offshore pipeline construction volume one

E N G I N E E R I N G C O N S U L T A N T S

Offshorepipeline

construction

2

All information contained in this document has been prepared solely to illustrateengineering principles for a training course, and is not suitable for use for engineeringpurposes. Use for any purpose other than general engineering design trainingconstitutes infringement of copyright and is strictly forbidden. No liability can beaccepted for any loss or damage of whatever nature, for whatever reason, arising fromuse of this information for purposes other than general engineering design training.

All rights reserved. No part of this publication may be reproduced or transmitted inany form or by any means whether electronic, mechanical, photographic or otherwise,or stored in any retrieval system of any nature without the written permission of thecopyright holder.

Copyright of this book remains the sole property of:

Trevor Jee Associates26 Camden RdTunbridge WellsKentTN1 2PTEngland

© Trevor Jee Associates 2004

3

TABLE OF CONTENTS

Contents of Volume OneS-LAY ................................................................................... 7

Expectation ...............................................................................................................9

What is S-Lay?........................................................................................................10

S-Lay Vessel Types ................................................................................................11

S-Lay Process..........................................................................................................18

Market and Vessels .................................................................................................37

Welding and NDT...................................................................................................52Procedure.........................................................................................................................52Methods ...........................................................................................................................57NDT.................................................................................................................................64

Insulated Lines ........................................................................................................71

Lay Curve Control ..................................................................................................75

J-LAY.................................................................................. 81Expectation .............................................................................................................83

What is J-Lay? ........................................................................................................84

Vessels ....................................................................................................................85

Projects....................................................................................................................99

J-Lay Sequence .....................................................................................................101

Performance ..........................................................................................................105

Rapid Pipe Welding ..............................................................................................108

Mechanical Connectors.........................................................................................111

Drilling Rig ...........................................................................................................117

Catenaries..............................................................................................................119

Worked Example...................................................................................................129

4

BUNDLES......................................................................... 135Expectation ...........................................................................................................137

Track Record.........................................................................................................138

Bundle Design.......................................................................................................139

Bundle Fabrication................................................................................................146

Towhead Structures...............................................................................................149

Towing Methods ...................................................................................................153

Insulation & Heating Systems...............................................................................160

Re-usable & Deepwater Bundles ..........................................................................165

Advantages of Bundles .........................................................................................170

FLEXIBLES ...................................................................... 177Expectation ...........................................................................................................179

Load-out ........................................................................................................................189Pipe lay ..........................................................................................................................192J tube pull ......................................................................................................................197End pull-ins ...................................................................................................................199Riser installation ............................................................................................................201

REEL LAY ........................................................................ 215Expectation ...........................................................................................................217

What is Reel-lay? ..................................................................................................218

Reel Lay Process...................................................................................................222

Reel-Lay Market & Vessels ..................................................................................236

Special Considerations..........................................................................................244

Technical Analyses ...............................................................................................248

LANDFALLS .................................................................... 261Expectation ...........................................................................................................263

Pull ashore.............................................................................................................266

Pull offshore..........................................................................................................270

Directionally drilled landfalls ...............................................................................274

TIE-INS ............................................................................. 283Expectation ...........................................................................................................285

Introduction...........................................................................................................286

Flanged connection by diver .................................................................................288

Hyperbaric welding...............................................................................................305

Diverless tie-ins ....................................................................................................314

5

Contents of Volume TwoPRECOMMISSONING...................................................... 335

Expectation ...........................................................................................................337

Introduction...........................................................................................................338

Gauging and Flooding...........................................................................................340

Hydrotesting..........................................................................................................344

Dewatering............................................................................................................349

Vacuum Drying.....................................................................................................353

Testing of valves and controls ..............................................................................355

MANAGEMENT................................................................ 357Expectation ...........................................................................................................359

Law .......................................................................................................................360

Quality Assurance .................................................................................................365

Health Safety and Environment ............................................................................373

Commercial risk management ..............................................................................382

SURVEY ........................................................................... 387Expectation ...........................................................................................................389

Introduction...........................................................................................................390

Survey methods.....................................................................................................392Geophysical surveys ......................................................................................................392Geotechnical surveys .....................................................................................................397Visual surveys................................................................................................................399

Survey Operations.................................................................................................404

SEABED MODIFICATIONS ............................................. 415Expectation ...........................................................................................................417

Sweeping...............................................................................................................418

Rock removal ........................................................................................................423

Protection ..............................................................................................................429

Rock dump ............................................................................................................436

Concrete Mattresses ..............................................................................................442

Protective structures..............................................................................................446

Crossings...............................................................................................................450

TRENCHING..................................................................... 455Expectation ...........................................................................................................457

Introduction...........................................................................................................458

Ploughing ..............................................................................................................459

6

Jetting....................................................................................................................466

Cutting...................................................................................................................471

Trench Transitions ................................................................................................478

Backfilling.............................................................................................................479

DIVING & ROV ................................................................. 485Expectation ...........................................................................................................487

Introduction...........................................................................................................488

Diving & Equipment.............................................................................................491Physiology .....................................................................................................................491Saturation diving............................................................................................................498Surface diving and hard suits.........................................................................................511Market............................................................................................................................514

Remotely Operated Vehicles ................................................................................522Types .............................................................................................................................522Tools ..............................................................................................................................529Specialist ROVs.............................................................................................................531Deck equipment.............................................................................................................540Market............................................................................................................................544

DECOMMISSIONING....................................................... 549Expectation ...........................................................................................................551

Introduction...........................................................................................................552

Legislation.............................................................................................................555

Decommissioning in-situ ......................................................................................558Cleaning.........................................................................................................................559Product removal.............................................................................................................561Trenching.......................................................................................................................562

Recovery ...............................................................................................................565

Re-use ...................................................................................................................571

PROFILES........................................................................ 575ACRONYMS & ABBREVIATIONS................................... 596ACKNOWLEDGEMENTS & REFERENCES ................... 603

S-LAY 9

EXPECTATION

EXPECTATION

Understand the principles of S-layDifferentiate between vessel typesUnderstand the processes required for S-layGain an idea of world markets and vesselsGain an overview of welding techniques andweld testingKnow the requirements for laying insulatedlinesUnderstand the principles of lay curvecontrol

Here we introduce the basic principles of the S-lay method and provide a descriptionof the differing types of lay vessel.

An overview of the S-lay process is provided, starting with pipe lay initiation, thenpipe joining and lay techniques and finishing with pipe lay termination.

The S-lay worldwide market and then some of the vessels available are examined.

The joining of pipe by welding is then examined in detail and the joining of otherpipe systems is also covered.

Finally consideration is given to the control of the lay curve for the S-lay process

OFFSHORE PIPELINE CONSTRUCTION10

WHAT IS S-LAY?

WHAT IS S-LAY ?

Takes its name from the shape of thesuspended pipePipe must be tensioned to hold its shape

Overbendarea

Sagbend area

Tension

S-lay takes its name from the suspended shape of the pipe at the end of the barge,which lays in a gentle ‘S’ from the stinger to the seabed. The crucial feature of thismethod is that the pipe must be held under tension to hold its shape.

There are two main activities that we must consider:

• The pipe assembly line, known as the ‘firing line’• Control of the lay curve, performed by the tensioners

There have been four generations of lay-barges and the vessels are of two types:anchor and dynamically positioned.

S-LAY 11

S-LAY VESSEL TYPES

FIRST GENERATION LAYBARGE

McDermott International Inc.‘DB 17’

The above picture shows the derrick laybarge (DB 17), it is a typical first generationS-lay barge, which is a relatively uncomplicated vessel design. The one shown is aflat-topped vessel used by J.Ray McDermott in the Gulf of Mexico. It wasconstructed in 1969 and can handle pipe diameters up to 1524 mm (60 in). There are5 welding stations and it can lay in water depths between (30 ft) and (1500 ft).

It takes 12 metre lengths of pipe which can be seen stacked on its deck. It placesthese in a firing line running down the centre of the vessel, prior to them beingwelded together. The pipe then runs out of the stern of the barge, down the stingerand into the water. As the pipe is welded up, so the vessel is winched forward on ananchor system. It utilises a 12-point mooring system for station keeping.


SECOND GENERATION LAYBARGE

‘Choctaw 1’

The second generation laybarges, e.g. the ‘Choctaw I’ shown above, were very muchlarger than the first generation vessels and were better equipped for the environmentalconditions of the North Sea. Some of these laybarges had ship shaped hulls, but themajority were semi-submersible vessels.

‘Choctaw I’, the first second-generation lay vessel, was built in 1969. It was designedto fit through the Panama canal and so proved too narrow to be an effective cranevessel. However, its service in the North Sea, as a pipelay barge, demonstrated thebenefits of the semi-submersible hull shape for that environment.

S-LAY 13

THIRD GENERATION LAYBARGE

McDermott International Inc.‘LB 200’

Third-generation vessels are larger than the second-generation laybarges, their largerwidth making them more stable. Semi-submersible hulls were utilised for the harshNorth Sea environment.

The ‘LB200’ S-lay barge (previously ‘Viking Piper’) is shown above and is ananchored semi-sub larger than a football pitch. It has a rigid stern ramp and doublejointing capability, where 12m pipe joints are welded offline and the 24m joint iswelded into the pipe-string in the firing line. It has a length of 162 m, a width of 60m and a work deck 13.2 m above sea level.

Other similar vessels include ‘Semac-1’ and the ‘Castoro Sei’.


FOURTH GENERATION LAYBARGE

Allseas‘Solitaire’

Fourth generation S-lay construction vessels have recently been brought into serviceand are mono-hull vessels which utilise powerful dynamic positioning thrusters tohold station and so are no longer reliant on anchors. Examples of fourth generationvessels are the ‘Solitaire’ and the ‘Lorelay’ operated by Allseas.

The Solitaire operates in deepwater and can lay pipe of comparable diameters to theJ-lay vessels. The lay rates of Solitaire are considerably better than J-lay and higherthan other S-lay vessels. The Solitaire vessel utilises two double-jointing plants,seven main firing line welding stations, one NDT station and two coating stations.

S-LAY 15

ANCHORED VESSELS

Anchored vesselsanchor spreadanchor handlingused to move vessel1st, 2nd, 3rdgeneration

Require anchor handling vesselsVessel moves forward by pulling onforward anchors and letting out aft anchors

Most S-lay vessels are of the anchored type. There are normally 8 or 12 anchorsdepending on vessel size. A failure of one anchor is not catastrophic, and failure of allanchors highly unlikely.

The anchor winches are fitted to the corners of the vessels and the anchors aredeployed by anchor handling tugs. When operating close to other pipelines andplatforms, the position of each anchor needs careful monitoring with a bargemanagement system. The anchor spread for a vessel is determined from the piperoute, other installations in the vicinity and environmental conditions.

Different types of anchors can be fitted, depending on the holding force required andthe seabed soil conditions along the pipe route.

The vessel moves along the pipe route by pulling on the forward anchors and holdingtension on the aft anchors. The port and starboard anchors hold the vessels’ lateralposition.

As water depths increase, the amount of time required to deploy anchors can affectlay-rates. Lengths of chain are incorporated in the anchor wires to reduce thecatenary length. The operation of an anchored laybarge is, therefore, restricted to‘shallow’ water in uncongested areas.


DYNAMICALLY POSITIONED VESSELS

Dynamically Positioned(DP) Vessel

Ship-shapedGreater manoeuvrabilitythan vessel withanchor spreadCan position closerto platformsFailure disrupts pipelayVessel mobilises under its own power

A dynamically positioned (DP) vessel has a number of thrusters located on its hull orhulls. These are linked to the vessel’s GPS and run constantly to maintain the vesselon its pre-set station or route.

Modern vessels operate on a DP system and, because they are independent of anywater depth limitations, a number of the earlier vessels are being converted.

A disadvantage of the system is that it requires large amounts of power. Vessels havedifferent ratings of DP, which give an indication as to the distances they can operatefrom fixed installations.

S-LAY 17

S-LAY VESSEL TYPES - SUMMARY

Four generations of vesselBarge type

Simple barge

Spud legged

Ship-shaped

Position fixingAnchored Vessels

Dynamically Positioned (DP) Vessels

Any questions?

There have been four generations of lay-barge. They began with simple flat-bottombarge designs, then moving to spud-legged semi-submersible type barges forimproved stability and now there are refurbished ship-shaped lay vessels.

The station holding capability of the S-lay vessels is provided by two differentmethods. Anchored vessels have a series of anchors to keep the vessel in a fixedstation. The anchors are moved intermittently by anchor-handling tugs, and the bargepulls itself along on these anchors. Then there are also dynamic positioning thrusterswhich are directional propeller systems that can be used to move the ship in lateraldirections and so hold position. Combinations of anchors and dynamic positioninghave been used on some vessels.


S-LAY PROCESS

S-LAY PROCESS OVERVIEW

InitiationLoading and storageEnd preparationDouble jointingFiring line:

WeldingNDTField joint

TensioningLaydown

The main stages of the S-lay process are shown above. These stages are:

• Initiation. The pipeline must be lowered to the seabed under controlled tension.A point of fixity is selected on the seabed, usually by an anchor or a pile. A cableis then linked from the point of fixity to a start-up head on the pipeline. Thevessel lowers the pipe to the seabed whilst maintaining the tension in the cable toensure the correct tension in the pipeline.

• Loading and storage. As pipe lay continues it will be necessary to re-supply thevessel with pipe joints. These can be supplied from shore on smaller pipe carriervessels and then loaded by crane onto the lay vessel.

• End preparation. Prior to welding, it is necessary to prepare the ends of each pipejoint. The ends are machined to produce the required bevel and remove defects.

• Double-jointing. To increase welding efficiency, some lay barges will weld twopipe joints together at welding stations independent of those on the firing line that

S-LAY 19

produce the main pipe string. This ability halves the number of welds requiredon the firing line.

• The firing line. The firing line is the section of the vessel that runs along the axisof the pipeline being laid. Along this line single or double joints are brought inline with the main pipeline axis and then welded onto the end. The firing lineconsists of stations for welding, testing and then field joint coating.

• Tensioning. The pipeline being laid then passes through tensioners beforeleaving the vessel. The tensioners maintain the constant tension in the laycurveto prevent unacceptable bending occurring. The tensioners must maintain aconstant tension and compensate for the dynamic motion of the vessel on thewater surface.

• Laydown. When the pipeline has been completely laid, the end of the pipe mustbe lowered to the seabed. It is important that the pipe end is lowered whilst therequired tension is maintained. The laydown process is then, in principle, thereverse of the initiation process with the pipe being lowered on a cable which isattached to an abandonment and recovery winch on the vessel.

