) - [{summation(AY)}^2/summation(A)]I x-x = 1.506E+10 mm^4Sxx = 2.295E+7 mm^3

Height of main plate = 1312.00 mmThickness of main plate = 80.00 mmArea of Main plate, Aweb = Height x Thickness = 104960.00 mm^2

About Y-Y axis

S/no Description Dimension Dimension X Area AX AX*X I y-y ownof 'a' 'b' (mm) A (mm^3) (mm^4) (mm^4)

Elements (mm) (mm) (mm^2)

1 NIL 0.00 0.00 0.00 0.00 0.00 0.0E+00 0.000E+02 NIL 0.00 0.00 0.00 0.00 0.00E+0 0.0E+00 0.000E+03 NIL 0.00 0.00 0.00 0.00 0.00E+0 0.0E+00 0.000E+04 80 x 1312 80.00 1312.00 0.00 104960.00 0.00 0.0E+00 5.598E+75 NIL 0.00 0.00 0.00 0.00 0.00 0.0E+00 0.000E+02a NIL 0.00 0.00 0.00 0.00 0.00E+0 0.0E+00 0.000E+03a NIL 0.00 0.00 0.00 0.00 0.00E+0 0.0E+00 0.000E+0

Summation 104960.00 0.000E+0 0.000E+0 5.598E+7

Xc , Distance to centroid of section measured from middle of main plate = summation(AX)/summation(A)Xc = 0.00 mm

I y-y = summation(I y-y own) + summation(AX*X) - [{summation(AX)}^2/summation(A)]I y-y = 5.598E+7 mm^4Syy = 1.399E+6 mm^3

130

CHECK ATTACHMENTS OF PADEYES (CONT'D)

Sling Angle (w.r.t Horizontal) theta = 60.00 DegreeTensile Force = SWL * SIN (theta) T = 415.69 tonsShear Force = SWL* COS (theta) SHF = 240.00 tonsOut-of-Plane Force = SWL*0.05 (5% of actual force) OPF = 24.00 tons

Dynamic Factor = 1.50Design Tensile Force = (Td = T* 1.50) Td = 6116.91 kNDesign Shear Force = (SHFd = SHF* 1.50) SHFd = 3531.60 kNDesign Out-of-Plane Force = (OPFd = OPF*1.50) OPFd = 353.16 kN

Height of Centerline of Hole H = 0.306 mDistance from bottom flange to centreline of hole Hm = 1.025 m

Mxx = SHFd x H - Td x (Hm -Yc) = 1176.47 kN-mMyy = OPFd x H = 108.07 kN-m

1. CHECK SHEAR STRESSAllow. Shear Stress Fv = 0.4 * Fy = 138.00 MPaIn-plane :Actual Shear Stress fvx = SHFd/Aweb = 33.65 MPa O.K!

Stress Ratio = 0.24

2. CHECK TENSILE STRESSAllow. Tensile Stress Ft = 0.6 * Fy = 207.00 MPaActual Tensile Stress ft = Td/Summation(A) = 58.28 MPa O.K!

Stress Ratio = 0.28

3. CHECK BENDING STRESSAllow. Bending Stress Fb = 0.6 * Fy = 207.00 MPaIn-plane :Actual Bending Stress fbx = Mxx/Sxx = 51.26 MPa O.K!

Stress Ratio = 0.25Out-of-plane :Actual Bending Stress fby = Myy/Syy = 77.22 MPa O.K!

Stress Ratio = 0.37

4. CHECK COMBINED STRESS

Combined Stress Ratio = ft/Ft + (fbx+fby)/Fb = 0.90 O.K!

5. CHECK VON MISES YIELDING CRITERIAAllow. Combined Stress Fc = 0.66 * Fy = 227.70 MPa

5.1 Check maximum combined stresses at main plate location.Sum of Stresses in X-Plane fx = ft + fbx = 109.54 MPaSum of Stresses in Y-Plane fy = = 77.22 MPaAve. Shear Stress txy = (SHFd/Aweb) = 33.65 MPa

Actual Combined Stress fc = (fx^2+fy^2-fx*fy+3*txy^2)^0.5= 113.58 MPa O.K!

Stress Ratio = 0.50

131

8.5 Trunnion Checking Max. Static sling force, Ps Ps = 480 x 0.5 x 1.1 ÷ (Sin60°) = 305 Mton Trunnion Cross Section Area, At At = (914 – 38) x 38 x π = 1004577 mm² Shear Stress, fv = 1.5 x (305 x 9.81 x 1000) ÷ (104577 x 0.5) = 85.83 N/mm² < Fv = 0.4 Fy = 0.4 x 345 = 138 N/mm² OK! Where, 1.5 = Dynamic factor Fy = 345, Material Yielding stress Ring Stress As per Roak Formulas, Cross sectional Area, A= 8 x 1.5 + 16.5 x 1.5 = 36.75 in² C = 6.811 in Moment Inertia, I = 1 /12 x 16.5 3 x 1.5 + 16.5 x 1.5 x (9.75 – 6.811)² + 8 x 1.5 x (6.811 – 0.75)² = 1216 in4 Sectional Modulars, S = 1216 / (18 – 6.811) = 108.68 in3

C

18”

8”

Plate thickness = 1.5”

132

ROARK CLOSED RING ANALYSIS SEMBAWANG SHELL EA PROJECT-LIFTING FRAME TRUNNEQUATIONS FROM 6th ED 01-Mar-01

(AS OF 20 JUNE 1992: MULTIPLE CASES AVAILABLE)THE FOLLOWING ARE ASSUMED CO (ONLY THE FIRST 4 CASES OF EACH CATAGORY)

1) CROSS SECTION2) MODULUS OF ELASTICITY3) POISSON'S RATIO4) RADIUS

CASE NUMBPARAMETERS:TOTAL W SHIFT ANGLE O O o

(kN) (DEG) (DEG) (DEG) (mm)

25 0.0000 0.00 0.0000 N.A. N.A.25 0.0000 0.00 0.0000 N.A. N.A.25 0.0000 0.00 0.0000 N.A. N.A.25 0.0000 0.00 0.0000 N.A. N.A.25 0.0000 0.00 0.0000 N.A. N.A.25 0.0000 0.00 0.0000 N.A. N.A.

16 0.0000 0.00 12.5000 12.5000 N.A.16 0.0000 0.00 25.7000 25.7000 N.A.16 0.0000 0.00 40.5000 40.5000 N.A.16 0.0000 0.00 60.0000 60.0000 N.A.16 0.0000 0.00 0.0000 0.0000 N.A.16 0.0000 0.00 0.0000 0.0000 N.A.

