derrick

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05. DERRICK

5.1 CONCEPTUAL DESIGN

- Derricks

Derricks and Masts consist of a steel framework with asquare or rectangular cross-section.Their purpose is to support the hoisting

equipment andrack the tubulars while tripping.The number of joints in a stand (single-double-triple) thatthe rig can pull is

dependent on the height of the derrick.

- Manufacturer Specifications

Derricks are manufactured in accordance with API 4F orrelated ISO (International Organization forStandardization) 13626 draft.This

specifications covers the design, manufacture, anduse of derricks, portable masts, crown block assembliesand substructures.

- Nameplate Information

Derricks built within API/ISO specs must have a specification nameplate attached in a visible placecontaining the following

information:

MANUFACTURERS NAME.

PLACE OF CONSTRUCTION.

STANDARD ADOPTED (ex. API 4F).

SERIAL NUMBER.

HEIGHT ( ft ).

MAXIMUM STATIC HOOK LOAD ( lbs) FOR STATED NUMBER OF LINES TO TRAVELLING BLOCKS.

MAX. RATED WIND VELOCITY (Knots) WITH RATED CAPACITY OF PIPE RACKED.

EDITION OF THE API SPEC. USED

GUYING DIAGRAM (when applicable)

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The following note: CAUTION: ACCELERATION OR IMPACT, ALSO SETBACK AND WIND LOADSWILL REDUCE THE MAXIMUM

RATED STATIC HOOK LOAD CAPACITY.

LOAD DISTRIBUTIONDIAGRAM.

GRAPH PLOTTING MAX. ALLOWABLE STATIC HOOK LOAD VERSUS WIND VELOCITY.

MAST SETUP DISTANCE FOR MAST WITH GUY LINES.

5.2 TYPES AND CHARACTERISTICS

There are 3 different types of derricks:

DERRICK

MAST

RAM RIG

- DERRICK

Pyramidal steel framework with square or rectangular cross section assembled as fixed structure.

- API Definition

A semipermanent structure of square or rectangular cross-section having members that arelatticed or trussed on all four sides.This

unit must be assembled in the vertical or operation position, as it includes no erectionmechanism. It may or may not be guyed.

- Derrick dimensions

Table 1 - Derrick Sizes and General Dimensions

The vertical distance from the top of the base plate to the bottom of the Crown Block supportBeam.

The distance between heel to heel of adjacent legs.

The window opening measured in the clear and parallel to the center line of the derrick sidefrom top of base plate.

The smallest clear dimension at the top of the derrick that would restrict passage of crownblock.

The clearance between the horizontal header of the gin pole and the top of the crown supportbeam.

Derrick Types

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Derrick are normally used onOffshore rigs and can be divided intocategories:

Stationary DerrickDerrick used on offshore fixedstructures

Dynamic DerrickHeavyweight derrick used on floatingrigs subjected to marine stress.

Installation onoffshore floating unit Dynamic Derrick mounted onDS SAIPEM 10000

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- MAST

A Mast is a steel framework with square or rectangular cross-section comprised of multiplesections assembled together.

Mast are normally used on land rigs; they are rarely used on offshore rigs.

Most masts have one side open (window side), while others have both the front and rear side open(full view).

Generally masts are assembled on the ground in horizontal position and are raised using thedrawworks. Some masts use telescopic

sections and are assembled in vertical (boot strap).

- API Definition

3.16 mast: A structural tower comprised of one or more sections assembled in a horizontalposition near the ground and then raised

to the operating position.

If the unit contains two or more sections, it may be telescoped or unfolded during the erectionprocedure.

Mast Types

There are 2 different types of masts for land drilling and service rigs:

STATIONARY BASE

WITH GUY LINES

Stationary Base With Guy Lines

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- Pyramid Mast sizes table

Example of MAST w ith GUY LINES

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- RAM RIG

The RAM RIG is a new concept used to hoistthe drill string.The Drawwork and the drilling line are replacedwith a system of hydraulic

pistons and rams.Ram rigs can be used with singles or stands,depending on the height of the derrick.They have only recently been

developed andare not yet classified within API/ISO Specs.

