lpu-epl-00-l-rp-903319-001

EXPORT PIPELINE BUCKLE ARRESTOR DESIGN

LPU-EPL-00-L-RP-903319-001 Rev C02 - 02 Nov 10 of 18

CONTENTS

Page

1 INTRODUCTION ..................................................................................................................... 3 1.1 OBJECTIVE ................................................................................................................................. 4 1.2 ABBREVIATIONS ........................................................................................................................ 4

2 SUMMARY AND CONCLUSION ............................................................................................ 5 2.1 SUMMARY................................................................................................................................... 5 2.2 CONCLUSIONS........................................................................................................................... 6

3 METHODOLOGY ....................................................................................................................7 3.1 TOTAL GUIDELINES................................................................................................................... 7 3.2 BUCKLE ARRESTOR DESIGN................................................................................................... 7

4 INPUT DATA ........................................................................................................................... 8 4.1 PIPELINE DIMENSIONAL PROPERTIES................................................................................... 8 4.2 PIPELINE MATERIAL PROPERTIES.......................................................................................... 8 4.3 GENERAL DESIGN DATA .......................................................................................................... 8 4.4 DESIGN FACTORS ..................................................................................................................... 8 4.5 SEABED PROFILE ...................................................................................................................... 9 4.6 GENERAL ENVIRONMENTAL DATA ......................................................................................... 9

5 RESULTS .............................................................................................................................. 10

6 REFERENCES ...................................................................................................................... 13 APPENDIX A ......................................................................................................................................... 14



1 INTRODUCTION

Allseas has been awarded the installation of the Production Flowlines from Laggan-Tormore to Shetlands and the Export Pipeline from Shetlands to the MCP-01 platform for the development of the Laggan and Tormore gas fields which are located in approximately 600 metres water depth in Blocks 206/1a (P911) and 205/5a (P1159) respectively, and are situated some 125km north west of the Shetland Islands on the UK Continental Shelf, refer to the figure below.

Allseas scope of work includes the following aspects: - Design of pipeline, structures, crossings and tie-in spools; - Procurement of permanent pipeline valves; - Fabrication of structures; - Installation of offshore and onshore pipelines; - Installation of onshore umbilical; - Pre-lay preparations, installation and rock dumping of pipeline crossings; - Dredging and rock dumping of landfalls; - Lateral buckling mitigation and rock dumping of hot tap tees; - Tie-ins offshore to onshore pipelines; - Flooding, cleaning, gauging and hydro-testing of pipelines. Composite Work Package A is scheduled to be installed in 2012 and consists of: 1. Offshore Export Pipeline, 227km of 30-inch from Shetlands to MCP-01; 2. Eight pipeline crossings, two hot tap tees and one dual inline tee; 3. Maximum water depth 150m; 4. Pipelay is planned with Solitaire; 5. Onshore scope: 30-inch pipeline, export valve station with a jumper umbilical up to the Shetland Gas

Plant.



Composite Work Package B is scheduled to be installed in 2011 and consists of: 1. Offshore Production Flowlines, 2 x 142km of 18-inch from Laggan & Tormore to Shetlands; 2. Each pipeline has two pipeline crossings, six hot tap tees and one inline tee; 3. Both 18-inch pipelines are ending with a PLET in the deep end; 4. Maximum water depth 640m; 5. Pipe lay is planned with Audacia; 6. Onshore; 2km of two 18-inch, an 8-inch and a 2-inch pipeline, including an onshore umbilical to the

Shetland Gas plant. After the pipelay operation the pipelines will be left in flooded condition upon completion of the cleaning, gauging and hydro-testing operations. 1.1 OBJECTIVE The objective of this document is to present the buckle arrestor design for the export pipeline. The determination of the buckle arrestor sizes and extents have been based on the requirements of DNV-OS-F101 [Ref. 1]. 1.2 ABBREVIATIONS The abbreviations listed below are used throughout this report. BA Buckle Arrestor CWC Concrete Weight Coating DNV Det Norske Veritas FUKA Frigg UK Area pipeline JPK J P Kenny KP Kilometre Point OD Outside Diameter PUF Polyurethane Foam SGP Shetland Gas Plant SPS Subsea Production System SVT Sullom Voe Terminal UOE U-ing, O-ing and Expanded WD Water Depth WT Wall Thickness