INITIATION

Lay barge movement

T

Fixed point

Wire

Chain

Pipeline

T

The pipelaying process begins with installing an anchored point on the seabed towhich the initiation head is attached.

The anchor may take many forms such as:

• Heavy-duty anchor• Dead-man anchor (DMA)• Pile in the seabed• Suction pile• Jacket leg

A chain is attached to the anchor and a steel wire connects the pipeline and chain. Thepipeline is always in tension, which increases as the pipe is laid.


LOADING & STORAGE

Laybarges are comparable in size to a football pitch and are accompanied by a fleet ofsmaller support vessels. There are four main types of support vessels, eachperforming a different role:

Pipe carrier: These transport the pipe from onshore to the laybarge. The pictureabove shows a storage rack of concrete coated 20” OD pipe. The white bands on thelinepipe in the foreground are anodes.

Anchor tugs: These position and deploy the anchors for anchored types of laybarges.

Survey vessel: These vessels carry and operate the sonar and ROV surveyingequipment to monitor the progress of the pipe as laid onto the seabed. They ensurethe pipeline is laid along the correct route and check integrity of pipeline after layingto determine if remedial work is required.

Supply vessel: These vessels re-supply the lay barge with all the ancillary equipmentassociated with the pipeline construction. This can include items required directly forthe pipeline construction, like welding material, anodes, joint coatings and itemsrequired by the crew such as food.

S-LAY 21

END PREPARATION

Initially the pipe is inspected and the ends machined ready for welding.

End preparation is done usually onboard the lay vessel, just prior to welding processto remove any damage and rust that may have occurred during transportation andhandling.

The machine is inserted into the end of the pipe. It is centred and then the cuttermoves around the pipe bevelling the edge and cleaning the outside of the pipe. Thecut is then inspected.


D O U B L E J O I N T I N GT h e p i p e c o m e s i n “ j o i n t s ” i . e . s e c t i o n s 1 2 m ( 4 0 ’ ) i n l e n g t h . D e p e n d i n g o n t h e b a r g e t h e f i r i n g l i n e c a n e

i t h e r a c c e p t s i n g l e j o i n t s o r d o u b l e j o i n t s .

I f d o u b l e j o i n t s a r e b e i n g u s e d t h e n t w o j o i n t s m u s t b e j o i n e d t o g e t h e r . T h i s i s d o n e u s i n g t o p d o w n S A W a s t h e p i p e i s r o t a t e d .

T h e w e l d i s t h e n i ns p e c t e d w i t h N D T a n d t h e n j o i n s t h e f i r i n g l i n e .

FIRING LINE

S-LAY 23

The firing line can be viewed as the factory assembly line for the pipeline. Thepipeline is welded, inspected and coated on the firing line. The pipe stays still but thevessel moves, thus the different stages can be completed. The firing line runs downthe centre of the barge.

The figure above shows the end of the firing line (just before the stinger) on theCastoro Sei. The firing line is angled by 10°.

FIRING LINE

Tensioners Weld stationsNDTCoating

234 1

The figure above shows the firing line for the Lorelay. In this, new pipes are alignedand root-welded at the front of the vessel and then passed from right to left throughthe welding stations, having a filler and cap weld added. The pipe then passesthrough the tensioners to the non-destructive testing stations where a radiograph istaken of the weld. From there, it passes to the back of the boat where a field jointcoating is applied, after which the pipe passes down the stinger and into the water.

The key to the firing line is to divide the time taken to complete the entire processevenly amongst the stations. For example, if it takes 45 minutes to complete theoperation from alignment through to field joint coating and there are 9 stations, thenthe objective would be to spend 5 minutes at each station. If it were necessary tospend, for example, 10 minutes at one station, then this would slow the vessel speedto half, so would double the cost of construction.


WELDING

An internal alignment clamp is installed, which aligns and brings the pipe endstogether for welding. Once aligned, the root pass of the weld is made. For largediameter pipe, the alignment clamp can incorporate an automatic welding unit toallow the initial root pass to be made from inside. It will otherwise incorporate aguard to prevent excessive weld intrusion. The hot pass may also be performed at thefirst station.

On completion of the initial weld passes, the alignment clamp is released and drawnback from the inside of the pipe, as the vessel moves forward. The weld moves downthrough the welding stations having hot-pass, fillers and cap welds added.

Welding is normally performed using automatic welding systems. Manual stickwelding is occasionally used on low production, shallow draft lay barges, butautomatic welding systems are quicker and produce welds of a consistently highquality. A defect rate of 1-2% is typical.

S-LAY 25

NDT

After welding, Non-Destructive Testing (NDT) of the welds is undertaken. NormalS-lay installation procedures will require the inspection of every welded joint. Mostjoints of an S-lay constructed pipeline will be tested using either radiography orultrasonic techniques. They are a range of different radiography techniques availablesuch as x-rays, iridium-192, cobalt-60, gamma rays, etc.

REPAIRS

Faulty weldBack-lay to appropriate stationGrind faulty weldRe-weldRepeat NDTLay process continues

One chance only

In the event of the NDT discovering a defect, all pipelaying is stopped and the pipe isretrieved from the sea by back-laying until the joint is adjacent to the appropriate


workstation. Once in position, the lay curve is held by the tensioner and the defectiveweld can be ground away. The joint end is then re-welded and inspected again. Afterpassing the inspection, the lay process continues as normal.

In general, the client’s representative gives only one chance of repair. If the repair isnot accepted, then a cut-out and full new weld will take place.

FIELD JOINT

Anti-corrosioncoating

Thermal insulationcoating

Following completion of the non-destructive examination of the weld, it is coatedwith an anti-corrosion coating and possibly a thermal insulation coating. A number ofpossible types of coating are available including:

• Mastic• Wrap• Polyurethane foam or solid• Polypropylene foam or solid• FBE

The coating can be applied using several, or combinations of, methods, e.g. paint,half shells, moulding, heat shrink-wrap sleeve etc, depending on supplier andrequirements.

S-LAY 27

TYPICAL CORROSION COATING

Mastic poured

inFlap

Heat shrink wrap

Thin metal cover

Concretecoating

WeldPipe wall FBE coating

Banding straps

Steelre-bar

The above diagram shows the usual design of a typical corrosion field joint coating.First the heat shrink wrap is wound around the pipe and heated until it shrinks andforms a tight protective layer around the pipe wall and weld. Then a tin cover sleeveis placed over the whole joint. In the top of the tin cover is a flap, through which themastic is poured. The mastic provides a permanent and flexible waterproof seal andfills the gap between the concrete coatings and the pipe. The flap is then closed andsealed to complete the field joint.

Because of the carcinogenic nature of bitumen, H&S now prefer to avoid the use ofsuch mastic fillers.


TYPICAL THERMAL COATING

Foam

Solid sheath

Foam half shell

Sprayed layer of FBE

Injected PU

WeldPipe wall FBE coating

Concretecoating

The above diagram shows the design of a typical thermal insulation field joint. Thethermal coating will be pre-applied to the pipe in a coating factory. The coating isdesigned to leave the ends of the pipe joint exposed so there is a section of the pipesteel accessible for welding. Once the weld is completed, the exposed section of thepipe outer wall and the weld are sprayed with a layer of Fusion Bonded Epoxy (FBE).Then around the joint two half-shells of foam are fitted and held into position. Tothen seal the joint and prevent water ingress a mould is fitted around the join. SolidPU is cast around the joint. The solid PU may be either flush with the pipelinecoating (as illustrated) or raised to improve the thermal performance of the field joint.

S-LAY 29

FINAL CONTROL OVER STINGER

As the pipeline is paid out, it is guided over the stinger into the sea. This controls theconfiguration of the overbend. The geometry and adjustment capability of the guiderollers allow the stresses in the pipe and weight coating to be set to within acceptablelimits for the pipe being laid. The stinger will be fitted and the radius set while thevessel is in port. Therefore, it is required to determine the required bend radius toensure pipe stresses are acceptable, prior to commending the pipelay operation.

TENSIONING


A tensioning system holds the weight of the completed pipeline behind the barge andallows the pipe to move off the barge at the desired rate as each new joint is weldedonto the line. These are caterpillar tracks that are hydraulically brought together togrip the pipe and apply a back tension.

The amount of force that must be applied by the tensioners to hold the pipe on thebarge varies with pipe size and weight and water depth. Large diameter deep waterpipes require around 300 to 400 tonnes and smaller pipes in shallow water requireabout 20 tonnes of tension. Multiple tensioners will be used to obtain the largertensioning forces. For example, Castoro Sei will utilise 3x100 tonne tensioners toprovide the required 300 tonne tensioning force.

Dead band for tension is between +25% and -10% of set level, so normally the pipe isstill. If it moves, then the welding kit moves with it. The dead band is required toaccommodate any surge in the lateral movement of the vessel that may result fromsea states.

The figure above shows a 45 tonne horizontal tensioning unit that can be used withpipe up to a maximum diameter of 48”.

BUCKLE DETECTION

Pig used to detect buckling at sagbend

Buckleat sagbend

Pig

Cable to vesselLay direction

During pipelay it is important that the sagbend is monitored to check for any localbuckles or ‘kinks’ in the pipe. One method is to use a type of pig that is sized to runfreely through the pipe when the pipe is at normal diameter. However, it will become‘stuck’ if the pipe diameter reduces. The pig is held on a cable which is off a fixedlength that ensures the pig remains just beyond the sagbend area on the lay curve.The cable is then attached to a tension monitor on the vessel.

As the pipe is laid, if a local buckle does occur the pig will become lodged at thebuckle and as the pipe continues to be laid, the tension in the fixed length cableattached to the pig will increase. The tension monitor will indicate a significantincrease in tension and notify the crew. Pipelay will then be halted and the bucklecan be rectified. This is usually done by back-laying the pipe until the defected jointis returned to the firing line. The joint can then be cut from the pipe string, and a

S-LAY 31

replacement joint welded in. The repaired pipe string is then returned to the seabedand normal laying resumes.

PIPE IN PIPE JACKET

Flow line

Metal jacket

Insulant Rubber water stop

Weld

Half-shellSteelhalf-shell

For a pipe in pipe system tensioning is a more difficult problem.

It is the outer jacket which is put in tension, so at least some of the jacket weld (bothgirth and seam welds) must be completed before the first tensioner. Normally at leastthe root weld and first pass are completed before the tensioner.

This requirement puts a limit on the use of tensioners (effectively the first pair aremade redundant as they are before the first jacket weld stations). This means thatdouble pipeline systems are laid approximately 1/2 to 1/3 times slower thanconventional ‘single’ pipelines.

Another problem is performing the NDT of the flowline efficiently.


12 POINT ANCHORED LAY BARGE

SB SBSB SB SBSBSBSBSBSB SB SB

SB SB SBSBSB SB

SB SBSB SB SBSBSBSBSBSB SB SBSBSBSBSBSBSB

Quarteranchor wire

HPipeline tensionStern anchor wire Bow anchor wire

Lay direction

~30 m

~2300 m

~3000 m

0 m

130 m c/c

180 m c/c

380 m c/c

Breastanchorwire

The vessel must react the tension that is required in the catenary lay curve. On first tothird generation lay vessels, this reaction is obtained through the use of anchors. Inthe diagram shown above, the anchors at the bow of the vessel are the primaryanchors for reacting the lay curve tension. The other anchors on the vessel sidesprovide principally a lateral stability, but they contribute to the lay curve tensionwhen the bow anchors are repositioned.

The process of laying pipe is nearly continuous (every five to ten minutes) and so thelay vessel must also be capable of moving continuously. To do so, it is necessary thatthe anchors are continually re-deployed to new positions, one-by-one. Thedeployment of anchors is done by anchor handling tugs that remain continually withthe lay vessel.

For a twelve-point anchored laybarge as shown above, there are generally two tugsmoving the lines. However, only one anchor is moved at each stage. This gives themoving lay vessel the appearance of a walking spider.

S-LAY 33

LAYDOWN

Process of lowering pipeto seabed

Risk of bad weatherEnd of construction

Reverse process topipelay initiation

Laydown head PipelineWire toA&R winch

In deteriorating sea conditions, when it is unsuitable to continue the laying process,the pipeline can be lowered to the seabed. As an example, Deep Blue abandonslaying when the significant wave height is approaching 8.5 m, to prevent fatigue dueto bouncing on the seabed, rollers and moorings.

A laydown head is welded to the end of the pipe which is then shackled to an A&R(Abandonment & Recovery) winch. The tensioner is released and the pipeline islowered as the vessel moves forward.

This process is reversed to recover the pipeline. Recovery of a pipeline end may alsobe required for removal of the pipeline at the end of its service life or to conductrepairs.


ABANDONMENT & RECOVERY HEADS

A&R HeadsFitted to pipeline endEnable attachment ofwinch cable

1. Balls fully extended2. Ballgrab fully inserted, balls in contact3. Radial grip force increases as axial load (lift) is applied

BallgrabA&R head

Pipeline

When lowering or raising a pipeline to/from the seabed it is necessary to ensure thetension is maintained in the laycurve throughout. To maintain this tension, a winchcable is fitted to the pipeline end on the vessel and the pipeline is lowered to theseabed on a winch.

To fix the cable to the pipe end, an Abandonment and Recovery (A&R) Head is used.A&R Heads usually provide some means of applying an even internal pressure to thepipe wall as the means of attachment. The winch is fixed to the A&R Head by aswivel and shackle.

The figures above illustrate the ‘Ballgrab’ A&R Head developed by BSW Limited.This design uses a series of spring loaded metal ball bearings around thecircumference of the section inserted into the pipeline end. As illustrated in theschematic, when an axial tensile load is applied to the installed Ballgrab, the ballbearings are forced into the inner pipe wall. This allows the head to grip the pipewith sufficient force to withstand the tensions required to lower the pipeline.

Crucially, there are no tearing actions or stress concentration points created. Theballs are totally dynamic and they continuously redistribute load. A simple disengagemechanism allows the too to be off-load released and recovered for re-use.

Remotely activated Ballgrabs are also available that allow the A&R head to be fittedto pipe ends located on the seabed and so enable recovery.

The same Ballgrab technology is more commonly used for quick release fromanchors for Tension Leg Platform and vessel moorings.

S-LAY 35

SAIPEM S-LAY - VIDEO

The video details the laying of sections of the Zeepipe pipeline that runs from theSleipner field in the North Sea to Zeebrugge in Belgium. The main sections of thepipe were constructed in 1991 and 1992 by EMC (now Saipem) semi-submersible S-lay vessels; the Castoro Sei and the Semac 1. The completed pipeline required over500 days of lay barge activity with the lay vessels usually operating 24 hours per day.