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- Hydraulic System

- Semisub Ram Rig Sketch

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- Ram Rig System Scheme

5.3 RIGGING UP

- Conventional Mast (Land rig)

Erection sequence

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- Phase 1

- Phase 2

- Vertical Mast (offshore Rig)

Boot Strap sequence:

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- Trailer Mounted Rig

Rigging Up Sequence of a Trailer Mounted Rig

- a) Deploying of substructure base

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- b) Anchoring of trailer to substructure base

- c) Extension of the t elescopic sections

- d) Installation of the hydraulic rams

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- e) Anchoring the mast to the substructure

- f) Raising the mast in vertical position

- Final Position

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5.4 DRILLING LOADS

- Forces on the Derrick

Derricks are subjected :

Weight of the derrick itself

Wind load

Stress induced by Floating hull motion(for floating vessels)

Horizontal component load of the drill stringwhen racked back

Hoisting load

The first 3 forces are considered in the structural design of the derrick.

- Calculation of Drilling Loads at Crown BlockCases

Case 1: Suspended load

The load on the support is equal to the weightbeing hung.

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Case 2a : Static Load

Drilling load is at rest, hoisted bythe Drawworks over a singlesheave on the Crown BlockThe load on the drawworks is equalto the

weight being hung from thecrown sheave.The crown supports both the drillingload and drawworks tension, so theforce supported is

double theweight being hung.

Case 2b : Dynamic Load

Drilling load is in motion, hoisted bythe Drawworks over the singlesheave on the Crown BlockThe load on the drawworks is equalto

the weight being hung fromcrown sheave PLUS frictions.The crown block supports both thedrilling load and the drawworkstension

PLUS frictions, so the forcesupported in more than the weightbeing hung.

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Case 3: Drilling load is in motion

Drilling load is in motion, hoisted bythe Drawworks through a series ofsheaves on the Crown andTravelling BlocksThe load supported

by the CrownBlock is the sum of the loadsupported by each of the lines.In this example with 3 lines, theload supported by Crown

block is 1500 kg.

The load supported by the Drawworks is the drilling load divided by the number of lines on thetraveling block.In this example the

force required by the drawworks to hoist a weight of 1000 kg is reduced byby using a travelling block with one sheave.The series of

sheaves in Crown-Travelling Blocks system reduces the load necessary to hoist aweight.

- Series of sheaves and Lines

- Load Supported by the DrawworksThe series of sheaves in Crown-Travelling Blocks system reduces the load necessary to hoist

aweight. The load supported by the drawworks is related to the number of lines installed on theTravelling Block.

- Example: In this case the travelling block has 4 shievesand 8 lines. The crown block has 5 shievesand 10 lines ( 8 lines from the

travelling block +Fastline and Dead line.)

Applying a Drilling Load of 120 ton,The load on each line is: 120 / 8 = 15 tonThe load at the crown block is:15 x 10 = 150 ton

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- Definition of Gross Nominal Capacity

- Gross Nominal CapacityGross nominal capacity is defined as the MAXIMUM STATIC LOAD with a stated number ofdrilling lines. API

regulation takes in consideration only the capability for hoisting the drill string.

- Calculation of GNC for Mast

In a MAST the maximum load to the crown block(Gross Nominal Capacity) is calculated asfollows:

with:GNC = Gross Nominal capacity;

n = lines number

SHL = Maximum static Hook Load.

Example of Load distribution on a Mast

- Calculation of GNC for Derrick

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In a DERRICK the maximum load applied at the crown block (Gross Nominal Capacity) is equallydivided on its 4 legs and its

calculated as follows:

with:GNC = Gross Nominal Capacity

n = Lines number

SHL = Maximum static Hook Load

Example of Load distribution on a Derrick

5.5 INSPECTION

- Periodic inspections

The API applicable references are:API RP 4G and API RP 54 (chapt. 9.2 and 9.3). and the Manufacturer's recommendations.

ENI policy is more strict and requires the API Category IV inspection (as per API RP 4G) every 5years instead of 10.

Mast/derricks and substructures on mobile offshore drilling units or fixed platforms are exemptedfrom the requirements of a

Category IV inspection.

derrick

Documents

derrick sizes

derrick sidefrom

derrick types112513

derrick dimensionstable

rectangular crosssection

used onoffshore rigs

allowable static hook

mast setup distance