25S 2984.6080 0.00 N.A. N.A. 558.800025S 0.0000 0.00 N.A. N.A. 0.000025S 0.0000 0.00 N.A. N.A. 0.000025S 0.0000 0.00 N.A. N.A. 0.000025S 0.0000 0.00 N.A. N.A. 0.000025S 0.0000 0.00 N.A. N.A. 0.0000

YIELD STR. CROSS SECT. PROPERTIESRADIUS TO RING MPa AREA (mm^2) SECT (mm^3)NEUTRAL AXIS (mm)= 284.2006 344.72 23709.6 1780946.1

133

RESU LTS: MAX. CHECK SEMBAWANG SHELL EA PROJECT-LIFTING FRAME TCIRCUM. TENCIRCUM. TEN MOMENT + BENDING

DEGREES MOMENT CIRCUM.TENADIAL SHEA STRESS RATIOSTRESS RATIOSTRESS RATIO(kN-m) (kN) (kN)

0 60.678 -559.488 0.000 0.114 0.165 0.2795 59.644 -565.277 83.137 0.115 0.162 0.277

10 56.579 -582.364 163.269 0.119 0.154 0.27215 51.594 -609.921 237.502 0.124 0.140 0.26420 44.869 -646.602 303.155 0.132 0.122 0.25425 36.648 -690.589 357.861 0.141 0.099 0.24030 27.226 -739.659 399.657 0.151 0.074 0.22535 16.943 -791.260 427.055 0.161 0.046 0.20740 6.170 -842.608 439.105 0.172 0.017 0.18945 -4.708 -890.786 435.436 0.182 0.013 0.19450 -15.301 -932.851 416.278 0.190 0.042 0.23255 -25.235 -965.947 382.464 0.197 0.069 0.26560 -34.162 -987.411 335.416 0.201 0.093 0.29465 -41.779 -994.882 277.104 0.203 0.113 0.31670 -47.834 -986.393 209.991 0.201 0.130 0.33175 -52.146 -960.461 136.959 0.196 0.142 0.33780 -54.605 -913.617 60.775 0.186 0.148 0.33585 -55.152 -833.370 -15.507 0.170 0.150 0.32090 -53.896 -746.152 -84.473 0.152 0.146 0.29895 -51.027 -653.255 -145.570 0.133 0.139 0.272

100 -46.744 -556.016 -198.361 0.113 0.127 0.240105 -41.259 -455.800 -242.527 0.093 0.112 0.205110 -34.787 -353.985 -277.867 0.072 0.094 0.167115 -27.550 -251.948 -304.302 0.051 0.075 0.126120 -19.767 -151.047 -321.873 0.031 0.054 0.084125 -11.656 -52.609 -330.737 0.011 0.032 0.042130 -3.431 42.085 -331.164 0.009 0.009 0.018135 4.704 131.813 -323.536 0.027 0.013 0.040140 12.554 215.430 -308.336 0.044 0.034 0.078145 19.940 291.871 -286.145 0.060 0.054 0.114150 26.696 360.172 -257.632 0.073 0.072 0.146155 32.673 419.475 -223.545 0.086 0.089 0.174160 37.745 469.036 -184.703 0.096 0.102 0.198165 41.803 508.238 -141.985 0.104 0.113 0.217170 44.763 536.592 -96.315 0.109 0.122 0.231175 46.564 553.746 -48.657 0.113 0.126 0.239180 47.168 559.488 0.000 0.114 0.128 0.242185 46.564 553.746 -48.657 0.113 0.126 0.239190 44.763 536.592 -96.315 0.109 0.122 0.231195 41.803 508.238 -141.985 0.104 0.113 0.217200 37.745 469.036 -184.703 0.096 0.102 0.198205 32.673 419.475 -223.545 0.086 0.089 0.174210 26.696 360.172 -257.632 0.073 0.072 0.146215 19.940 291.871 -286.145 0.060 0.054 0.114220 12.554 215.430 -308.336 0.044 0.034 0.078225 4.704 131.813 -323.536 0.027 0.013 0.040230 -3.431 42.085 -331.164 0.009 0.009 0.018235 -11.656 -52.609 -330.737 0.011 0.032 0.042240 -19.767 -151.047 -321.873 0.031 0.054 0.084245 -27.550 -251.948 -304.302 0.051 0.075 0.126250 -34.787 -353.985 -277.867 0.072 0.094 0.167255 -41.259 -455.800 -242.527 0.093 0.112 0.205

134

CIRCUM. TENCIRCUM. TEN MOMENT + BENDING

DEGREES MOMENT CIRCUM. TENADIAL SHEA STRESS RATIOSTRESS RATIOSTRESS RATIO(kN-m) (kN) (kN)

260 -46.744 -556.016 -198.361 0.113 0.127 0.240265 -51.027 -653.255 -145.570 0.133 0.139 0.272270 -53.896 -746.152 -84.473 0.152 0.146 0.298275 -55.152 -833.370 -15.507 0.170 0.150 0.320280 -54.605 -913.617 60.775 0.186 0.148 0.335285 -52.146 -960.461 136.959 0.196 0.142 0.337290 -47.834 -986.393 209.991 0.201 0.130 0.331295 -41.779 -994.882 277.104 0.203 0.113 0.316300 -34.162 -987.411 335.416 0.201 0.093 0.294305 -25.235 -965.947 382.464 0.197 0.069 0.265310 -15.301 -932.851 416.278 0.190 0.042 0.232315 -4.708 -890.786 435.436 0.182 0.013 0.194320 6.170 -842.608 439.105 0.172 0.017 0.189325 16.943 -791.260 427.055 0.161 0.046 0.207330 27.226 -739.659 399.657 0.151 0.074 0.225335 36.648 -690.589 357.861 0.141 0.099 0.240340 44.869 -646.602 303.155 0.132 0.122 0.254345 51.594 -609.921 237.502 0.124 0.140 0.264350 56.579 -582.364 163.269 0.119 0.154 0.272355 59.644 -565.277 83.137 0.115 0.162 0.277360 60.678 -559.488 0.000 0.114 0.165 0.279

135

8.6 Summary The final design of the lifting frame is shown in Figure 8.1.

The lifting devices of the above spreader frame are the combination of padeye and

lifting trunnions. Padeyes are designed underneath of spreader frame, while the lower

slings remain un-changed, these save lots of rigging changing time during actual lifting

operation. The trunnions above the spreader frame make operator much easier for re-

rigging of slings for next lift. The trunnions are also catered for different COG. The

concept of X-Brace at centre and introduction of thicker joint-can eventually lead into

a lighter frame, 69 ton only. Other concept, four braces at corner, was studied and

found not cost saving. A 50mm thick of the main plate of padeye/trunnions per design

are good enough for the lifting. The above analysis was based on the fabricator stock

of main plate 80 mm thick.

136

Table 8.1 Weight and COG data

C.O.G (See Note) Lifting Point Dist S/No

.