In addition to the lay vessels, a number of support vessels were also required. Theseincluded pipe carrier vessels, supply boats, anchor handling tugs, guard vessels andsurvey vessels. At times the fleet of vessels reached 25 in total. It was also necessaryto reserve the use of a large number of pipe carrier vessels. 13 were required tosupply the lay vessels with over 80000 pipe joints from the Statoil pipe coating plantsat Rotterdam in Holland and Leith in Scotland. At the coating plants the pipe jointswere cleaned prior to loading on the vessel. Also each joint was given anidentification marking and a computerised tally of each pipe joint was made to alloweasy traceability of any pipe joint entering the pipe string.

Once loaded onto the lay vessel, the ends of each joint were prepared and the jointmoved to the double-joint welding stations. Two double-joint welding stations areused where two joints are welded together and the welds tested before the joints enterthe main firing line. On the firing line the double-joints are welded onto the pipestring. The final welds were 100% X-rayed and the field joints then coated. The pipewas then passed through the tensioners and lowered to the seabed.


S-LAY PROCESS - SUMMARY

InitiationLoading and storageEnd preparationDouble jointingFiring line:

Welding, NDT, Field jointTensioningLaydown

Any questions?

The following summarises the S-Lay process:

• S-Lay relates to the shape of the pipe laycurve during the laying process. This ismaintained by tension that must be applied throughout the operation.

• It is a continuous process, with near-horizontal welding being carried out overseveral stations in the Firing Line.

• The Firing Line is the area on board the deck of the lay vessel where the pre-weldprepped pipe lengths or double lengths are welded, inspected and coated.

• The S-Lay method can be applied to pipes up to approx. 60” dia.

• The capacity of the tensioners governs the maximum operational water depth(e.g. on Lorelay 300-400 tonne and 1775m max. water depth).

• Control of stresses in the pipe and in the concrete weight coat during the layoperation is by the level of the tension applied, as well as the geometry andadjustment of the stinger.

• S-Lay vessels are either of the anchored type or dynamically positioned; the latterproviding greater positional control but at a greater operating cost.

• Average pipelay speeds of up to 4.5 km/day are achievable.

S-LAY 37

MARKET AND VESSELS

MAJOR S-LAY CONTRACTORS

Global IndustriesJ.Ray McDermottSaipemHorizon OffshoreStolt OffshoreTorch Offshore Inc.Allseas EngineeringCloughHyundai

A list of the major installation contractors is given above. Most contractors have theability to use more than one installation method.

Due to the boom and bust nature of the industry, and more companies chasing fewerjobs, there have recently been a number of joint ventures, mergers and takeovers.

The major companies S-laying pipe in Northern Europe are Allseas, Saipem and StoltOffshore.


GLOBAL INDUSTRIES: CHEROKEE

‘Cherokee’

A first-generation Derrick/Laybarge.

Dimensions: 350 x 100 x 25 ftRange of Pipe Diameters Handled: 2 to 48 in.Stations: Welding, 5Welding Method(s) Used: Usually ManualPipe Installation Method(s) Used: S-layMinimum Pipelaying Water Depth: 20 ftMaximum Pipelaying Water Depth: 1,000 ftMooring Station Keeping System: 8-point mooringArea(s) of Operations: Gulf of Mexico/West Africa

S-LAY 39

GLOBAL INDUSTRIES: DLB 264

‘DLB 264’

A first-generation Derrick/Laybarge

Dimensions: 400 x 100 x 30 ftRange of Pipe Diameters Handled: 60 in. OD with coatingStations: Welding, 5; 1 X-ray, 1 field jointWelding Method(s) Used: SMAW, GMAW, FCAWPipe Installation Method(s) Used: S-layMinimum Pipelaying Water Depth: 20 ftMaximum Pipelaying Water Depth: 1,500 ftMooring Station Keeping System: 8-point mooringArea(s) of Operation: Southeast Asia


GLOBAL INDUSTRIES: HERCULES

‘Hercules’

Type of vessel: Derrick/LaybargeDimensions: 445 x 140 x 25 ftRange of Pipe Diameters Handled: 2 to 60 in. (18 in Reel lay)Stations: Welding, 7; Other, 2Welding Method(s) Used: Automatic and manualPipe Installation Method(s) Used: Reel/S-layMinimum Pipelaying Water Depth: 45 ftMaximum Pipelaying Water Depth: 8,000+ ftMooring Station Keeping System: DP/8-point mooringLifting Capacity: 2,000 tonReel Capacity: 7500 TonMooring system: Converted to DP

S-LAY 41

J.RAY MCDERMOTT: DB 17

‘DB 17’

Another first-generation Derrick/Laybarge.

Dimensions: 400 x 106 x 29 ftArea(s) of Operation: Gulf of Mexico


SAIPEM: CASTORO OTTO

‘Castoro Otto’

A ship shaped Derrick/Laybarge operated by Saipem.

Dimensions: 192 x 35 mRange of Pipe Diameters Handled: Up to 60 in.Stations: Welding, 6; NDT, 2; Coating, 2Minimum Pipelaying Water Depth: 22 ftMaximum Pipelaying Water Depth: 1,200 ftArea(s) of Operation: Worldwide

Propulsion System: Two variable pitch propellers at vessel stern, in steerable kort-nozzles and 4,000 HP each, producing total propulsion power of 8,000 HP. It is self-propelled, not DP.

S-LAY 43

SAIPEM: SEMAC 1

‘Semac-1’

A third-generation semi-submersible laybarge used to lay either single or dual (asshown above) pipelines worldwide, also equipped with davits for above-water tie-ins.

Dimensions: 149 x 55 x 28 mRange of Pipe Diameters Handled: Up to 60 in.Stations: Welding, 5; Other, 4Welding Methods Used: AutomaticPipe Installation Method Used: S-LayTensioners: 3 x 75 tonnesMooring System: 12 x 22 tonne anchorsMinimum Pipelaying Water Depth: 11 mMaximum Pipelaying Water Depth: 900 mArea(s) of Operation: Worldwide


HORIZON OFFSHORE: LONE STAR HORIZON

‘Lone Star Horizon’

A typical first-generation laybarge, operating in Venezuela and the Gulf of Mexico.

Dimensions: 329 x 90 x 12 ftRange of Pipe Diameters Handled: Up to 48 in.Stations: Welding, 5Minimum Pipelaying Water Depth: 25 ftMaximum Pipelaying Water Depth: 800 ftMooring Station Keeping System: 10 point mooring.

The stinger is clearly visible lifted out of the water, and the davit system for liftingpipe on the starboard side of the vessel.

S-LAY 45

STOLT OFFSHORE: POLARIS

‘Polaris’

A Derrick/Laybarge that has recently been upgraded to DP for major projects in WestAfrica, including the deepwater Girassol project (1300 metres).

Dimensions: 137 x 39 x 9 mRange of Pipe Diameters Handled: Up to 60 in.Stations: Welding, 4; Other, 3Welding Method(s) Used: AutomaticPipe Installation Method(s) Used: S-lay, J-layMinimum Pipelaying Water Depth: 6 mMaximum Pipelaying Water Depth: 2,000 m

The above picture shows the barge being used to upend a jacket.


STOLT OFFSHORE: LB 200

‘LB 200’

A third-generation, semi-submersible pipelay barge. The stinger is clearly seen, as arethe anchor wires.Dimensions: 167.5 x 58.5 x 33 mRange of Pipe Diameters Handled: Up to 60 in.Stations: Welding, 5; Other, 2Welding Method(s) Used: AutomaticPipe Installation Method(s) Used: S-layMinimum Pipelaying Water Depth: 15 mMaximum Pipelaying Water Depth: 600 m

S-LAY 47

TORCH INC.: MIDNIGHT BRAVE

‘Midnight Brave’

A first-generation pipelay/bury barge operated in the Gulf of Mexico and recentlyupgraded with additional tensioners and mooring winches.

Dimensions: 275 x 70 x 18 ftRange of Pipe Diameters Handled: Up to 24 in.Maximum Pipelaying Water Depth: 400 ft


ALLSEAS: LORELAY

‘Lorelay’

The first dynamically positioned, ship shaped laybarge and now has an extensivetrack record.

Dimensions: 182.5 x 26 x 15.5 mRange of Pipe Diameters Handled: 2 to 36 in.Stations: Welding, 7; Other, 2Welding Method(s) Used: AutomaticPipe Installation Method(s) Used: S-layMaximum Pipelaying Water Depth: 1,775 mMooring Station Keeping System: DPArea(s) of Operation: Worldwide

S-LAY 49

ALLSEAS: SOLITAIRE

‘Solitaire’

A major S-Lay vessel that has recently entered service. Its primary market is theinstallation of long lengths of large diameter trunk line worldwide. It is currently thelargest vessel operating with 6 to 8 workstations.

Dimensions: 299.5 x 40.6 x 24 mYear Built: 1972 (converted 1997/98)Range of Pipe Diameters Handled: Up to 60 in.Stations: Welding, 2 x 4 double joint stations; 6 to 8 main firing line weldingstations; Other: 2 coating stationsWelding Method(s) Used: AutomaticPipe Installation Method(s) Used: S-layMaximum Pipelaying Water Depth: Say 2,500 mMooring Station Keeping System: DPArea(s) of Operation: Worldwide


S-LAY PERFORMANCE AND COST

8 minute cycle time for each stage in the firing lineMaximum diameter is 72in (Solitaire), but mostcommon ‘maximum’ is 60in (9 vessels)

No restriction on wall thickness

Average pipelay speeds up to 4.5 km per day‘Solitaire’ has achieved 7 km per day

Vessel ‘hire cost’ up to US$ 350k per dayWeather limit

Semi-sub - anchor handling and pipe supply criticalShip-shaped - vessel motion and pipe supply critical

The above slide contains some ball-park information on pipelay speeds, limitationsand vessel costs. However, it should be noted that these vary considerably fromvessel to vessel.

At present, the pipelay market is an opportunity rather than a commodity market.The prices do not therefore necessarily reflect the cost of building and running thevessels. Instead, they climb in busy years, and drop in quiet years.

S-LAY MARKET AND VESSELS - SUMMARY

Details of major contractorsExamples of various available laybargesPerformance and costs

Max diameter is 72in (Solitaire)Average pipelay speed

Approximately 4.5 km/day

Max vessel hire costApproximately $350k per day

Weather limitationsAny questions?

S-LAY 51

In this section, we have introduced the various s-lay contracting companies and thespecifications of some of their vessels. Also discussed were some approximate limitson the performance and costs of these vessels.


WELDING AND NDT

Procedure

Prepare ends of pipe jointsAlign two jointsWeld

Root passHot passFill weldsCap weld

NDT

WELDING PROCEDURE

Root weldHot pass weld

Filler welds

Cap weld

Pipe wall - outer surface

Pipe wall - inner surface

Welding is the preferred method adopted by the oil and gas industry for connectingtwo pipe joints to form a pipe string. Along the ‘firing line’, where pipe joints arewelded onto the pipe string, there will be the following main processes occurring:

• End preparation: The ends of each pipe joint must be prepared for welding. Thiswill involve re-facing the ends to cut a fresh bevel and remove any damageincurred during transport.

• Align the joints: The next joint in the pipe string must be aligned with the lastwelded joint at the end of the string. This is usually done by supporting the newjoint on rollers and using an internal mandrel for final alignment.

• Weld the joint: Usually semi or fully-automatic welding machines will then beused to perform the welding in a controlled manner. The weld is built up from aseries of layers of filler material. The first later is the root weld on the inner

S-LAY 53

diameter of the pipe, then a hot pass, then filler welds that form the bulk of theweld and finally a cap weld at the outside pipe diameter.

• Non Destructive Testing (NDT): Finally the weld needs testing to ensure thereare no flaws. All welds are tested using non-destructive methods such asradiography of ultrasonic testing.

END PREPARATION

Re-dress bevelUtilise pipe facingmachine (PFM)

Pipe facing machine

Good joint end preparation is the first step in preventing weld defects. The end ofpipe must be clean and if bevelled must have the correct angle and thickness of bevel.It is particularly important to re-dress the pipe ends just prior to welding as this canthen remove damage incurred during transportation. General preparation will requirethat any dirt, loose mill scale, paint, grease, oxide, rust, etc are removed prior toalignment. Cleaning should extend for at least 30 mm from joint on both internaland external faces. Burrs, score marks indentations or other small imperfections mayrequire smoothing out by filling or grinding. If these are serious then the pipe endmay require cutting back and the joint re-prepared. It may also be necessary toremove moisture from the pipe, as excess moisture and the associated hydrogen canlead to brittleness of the weld.

Line pipe is often delivered with ends prepared with the required bevel. The bevelwill then need inspecting and may need re-dressing prior to welding to remove anydamage that may have occurred during transportation. Alternatively, the linepipemay be supplied with plain ends and the bevel is then cut on the barge. This is donewith a pipe facing machine (PFM), which cuts a new bevel.

To increase productivity when undertaking automatic welding, a J-shape bevel asopposed to the standard 30°. This then creates a U-shape when two pipe ends areplaced together for welding. A U-shaped bevel requires less filler material than the30° bevel. This reduces the required number weld passes for each joint connection.The re-dressing of the pipe ends is an operation that normally takes between 2 to 5minutes, depending on the pipe wall thickness and skill of the operator.


ALIGNMENT

Internal mandrelMay also performinternal welding

The gap between the ends of the pipe must be prescribed for the pipe size andwelding methods used, and two joints must be properly aligned before weldingbegins. Internal line-up clamps are used to provide the concentricity of pipe bore.The internal mandrel shown above is supplied by CRC Evans. The clamp includeswelding equipment that produces the root weld from inside the pipe. This eliminatesthe difficulty of applying the root weld from outside the pipe.

WELDING

Welding techniquesManual (SMAW or stick)Semi-automaticFully automatic

Automated methodsGMAW (MIG)GTAW (TIG)

Applicable codesUK - BS 4515USA - API 1104

Typical welding station

S-LAY 55

The most common welding process used around the world is Shielded Metal ArcWelding (SMAW). To improve efficiency and weld quality, most pipe joint weldingwill nowadays utilise semi or full-automatic welding techniques, as opposed to theolder and simpler method of manual “stick welding”, with stick welding only beingused for welding exotic pipe materials. The most common methods of automatedwelding are gas metal-arc welding (GMAW) or gas tungsten-arc welding (GTAW),more commonly known as MIG and TIG welding, respectively. These are explainedin more detail on subsequent slides.

The design codes normally used for offshore pipeline welding when on the UnitedKingdom continental shelf (UKCS) are BS 4515 “Welding of onshore steelpipelines”, or for the USA then API Std 1104 “Welding of pipelines”.