2 SUMMARY AND CONCLUSION

2.1 SUMMARY Table 2-1 summarise the buckle arrestor requirements for the export pipeline. The selected buckle arrestor wall thickness is based on the value calculated in the Basic Engineering and defined in early contracts documentation [Ref. 8]. This buckle arrestor wall thickness, of 25.7mm, is shown herein to be conservative. However the extents of the buckle arrestors are based on values determined during the Detailed Design. Buckle arrestors have been specified for all sections of the export pipeline route where the external hydrostatic pressure is sufficient to propagate a buckle in the installation condition as per the guidelines of DNV-OS-F101 [Ref. 1]. Further per the Total General Specification [Ref. 2]: - The specified buckle arrestors are integral parts of the pipeline with an interval between subsequent

buckle arrestors equal to the suspended length of pipeline during installation.

- The wall thickness specified is sufficient to prevent propagation buckling in the installation condition only.

Table 2-1 Summary of Selected Buckle Arrestor Wall Thickness and Extents

KP Start KP End Length

(km) Pipe WT

(mm) BA Thickness (1, 2)

(mm) BA Spacing (3)

(m)

No. of Buckle

Arrestors

0.0 30.7 30.7 32.9 / 20.4 None (5) - -

30.7 54.8 24.1 25.7 470 52

54.8 68.2 13.4 None (5) - -

68.2 144.7 76.5 25.7 470 163

144.7 155.1 10.4 None (5) - -

155.1 222.7 67.6 25.7 470 144

222.7 227.4 4.7

20.4

None (5) - -

Total No. of Buckle Arrestors Required 359 (4) Notes

1 BA design based on an integral pipe joint of 11.698m i.e. 12.3m pipe joint minus 301mm taper length each end.

2 To ease procurement of the buckle arrestors the design is based on UOE linepipe and a normal material strength factor i.e. αU= 0.96.

3 Length of pipeline suspended during installation is based on information provided by Allseas [Ref. 7].

4 Total no. of buckle arrestors does not include for any construction spares.

5 Buckle arrestor wall thickness required is less than export pipeline nominal wall thickness.

Figure 5-1 shows the buckle arrestor fabrication detail sketch for the export pipeline. A sample Mathcad for the BA design calculation is presented in Appendix A.



2.2 CONCLUSIONS - Buckle arrestors have been specified for all sections of the export pipeline route where the external

hydrostatic pressure is sufficient to propagate a buckle in the installation condition.

- The buckle arrestor design is based on an integral pipe joint of 11.698m i.e. 12.3m pipe joint minus 301mm taper length each end;.

- To ease procurement of the linepipe the integral buckle arrestor design is based on UOE linepipe and a normal material strength factor i.e. αUBA= 0.96.

- The buckle arrestor wall thickness of 25.7mm [Ref. 6] defined in the Basic Engineering is found to be sufficient.

- Buckle arrestors are required for the export pipeline route locations where water depth exceeds 124m, see Figure 5-2.



3 METHODOLOGY

3.1 TOTAL GUIDELINES

The following guidelines are taken from the Total General Specification [Ref. 2] and have been used in the design of the buckle arrestors for the export pipeline:

- Buckle arrestors should be an integral part of the pipeline and the interval between subsequent buckle arrestors should be equal to the suspended length of pipeline during installation;

- Propagation buckling shall be checked for the installation phase only with the pipeline being empty and not corroded.

3.2 BUCKLE ARRESTOR DESIGN The design of the buckle arrestors for the export pipeline is based on the guidelines presented in DNV-OS-F101 [Ref. 1]. In order to initiate propagation buckling the external hydrostatic pressure has to exceed the following criteria:

SCm

pre

PP

γγ ⋅< Equation 3.1

Where

eP - external pressure,

prP - propagating pressure,

mγ - material resistance factor,

SCγ - safety class resistance factor. For sections of the export pipeline where the external hydrostatic pressure is sufficient to initiate propagation buckling the design of the integral buckle arrestors will be based on the following conditions [Ref. 1]:

SCm

Xe

PPγγ ⋅⋅

≤1.1

Equation 3.2

Where the crossover pressure XP is

⎥⎦

⎤⎢⎣

⎡⎟⎠⎞

⎜⎝⎛ ⋅−−⋅−+= 2

2, 201)(

DLtEXPPPPP BA

prBAprprX Equation 3.3

Where

BAprP , - is the propagating buckle capacity of an infinite arrestor,

2t - pipe wall thickness, D - nominal outside diameter,

BAL - buckle arrestor length.