PALLET DESCRIPTION

Pallet Weight

(ton) X

(mm) Y

(mm) X

(mm) Y

(mm)

1 Power Generation Starboard 780 12640 9840 18060 18480

2 Separation Pallet Starboard 680 9330 9240 18060 18480

3 Separation Pallet Port 860 9830 9840 18060 16740

4 Compression Pallet Starboard 619 8840 9240 18060 18480

5 Compression Pallet Port 595 9840 6740 18060 18480

6 Power Generation Port 1063 13040 10840 18060 22015

Table 8.2 Total Weight and COG

Lifting Weight (m.ton) Revised C.O.G (based on frame)

DESCRIPTION Pallet 15%

contin.

Computer Model Frame

5% contin

Misc. Load Rigging &

Padeye

X (mm)

Y (mm)

Power Generation Starboard 897 58 29 12325 9788

Separation Pallet Starboard 782 58 29 9301 9240

Separation Pallet Port 989 58 29 9766 10592

Compression Pallet Starboard 712 58 29 8861 9240

Compression Pallet Port 684 58 29 9750 7020

Power Generation Port 1222 58 29 12777 9084

Note: Origin is located at the lower left lifting point, shown on the left.

x

y

137

TABLE 8.3 MEMBER ANALYSIS RESULT SUMMARY

SACS Group ID 1 2 3 4

PALLET NAME

Criti.

Memb

Max.

UC*

Criti.

Memb

Max.

UC

Criti.

Memb

Max.

UC

Criti.

Memb

Max.

UC

Power Generation Starboard 4-12 0.48 4-21 0.35 2-21 0.28 2-4 0.37

Separation Pallet Starboard 12-20 0.33 1-21 0.20 3-21 0.19 2-4 0.16

Separation Pallet Port 12-20 0.49 4-21 0.31 3-21 0.20 2-4 0.33

Compression Pallet Starboard 12-20 0.29 1-21 0.20 3-21 0.19 1-3 0.13

Compression Pallet Port 15-10 0.39 1-21 0.18 2-21 0.26 2-4 0.27

Power Generation Port 15-10 0.63 4-21 0.64 2-21 0.64 2-4 0.86

* UC: Unity Check = Actual Stress over Allowable stress

138

1

B

DETAIL

1

2

DETAIL

2

SIM

. D

ETAIL

1

A

1

B

SIM

. D

ETAIL

2

2

B

DETAIL

3

R02

0

Figure 8.1 Lifting Frame Details

139

CHAPTER 9 FINITE ELEMENT ANALYSIS FOR LIFTING

DESIGN 9.1 Introduction

Finite Element Analysis (FEA) is a computer based method to simulate and analyse the

behaviour of engineering structures and components under a variety of conditions. It is

an advanced tool that is used in engineering design. The method is comprised of three

stages: (A) pre-processing, in which the analyst develops a finite element mesh of the

geometry and applies material properties, boundary conditions and loads; (B) solution,

during which the program derives the governing matrix equations (stiffness x

displacement = load) from the model and solves for the displacements, strains and

stresses and (C) post-processing, in which the analyst obtains results usually in the

form of deformed shapes and contour plots which help to check the validity of the

solution.

FEA is widely accepted in almost all engineering disciplines. The technique is based

on the premise that an approximate solution to any complex engineering problem can

be reached by subdividing the structural component into smaller and more manageable

(finite) elements. The Finite Element Model (FEM) is analysed with an inherently

greater precision than would otherwise be possible using manual calculations, since the

actual shape, load and constraints, as well as material property combinations can be

specified with much greater accuracy than that used in manual calculations.

It is possible to perform a simulation of a design concept and to determine its real

world behaviour under envisaged environments to enable the concept to be refined

prior to the creation of drawings, when minor cost expenditure is committed and

140

changes are inexpensive. Once a model has been developed, the analysis helps in

evaluating the feasibility of the new design as well as trouble shooting failed

components to refine the design.

This chapter discusses FEM structural analysis in heavy lift design and analysis. Two

critical lift applications, namely, living quarter module lifting and lifting padeye joints,

will be investigated using different finite element models.

9.2 Finite Element Analysis for Module Lifts

9.2.1 Structural and Material Details

A typical living quarter module in North Sea field development project consists of the

following structural components:

• Utility Area,

• Living Quarter Area,

• Cellar deck,

• Helicopter deck,

• Bridge,

• Drain caisson,

• Deluge caisson,

• Sewage caisson,

• Seawater caisson and

• Fire water caisson.

All decks except the cellar deck are plated decks. As for the cellar deck, there is an

open frame structure for free ventilation. The utility area and the living quarter area are

closed and airtight. The deck structure is made to fit the jacket and supported on three

141

points. The interface point is at elevation LAT (Low Astronomical Tide) +20.0m. The

helideck is an octagon of 22.8m internal diameter and is located approximately 4.0m

above the roof. The helicopter deck is designed for landing of a Westland EH101

helicopter.

The lifting analysis is performed using the SACS software. The computer model of the

module consists of eight levels, including the roof and helideck level, from EL.+22.0m

to EL.+50.5m. The module is to be lifted offshore using single hook with a lifting

spreader frame.

The analysis consists of 92 load combinations. They are two for basic load

combinations of two diagonally opposite lifting points carrying 75% of the lift weight;

two combinations with the basic loads and factors; eight combinations with the basic

loads, the factors and couples which simulate CoG (centre of gravity) shift of one

meter towards each frame corner and eighty combinations with horizontal force of 5%

lift weight incorporated in eight directions each to check lifting spreader frame.

The maximum expected lift weight of 1556 ton, which includes module weight of

1391 ton, rigging weight of 65 ton and grillage and sea-fastening weight of 100 ton, is

used as per the design requirements. The consequence factor of 1.15 is added for

members connecting directly to the padeye as per code requirement.

All the members and the joints were checked against the DANISH code as per project

requirement. The load factor used in lifting analysis is tabulated in Table 9.1.

It was considered at the same time that the lift design weight was distributed over the

142

lifting points on the spreader frame such that the two diagonally opposite lift points

carried 75% of the lift weight. In addition, CoG shift of 1m towards each corner of the

frame was considered instead of CoG Shift (fcog) factor of 1.05 in load case 210, 220,

230, 240, 310, 320, 330 and 340.

Design Load Factor = (γc)*(γf)*(DAF)*( fcog)*(SKLt) (9.1) = 1.368 (for load case 200 and 300)

Design Load Factor = (γc)*(γf)*(DAF)* (SKLt) (9.2) = 1.303 (for load case 210, 220, 230, 240, 310, 320, 330 and 340)

Material for secondary beam, external cladding except in Row A and Row B in

accommodation area, internal cladding and deck plate of level one, level three, level

four, level five and level six will be mild steel with yielding stress of 248 MPa.