Other pipe welding codes include:

• BS 2633 Class 1 arc welding of pipework• BS 2971 Class 2 arc welding of pipework• BS 4677 arc welding of stainless steel pipework• BS EN 288-9 welding procedures• ASME B 31.3 process piping

AUTOMATIC WELDING

Semi-automaticWelder monitors positionof weld depositMethods

GMAW and GTAW

Fully automaticMachine monitorsposition of weld depositMethods

GMAW and GTAW

Single nozzle GTAW bug

Filler wire Gas nozzleand electrode

Automated welding methods utilise a welding machine (known as a ‘bug’) that runsaround the pipe circumference. The bug carries the electrode and automatically feedsin the filler wire. It is strapped to a band that is fixed around the pipe circumference.The bug then automatically travels around the band. For semi-automatic welding thewelder is required only to watch the position of the weld deposit and will make slightadjustments to the position of the arc to account for the minor misalignments of thepipe bevels. The filler wire is automatically and continually fed into the weld headand does not need to be replaced by the welder. Automated welding machines differin that they utilise a control system that can automatically monitor the misalignmentsand make the required alterations to the position of the weld deposit.


The welds are made on one side of the pipeline from the top (12 o’clock position)down to the bottom of the pipe (6 o’clock location). The weld on the other side of thepipe is then completed. After the internal or external root bead, the hot pass iscompleted. Then a number of fill passes are carried out (dependent upon thethickness of pipe). Finally a fill cap weld is added in the same manner. Typically,on large diameter lines, the whole operation from clamping to completion of the rootbead is a matter of a few minutes, with rates of 1 - 1½ m/min for the filler runs.Multiple stations are used to increase productivity.

Among the advantages of automated welding machines are an increased welddeposition rate, reduced volume of weld metal, improved consistency of weldstrength, toughness and NDT quality, reduced vulnerability of weld quality to humanerror, reduced physical strain on welder/operator, ease of training operations, reducedmanpower and equipment requirements for heavy wall and large diameter pipe.

TESTING

Ensure confidence in weld qualityNon Destructive Testing (NDT)Two main methods

RadiographyX-ray, gamma ray

Ultrasonic inspection (UI)Welding and NDT codes

BS EN 14163:2001 and API 1104Record all weld test data for future referenceand welder assessment

Once the weld has been completed it is tested for any defects to ensure the weld is fitfor purpose. The methods of testing must be non-destructive, i.e. they cannotphysically affect the weld to assess if it will fail or not. Therefore, they are known asnon-destructive testing (NDT) or sometimes non-destructive examination (NDE).The most common methods of weld testing used in the oil and gas industry areradiography and ultrasonic inspection. Other methods exist, but are used lesscommonly.

Codes are available for conducting non-destructive testing of pipe welds:• BS EN 14163:2001 (previously ISO 13847:2000) - Welding of pipelines• ISO 9712:1999 - Non-destructive testing - Qualification and certification of

personnel• ISO 3452 and 3453 - Non destructive testing - Liquid penetrant inspection• ISO 6497:1990 - Welds - Working positions - Definitions of angles of slope and

rotation• ISO 10474:1991 - Steel and steel products - Inspection documents• API 1104 - Welding and testing of pipelines and related facilities

S-LAY 57

Once a weld has been tested, it is important that all test records are held for futurereference. The records should be catalogued to enable the exact location of any weldin the pipeline. Therefore, in the event of a failure, it will be possible to assess ifthere was a possible flaw in the weld that was the cause.

As part of the weld quality procedure, it is usually required that the test records ofeach weld can be linked to the welder. Therefore, a lowering of weld qualityassociated with a particular welder can be identified and that welder sent for re-training.

Methods

SHIELDED METAL ARC WELDING (SMAW)

Consumableelectrode

Flux coating

Core wire

Arc betweenelectrode and pipe

Evolved gas shield

Parent metal or previous weld pass

Slag layer(to be removed)

Weld metal

Shielded metal arc welding is also known as stick welding or manual metal arc(MMA). Heat is provided by an electric arc that melts a consumable electrode andsome of the parent metal being welded. When it cools, it hardens to form one pass ofthe weld. The welder positions the electrode and compensates for its consumption.

The consumable electrode serves as one pole of the arc, the pipe steel being weldedas the other pole. Electrode, steel pipe and arc make up an electric circuit back to thepower source, which may be either DC or AC. A covered electrode has a solid metalcore and an outer layer of material that insulates the core from accidental contact withthe pipe wall. The core covering also provides gas to shield the weld from air and itmay also contain special elements to improve weld quality.

Manual methods using stick electrodes are limited in the amount of weld metal thatcan be deposited in a single operation. This is due to the volume of metal containedwithin the electrode. Before a new electrode is started, the weld metal needs to beexposed by removal of the slag layer.

SMAW is mainly used on steels including carbon, stainless steels and nickel alloysand can be applied over a wide range of thicknesses. Materials require cleaningfollowing welding, but because of the flux/slag, some minor contamination isacceptable.


SMAW CROSS-SECTION

30° angle bevel25 mm (1in) plate1.5 mm (1/16in) root faceCourtesy of CRC-Evans

Cap pass

Filler passes

Hot passRoot pass

The root and hot passes may be completed by the line-up team, with the bulk of thewelding finished by follow-up welders. The thinner capping layer aims for a smoothfinish to eliminate stress concentration build-up. The root pass is critical - it can“burn through” the wall and melt away the metal, dropping it into the pipe. The aimis to deposit a similar amount of weld material on each pass. It is not possible toplace too much in a single pass because of stresses that build up on cooling.Cracking of the adjacent parent metal then can occur.

The root pass can be made from inside the pipe and subsequent passes from theoutside (though normally, all would be made from the outside). If a metal slag isproduced, it needs removing before the next weld pass. Thin-walled pipe may onlyrequire one filler pass.

Limitations of this method are that it is not an easily controlled process, and cantherefore result in shape defects, slag inclusions, Hydrogen Induced CorrosionCracking (HICC) and arc strikes. The direction of welding (whether it is from above,or vertical or even from beneath) must be taken into account. Access for the welderand the length of the rod must also be considered, especially when underneath thepipe.

S-LAY 59

SMAW SUMMARY

Consumable stick electrodewith covering (usuallycellulose)Weld shielding by CO2released from electrodecoatingWelder positions electrode andcompensates for electrode consumptionWelder has to stop when electrode fullyconsumed

GAS METAL ARC WELDING (GMAW)

Gas Metal Arc Welding (GMAW)Also known asMetal Inert Gas (MIG)Semi-automatic orautomaticConsumable electrodewire fed continuouslyto the weldShielding by externally supplied inert gas(usually argon)

Gas metal arc welding (GMAW) also uses heat from an electric arc. The arc iscovered by an inert gas, such as argon or helium. The inert gas shielded metal arcprocess uses a consumable, continuous electrode. Since this process requires no flux,no slag is produced on top of the weld. Gas for shielding is delivered to the weld areathrough a tube. GMAW is particularly applicable to difficult metals and alloys


susceptible to contamination from the atmosphere and porosity. CO2 can be used as ashielding gas in this method.

It can weld similar metals to GTAW and weld joint thicknesses from thin to verythick sections. Pre-cleaning of the parent materials is required as there is noflux/slag.

Its limitations include:

• Lack of fusion• Porosity• Silica inclusions• Solidification problems (cracking etc)

The GMAW process is relatively faster and more ‘furious’ than the SMAW process.

GMAW

Consumableelectrode (filler wire)

Reel feed

Arc

Parent metal or earlier weld pass

Weld metal

Gas shield

Gasnozzle

No slag

The method is similar to Gas Tungsten Arc welding (GTAW) method, but theelectrode is now consumed from a reel. This is the method adopted by CRC-Evansfor their semi-automatic welding machines that were popular and have a long trackrecord of offshore welding around the world from the 1980’s onwards.

S-LAY 61

GAS TUNGSTEN ARC WELDING (GTAW)

Gas Tungsten Arc WeldingAlso known as Tungsten InertGas (TIG)Semi-automatic or automaticNon consumable tungstenelectrodeFiller metal wire fedcontinuously to weldShielding by externallysupplied inert gas

An inert gas shield is required when welding with tungsten electrodes using the gas-tungsten arc welding (GTAW) process.

This process is particularly suited to welding thin material and to depositing the firstweld bead (root pass) because penetration can be controlled more easily than withother welding processes. Good heat control is possible with this process and it ispossible to weld with or without filler metal.

The non-consumable electrodes are not deposited as part of the metal weld. The steelbeing welded is melted, and the electrode serves only as one pole of the electricalcircuit. Usually with pipeline welding however, a filler wire is fed into the weldjoint, providing additional metal.


GTAW

Arc

Parent metal or earlier weld pass

Weld metal

Gas shield

Ceramic gas nozzle

Filler wire

Tungsten electrode

GTAW has a quiet, less frantic arc but the process is slower than GMAW. GTAW ismainly used for the root pass.

WELDING AND NDT - AGENDA

Welding and NDTProcedureMethodsDefectsNDT

S-LAY 63

Defects

WELD DEFECTS

Imperfections caused byPoor welding techniqueHigh residual stresses in component

Steels susceptible toPorosityCracking

SolidificationHydrogenReheat

Weld repair

Transverse crack

Root crack

Axial crack

Slag inclusions Lamination in parent plate

initiates crack in weldor lack of fusion

Full details and records should be kept on all welds and welders. If faults occur, thentoo high a failure rate in a particular welder can be identified. Very strict controls onweld quality requires ensuring weld integrity with testing. Comprehensive inspectionof all completed welds is also required. Weld defects must be identified andprevented in future.

Cracking can be caused by Hydrogen generated during the welding process orresidual stresses acting on welded joint. It is related to parent material composition,thickness, heat input, stresses and hydrogen content.

If a weld does contain imperfections (other than cracks) they may be repaired, but arepair should only be attempted once at each weld. All imperfections should beremoved by grinding to clean sound metal. Should laminations, split ends orlongitudinal seam defects be discovered in pipe, the whole joint should be removedfrom the line.


WELDING AND NDT - AGENDA

Welding and NDTProcedureMethodsDefectsNDT

NDT

RADIOGRAPHY

Radiography can be X-ray or gamma rayPermanent record of weldHazardous to healthDoes not pick up all flawsAccess needed on both sides of weld

JME pipeline crawlerPipe weld X-ray by Applied Inspection Ltd

Radiography or “bombing” imposes electromagnetic radiation on the test object,causing radiation to be transmitted to varying degrees dependant on density ofmaterial through which it is travelling. Variations in transmission are detected byphotographic film or fluorescent screens. It is applicable to all metals, non-metalsand composites. A film is wrapped onto the outside of the pipe weld along with

S-LAY 65

identifying alphanumeric lead markers. A radioactive source is exposed on the insideof the pipe.

Radiographic inspection is particularly good at detecting volumetric flaws such asvoids, gas pores and solid inclusions, and is good at determining the nature anddimensions of flaws. However, it cannot be used to measure the dimensions of flawsin the through-thickness direction. EN 14163 code specifies that the technique forradiographic inspection should be X-ray (in accordance with ISO 1106-3), gammaray should only be used if agreed by the company. X-ray radiography is generallypreferred over gamma-ray because of the increased health and safety issuesassociated with the handling and use of gamma-radiation sources.

The procedure for conducting a weld radiograph is to first provide a data sheet tocatalogue the test results. The sheet should include project name, pipelineidentification, weld number, type of weld (normal, repair or replacement) and shouldidentify the position on the circumference where the radiograph image was made. Itis then important that each radiograph image is tagged and the tag linked to theappropriate record in the catalogue. The films should then be stored in suitablecontainers. The radioactive source is contained within a ‘crawler’ which is insertedinto the pipe and can move from weld to weld. A radiation sensitive film is thenwrapped around the full circumference of the pipe weld. The radiation is releasedand passes through the pipe wall reacting with the film. This produces an image onthe film that indicates a defect.

Its advantages are it provides a permanent record showing internal flaws. It can beused on most materials giving a direct image of flaws. Its disadvantages are that it isa health hazard so cannot be used adjacent to other workers (such as the weldingcrews), it is sensitive to defect orientation with has limited ability to detect finecracks. Access to both sides (internal and external) is required, and it is limited bymaterial thickness. Skilled interpretation is required, which results in relatively slowresults with high capital outlay and running costs.

BS8010 specifies all welds in areas where leakage is a hazard (e.g. road, rail, andwatercourse crossings) or where repair is difficult require 100% radiographicinspection.


DEFECTS DETECTED BY RADIOGRAPHY

Inclusions

Crack

Lack of fusion

The defects shown above can be detected by radiography.

• Cracks: The picture shows cracking along the coarse grain structure in the HAZ.Three combined factors cause cracking; hydrogen generated in the weldingprocess, a hard brittle structure susceptible to cracking and residual tensilestresses.

• Inclusions: The picture shows a radiograph of a butt weld with two slag lines inthe weld root, commonly known as “wagon tracks”. Slag is the residue of the fluxassociated with MMA electrodes, the flux in cored wires and in submerged arcwelding. The slag becomes trapped in the weld when two adjacent weld beads aredeposited with inadequate overlap and a void is formed. Excessive undercut inthe weld toe or the uneven surface profile of the preceding weld runs are othercauses of slag entrapment.

• Lack of fusion: The dark patches on the picture at the sides of the weld indicate alack of fusion. The parent pipe was not heated high enough to melt, therefore agap develops on cooling.

Inspection and flow assessment are in accordance with BS EN 1435. Theacceptability of flaws are assessed with BS 7910.

S-LAY 67

ULTRASONIC TESTING

Automated Ultrasonic Testing (UT) growingin popularityFollows close behind weldersCost comparable to radiographyShows weld defects in 3DMore confidence insmall defectsWall thicknesshas no effect

Manual UT of test weld byApplied Inspection Ltd

Until recently, pipeline weld inspection has been traditionally solely the domain ofradiography. With the advent of mechanised GMAW, ultrasonics as a method ofnondestructive examination has proven to be an effective option to detect non-fusiondefects orientated unfavourably for radiography. The mechanised UT of pipelinegirth welds is now readily available.

With ultrasonic inspection, high frequency sound waves are introduced to material,interfaces between materials of differing acoustic properties reflect or transmit sound,the reflected sound is displayed on a monitor. Both manual and automatic techniquesare used - sometimes in conjunction with each other or with radiography.