4 INPUT DATA

This section presents the design data used for the export pipeline buckle arrestor design. All input data is taken from Design Basis [Ref. 3] unless stated otherwise. 4.1 PIPELINE DIMENSIONAL PROPERTIES Table 4-1 presents the pipeline dimensional properties used for the export pipeline buckle arrestor design.

Table 4-1 Pipeline Dimensional Properties

Start KP End KP OD (mm)

WT (mm)

0 2.0 787 32.9

2.0 227.4 762 20.4 4.2 PIPELINE MATERIAL PROPERTIES Table 4-2 presents the pipeline material properties used for the export pipeline buckle arrestor design.

Table 4-2 Pipeline Material Properties

Parameter Value

Specified Minimum Yield Stress 450 MPa

Specified Minimum Tensile Stress 535 MPa

Steel Density 7850 kg/m3 4.3 GENERAL DESIGN DATA

Table 4-3 presents the general design data used for the export pipeline buckle arrestor design.

Table 4-3 General Design Data

Parameter Value

Contents Density 0.0 kg/m3

Internal Pressure 0.0 barg

BA Joint Length 12.3 m

BA Taper Length 301 mm [Ref. 7]

Length of BA considered in Design (i.e. Joint Length - Taper Length) 11.698 m

4.4 DESIGN FACTORS

Table 4-4 presents the design factors used for the export pipeline buckle arrestor design. To ease procurement of the buckle arrestors the design is based on UOE linepipe and a normal material strength factor.



Table 4-4 Design Factors [Ref. 1]

4.5 SEABED PROFILE Figure 4-1 shows the seabed profile along the export pipeline route from the Firths Voe landfall to the laydown point at MCP-01.

0

20

40

60

80

100

120

140

1600 30 60 90 120 150 180 210 240

KP (km)

WD

(m)

Lay down pointat MCP-01

Firths Voe

Figure 4-1 Export Pipeline Seabed Profile

4.6 GENERAL ENVIRONMENTAL DATA

Table 4-5 presents general environmental data used for the export pipeline buckle arrestor design. The significant wave height used in the calculation is based on the largest 1-year omni directional significant wave predicted for the export pipeline location.

Table 4-5 General Environmental Data

Parameter Value

Sea Water Density 1025 kg/m3

Tide and Surge 2.96 m [Ref. 4]

Significant Wave Height 10.1 m [Ref. 5]

Parameter Value

Material Resistance Factor (γm) 1.15

Safety Class Resistance Factor (γsc) (1) 1.04

Fabrication Factor for UOE Linepipe (αfab) 0.85

Material Strength (αuBA) 0.96



5 RESULTS

Table 5-1 summarises the buckle arrestor requirements for the export pipeline.

Table 5-1 Summary of Buckle Arrestor Requirements Determined in the Detailed Design

KP Start KP End Length (km)

Pipe WT (mm)

BA Thickness (1, 2) (mm)

BA Spacing (3) (m)

No. of Buckle

Arrestors

0 30.7 30.7 32.9 / 20.4 None (6) - -

30.7 54.8 24.1 23.3 (5) 470 52

54.8 68.2 13.4 None (6) - -

68.2 144.7 76.5 23.3 (5) 470 163

144.7 155.1 10.4 None (6) - -

155.1 222.7 67.6 23.3 (5) 470 144

222.7 227.4 4.7

20.4

None (6) - -

Total No. of Buckle Arrestors Required 359 (4) Notes

1 BA design based on an integral pipe joint of 11.698m i.e. 12.3m pipe joint minus 301mm taper length either side.

2 To ease procurement of the buckle arrestors the design is based on UOE linepipe and a normal material strength factor i.e. αU= 0.96.

3 Length of pipeline suspended during installation (minimum 470m) is based on information provided by Allseas [Ref. 7].

4 Total no. of buckle arrestors does not include for any constructions spares.

5 The buckle arrestor wall thickness of 25.7mm [Ref. 6] selected in the Basic Engineering is considered conservative and is selected for the final design, see Table 2-1.