Material for main beam, plates to be used as part of main steel, external cladding in

Row A and Row B in accommodation area and deck plate of level two, roof and

mezzanine deck, as well as lifting spreader frame will be high strength steel with

yielding stress of 345 MPa.

Deck plate thickness is 6mm except for lay-down area where 15mm is used. External

cladding in Row A and Row B in accommodation area is 6.0mm corrugated plate, in

Row 1 and Row 2, while the others in 4.5mm. Rib pattern dimensions are 230mm

length with 68mm depth and 45° bevel.

The design value of material parameter will be determined by dividing characteristic

value by the partial coefficients γm as given in Table 9.2.

143

The module is designed to be lifted offshore using spreader frame with one hook point.

The frame was connected with the module on the top of helideck at the point A2 (joint

8220) and B2 (joint 8120) as well as on the roof at the point A3 (joint 7230) and B3

(joint 7130). Temporary braces between the roof and helideck level on Row A and Row

B, as well as on Row 2 and Row 3 were provided.

9.2.2 Finite Element Modelling and Analysis

The sling was modelled as weightless tubular with moments at the two ends released.

The minimum sling angle considered was 70 degree as per the information provided by

the installation contractor, Heerema Marine Contractors. Since the system with four

slings connecting a hook is structurally under-constrained, two springs were required to

ensure numerical stability by the SACS program. The two artificial springs were applied

onto joints 1220(A2) and 1130(B3) at EL (+) 17.187. To simulate the uneven

distribution of lift weight at two diagonal opposite lifting points, the elastic modulus of

slings was adjusted proportionally, which was achieved by several SACS runs and using

an iterative method.

Deck plates and external corrugated wall in accommodation area were modelled as shear

plate and corrugated plate respectively.

Members with the same properties are grouped by the computer. A sample list of

member group properties generated by the computer and section properties are

extracted and shown in Table 9.3 and Table 9.4. Plates with the same properties are

grouped by the computer. A list of ‘plate group’ properties generated by the computer

and section properties is extracted and shown in Table 9.5 and Table 9.6.

144

The weight of main steel was generated by SACS program. Other gravity loadings,

which included rigging, secondary and miscellaneous steel, architectural components,

mechanical, piping, and electrical & instrument were manually calculated and added to

the model. The summary of loads is shown in Table 9.7, while Table 9.8 gives sample

of loading description.

Structural Loads

It consists of two groups of loading. One is the computer generated self-weight of the

model. The other is the structural weight derived from manual calculation which

includes leg stabbing guide, secondary beam, plating & grating, corrugated wall,

handrail, staircase and miscellaneous steel.

Architectural Loads

It consists of deck and wall insulation, floor finishes, partition, cladding, ceiling,

furniture, etc.

Mechanical Loads

This consists of dry and operating load from mechanical equipment, HVAC ducting

and fire safety equipment. The loading is separated to three groups.

Piping Loads

It consists of the dry weight of pipes and ducts etc.

Electrical and Instrument Loads

145

This consists of electrical bulk weight and electrical and communication equipment

weight.

Rigging Weight and Grillage & Sea-fastening

This consists of rigging weight of 65 ton and grillage & sea-fastening weight.

Couples to simulate CoG shift of one meter

Couples to simulate CoG shift of one meter towards spreader frame corners.

Horizontal Force of 5% of Lift Weight

5% of lift weight acted on lifting spreader frame horizontally to check the frame.

Structural Analysis Computer System (SACS) suite of software was used to perform

the lifting analysis. A total of ninety-two (92) load-cases were considered in the

analysis. These combinations covered module basic weight combination (2), lifting

case without CoG shift (2), lifting cases with CoG. shift (8) and lifting case with

horizontal force (80), see Table 9.10 for the example. Table 9.11 gives the sample of

75% lifting weight factor of point B2 and A3 at different loading conditions.

Analysis results, such as combined load summation, support reactions and spring

reactions, are given in Table 9.12 to 9.14. All members are found to have stress ratios

less than unity. Members with stress ratios greater than 0.9 are listed in Table 9.15.

All joints are found to have stress ratios less than unity shown in Table 9.16. The

summary of the four sling forces is given in Table 9.17.

146

9.2.3 Discussions

Support condition

The hook point is treated as a fixed point. Slings attached to module are treated as

moment free members. Artificial spring supports must be added for the numerical

stability in computations. Spring stiffness factors should be small to minimise

significant horizontal forces as Table 9.9.

CoG shifting/Load distribution

The above analysis has taken into account of CoG shift of 1.0m, with 75% and 25% of

load distribution on two diagonally opposite lifting points. This is normally not

considered if API RP 2A method is chosen as design code.

Early Weight Control

Weight control report for accurate lifting weight and CoG is still not ready; therefore,

the computer analysis results are good enough for the selection of rigging and lifting

crane vessel.

Rigging system modelling

The requirement of spreader bar/frame per module layout of top level needs to be

identified. The correct sling property (weight less), sling length and offset at padeye

points need to be assessed, and proper releases of all slings need to be specified.

Joint displacement

Designer often tends to make mistake of misalignment of CoG and hook, which leads

the joint displacements to be very large. To overcome this, a few computer runs are

required to find out CoG location and to adjust hook point accordingly.

147

9.3 Finite Element Analysis for Lifting Padeye Connection

9.3.1 Structural Details

The Dan FG jacket is a conventional space frame structure, consisting of 4 legs with

the top of the jacket work points arranged in a grid with a transverse spacing of 20

metres at EL(+) 13.5m. 2 pile sleeves will be attached to each leg of the jacket. The

four legs are double battered at 1:9.4 in both transverse and longitudinal directions.

The top of the jacket cut-off elevation for all four legs of the jacket are at EL(+)

15.000m. Jacket horizontal bracing levels are at EL(-) 39.5m, EL(-) 29.8m and EL(+)

12.6m. The jacket is designed for 42.9m water depth. The height of jacket is 58.4m.

The estimated possible lifting weight for Jacket is 3038 tons, based on the weight

control report.

The jacket will be fabricated in a horizontal position. The fabricated jacket will be

loaded out by lifting it off using ‘Asian Hercules II’ from quayside onto the barge. The

lifting arrangement for loadout is shown in Figure 9.3. Loadout analyses were carried

out to simulate the lifting operation to evaluate the adequacy of the jacket together

with appurtenances & rigging gear during loadout lift.

On reaching its tow destination in the Danish sector of the North Sea, SAIPEM will

carry out the upending with SSCV S7000, see Figure 3.5. The S7000, operating in

dynamic mode at a heavy lift draught of 27.5m, in 43m of water depth, will lift the

jacket off the vessel and upend it using the cranes in tandem. The upending process is

explained in Figure 9.4. 11 steps of upending analyses were performed to simulate

different orientations of the jacket from the initial horizontal position to the final

vertical position of the jacket.