With mechanised UT inspection, the array of probes is moved around the girth weldby a motorised carrier, which travels along the same track the welding apparatus uses.Signals received by the ultrasonic instruments are monitored by electronic gates andboth amplitude of signal and its time of arrival can be collected. In evaluating thescan results, the operator makes a decision as to weld acceptability based on thelength of the signal exceeding a threshold. Acceptability criteria for ultrasonic NDTis currently being prepared.

Its advantages are that it is sensitive to cracks at various orientations, it is portableand safe, with the ability to penetrate thick sections. It measures depth and through-wall extent. With automatic UI, the actual shape of the weld defect can bedetermined in 3D. This enables acceptance of some minor defects that might haverequired repair when using radiography.

Its disadvantages are that it is not easily applied to complex geometry and roughsurfaces (though this is not a problem with straight runs of line pipe), it is unsuited tocoarse-grained materials, and requires highly skilled and experienced technicians.


DEFECTS DETECTED BY UT

Root

Hot pass

1st fill

2nd fill

Cap

Lack of fusion

Porosity

Solidification crack

Lack of fusion(subsurface)

Undercut

The following defects, as shown above, can be detected by ultrasonic testing.

• Lack of fusion: Parent metal not heated high enough to melt• Porosity: Gas pockets or slag trapped in the weld. Small amounts can be

accepted as they may not detract from the strength of the weld.• Solidification crack: Weld allowed to cool too quickly and so becomes brittle and

susceptible to cracking• Lack of fusion (subsurface): Parent metal not heated high enough to melt• Undercut: Parent metal not heated high enough, misalignment of two pipes being

joined or weld applied to quickly.

S-LAY 69

Dye penetrant inspection (DPI)Also known as penetrant flaw detection (PFD)

Magnetic particle inspection (MPI)Principle is magnetic flux leakage

Shows presence of defect but not depth

OTHER NDT METHODS

Flux

Pipe wall

DPI is a surface-only inspection method, applicable to all non-porous, non-absorbingmaterials. Advantages of DPI is that it can be used on non-ferromagnetic material,with the ability to test large parts with portable kit. It is simple, cheap and easy tointerpret. Its disadvantages are that it only detects defects open to the surface; carefulsurface preparation is required; it is not applicable to porous materials; it istemperature-dependant and it is not possible to retest indefinitely; compatibility ofchemicals needs to be assured.

MPI detects surface and sub-surface indications in ferromagnetic materials. Amagnetic field is induced in the component with defects disrupting the magnetic flux.Defects are revealed by applying ferromagnetic particles. Advantages of MPI is thatit detects dome sub-surface defects; it is rapid and simple to understand; pre-cleaningis not as critical as with DPI. It works through thin coatings using cheap and ruggedequipment. It is a direct test method.

The disadvantages of MPI are that it is applicable to ferromagnetic materials only,with a requirement to test in two directions. Demagnetisation may be required, andodd shaped parts are difficult to test. It can also damage the component under test.MPI may be required in conjunction with UT to verify freedom from surface andnear-surface defects in the so-called ‘dead zone’ of the ultrasonic probes. Whererequired, magnetic particle inspection to BS 6072 is typical.

DPI and MPI are generally used to detect very small cracks. They are mostly usedwhen it is not possible to hydrotest the pipeline after weld completion, such as whenconducting a hyperbaric tie-in weld.


WELDING - SUMMARY

Main types of weldingSMAW (stick welding, MMA)GTAW (TIG)GMAW (MIG)

Joint preparationManual, semi and fully-automatedWelding specifications for steel pipeDefects and defect detection

NDT (DPI, MPI, radiography, ultrasonic)Any questions?

There are three main methods of welding:• SMAW (Shielded Metal Arc Welding), also known as Stick Welding and Manual

Metal Arc welding• GTAW (Gas Tungsten Arc Welding)• GMAW (Gas Metal Arc Welding)

Prior to welding, the pipe joints must be prepared to maximise weld integrity. Thereare various automated methods of welding pipe sections used in the field of pipelineconstruction to increase efficiency. Once welded, we are then required to check weldintegrity, particularly at critical points such as crossings. Several methods of weldtesting have been discussed.

S-LAY 71

INSULATED LINES

PIPE-IN-PIPE SYSTEMS

Pipe-in-pipe systemsPre-insulated pipeHigh thermal insulation

Effect on S-Lay processRequire additionalconnection

mechanicalwelding

Reduced lay rate

Gulveig pipe-in-pipe

Pipe-in-pipe systems provide a high level of thermal performance. The associatedfield joint is time-consuming to make-up and consequently results in reduced lay rate.

The field joint for a pipe-in-pipe system requires installation of a bridging section forthe sleeve pipe, as well as installing the insulation materials around the pipe.

The extra steps required to complete the connections provide a significant bottleneck.In practice, operators have chosen to use a combination of welding, mechanical andadhesive techniques to make the connection.


PIPE-IN-PIPE SYSTEMS

Pipe-in-pipe manufacturersITPBPCLLogstor RorCORUS

Insulants used are:MicrospheresRockwoolPUFVacuum

Inner pipe

Carrier pipe

Microsphere insulation

Annulus

Rockwool or PUFinsulation

Several companies manufacture pipe-in-pipe systems, these are listed above. Whenconstructing a pipe-in-pipe system, the main sources of insulation are Microspheres,Rockwool, Polyuerethane Foam (PUF) and a vacuum. The first three are commonlyused to insulate pipe-in-pipe systems and vacuum insulation has only be used atpresent to insulate the field joints for the Bonga export pipeline.

The two diagrams above show two different insulating methods for the pipe-in-pipesystems. The top diagram shows the system design for using microspheresinsulation. The microspheres are tightly packed into the annulus between the innerand carrier pipes. The advantage of this system is that the hydrostatic pressures canbe transferred from the carrier pipe through to the inner pipe, by the microsphereinsulating layer. Therefore, the wall thickness of the carrier pipe can be reduced as itis not required to withstand the hydrostatic pressure alone.

The lower diagram shows the pipe-in-pipe system design when using Rockwool orPUF insulation. With this method, the inner pipe is coated with the insulation andinserted into the carrier pipe. The annulus is then filled with a pressurised gas(usually nitrogen) to assist the carrier pipe in resisting the hydrostatic pressures. Thegas will diffuse through the layer of insulation and so an even pressure acts throughthe thickness of the layer. Therefore, the pressurised gas will not act to crush thelayer of insulation.

S-LAY 73

SLEEVE PIPE CONNECTION SYSTEMS

This shows an example of a connection system which illustrates the degree ofcomplexity that might be involved. This system involves a threaded sleeve which canbe slid over the joint and made up. Other systems require the installation of half-shells, which are welded in place with full penetration butt welds.

INSULATED LINES - SUMMARY

Pipe-in-pipe systemsImproved thermal performanceComplex field-joint design

Affect on S-lay processReduced lay-rates

Trade-offIncreased thermal performance against reduced lay-rate

Any questions?

Pipelines may require thermal insulation to maintain the product temperature. Pipe-in-pipe systems give a good thermal performance. However, the field-joints requiredto connect together pipe-in-pipe sections is complicated and is a time-consuming


process. Therefore, using pipe-in-pipe systems reduces the lay rates and so increasesthe construction costs. We then have a trade-off between improved thermalperformance and increased construction cost.

S-LAY 75

LAY CURVE CONTROL

LAY CURVE CONTROL

Stinger radiusTension vs. depthHigh residual tension

Overbend(or hogbend)

area

Sagbend areaResidual

tension

Laycurve

Stinger

radius

The installation contractor will check the stresses in the lay curve, and from this willdetermine the optimum stinger settings (these cannot easily be adjusted once pipelayhas commenced) and the tension to apply for a given water depth.

The S-Lay technique will leave a higher residual tension in the pipeline incomparison to other pipelay techniques.

This has the following consequences:

• Changes in lay direction for routing require greater horizontal radii.• Prevention of the laid pipe from following the undulations of the seabed profile

as closely. This generally results in longer span lengths than other installationtechniques, such as J-Lay.

• Increased resistance to lateral or upheaval buckling from reduced compressiveforces generated from thermal expansion during pipeline operation.


STINGER RADIUS

OverbendStinger radiusAdjust stinger angle and roller settings

R

RrE

b⋅

=σ

Stresses in the overbend are controlled by the stinger radius, the departure angle androller settings.

Bending stresses are normally limited to 90% yield and can be calculated from theequation above, where:

σb = bending stressE = Young’s modulusr = pipe outside radiusR = stinger radius

S-LAY 77


The above slide shows the typical bending stress envelope for the S-lay of a pipesubjected to dynamic loading. The vertical axis indicates the percentage of yieldstress that is present in the pipe and the horizontal axis is the distance along the laycurve. As a rule of thumb, for typical pipe lay in normal conditions a stinger radiuswill be selected to produce a mean bending stress in the pipe of around 90% of yield.The tension in the lay curve will then be selected to produce mean pipe stress at thetouchdown point of around 60% of yield. The reason for having a reduced allowablestress at the touchdown point is due to the dynamic effects that must be consideredduring pipelay.

Dynamic effects are the result of wave motions which cause movements of the laybarge. The sea motion will introduce both horizontal surge and vertical heave of thebarge. These resulting accelerations can be relatively small at the sea surface but areamplified as they travel down through the lay curve and can result in largeaccelerations at the touchdown point. For this reason, it is necessary to be able toaccurately predict the peak stresses that can occur at the touchdown point.

As displayed in the above figure, the touchdown point may move relative to thevessel. This results in a relatively wide band of possible bending stresses that may beinduced in the pipeline at the touchdown point. At the touchdown point, thehorizontal movement is not restrained and so the stresses will be between maximumand minimum values. As described above, a rule of thumb will be to select a tensionthat gives a mean stress of around 60% of yield and should ensure the peak stressdoes not exceed approximately 90%.

At the vessel, the stinger radius is fixed and there will be a very limited variation inthe bending stresses. This limited variation will hold provided that there is sufficienttension maintained in the lay curve to prevent the pipe bending about the last rolleron the stinger. Such hinging of the pipe about the last roller will cause a very large‘spike’ in the pipe bending stress at the roller location, as indicated in the abovefigure.

ANALYSIS OF LAY STRESSES

Full analysisDynamicWaves & currentsPipe characteristicsPipeline movementVessel movementTensionHydrostatic pressure

ResponseAmplitudeOperators

Sway

Heave

Surge

Pitch Roll

Yaw

S-LAY 79

Vessel movement due to wave loading occurs in six degrees of freedom (as shownabove). The vessel’s responses to these loads are known as Response AmplitudeOperators (RAO).

Due to the length of the span of pipe and the inertia of the vessel, movements of pipeand vessel will be out of phase.

Commercial software packages, such as Offpipe, ANSYS ABAQUS and OrcaFlex,are used to assess the lay stresses. The analysis is dynamic and incorporates the loadsand movements due to wave and current action on both the pipe and vessel.

The programs can assist the pipeline engineer at any stage during the design of apipeline operation, and can even be used on-board to give fast assessment of theeffect of changing key parameters on the pipeline stress distribution and pipelineposition.

LAY CURVE CONTROL - SUMMARY

Lay curve control by:Stinger radiusTension vs. depth

Analysis to considerDynamic behaviour

Any questions?

As with the J-lay and reel-lay installation methods, the stresses in the lay curve mustbe controlled to ensure the pipe is not damaged during laying. The two parametersthat significantly alter the stresses in the lay curve are the radius of the stinger and thetension in the pipeline. A stinger of fixed radius will be fitted to the vessel prior to itleaving port and so during pipelay the only controllable parameter the vessel has thetension in the lay curve. The stinger radius is set to give the required bend radius ofthe pipe at the overbend area. Tension is set to give the required bend radius of thepipe as it leaves the stinger and at the sagbend area.

The dynamic behaviour of the vessel during pipelay must be considered whenselecting a stinger radius and the tension in the lay curve. Dynamic analysis of pipelay requires knowledge of the vessel’s Response Amplitude Operators (RAOs) to thepredicted sea states that will be encountered during pipelay. The complexity of adynamic analysis will usually require software packages to enable accuratepredictions of the pipe stresses that will occur during pipe lay.


S-LAY - SUMMARY

You should now:Understand the principles of S-layDifferentiate between vessel typesUnderstand the processes required for S-layGain an idea of the world markets and vesselsGain an overview of welding techniques and weldtestingKnow the requirements for laying insulated linesUnderstand the principles of lay curve control

Any questions?

The various S-Lay vessel capabilities and the market has been detailed. Two types ofS-Lay vessel have been discussed; dynamically positioned (DP) or multi-anchoredvessels. One of the main differences between the S-Lay installation technique andother techniques is that the firing line is horizontal. This enables the rapid welding ofdouble pipe joints with diameters up to 72 in.

The bending stresses in the lay curve are controlled via the stinger and tensioners.The S-Lay technique enables pipelines to be laid with high residual tensions, whichhas advantages in the prevention of thermal buckling and disadvantages of increasedspan lengths and larger horizontal radii for routing.

Also discussed has been the welding and testing of pipe joints. Both Manual, semiand fully automatic welding techniques have been discussed, with the three maintypes being; SMAW, GMAW and GTAW. The main techniques of weld joint testingthat were discussed are Ultrasonic and radiography.

J-LAY 83

EXPECTATION

EXPECTATION

Understand the Principles of the J-LayReview J-Lay VesselsUnderstand the J-Lay processIntroduce one shot welding methodsReview mechanical connectorsUnderstand basic catenary equations

We start by looking at the basic principles of the J-Lay method and lay vesselsavailable, then lead into an overview of the individual stages applied to achieve asuccessful and controlled installation.

Performance figures and costs for J-Lay are considered and compared with S-Laycapabilities.

One shot welding methods available are reviewed.

The use of mechanical connectors as a time saving alternative to welded joints isexplained, associated with the use of drilling rigs for J-Lay operations.

Catenaries, their basic equations and lay stresses are considered.


WHAT IS J-LAY?

WHAT IS J-LAY?

J-Curve andhighdepartureangleLow stressOne or twoworkstations

Upending Ramp

Horizontal firing line(s) orpre-assembled pipe racks

Work Station

J-Lay takes its name from the shape of the suspended pipe, which forms a ‘J’ goingfrom the surface of the vessel to the seabed. This curve is similar to a catenary anddevelops low stress levels in the pipe compared with S-Lay.

The main limitation of J-Lay is that in most cases it only has a single work station inwhich to assemble the pipe, (the exception being on the S7000 laybarge which hastwo).

Consequently, most J-Lay systems make use of pre-assembled strings of 4 to 6 pipes.The additional time spent making a joint at a single work station is compensated forto some extent by attaching 4 to 6 pipe joints rather than just one pipe joint.