6 Buckle arrestor wall thickness required is less than export pipeline nominal wall thickness.

Figure 5-1 shows the buckle arrestor fabrication detail sketch for the export pipeline. The length of the taper transition and taper detail are based on information supplied by Allseas [Ref. 7].

Figure 5-1 Buckle Arrestor Fabrication Detail Sketch



The buckle arrestor wall thickness of 25.7mm [Ref. 6] selected in the Basic Engineering is considered conservative. However the following points are noted:

– The BA wall thickness selected in the Basic Engineering includes a 1.5mm corrosion allowance. This is not in compliance with the Total general specification which states that propagation buckling should only be considered for the installation condition with the pipeline being empty and not corroded [Ref. 2];

– The Basic Engineering specified the use of buckle arrestors for the entire export pipeline. This is considered over conservative as the external hydrostatic force is not sufficient to propagate a buckle for approximately 60km of the export pipeline;

- The Basic Engineering considered a 100 year maximum wave in the design of the BA. This is considered over conservative as pipelay operations would not occur in such a sea state.



0

5

10

15

20

25

30

35

40

0 30 60 90 120 150 180 210

KP

Wal

l Thi

ckne

ss (m

m)

0

20

40

60

80

100

120

140

160

Wat

er D

epth

(m)

Minimum BA Wall Thickness (UOE) Selected BA ThicknessSeabed ProfileRisk of Propagation Buckling

23.3mm

20.4mm

Figure 5-2 Export Pipeline BA Requirements



6 REFERENCES

1. DNV-OS-F101, Submarine Pipeline Systems, October 2007 (with amendments in October 2008) 2. GS EP PLR 100, Total General Specification, Pipelines – Risers, October 2007 3. LPU-GEN-00-G-BA-002502-001, Design Basis 4. SVE-L-RP-90312, Basic Engineering, Export Pipeline Wall Thickness Selection, August 2009 5. C-183-06-R266-1D, PhysE Wave & Current Conditions for the Laggan Export Pipelines: Volume 1

Overview and 51 Metocean Reference Documents (MRD) – Locations S29 to S39 and Locations 9 to 12, December 2007

6. SVE-L-RP-90120, Basic Engineering, Buckle Arrestor Design for the Export Pipeline, August 2009

7. Email Correspondence on the 4th August 2010 from Allseas to Steve Langford

8. ITT Documentation, Total E&P UK Ltd, Laggan-Tormore Development, Installation of Pipelines &

Umbilicals, Exhibit I Company Items and Early Contracts, 20/4/10



APPENDIX A

SAMPLE CALCULATION SHEET

J P KENNYLaggan - Tormore Project By: AY.

Chk: RD Appr: SL

Laggan - Tormore ProjectDNV-OS-F101 Buckle Arrestor Design

Load Case: Buckle Arrestor for 30'' Export Pipeline

1.0 Introduction

This MathCAD calculates the required wall thickness / length relationship for a Buckle Arrestor to halt a propagatingbuckle for a given water depth. This is executed in accordance with the methodology in DNV-OS-F101. 2.0 Design Data Summary3.0 DNV-OS-F101 Methodology4.0 Results

2.0 Design Data SummaryLoadcase 0= Loadcase 0 = installation

1 = operational

Length 227.4km= Pipeline length

ID 721.2mm= Pipeline Internal Diameter (Constant ID)

LBA1 11.698m= Length of buckle arrestor (Single Joint - Taper Length)

SMYS 450 MPa⋅= Specified Minimum Yield Stress

Toper 6.1°C= Operational Contents Temperature

Tamb 6.1 °C⋅= Ambient Sea Temperature

tempdr "no"= Include temperature de-rating?

Emod 2.07 105⋅ MPa= Young's Modulus

dmax 148.14m= Maximum Water Depth

dssmax 2.96m= Storm Surge

Hmax 10.1 m⋅= Significant Wave Height (1 yr return)

ρw 1025 kg⋅ m 3−⋅= Sea Water Density

γm 1.15= Material Resistance Factor Section 5 C205

γsc 1.04= Safety Class Resistance Factor Section 5 C206

αfab 0.85= Fabrication Factor for the Pipeline Section 5 C307

αfabBA1 0.85= Fabrication Factor for UOE Buckle Arrestor material Section 5 C307

αfabBA2 0.93= Fabrication Factor for TRB Buckle Arrestor material Section 5 C307

αU 1.0= Material Strength Factor for Pipeline Section 5 C306

αUBA 0.96= Material Strength Factor for Buckle Arrestor material Section 5 C306

Export BA Design.xmcd Page 1 of 4 of 18

J P KENNY

Input KP Step size for plotting KPStep 1000m= Input vector index for plotting x 0 1LengthKPStep