148

During the above analysis, the lifting points were found essentially important. The

critical padeye, hereafter called Joint 164 (from SACS), on Jacket pile sleeve is

analysed using the finite element method (FEM) with the computer program of

MSC/NASTRAN. The purpose is to compute the stress distribution in the four loading

cases during load out and upending as shown in Figure 9.5. As illustrated in Figure 9.6,

the joint 164 consists of two chord members, three bracing members and a pad-eye

member. To simulate the actual loading conditions, loads subjected to lifting by the

sling are applied at the centre of the pad-eye while the other end of each chord or

brace, where the member is strongly supported by other members, is fixed. The fixed

boundaries for all the chords and braces are shown in Figure 9.7. What is concerned in

the analysis is the stress distribution in the adjacent areas around the joint. If the stress

level was found too high, the structure will be improved and re-analyzed till satisfying

results are achieved.

Except the pad-eye member, dimensions and length of members 2 to 6 are listed in

Table 9.18. For the pad-eye, the main plate is 100mm thick and the two cheek plates

are 100mm thick also. In addition, the joint is reinforced with three 100mm thick full

ring plates.

9.3.2 Loading Cases

The forces of each member from one load out analysis and three upending analysis by

SACS IV have been listed in Table A.1 in Appendix A. The joint is modelled with all

braces members (members 2, 3, 4 and 6) being extended to the locations where

supports are provided by other strong braces. The other ends (away from joint 164) of

these four members are fixed. Since there is no support at the other end of chord

149

member 5, no constraints are applied over there. The sling forces being applied on the

pad-eye for cases A, B, C & D are shown in Figure A.1 in Appendix A. Thus the force

will distribute mainly based on the stiffness of members automatically, which is the

most reasonable way.

9.3.3 Finite Element Modelling The FE model for the structure is illustrated in Figure 9.8. The four-sided solid element

(labelled as CTETRA in NASTRAN) with ten nodes and five-sided solid elements

(labelled CPENTA in NASTRAN) are employed to model the structure. They are 2nd-

order isoparametric elements.

Particularly fine mesh is generated in the welding-line area to ensure computation

accuracy; 128 elements are used around the circumference. The pad-eye and stiffeners

are also modelled with element size of 20~50 millimetres. Other parts of the structure

are modelled with relatively coarse mesh with an element size of 100 millimetres. The

model consists of 211,113 elements with 376,104 nodes.

9.3.4 Result Analysis Stress of the structure under one load out and three upending conditions is computed

for the above FEM model using MSC/NASTAN. The 1st-principal stress distributions

and Von Mises stress distributions of the Case D only are shown from Figure 9.9 to

Figure 9.10 respectively. The maximum stress values are summarised and listed in

Table 9.19.

More detailed results of the maximum stresses on the braces are given in Appendix A.

The maximum stress values are summarised and listed in Table 9.20.

150

Stress analysis of the pad-eye Joint 164 under the loadout (1 case) and upending (3

cases) conditions was conducted. The Von Mises stress and 1st-principal stress results

are presented for each case. Since the maximum stresses (both 1st-principal stress and

Von Mises stress) are less than or close to the yield strength of the steel material used

for the structure, the structure should globally be safe under the four aforementioned

load conditions. Since the maximum 1st-principal stress of case D is a little bit larger

than the yield strength, it would be better if small side-stiffeners can be added at the

bottom connection of main plate to the pile sleeve.

151

9.4 Summary

Finite element analyses have been performed on a living quarters module and detailed

behaviour of a padeye connection. In the numerical modelling, the hook point is

treated as fixed. Spring support must be input for structural stability. The spring

stiffness factor should be small to minimise the horizontal reaction force. It is

important to identify the requirement of spreader bar/frame according to the module

layout at the top level and to model correct sling property (weight less), sling length

and offset at padeye locations. Finite element analysis can also provide important

information for detailed stress evaluation and safety check at the padeye connection.

152

Table 9.1 Load factor used for lifting analysis Factor Single Crane Lift

Load Contingency Factor (γf) 1.15 Dynamic Amplification Factor (DAF) 1.10 C of G Shift (fcog) 1.05 Tilt Factor (SKLt) 1.03 Yaw Factor (for local design of trunions) N/A Consequence Factor (γc) Trunion attachment joint Members local to lift point Other structural steel members

N/A 1.15 1.00

Table 9.2 Design Value of Material Parameter

Material Parameters Safety Class high and Strict

Material Control (Primary steel

members)

Safety Class high and Normal Material Control(Primary steel

members)

Safety Class normal

(Secondary steel

members)

Yield stress Fy 1.28 1.21 1.15

Tensile strength Fu 1.56 1.48 1.41

Punching strength τg 1.41 1.34 1.28

Modulus of elasticity E 1.48 1.48 1.34

Note: The material parameters, Fy of 1.21, E of 1.48 and τg of 1.34, were used in computer analysis

by SACS software .

153

Table 9.3 Sample of Member Group Properties (units: cm, kN)

SACS Group ID

SACS SECT ID

Outside Diameter

Wall Thick

E G FY KY KZ SPC SAM

DEN LEN

*1000 *1000 0B1 21.9 1.27 20 8 34.5 1 1 0.5 7.849 0B2 27.3 1.27 20 8 34.5 1 1 0.5 7.849 1H3 HEB300 20 8 34.5 1 1 0.5 7.849 1H4 HEB400 20 8 34.5 1 1 0.5 7.849 1H5 HEB500 20 8 34.5 1 1 0.5 7.849 1I5 IPE500 20 8 34.5 1 1 0.5 7.849 2B5 2B5 20 8 34.5 1 1 0.5 7.849 0.5 2B5 IPE500 20 8 34.5 1 1 0.5 7.849 2C1 2C1 20 8 34.5 1 1 0.5 7.849 2C5 2I5C 20 8 34.5 1 1 0.5 7.849 SL1 27.3 7.5 4 8 24.8 1 1 0.5 0.001 SL2 27.3 7.5 4 8 24.8 1 1 0.5 0.001

Where: * data in column SPC for tubular shear checking only ** data in column LEN for segment length *** data in column E for ID SL1 & SL2 will be variable: E for SL2 = 20000kN/cm2

E for SL1 = 4000kN/cm2

Table 9.4 Sample of SACS Section Properties (unit: cm)

SACS Section ID

Type A B C D

0D5 WF 30 2.8 70 1.45 2I5C WF 20 2.0 50 1.5 HS2 BOX 30 1.2 30 1.2 PG2 BOX 70 4.0 85 5.0 TP2 CON 45.7 3.175 76.2 TP3 CON 145 2.5 76.2

Note: A -- depth for Box section, flange width for WF section, one end

diameter for CON section B -- side wall thickness for Box section, flange thickness for WF section, thickness for CON section C -- width for Box section, depth for WF section, one end diameter for CON section D -- top and bottom wall thickness for Box section, web thickness for WF section