Needs deeper water than S-Lay.

J-LAY 85

VESSELS

J-LAY VESSELS

Fitted to a numberof semi-submersible cranevessels (SSCV’s)

Modular systemscan be moved fromone vessel toanother

J-Lay tower on theSAIPEM 7000 Saipem S-7000

The majority of J-Lay systems have been fitted to semi-submersible crane vessels(SSCV’s) such as the S-7000 (shown above), the Hermod, Balder and the DB50.

As these vessels also have other tasks to undertake, the systems are modular and thuscan be removed when not required. The J-Lay tower on S-7000 weighs 4500 tonnes.

The systems have been designed to accommodate the future requirements for ultra-deep water pipelines, with the S-7000 system designed specifically to install the BlueStream pipeline, although up-rating of each system is envisaged.

Using an SSCV has the advantage that if the field is distant from an offshore base, thevessel can perform any heavy lift that is required and lay the flowlines for a fielddevelopment.


J-LAY VESSELS

Semi-Submersible Crane Vessels(SSCV’s)

Saipem 7000DB50Balder and Thialf

Multi Support Vessels (MSV’s)Uncle JohnOcean Intervention I & II

ShipsCSO ConstructorCSO Deep BlueSeaway PolarisSeaway FalconSaipem FDS

J-LAY VESSEL LAYOUT

Details of DB 50 Laybarge

Pipe handling systemwhich contains

Pipe rackStrongback system

J-lay tower whichcontains

TensionersSingle workstation

The two main components of the J-Lay system are the pipe handling system and J-Lay tower.

J-LAY 87

J-LAY PROJECTS

Contractor Operator Project Pipe OD Vessel WaterDepth

Year

J.R.McDermott Shell Auger 12” DB50 830m 1993

Shell Ursa 18” DB50 1210m 1999

Shell Europa 8/12” DB50 1210 1999

Shell Crosby 8/12” DB50 1350 2001

Heerema Shell Maui B 20” Balder 110m 1996

Saipem Exxon Diana 18” Saipem 7000 1460m 1998

Gasprom Blue Stream 24” Saipem 7000 2150m 2002

Stolt Offshore SNEPCO Bonga 10” Polaris 1100m Ongoing

Coflexip Stena KerrMcGee NansenBoomvang

6” Deep Blue 1130m 2001

Saipem TotalFina Elf Canyon Express 12” FDS 2215m 2002

SAIPEM 7000

The picture is of Saipem’s S-7000 semisubmersible crane vessel, which was recentlyconverted in Rotterdam to J-Lay capability by the addition of a 135m high towerweighing 4500t (removable using the onboard heavy lift cranes). This is a DP vessel.


J-Lay system:Pipe Diameter Range: From 4" to 32”Main Laying Tension System: 525t with tensioners, up to 2,000t withfriction clampsLaying Tower Angle: 90º - 110ºAbandonment/Recovery System: Double capstan winch with 550t capacity(up to 2000t with clamps)Number of Welding Stations: 2Number of NDT and Field Joint Stations: 1Pipe String: Quadruple JointPipe storage capacity: Up to 10,000t

CAPABILITY ENVELOPE OF S7000

CAPABILITY ENVELOPE OF S7000 J-LAY

0

1000

2000

3000

4000

5000

10 20 30 40PIPE DIAMETER (in)

WA

TER

DEP

TH (m

)

1500T HOLDINGCAPACITY450T HOLDINGCAPACITY

Blue Stream

The figure shows the capability envelope of the Saipem S7000 J-lay vessel.

The 1500t holding capacity is available when the vessel uses friction clamps to holdthe pipeline. The 450t capacity is available when using a tensioner system.

The figure is based on a pipe in seawater having a specific gravity of 5.

J-LAY 89

MCDERMOTT DERRICK/J-LAY BARGE - DB 50

The J. Ray McDemott Derrick/Lay Barge DB 50 has both J-Lay and Reel Laysystems.

Dimensions: 497 x 150 x 41 ftMax Pipe OD for J-Lay: 20”Lay Down Hoist: 775 kips at 41.5 ft/minWire rope: 12,133 ft 4.25” for J-LayMain Crane: 3,527 tons at 82 ftMoorings: DP or 8-point system


HEEREMA DCV BALDER

Previous configuration Upgraded configuration

Heerema have upgraded the capacity of their Deepwater Construction Vehicle (DCV)‘Balder’ to improve J-lay performance. The main upgrade was a new modular J-laytower weighing 2500 tonne (2756 ton). The new tower enables pipelay of up to 813mm (32 in) diameter pipe in water depths up to 3000 m (9843 ft). The static tensioncapacity is 525 tonne in hex mode and 1050 mT in quad mode. It can provide adynamic tension of 800 tonne (882 ton) in hex mode during pipelay with a potentialupgrade to 1600 tonne (1764 ton). The tower can be removed and fitted to othervessels as required.

The new J-lay tower was located on the port side of the vessel as opposed to theprevious position of the stern. With the tower located on the side of the vessel, it willnot interfere with the two lifting cranes and so maintains Balder’s capability of beinga heavy load-lifting vessel without the need to remove the J-lay tower. The newsystem enables Balder to install pipelines, in-field flowlines, pipe-in-pipe systems,water injection lines with internal liners and riser systems including steel catenaryrisers, free-standing risers and tension leg risers.

Balder has been used in the Gulf of Mexico since 2002 to install pipelines of 406 mm(16 in) and 711 mm (28 in) diameter in depths in excess of 2100 m (6890 ft). It wasused to install the Mardi Gras export line. A layrate of 4-km (2.48 mile) per day wasachieved for the laying of 406 mm (16 in) diameter pipe.

J-LAY 91

DCV BALDER - HEXJOINT RAISING

Hang-off table

Weld station

Grips holding pipeline

Hex-joint

DCV Balder installs pipe in 72 m (236 ft) hex-joint sections. Each hex-joint is made-up of a 24 m (78.7 ft) and a 48 (157 ft) m long section that are pre-welded on shore.At one end of the hexjoint there is an integral collar. The collar gives a position togrip the pipe when supported vertically in the tower.

The 24 m and 48 m sections are welded together on the deck of the vessel and thehex-joint is then lifted into the tower. The hexjoint is held in the tower by a clampthat grips the integral collar. The bottom of the joint is then welded onto the pipelineand the pipeline is then lowered ready for inclusion of the next hex-joint.


DCV BALDER - COLLAR & CLAMP SYSTEM

Integral collar at top of each hex-joint

Dual use as buckle arrestor

Head-clamp at hang-off table

Each hex-joint section installed by Balder incorporates an integral collar at the topend of the section. The collar provides the point of suspending the pipe when it islocated in the J-lay tower and being welded onto the pipeline. The figures aboveshow the results of a finite element analysis conducted on a hex-joint collar and the‘head-clamp’ used to grip the collar in the Hang-off table at the top of the tower.

The use of collars to hold the pipe is an alternative to the tensioner based system usedmore commonly on other traditional J-lay barges. The collar system enables a greaterlength of pipe to be supported by the vessel, which then enables pipe to be laid togreater depths. Another advantage of the collar is that they also act as bucklearrestors, limiting buckle propagation from hydrostatic collapse to the length of eachhex-joint section, i.e.72 m (236 ft).

J-LAY 93

DCV BALDER - IN-LINE INSTALLATION

Grips holding pipeline released

In-line vertical tee structure

Weld station

Crane supportingpipeline catenaryoutside of tower

The Balder J-lay vessel also has the capability of installing in-line structures into thepipeline as the pipeline is being laid. These in-line structures include in-line sledassemblies, pipeline end manifolds, base manifolds and templates. The figure aboveshows the installation of an in-line vertical tee tie-in structure, enabling future tie-inof a riser or flowline.

Balder utilises an open tower design and the proximity of the portside heavy lift craneto allow the pipe catenary to be supported by the crane and then released from thetower, as shown above. With the pipe string moved away from the tower, an in-linestructure can be welded onto the pipeline. The pipeline is then lowered and boughtback into the J-lay tower ready for the addition of the next hex-joint.


HEEREMA SSCV THIALF

The Heerema Marine Contractors (HMC) vessel ‘Thialf’ is a semi-submersible cranevessel (SSCV) and one of the largest in the world. At present it is used mostly forheavy lifting projects such as topside installation and removal. It was also used torecover the sunken Russian submarine, the ‘Kursk’. However, it can be adapted toundertake deepwater J-lay pipeline installation using the modular J-lay towercurrently installed on the HMC Balder vessel.

MSV UNCLE JOHN

J-LAY 95

‘MSV Uncle John’

Dimensions: 160 x 158 ftRange of Pipe Diameters Handled: Reel-Lay, 2 to 4.5 inch. J-Lay, 6 to 10inchMinimum Pipelaying Water Depth: 200 ft, reel; 700 ft, J-LayMaximum Pipelaying Water Depth: 2,000 ft, reel; 4,500 ft, J-LayMooring Station Keeping Method: DP

CSO DEEP BLUE

‘Deep Blue’

The ‘Deep Blue’ can lay flexibles, rigid reeled and J-Lay pipe. In J-Lay mode, 30”pipe can be laid in water depths of up to 2500m, using up to 550 tonnes of tension.

Details of this vessel are presented in the ‘Reel-Lay’ section.


STOLT SEAWAY POLARIS

Vessel capable of J-Lay and S- Lay

Seaway Polaris(formally DLB Polaris)

Dimensions: 137 x 39 x 9 mYear Built: 1979Range of Pipe Diameters Handled: Up to 60 inch (S-Lay) and 16 inch (J-Lay)Stations: Welding, 4; Other, 3Welding Method(s) Used: AutomaticPipe Installation Method(s) Used: S-Lay, J-LayMinimum Pipelaying Water Depth: 6 mMaximum Pipelaying Water Depth: 2,000 m

J-LAY 97

STOLT SEAWAY FALCON

J-Lay with a differenceCombines features of J-Lay, S-Lay and Reel-lay

Horizontal firing lineBending and straightening as per reelJ-Lay installation curve

Another J-Lay vessel is the Stolt Offshore Falcon. This combines features of all 3methods. It has a single welding station in the horizontal on deck. The pipe isyielded one way to run it to the top of the ramp, and is yielded the other way as itruns over the top of the ramp. It is re-straightened on the ramp and is then J-laid fromthere.

SAIPEM FDS

Field Development Ship (FDS)J-Laycapabilities


The Saipem FDS (Field Development Ship) is a multi purpose vessel with J-Laycapabilities. It can also be used for laying flexibles.

Class: DNV+1A1-SF-Crane Vessel-Pipelaying VesselDisplacement: 26,600 tLength: 163 m/535 ftBreadth: 30 m (98 ft)Deck capacity: 3,300 m²/10 t/m²/max. load 4,000 tDP capabilityAUTR with 50 t bollard pull/seastate 5 for pipelaying, AUTRO for lifting and divingoperationsCrane capacity: 600 t at 30 m/300 t at 55 mAR winch: 400 t capacity at 3,000 m WDHandling module tower: 100 t at 3,000 m WDJ-Lay tower for ultra deepwater pipe laying: nominal diameter 18" at 1,500 m WD,14" at 2,000 m WD, 12" at 3,000 m WDMaxi handling: OD 22”Handling capacity: 400 t (static) using 4 clamps (not tensioners)

J-LAY VESSELS - SUMMARY

Modular systemsTemporary or permanent fixtureFitted on range of different vessel types

Semi-submersible crane vesselsMulti-support vesselsShips

Any questions?

J-lay equipment can be fitted to various types of vessel as both temporary orpermanent fixtures. Semi-submersible crane vessels are most commonly converted toJ-lay construction vessels, but other vessel types have been converted also.

J-LAY 99

PROJECTS

BLUE STREAM PROJECT

Blue Stream is one of the most significant projects in the international gas sector,both from a strategic and a technological point of view. The project involves theconstruction of a system to transport natural gas from Russia to Turkey, and acrossthe Black Sea. The total length of the system is approximately 1,250 kilometres. Thisgas line is designed to link the gas distribution network of the Krasnodar region insouthern Russia to the central Turkish grid in the capital city of Ankara.

The crossing of the Black Sea is certainly the most challenging part of the entireproject and is Saipem's scope of work. Two 24" diameter sealines enter the sea onthe Russian side, where the seabed profile near Beregovaya falls dramatically. Alongtheir sub-sea route, the two pipelines descend to a record depth of 2,150 metresbefore emerging on the Turkish side at the city of Samsun. Saipem 7000, the largestdynamically positioned combined derrick lay vessel, is the main craft carrying out thepipelay work, using the J-Lay method.


The low tension required with this method enables the pipeline to follow the seabedcontours and reduces the number of free spans.

SHELL BONGA PROJECT

Seaway PolarisSteel catenary risers installed by J-Lay

The installation workscope includes rigid steel flowlines, together with steel catenaryoil and gas production risers. The Seaway Polaris is installing 36km of 10in-diameterproduction flowlines and all the project's steel catenary risers using the J-Lay method.

J-LAY 101

J-LAY SEQUENCE

J-LAY SEQUENCE

Make quads/hexesonshoreSupply to vessel

Prep endsStrongback liftsquad/hex into tower

As pipe stalks of three or more joints are delivered to the vessel, a more complexhandling system is required to lift these stalks from the horizontal into the J-Laytower than is required for S-Lay.

Once in the tower the pipe-stalk is aligned with, and then welded to the pipe string.


J-LAY SEQUENCE

Align joint with end of pipelineWeld connectionCarry out NDTApply field joint coating

Need a gripper band between FBE and concretecoating at upper end of stalk

Move vessel forwardPay out tensioner

In most cases, the weld, NDT and coating application are all performed at the onestation.

Most pipelines laid by J-Lay are NOT concrete-coated. In deepwater, stability is lessof a concern, therefore the extra weight is not usually required.

The clamps holding the pipe are released, the vessel moves forward and the jointpasses down the tower to receive the next spool.

GRIPPER BANDS

Concretecoating

Tensioner

FBE pipecoating

Tension in pipefrom catenary

Shear force from tensionerresults in compression in pipe

Gripperband

Compressive forcetransferred to gripper band

Compressive loadapplied by tensioner

J-LAY 103

A Gripper Band is a typically a 1m wide layer of adhesive with grit sprayed onto it.It provides a shear key for the concrete weight coat which otherwise could slip overthe smooth FBE anti-corrosion coating. The objective of the gripper band is totransfer the compressive forces generated by the tensioners during pipe lay. Thegripper band must be at the top of the pipe joint such that the concrete goes intocompression, as shown in the diagram.