=

Water Depth Pipeline Wall Thickness

KP (km) Wall Thickness (mm)0 32.9

2.0 32.92.0 20.4

227.4 20.4

Interpolation of data

Seabed profile

dx linterp KPwd depth x KPStep⋅( )=

Wall thickness

tdnomxlinterp KPwtsel wtsel x KPStep⋅=

KP (km) Water Depth (m)0 5.33

0.1 5.330.2 5.330.3 5.330.4 9.80.5 11.070.6 11.530.7 13.280.8 15.570.9 18.571 20.72

1.1 22.21.2 22.681.3 22.821.4 22.74


J P KENNY

3.0 DNV-OS-F101 Methodology

Maximum water depthdepthmaxx

dx dssmaxHmax

2+

⎛⎜⎝

⎞⎟⎠

dx

dmax⋅+=

External pressure (max) pexρw g⋅ depthmaxx

⋅=

Minimum Crossover PressureRef. DNV-OS-F101 Eqn 5.17

pxx1.1γm γsc⋅ pex

⋅=

Pipeline - OD ODx ID 2 tdnomx⋅+=

Propagating Buckling PressureRef. DNV-OS-F101 Eqn 5.16 Pprx

35 SMYS αU⋅⋅ αfab⋅

tdnomx

ODx

⎛⎜⎜⎝

⎞⎟⎟⎠

2.5

⋅=

Eqns 5.16 & 5.18 from DNV-OS-F101

Given

tarr 0.1mm=

px Ppr 35 SMYS αUBA⋅⋅ αfabBA1⋅tarr

ID 2 tarr⋅+

⎛⎜⎜⎝

⎞⎟⎟⎠

2.5

⋅ Ppr−

⎡⎢⎢⎣

⎤⎥⎥⎦

1 exp 20−t2 LBA1⋅

OD( )2⋅

⎡⎢⎢⎣

⎤⎥⎥⎦

−⎡⎢⎢⎣

⎤⎥⎥⎦

⋅+=

tuoe px Ppr x t2 OD Find tarr=

Bauoerequiredxtuoe pxx

Pprxx tdnomx

ODx⎛⎝

⎞⎠

⎛⎝

⎞⎠

=

Given

tarr 0.1mm=

px Ppr 35 SMYS αUBA⋅⋅ αfabBA2⋅tarr

ID 2 tarr⋅+

⎛⎜⎜⎝

⎞⎟⎟⎠

2.5

⋅ Ppr−

⎡⎢⎢⎣

⎤⎥⎥⎦

1 exp 20−t2 LBA1⋅

OD( )2⋅

⎡⎢⎢⎣

⎤⎥⎥⎦

−⎡⎢⎢⎣

⎤⎥⎥⎦

⋅+=

ttrb px Ppr x t2 OD Find tarr=

Batrbrequiredxttrb pxx

Pprxx tdnomx

ODx⎛⎝

⎞⎠

⎛⎝

⎞⎠

=


J P KENNY

4.0 Results x2x x KPStep⋅=

Summary Data for Excel

KPWater Depth

(m)BA (UOE)

Thickness (mm)BA (TRB)

Thickness (mm) BA required?

0 5.3 5.9 5.7 Not Required1.0 20.7 10.3 9.9 Not Required2.0 34.8 12.7 12.2 Not Required3.0 44.3 14.0 13.5 Not Required4.0 47.4 14.4 13.9 Not Required5.0 94.7 19.3 18.6 Not Required6.0 97.6 19.5 18.8 Not Required7.0 68.5 16.8 16.2 Not Required8.0 63.5 16.3 15.7 Not Required9.0 57.4 15.6 15.1 Not Required

Graphed Results

0 100 200

0

100

50

0

0

10

20

30

Seabed ProfileCriteria Selected BA UOE BATRB BA

KP

WD

(m)

Thic

knes

s (m

m)


lpu-epl-00-l-rp-903319-001

Documents

general design data

design factors

pipeline material properties

contents page

rev c02

general environmental

input data

introduction allseas