154

Table 9.5 Sample of SACS Plate Group Properties (units: cm, kN) ID THIC

K M E U FY PLZO SECT AV.SP L T DEN

1F1 0.6 S 20 0.25 24.8 25 TROUGH 35 X B 0.001 2F1 0.6 S 20 0.25 24.8 25 HP100X8 80 X B 0.001 2W1 0.42 Y 20 0.25 24.8 3.0 CORR 33 Y T 0.001 2W4 0.42 Y 20 0.25 24.8 3.0 CORR 33 Y T 0.001 2WA 0.503 Y 20 0.25 34.5 3.0 CORR6 33 Y T 0.001 2WB 0.503 Y 20 0.25 34.5 3.0 CORR6 33 Y T 0.001 6F1 0.6 S 20 0.25 24.8 18 HP120X8 50 X B 0.001 7F1 1 S 20 0.25 34.5 20 TROUGH 35 Y B 0.001

Note: Column M S -- Shear plate Y -- Corrugated in local Y direction I -- Isotropic plate (used for deflection checking only for plate group 1F1, 2F1, 3F1, 4F1, 5F1 and 6F1)

Table 9.6 Sample of SACS Plate Stiffener Properties (unit: cm) Type Label A B C D E F IBM HP120X8 12 0.8 2.3 0.8 1.4 1.4 BOX CORR 6.0 23 10 0.5 0 0 BOX CORR6 6.0 23 10 0.6 0 0 IBM HP100X8 10 0.8 2.17 0.8 1.27 1.27 BOX TROUGH 27.5 35 15 0.5 0.001 0.5 Table 9.7 SACS Loading Summary

Item Lift Wt (Mton)

Contingency Final Lift WT (mton)

Structural (a) Model 399.14 1.05 419.10 (b) Misc Loading 373.05 1.05 391.70 Architectural 183.50 1.10 201.85 Mechanical 102.09 1.10 112.30 HVAC 35.95 1.10 39.55 Fire and Safety 51.24 1.10 56.36 Electrical 95.07 1.10 104.58 Piping 59.28 1.10 65.21 Rigging 65.00 1.00 65.00 Grillage & seafatener 100.00 1.00 100.00 Total 1464.32 1555.64

155

Table 9.8 Sample of SACS Loading ID and Description

Loading Description

D01 Main Steel Weight (created by computer) D02 Miscellaneous Weight (leg stabbing guide, secondary steel, plating &

grating, corrugated wall, handrail, staircase, louver and wind shield) D03 Architectural Weight (wall insulation, partition, floor, ceiling, door,

window, furniture) D21 Mechanical Equipment Lift Weight D22 HVAC Bulk Weight and Equipment Dry Weight D23 Fire and Safety Bulk Weight and Equipment Dry Weight D41 Piping Dry Weight D51 Electrical and Instrument Bulk Weight and Equipment Dry Weight X01 Lifting rigging Weight and Grillage & Seafastener Weight XA2 Couples to simulate CoG shift of one meter towards A2 XA3 Couples to simulate CoG shift of one meter towards A3 XB2 Couples to simulate CoG shift of one meter towards B2 XB3 Couples to simulate CoG shift of one meter towards B3 X000 Horizontal force induced by 5% of lift weight (at 0 degree) X090 Horizontal force induced by 5% of lift weight (at 90 degree)

156

Table 9.9 Type of Support Constraints and Member Releases

TYPE LOCATION JOINT NO. RELEASES

Fixed Support EL(+)69m hook

XY-Spring

EL(+)21.8m 1220, 1130 Stiffness = 1kN/mm Mx, My, Mz, Fz

Sling Lifting Frame One end: Mx, My, Mz The other end: My, Mz

Horizontal Brace Member 8.625”ø x 0.5”

Level 1 One end: Mx, My, Mz The other end: My, Mz

Table 9.10 SACS Load Combinations

75% of lift weight at point B2 & A3 75% of lift weight at point A2 & B3 100 200 210 220 230 240 110 300 310 320 330 340 Loading

Number D01 -1.05 -1.05

D02 -1.05 -1.05

D03 -1.1 -1.1

D21 -1.1 -1.1

D22 -1.1 -1.1

D23 -1.1 -1.1

D41 -1.1 -1.1

D51 -1.1 -1.1

X01 -1.0 -1.0

XA2 1.303 1.303

XA3 1.303 1.303

XB2 1.303 1.303

XB3 1.303 1.303

100 -1.368 -1.303 -1.303 -1.303 -1.303 -1.368 -1.303 -1.303 -1.303 -1.303

157

Table 9.11 Sample of 75% Lifting Weight Factor 75% of lift weight at point B2 & A3 Loading

Number 221 222 223 224 225 226 227 228 220 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 X000 2.052 1.451 -1.451 -2.052 -1.451 1.451 X090 1.451 2.052 1.451 -1.451 -2.052 -1.451

75% of lift weight at point B2 & A3 Loading Number 231 232 233 234 235 236 237 238 230 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 X000 2.052 1.451 -1.451 -2.052 -1.451 1.451 X090 1.451 2.052 1.451 -1.451 -2.052 -1.451

75% of lift weight at point B2 & A3 Loading Number 241 242 243 244 245 246 247 248 240 1.15 1.15 1.15 1.15 1.15 1.15 1.15 1.15 X000 2.052 1.451 -1.451 -2.052 -1.451 1.451 X090 1.451 2.052 1.451 -1.451 -2.052 -1.451

Note: Factor 2.052 = 1.368*1.5 (where 1.5 = sling force 75%/25% distribution) Factor 1.451 = 2.052*sin(45)

Factor 1.15 = Consequence factor for member connecting to padeye

Table 9.12 SACS Combined Load Summation LOAD CASE Fx (kN) Fy (kN) Fz (kN)

100 -0.25 -2.50 15241.50 200 -0.33 -3.42 20850.39 210 202.49 -281.38 19859.67 220 -242.24 -248.09 19859.70 230 204.75 273.19 19859.65 240 -244.32 239.49 19859.69 110 -0.25 -2.50 15241.50 300 -0.33 -3.41 20850.39 310 202.49 -281.38 19859.67 320 -242.24 -248.09 19859.70 330 204.75 273.19 19859.65 340 -244.32 239.49 19859.69

158

Table 9.13 Support Reactions (UNIT: kN) Joint HKA2 Joint HKA3 LOAD Fx Fy Fz Fx Fy Fz