HEEREMA MARINE J-LAY - VIDEO

The above video shows the Heerema J-Lay system attached to the Balder. It detailsthe sequence of up-ending a quad (length of 4 pipe joints) into a near verticalposition, welding this and then moving the vessel forward and J-Laying the pipelineonto the seabed.


J-LAY SEQUENCE - SUMMARY

Joints made-up onshoreQuads or Hexes

Vessel suppliedJoints loaded into towerWelded to pipe stringPipe string paid-out

Pipe tension transferred from tensioners to steelpipe wall via ‘Gripper Bands’

Any questions?

The general operations that make-up the overall J-lay sequence are shown above.Quad or Hex joints are made-up onshore to limit the welding time required offshore.

J-LAY 105

PERFORMANCE

J-LAY PERFORMANCE AND COSTS

Average pipelay speeds up to 2.3 km per day(half S-Lay)Vessel cost up to US$ 350k per dayIdeal for deep waterMaximum pipelay depth 2215 m (CanyonExpress)

The above overhead shows ball-park lay speeds and vessel costs. This system is idealfor use in deep water, where the low lay stresses and low horizontal tensions requiredlend themselves to installation from dynamically positioned vessels.

One further way of improving the speed of assembly at a single work station is to usesingle-shot welding systems or mechanical connectors.


J-LAY BENEFITS

Less horizontal tension, therefore less fuelthan S-LayFree spans reducedSmaller curves on seabed compared to S-LayLess strain hardening than Reel-LayLess fatigue in overbend compared to S-LayEasier to install tees and appurtenances

The above overhead lists some of the additional benefits of using the J-Lay method.

J-LAY CAPABILITY

Dynamically Positioned (DP) vesselsTend to be 16in up due to reel competitionJ-Lay - maximum diameter is 32in (S-7000)

No restriction on wall thicknessLay speed is primary concern

One or sometimes two weld stationsLay quads or hexes

J-LAY 107

COMPARISON OF LAY CAPABILITIES

COMPARISON OF LAY CAPABILITY FORJ-LAY & S-LAY SYSTEMS

010002000

300040005000

10 20 30 40PIPE DIAMETER (in)

WA

TER

DEPT

H (m

) J-Lay potential capability

Current S-Lay capability Greenstream

Bluestream

J-LAY PERFORMANCE - SUMMARY

Low stress levels compared with S-LayLess horizontal tensionTypically single work stationOperational water depth limit - 2500 m +Effectively no wall thickness limit

Pipe size limit 32in diameterAverage pipelay speeds up to 2.3 km per day

Any questions?

Note that Saipem S 7000 has 2 workstations; one welding station 50m above the deckand one coating station at deck level.


RAPID PIPE WELDING

SINGLE SHOT PIPE WELDING

Electron Beam (EB)Friction WeldingLaser WeldingFlash ButtFriction Stir Welding

Compact reducedpressure EB guncolumn

Radial FrictionWelding

The following one-shot welding processes are potential candidates for J-layingwelding process requirements:

• Electron Beam Welding - a fusion process for joining metals using a highlyfocused beam of electrons as a heat source. It is normally generated in a relativelyhigh vacuum, but it is possible to project high-power electron beams into theatmosphere and produce single-pass welds in steel of greater than 40mmthickness. With EBW, the materials to be joined are locally melted and no fillermaterials or consumable are necessary. Reduced pressure ( 0.1 to 10mbar),coarse vacuum single-pass welding is now possible in thicknesses from 0.1mm to200mm.

Total - CFP have proven this method on a 24” diameter pipe of 1.1/4” w.t., claiming aweld time of 3 min compared to 1 to 1.1/2 hrs by conventional methods. The methodwas applied to a 18.5/8” dia riser - 1800m water depth.

J-LAY 109

TWI at Abington are currently carrying out a major project for Saipem to developelectron beam welding equipment for use on pipelay barges for J-Lay applications.

• Friction Welding -Radial friction welding is undertaken either by spinning a pipepiece or an external annular ring to generate heat, and then compressing itradially.

It has been developed by Stolt Offshore to increase production rates for pipe layingusing the Seaway Falcon. Its particular potential is the welding of exotic materials,such as duplex stainless steel and 13% chrome steel, which are difficult and time-consuming to weld offshore.

SINGLE SHOT PIPE WELDING

LaserWelding

Othermethods ofwelding arebeingdeveloped

Friction Stir Process(FSW)

Nd:YAG Laser Welding of 6 mm thick Stainless Steel

Other welding systems are being developed as listed below. One or more of thesesystems may eventually prove suitable for completing the welds between the pipestrings on a J-Lay vessel, thereby increasing the layrate.

• Laser Welding - is of three types: CO2 laser welding (power up to 60kW),transmission laser welding Nd: YAG (power up to 6-9kW) and diode laserwelding (>100W). Nd: YAG lasers can be delivered to the workpiece via a fibreoptic cable. The process is highly suitable for remote welding as the laser can beoutside the active area and can be readily deployed on robotic or similar systems.

• Flash Butt - Flash butt resistance welding is of lower suitability because the highpower requirements of the process result in a practical size limitation of approx.30”dia. Poor process control in the past has tended to leave potential usersreluctant to choose this option because the finished product is perceived to beinferior.

• Friction Stir Welding - Friction stir welding (FSW), developed in the earlynineties, involves a rotating tool traversing along the joint leaving a ‘forged’ weldin its wake. The heat generated causes intense plastic deformation. The process


is being developed still further and, in Oct 98, TWI reported success in thewelding of 25mm thick steel plate.

J-LAY 111

MECHANICAL CONNECTORS

USE OF MECHANICAL CONNECTORS

A mechanical connector enables pipe-jointconnection without need for welding

AdvantagesEnable fast make-up and increase in lay rate

No HAZ which facilitates use of full precoating and liners.

DisadvantagesPerceived decrease in reliability because of the largenumber of joints and increased risk of leak

High cost of the connector

The use of mechanical connectors provides the following main advantages:

• They enable a more rapid make-up compared to welding, and increase the layrateaccordingly.

• They have no heat-affected zone which facilitates the use of internal coatings andpolymer based linings for corrosion protection.

In addition, it is argued that they provide means to place quality upfront and eliminatethe need for inspection after assembly.

The main argument against their use is the large number of joints and potential leakpaths in the pipeline. A further factor is the cost of the connector that has to bewelded to both ends of each pipe spool.


It is possible too individually hydrotest the sealing assembly at the time of make-up,but this will add to the time taken to complete the connection and reduce the layrateaccordingly.


Designed to be as strong as the pipe undertension and bendingEvaluated in a JIP for use in J-LayHave been used for subsea

Harding export line24in2.4 kmSubsea installationusing divers

Not yet used inJ-Lay

The connectors are designed to be as strong as the parent pipe and several designswere evaluated in the TJA/Oil States JIP, sponsored by over 20 organisations. Thisconsidered the installation and operation-loading regime for J-Lay and TJAsubsequently developed a testing specification, published by the Institute ofPetroleum, for qualifying connectors.

One of the most significant offshore installations using a connector suitable for J-Layis the Harding export line. This was assembled subsea using a purpose-built trackedassembly machine. The Oil States ‘Merlin’ connector was used for this pipeline.This connector is a non-rotational threaded connector.

A number of risers have been installed in the Gulf of Mexico using the ‘Hydril 2000’connector. This connector would also be suitable for J-Lay applications.

There have been numerous other offshore installations of pipe with mechanicalconnectors, but most have used rotational make-up connectors designed for downholeor onshore flowline service. The only other non-rotating connector that has been usedoffshore is the ‘Jetair PSC’ connector (8”).

None of these connectors would be suitable for J-Lay.

J-LAY 113


Pre-date welding

The picture above shows the assembly of a pipeline in Persia in 1921. They are usinglarge spanners to torque the pipe into a connector. At that time, the threads wereeither parallel or conical (meaning that the further the pipe is twisted in, the tighterthe threads engage) but in both cases relied on the dope (thread lubricant) to seal thejoint.

During the 1940s, welding techniques were advanced to the point where the weldprovided a much more reliable joint, and from that time onwards the vast majority ofpipelines have been welded. This will undoubtedly continue for the foreseeablefuture. However, connectors have now made technical advances which mean thatthey can be used as an alternative on occasions such as the J-Laying of deepwaterflowlines.



Non-rotating connectors are availableScope to hydrotest the seal if requiredSuppliers

Oil States Merlinused for Harding export linecan be assembled within 10 minutesused to support TLP tethers (critical application)

Hydril 2000Zap-Lok

Non rotating connectors are available from a number of sources including Oil States,Hydril, Dril-Quip and ABB. Most can also be easily taken apart and include facilitiesenabling the sealing mechanism to be tested immediately after make-up by applyingpressure between a pair of seals.

These connector systems are used in critical applications for the attachment of thetethers to the hull of a TLP.

J-LAY 115

MERLIN CONNECTOR

High integrity andrapid assemblyMetal to metal seals

1 - Stabbed

2 - Clamp and pressure injectorpositioned

3 - Seal tested

Injector

One example of a technologically-advanced connector is the ‘Merlin’ shown above.Features which make this attractive for pipeline duties are:

• High integrity metal to metal seals, both inside and outside• Uniform bore.• Non-rotational make up. This means that the two halves are pushed together

using an assembly tool and the threads engage only when the connector is fullyhome.

Joints like this might typically be assembled in 10 minutes, compared with 40minutes for a weld. The assembly time is also reasonably independent of thediameter, so large diameters take no longer to assemble than small ones.


MECHANICAL CONNECTORS - SUMMARY

Remove the need for weldingAdvantage

Increase lay rates

DisadvantageHigher cost per joint than welding

Not yet used in J-lay

Any questions?

Mechanical connectors have an advantage over welding in that they enable a muchquicker connection of pipe joints onto the pipe string. However, potential increasesin lay rates may be offset by the increased cost per joint when using connectors asopposed to welding.

Connectors have not as yet been used in J-lay operations.

J-LAY 117

DRILLING RIG

J-LAY FROM DRILLING RIG

Rig may be on site completing wellsHas equipment for making up usingconnectorsConnect back to production facilityBetter for deepwater because cannotangle derrickUse for short stepouts

This is a method which has potential for deepwater applications, and takes advantageof the presence of the drilling rig, which is on site anyway. This avoids the need for aseparate pipelay vessel. It saves in mobilisation costs for a dedicated pipelay vessel.This method is potentially attractive because rigs that handle and make-up threadedpipe joints are generally available at lower day-rates than laybarges using weldingtechniques. It is a method which is perhaps more suited to niche opportunities thatcan take advantage of the market conditions prevailing at the time, and of particularproject circumstances.

An example of the successful application of this method has been proven on a 4” linein the Gulf of Mexico on a jack-up rig in 30m of water.

“Stepouts” are new pipeline links between newly developed wellheads and anexisting operating platform.


PROS & CONS

PROS

Already mobilisedLower day ratesRapid assemblyPressure testNon-weldablematerials(e.g. 13% Chrome)

CONS

Bending limitationLay curve controlsystemSlow if moved bymooring systemattached to anchorsNo dynamicpositioning

Whilst linepipe materials containing 13% Chrome have good corrosion resistantproperties, they are difficult to weld due to the brittleness of the material. They canbe susceptible to cracking after cooling from welding temperatures. In thesecircumstances, it may become feasible to use mechanical connectors.

J-LAY 119

CATENARIES

CATENARIES

Catenaries occur in each of the following:

J-Lay curveSecond half of S-Lay curveSteel Catenary Riser (SCR) curve

Catenary - the curve formed by a heavy uniform flexible cord hanging freely fromtwo points.

The configuration of each of the above catenaries needs to be considered as theyoccur during pipeline installation

(SCRs are discussed in the ‘riser’ section of the Overview course).


J-LAY CATENARY

Basic catenary equationsLook at how the J-Lay tower angle andapplied tension control the catenary shapeand stresses

We will look at basic catenary calculations. The purpose of this is to look at how theJ-Lay tower angle and the applied tension are used to control the shape of the pipecatenary and the induced stresses.

RIGID PIPE

H

T

x

α

w, weight perunit length

V

ds

y

H

The aim of the installation contractor is to have a catenary shape that keeps thesagbend below the code allowables and the top tension to a minimum. The pipe is

J-LAY 121

rigid over short lengths, but the string shape approximates that of the catenary as it ismuch longer.

As the vessel moves forward and holds tension on the pipe this, along with the pipestring weight and water depth, dictates the catenary shape.

The lay tension also results in a residual tension remaining in the laid pipeline, due tothe reaction of the soil friction.

In relation to the diagram above:d = Water depth (m)α = Ramp angle (deg)s = Pipe span length (m)x = Distance to touchdown (m)H = Horizontal force component (N)T = Lay tension (N)w = Submerged pipe weight (N/m)

CATENARY

The variables we are interested in are:T, α, w, d, s, x

We know:w, d

We control:T, α(and thus we control H, V)


CATENARY

We wish to controlSpan length, sLength to touchdown, xBending and axial stress

BASIC CATENARY EQUATIONS

Basic catenary equation

Horizontal component of tension

wdTH −=

−

= 1coshHwx

wHy

The above-simplified equations are used to calculate the catenary parameters, andthey enable the installation contractor to assess the effects of changes to the each ofthe variables on the other parameters.

x and y are the coordinates from the touchdown point.

J-LAY 123

DERIVED TOUCHDOWN EQUATIONS

Pipe span length

Touchdown length

αwH

s tan=

α)(wH

SX tan1sinh−=

BENDING STRESS

Bending stress

where

bendrDE

b ⋅⋅

=σ2

( )yyrbend ′′′+

=23

21

E = Young’s modulus of steel (N/m2)D = Outside diameter of steel (m)σb = bending stress (N/m2)rbend = bending radius in catenary at location x,y (m)


See following slide for definitions of y’ and y’’

BENDING RADIUS

Given

then

this gives

−= 1

Hwx

coshwH

y

=′′

=′

Hwx

Hwy

Hwxy

cosh

sinh

=

+=

Hwx

Hwx

coshHw

/

Hwx

sinhbend

r

coshwH 2

2321

Note:

cosh2(x) = [cosh(x)]2

EFFECTIVE AXIAL FORCE

From catenary equation

Effective axial force

( ) ( ) ( ) ( )( )oAyoPiAiPyTyaF ⋅−⋅+=

( ) wyHyT +=

PiAi PoAo

J-LAY 125

The first equation gives the tension in the pipe catenary at a given height from theseabed. However, the applied external hydrostatic pressure and any internalpressures in the pipe will apply an additional force to the pipe wall. This additionalforce may be sufficient to produce a compressive axial force in the pipe at significantwater depths. The second equation gives the effective axial force in the pipe based onthe tension and applied internal and external pressures at a given height from theseabed. This effective axial force should be used to determine the stress in the pipewall. However, it should be noted that the net effect of the external pressure will bezero over the full length of the catenary (from touchdown to the vessel). Therefore,the external applied tension (T) remains the same as that calculated from the generalcatenary equation.