100 447.62 -611.74 2400.16 -1296.20 -1315.20 5160.21200 612.35 -836.86 3283.43 -1773.20 -1799.19 7059.17210 678.87 -927.77 3640.12 -1698.38 -1723.28 6761.33220 577.38 -789.06 3095.90 -1818.55 -1845.21 7239.71230 575.31 -786.24 3084.82 -1562.25 -1585.15 6219.37240 485.45 -663.43 2602.99 -1700.04 -1724.96 6767.90110 1171.37 -1600.83 6280.89 -321.39 -326.10 1279.48300 1602.44 -2189.94 8592.26 -439.66 -446.11 1750.33310 1621.15 -2215.51 8692.60 -429.25 -435.54 1708.85320 1521.50 -2079.32 8158.25 -546.93 -554.95 2177.36330 1517.42 -2073.76 8136.42 -293.33 -297.63 1167.77340 1429.44 -1953.52 7664.65 -428.59 -434.87 1706.23

Table 9.14 Spring Reaction (Unit: kN) LOAD Joint 1220 Joint 1130 CASE Fx Fy Fz Fx Fy Fz

100 -1.25 -5.52 0.00 1.13 -2.82 0.00 200 -1.71 -7.55 0.00 1.55 -3.85 0.00 210 89.18 -155.58 0.00 113.47 -133.40 0.00 220 -130.86 -136.94 0.00 -111.20 -118.75 0.00 230 110.42 139.46 0.00 94.50 126.13 0.00 240 -114.22 122.47 0.00 -129.93 109.42 0.00 110 -1.73 -4.96 0.00 1.61 -3.37 0.00 300 -2.37 -6.79 0.00 2.21 -4.61 0.00 310 88.56 -154.86 0.00 114.09 -134.12 0.00 320 -131.49 -136.22 0.00 -110.58 -119.47 0.00 330 109.80 140.18 0.00 95.12 125.41 0.00 340 -114.85 123.19 0.00 -129.30 108.69 0.00

Table 9.15 Sample of SACS Member Stress Listing

BEND STRESS SHEARFORCE AXIALSTRES Y Z

MEMBER

GROUP ID

MAX COMB UNITY CK

LOAD COND NO.

DIST FROM END

(N/MM²) FY KN

FZ KN

KLY/RY

KLZ/RZ

7267-8220 LFD 0.95 325 3.6 176.5 8.6 0.0 0.0 0.0 64.5 64.5 7167-8120 LFD 0.95 205 3.6 175.3 9.1 0.0 0.0 0.0 64.5 64.5 H231-H230 LF4 0.92 201 3.0 186.2 -29.0 -71.3 -161.5 -21.7 32.9 32.9 H131-H130 LF4 0.91 301 2.9 181.1 27.9 -73.4 -182.4 11.4 32.3 32.3 7120-7121 4I3 0.91 200 0.0 60.1 -167.3 -37.1 11.1 151.1 40.5 31.1 7110-8120 LFD 0.90 218 3.2 169.1 6.4 0.0 0.0 0.0 57.1 57.1

159

Table 9.16 Joint Stress Ratio Listing DIAMETER THICKNESS YLD STRSS JOINT (CM) (CM) (KN/CM2) UC

H000 76.2 2.54 34.5 0.527 H120 76.2 2.54 34.5 0.81 H130 76.2 2.54 34.5 0.654 H131 45.72 3.175 34.5 0.148 H220 76.2 2.54 34.5 0.747 H230 76.2 2.54 34.5 0.685 H231 45.72 3.175 34.5 0.165 H330 76.2 1.9 34.5 0.331

Table 9.17 Sling Force Summary: (unit: kN) Member ID H130-HKB3 H220-HKA2 H120-HKB2 H230-HKA3

Section SL1 SL1 SL2 SL2 100 1416.28 2517.13 6649.08 5480.92 200 1937.47 3443.43 9095.96 7497.90 210 1313.86 3817.52 8612.04 7181.54 220 1884.43 3246.77 8117.72 7689.66 230 1883.43 3235.14 9199.25 6605.91 240 2390.11 2729.83 8629.15 7188.53 110 5534.20 6586.99 2583.27 1358.99 300 7570.79 9011.01 3533.93 1859.10 310 6675.16 9116.24 3318.60 1815.04 320 7256.20 8555.85 2813.93 2312.67 330 7243.80 8532.95 3906.73 1240.33

Load

Cas

e

340 7761.16 8038.19 3326.07 1812.26

160

Table 9.18 Dimensions and length of each tubular member

Member No. Outer diameter (mm) Thickness (mm) Length in the model (m)

2 700 30 4.91

3 1200 70 5.36

4 1200 40 4.16

5 2522 70 3.86

6 2522 70 7.00

Table 9.19 Maximum stress (MPa) of each case

Case No. Von Mises 1st-Principal Corresponding Location

A 305 350 Connection of central ring plate to main plate

B 242 300 Bottom connection of main plate to p-sleeve

C 328 356 Connection of central ring plate to main plate

D 358 431 Bottom connection of main plate to p-sleeve

Table 9.20 Maximum stress (MPa) for braces

Case No. Von Mises 1st-Principal Corresponding Location

A 147 165 Weld for braces 3 and 4

B 98.9 59.5 Weld for brace 3

C 300 306 Connection of central ring plate to brace 2

D 76.3 60.6 Bottom ring plate

161

Figure 9.1 Computer Lifting Model Plot

Hook Point

162

HALFDAN PHASE III HDB

C.O.G. SHIFT OF MODULE DURING LIFTING2 3

H230H220 A

H120 H130COORDINATES OF JOINTS B

Coordinates (m)X Y Z

H220 5.06 7 51.2H230 17.19 7 51.2H120 5.06 -7 51.2H130 17.19 -7 51.2

DIMENSIONS OF MODULESpan between A2 and A3 = 12.13 mSpan between A2 and B2 = 14.00 m

SELFWT AND MISCELLANEOUS WT. OF MODULE (WITH CONTIGENCY)Total Weight =

Centre of Gravity C.O.G.x = 10.230 my = -0.059 m

Envelope of C.O.G ShiftShift of 1m towards each leg:

A2 (H220) (H230) A3

α = 53.779 α = 45.406x ecc. = -0.591 x ecc. = 0.702y ecc. = 0.807 y ecc. = 0.712

New C.O.G., (x, y)= (9.639, 0.748) New C.O.G., (x, y)= (10.932, 0.653)COG = (10.23, -0.059)

New C.O.G., (x, y)= (9.633, -0.861) New C.O.G., (x, y)= (10.938, -0.765)α = -53.318 α = -44.923

x ecc. = -0.597 x ecc. = 0.708y ecc. = -0.802 y ecc. = -0.706

B2 (H120) (H130) B3

APPLIED FORCE TO MAINTAIN EQUILIBRIUM DUE TO C.O.G. SHIFTHorizontal span to distributed My across Row A2 and Row A3 = 12.13 mHorizontal span to distributed Mx across Row A2 and Row B2 = 14.00 m

Description Eccentricity (m) M Induced (kN.m) Force To Counter Induced Moment (kN)x-dir y-dir My Mx A2 A3 B2 B3

1. Loadcase 201 -0.59 0.81 -9006.73 -12296.63 -810.42 -67.91 67.91 810.422. Loadcase 202 0.70 0.71 10701.37 -10853.98 53.47 -828.75 828.75 -53.473. Loadcase 203 -0.60 -0.80 -9105.36 12223.78 61.24 811.89 -811.89 -61.244. Loadcase 204 0.71 -0.71 10792.34 10763.53 829.27 -60.45 60.45 -829.27

-15242.32 kN

yx

C.

Envelope of C.O.G.

a

b

α

α

α

α

Figure 9.2 COG Shift of Module During Lifting

163

Figure 9.3 Jacket Loadout arrangement

164

Figure 9.4 Upending process of Jacket

165

Figure 9.5 Jacket positions for the four load cases

CASE A

CASE B

CASE C

CASE D

166

Figure 9.6 Configuration of Joint 164

Figure 9.7 Boundary conditions for the FE model

167

(a) Side view in xy-plane

(c) Local view (d) Local view for pad-eye

Figure 9.8 Finite element mesh

168

(a) Global view

(b) Local view

Figure 9.9 1st-principal stress contour of load case D

169

Figure 9.10 Local view of Von Mises stress contour of load case D

170

CHAPTER 10 CONCLUSIONS AND RECOMMENDATIONS

FOR FUTURE WORK

10.1 Conclusions

Lifting criteria and sling specifications in practice are reviewed and discussed in this

thesis. Relevant justification is made based on the lift projects in construction yard.

The practical and dominating considerations in rigging are sling design loads, shackle

design loads, lift point design loads, shackle sizing, tilt control and CoG (centre of

gravity) shift factor.

Crane barges, rigging components including shackles, slings and grommets and lift

point connections (including padeyes and trunnions) are discussed based on practical

consideration in heavy lift design. The rigging system is the only connection of module

to barge. Lifting plays a very important role in major offshore engineering

construction. The selection or design of a rigging arrangement is dependent on the

crane barge characteristics, module structural pattern and behaviour during lift, and the

site parameters.

Rigging configuration affects the tensions in rigging slings, loads in lift points and

forces in shackles and link plates, and thus affects the design of those lift components.

Furthermore, it also affects the selection of the boom and jib angles of a crane barge to

fulfil lift requirements. The algorithms and formulations for the determination of

configurations of rigging sling systems with four, six and eight lift points, which cover

the majority of heavy lifts in offshore and marine industries, are presented in this

thesis. The sling arrangements can be with single slings, doubled slings or doubled

171

make-up slings. The type of spreader structures included in the discussion can be a

simple spreader bar, two parallel spreader bars or a spreader frame.

Jackets which are built and transported vertically offer significant savings over jackets

built on their side. Considerations for lift jacket structures horizontally and vertically

are discussed. Lifting a large jacket may require substantial loadout frame which needs

proper design.

Practical considerations for module lifts, which include vertical lifts and flip-over, are

investigated. One of the most important aspects of the design of large lifts is the

control of weight and the centre of gravity (CoG) of the module. This requires a proper

sequence of weighing scheme to ensure the accuracy of these parameters. For deck

panel flip-over operation, force distribution between two cranes or two hooks should

be calculated precisely since they vary with the change of the module incline angle

during flip-over.

Lift procedures and considerations for FPSO modules are discussed and rigging

systems with multiple spreader bars are highlighted. Practical design and analysis

considerations for lifting lower turret, gas recompression module and flare tower,

which are unique for stringent requirement of installation accuracy, heavy load and

geometry, are discussed based on real projects.

A versatile spreader frame is designed that includes the combination of padeye and

lifting trunnions. Padeyes are designed underneath of spreader frame, while the lower

slings remain un-changed, these save significant rigging changing time during actual

172

lifting operations. The trunnions above the spreader frame enable the riggers easier

access for re-rigging of slings for subsequent lift.

Finite element methods are used for lifting module and padeye connection analysis. In

the modelling, the hook point is considered fixed. Spring supports needs to be input to

prevent numerical problems with regards to rigid body modes and the specified spring

stiffness should be significantly smaller than the structural stiffness. It has been

illustrated that detailed finite element analysis can provide important information for

the stress design and safety check for padeye connections.

10.2 Recommendation for Future Work

Based on the detailed investigations by the author, the thesis has reported some

findings which will be useful for future reference. In view of the important nature of

installation engineering for offshore structures, the following areas may be

recommended for further investigation:

- Structural steel optimization of offshore platforms due to lifting considerations.

As most of structural members connected to the lift points are normally governed

by lifting operation, structural optimisation can result in significant cost saving.

- Investigation of padeye configuration with ring stiffeners. The FEM results in

Section 9.3 show that some stiffeners are not fully utilized, more optimized

configuration with regards to number and location of ring stiffeners is

recommended for further study.

173

- Study of the impact of accidental loadings on rigging system. Accidental loadings,

such as gust wind load, wave surge load, etc., have significant effect on the safety

of lifting operation and thus studies on these aspects are crucial to lifting design.

174

BIBLIOGRAPHY

• American Petroleum Institute (API). Recommended Practice for Planning, Designing

and Constructing Fixed Offshore Platforms – Working Stress Design, API-RP 2A -

WSD, 21st edition, December 2000.

• American Institute Steel Construction (AISC), Allowable Stress Design, 9th Edition,

1991.

• Structural Analysis Computer System (SACS) Release 5.1, 2003, by EDI, USA.

• DNV Marine Operation Part 2 Recommended Practice RP5 Lifting, 1996

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APPENDIX A FEM ANALYSIS FOR JACKET UPENDING PADEYE

Additional FFM results for Jacket upending padeye with various loading cases are

summarized in this section.

• Summary of load cases and member forces

Table A.1 Member forces coming out from SACS analysis

182

183

• Summary of loading applied to padeye

(A.1) Load out (wire-frame view) (A.2) Load out (solid view)

(B.1) Upending in vertical position (wire-frame view) (B.2) Upending in vertical position (solid view)

(C.1) Upending in horizontal (C.2) Upending in

position (wire-frame view) horizontal position (solid view)

Figure A.1 Load conditions (to be continued)

184

(D.1) Upending in tilted (D.2) Upending in tilted

position (wire-frame view) position (solid view)

Figure A.1 Load conditions

185

• Stress distribution of upending padeye

(a) 1st- Principal stress

(b) Von Mises stress

Figure A.2 Stress distribution for the braces of load case A

186

(a) 1st- Principal stress

(b) Von Mises stress

Figure A.3 Stress distribution for the braces of load case B

187

(a) 1st- Principal stress

(b) Von Mises stress

Figure A.4 Stress distribution for the braces of load case C

188

(a) 1st- Principal stress

(b) Von Mises stress

Figure A.5 Stress distribution for the braces of load case D