H is the horizontal force component, N (lbf)T is the lay tension, N (lbf)w is the submerged weight per unit length of pipe, N/m (lbf/ft)y is the vertical height from the seabed, m (ft)Fa is the effective axial force, N (lbf)Pi is the internal pressure in the pipe, N/m2 (psi)Ai is the internal area of the pipe bore, m2 (in2)Po is the external hydrostatic pressure, N/m2 (psi)Ao is the external area of the pipe based on the hydrodynamic diameter (whichincludes coatings), m2 (in2)

AXIAL STRESS

Since internal pressure (Pi) will be zero fora pipeline laid empty

Considering axial force, equation becomes

( )

π⋅−⋅⋅ρ−−−=4

)(2DydgydwTF seaa

steelAaF

a =σ

g is the gravitational constantρsea is the density of seawater, kg/m3 (pcf)Dhyd is the hydrodynamic pipe diameter, m (ft)Asteel is the cross sectional area of the steel pipe, m2 (ft2)g is the acceleration due to gravity, 9.80665 m/s² (32 ft/s/s)


HOOP STRESS

Hoop stress due to hydrostatic pressure

where

t

DyPh ⋅

⋅−=σ

2

y)-(dgseawater ⋅⋅ρ=yP

Py = hydrostatic pressure (N/m2)t = wall thickness of pipe (m)g = gravity constant = 9.81 (m/s2)ρseawater = density of seawater ≈ 1025 (kg/m3)

EQUIVALENT STRESS

Equivalent stress

For Touchdown

( ) ( )

σ⋅σ+σ−σ+σ+σ=σ habhabeq

22

wHd

wT

r =−=

J-LAY 127


The shape of the lay curve produced when installing pipe with the J-lay method canbe approximated to a catenary. This is also the case for the bottom section of the laycurve if installing by S-lay and the shape adopted by steel catenary risers.

Mathematical expressions can be used to relate the shape of the lay curve (in terms oftouchdown point, span length and bend radius) and the stresses in the pipe wall(bending and axial) to the applied tension and angle of tower on the J-lay vessel.

J-LAY 129

WORKED EXAMPLE

WORKED EXAMPLE

Objective:To find stresses in J-Lay catenary

Pipe diameter D=0.2191 m (8.625in)Wall thickness t=0.0127 m (0.5in)Water depth d=1000 m (3280 ft)Applied tension T=300 kN (67 kips)Water density ρseawater=1025 kg/m3 (64 lb/ft3)Steel density ρsteel=7850 kg/m3 (490 lb/ft3)Young’s modulus E=2.07E11 N/m2 (30000 ksi)


WORKED EXAMPLE

Pipe submerged weightCross-sectional area of steel

Cross-sectional area of displaced water

Submerged weight of pipe

( )

mN

gseawaterwater

Asteelsteel

Aw

mwater

A

mtDDsteel

A

D

/255

)(

2038.04

200824.02224

2

=

⋅⋅−⋅=

=⋅=

=⋅−−⋅=

ρρ

π

π )7.12( 2in

)9.58( 2in

)/5.17( ftlbf

WORKED EXAMPLE

Horizontal component of tension

Departure angle

Length to touchdown

kNwdTH 45=−=

°=

−=α 4.811cosTH

)kips 10(

)ft 1496(mα)(wH

SX 456tan1sinh =−=

J-LAY 131

WORKED EXAMPLE

Stresses at touchdownCo-ordinates of touchdown point

Bending radius at touchdown

mymx

00

==

)ft 580(mwHr

xHwx

wHr

bend

bend

176

0 when

cosh2

==

=

=

WORKED EXAMPLE

Bending stress at touchdown

MPabendr

DEb

4.1282

=⋅

⋅=σ )ksi 6.18(


WORKED EXAMPLE

Axial stress at touchdownForce at touchdown

Axial stress at touchdown

MPasteelA

aFa 6.40−==σ

)kips 75(−

)ksi 8.0(

( ) kND

ydgydwTF hydseaa 334

4)(

2

−=

π⋅−⋅⋅ρ−−−=

WORKED EXAMPLE

Hoop stress at touchdownHydrostatic pressure

Hoop stress at touchdown

MPat

DyP

h

MPaydgseawatery

P

7.862

1.10)(

−=⋅

⋅−=σ

=−⋅⋅ρ= )ksi 5.1(

)ksi 6.12(−

J-LAY 133

WORKED EXAMPLE

Equivalent stress

( ) ( )

MPa

habhabeq

2.151

22

=

σ⋅σ+σ−σ+σ+σ=σ

)ksi 9.21(

WORKED EXAMPLE

At top of catenaryCo-ordinates, x = Xs = 456 m, y = d = 1000 mBending radius, rbend = 5860 mBending stress, σb = 3.9 MPaAxial force, Fa = T = 300 kNAxial stress, σa = 36.4 MPaHydrostatic pressure, Py = 0 MPaHoop stress, σh = 0 MPaEquivalent stress, σeq = 40.3 MPa


J-LAY - SUMMARY

You should now:Understand the principles of J-LayReview J-Lay VesselsUnderstand the J-Lay processIntroduce one shot welding methodsReview mechanical connectorsUnderstand basic catenary equations

Any questions?

We have looked at the basic principles of the J-Lay method and lay vessels available,this led into an overview of the individual stages applied to achieve a successful andcontrolled installation.

Performance figures and costs for J-Lay were considered and compared with S-Laycapabilities.

One shot welding methods available were reviewed.

The use of mechanical connectors as a time saving alternative to welded joints wasexplained, associated with the use of drilling rigs for J-Lay operations.

Catenaries, their basic equations and lay stresses were considered.

BUNDLES

BUNDLES 137

EXPECTATION

EXPECTATION

Know what bundles areKnow their track recordUnderstand bundle design and fabricationKnow what towhead structures areKnow the towing methodsUnderstand insulation & heating systemsKnow about re-usable and deepwaterbundlesKnow the advantages of bundles

We address the following:

• What bundles are and their track record• Considerations in bundle design• The 2 alternative procedures for the beach located fabrication of the bundles• The 4 primary methods used to position and install the bundles offshore• Insulation and heating systems for bundles• Re-usable and deepwater bundles• Why bundles are selected for some projects


TRACK RECORD

PIPELINE BUNDLE PROJECTS - CDTM

Operator Field Year Carrier(ins)

Longestlength

(m)

Waterdepth

(m)Statoil Asgard 1997 42.5 3810 320

Maersk Dan 1997 38.5 1800 42

Shell Gannet 1997 32 7110 100

Conoco & Chevron Britannia 1997 37.25 7500 150

BP Bruce 1998 44.0 5720 122

Statoil/Gulfaks NorthSouth

19981998

38.534.0

63763397

135135

TotalFina Elf Elgin Franklin 1999 42.7 & 52 5268 92

Statoil Asgard 1999 41.0 6776 320

ExxonMobil Buckland 1999 40.5 6162 117

BHP Keith 2000 24.6 6792 124

Kerr McGee Leadon 2000 42.5 & 47.5 4311 120

ExxonMobil Skene 2001 45.5 7449 118

Courtesy of Halliburton & Smit Land & Marine Engineering Ltd

Summary

A summary of bundles installed using the Controlled Depth Tow Method (CDTM)

• More than 50 bundles installed in North Sea• Longest to date in a single tow is 7.5km• Costs can vary from £3 million to £7 million per km, depending upon complexity

and scope of work to be undertaken

BUNDLES 139

BUNDLE DESIGN

CONSIDERATIONS

Flowlinewall thickness

Carrierbuoyancy

C of G below C of B resist N2 internal pressure

Carrier Pulloutwall thickness -

handling, expansion loads, pullout forces

Bulkheadsforces

thermalleakage

Spacers Thermal Designinsulation

active heating

Theory of bundle design

Considerations are:

• Flow line pipes:Wall thickness sized to suit internal pressure requirements

• Carrier pipe design:1. Geometric restraints of the flow lines and umbilicals2. Wall thickness to suit internal N2 pressure (necessary to provide balanced internalpressure so avoiding hydro-collapse)3. Wall thickness necessary to accommodate the pull force during launch from thebeach and tow in the sea to site location4. Wall thickness to provide external protection


• Ballast chains:Centres determined to provide neutral buoyancy of the bundle and towheadassemblies in the sea prior to and during the tow (adjusted by divers using trimminglinks)

• Bulkheads:Thickness sized to suit end force, due to internal N2 pressure, withstand thermalexpansion loads and avoid product leakage

• Spacer units :Designed to suit specific configuration of flowlines and umbilicals

FLOWLINE

Assumptions:Thin wall

i.e. ignore radial stress in pipe wall

Equations:

( )t

ODPP

tIDP

oihoop

ihoop

2

2

AreaForceStress

⋅−=σ

⋅=σ

=

, Pi only

For more in-depth information, delegates are referred to the TJA ‘Subsea PipelineDesign Essentials for Engineers’ course.

BUNDLES 141

CARRIER PIPE

Sized to contain flowline pipes & umbilicalsProvides buoyancy (Cof G below C of B)Wall thickness to suitN2 internal pressure atmax. water depthWall thickness sized towithstand pullout forcesand expansion loads

CARRIER PIPE

What is problem ifCentre of Gravity is notunder Centre ofBuoyancy ?

C of G

C of B


BALLAST CHAINS

“Extra” Links on seabed for stability to bundleduring trimming for tow and at field location

Neutrally BuoyantBundle

WebbingStrap

ChainFusewire

BALLAST CHAINS

2 to 3 m of chain (carriersits ~5 m above seabed)

Bundle design - Ballast Chains

• Centres determined so as to provide neutral buoyancy of the bundle and pullheadassembly in the sea prior to and during the tow (adjustment made by divers usingtrimming links)

• A target net downward force on the sea bed of approximately 30 N/m (2 lb/ft) isachieved

• Chains typically at between 8 m and 10 m centres. They normally have an oddnumber of links to help stability during tow. Every fifth or seventh chain has thefuse wire and additional links.

BUNDLES 143

TOWING CONFIGURATION

Controlled Depth Tow

Trail Tug Tow Tug

Ballast chains

Transponders

TowheadTrailhead

Hydrodynamic lift on ballast chains causing bundle to rise in water column.

CONTROLLED DEPTH TOW - FORCES

WEIGHT

LIFT

TOWSPEEDDRAG

Hydrodynamic lift on ballast chains causing bundle to rise in water column.


BULKHEADS

Thickness sized toaccommodate thermalexpansion seen inserviceThickness sized to suithydrostatic end forcesThickness sized toensure freedom fromleakageUsually machined fromforged castings

ColdRestrained

Hot

FE stress in Britannia Bulkhead

SPACERS

To support flowlinesand umbilicals inconfiguration foroptimum stabilityTo support flowlines toprevent bending andbucklingRollers attached toassist in bundleassembly

BUNDLES 145

BUNDLE DESIGN - SUMMARY

Components of a bundle that requiredesigning

Flowline pipesCarrier pipeBallast chainsBulkheadsSpacer units

Any questions?

Bundles are constructed from the components listed above. Each of thesecomponents has unique considerations for design.


BUNDLE FABRICATION

FABRICATION PROCEDURE

FabricationBuilding

UmbilicalComponents

Pipeline welding, NDT andjoint coating

ConveyorsPulling Head

Carrier

Winch for pullingbundle into carrier

Spacer units

There are two alternatives to the fabrication procedure:

• Fabricate the carrier pipe first• Pull the flowlines from fabrication building into carrier pipe using a winch

Or

• Fabricate the flowlines first• Sleeve the carrier pipe sections over the flowlines and complete the field welds

These are followed by:

• Attachment of the towhead structures at each end of the bundle• Hydrotesting and pre-commissioning of completed bundle onshore, prior to

launching

BUNDLES 147

BUNDLE ASSEMBLY

Bundlebeingassembled

Fabrication

NDT

Field joints

Spacer attachment

The above slide depicts a bundle being assembled and shows:

• The Fabrication building• The NDT area• The building for the completion of the field joints• The building for the attachment of the first part of the spacer units

BUNDLE FABRICATION - SUMMARY

Two methods of fabricating a bundleonshore

Fabricate carrier pipe firstThen pull in flowlines using a winch

Fabricate flowlines firstThen slide over carrier pipe sections and weld

Any questions?


The two methods used for fabricating a bundle are outlined above. Once fabricated,the towheads are attached and then the bundle is hydrotested, precommissioned andlaunched. We describe these subsequent activities in more detail in the followingslides.

BUNDLES 149

TOWHEAD STRUCTURES

TOWHEAD STRUCTURES

Britannia BundletowheadIncorporates twosubsea isolationvalves (SSIVs)~170 tonneTemporarybuoyancy tanks

If bundles can incorporate other subsea structures or equipment, it can make themmore cost effective.

The above picture shows the Britannia towhead containing two subsea isolationvalves (SSIVs). It is a gravity based structure weighing 166 tonnes.

It is located near the Britannia platform with a separate umbilical to operate thevalves.


TOWHEAD MANIFOLD

The overhead shows a model of a typical integrated towhead manifold that can betowed and installed in the field with the bundles.

The pipework and valving for each well within the manifold is a series of repeatedmodules for water injection or production. The towhead manifold can incorporatepigging loops and electric hydraulic control systems for the manifold valves andassociated trees.

A typical structure will be 30 metres long, 4 metres, wide and 3 metres high with aweight in the region of 100 tonnes.

It can be designed either as a gravity based structure or piled in position. Overheadprotection can be provided by hinged grillages or separate protection structures asrequired.

BUNDLES 151

INTERMEDIATE STRUCTURES

Intermediate structures can be incorporated within a bundle for future tie-ins.

The above slide shows the intermediate structure in the Britannia bundle duringlaunching with its integrated protection structure in place.

INTEGRATED DYNAMIC RISERS

Mid-water arch buoyancy units

Risers

Tether

Towhead structureBuoyancy units

Elevation - Installed risers

FPSO turret

Plan - Tow-out Storage Position

45 m 45 m50 m

By connecting flexible dynamic risers to flowline bundle towhead structures prior totransportation to the field, significant cost savings can be achieved.


• Riser connections can be made onshore eliminating the need for subsea activityand DSVs

• Steep riser configurations can be used if the towhead structure is utilised as ariser/tether gravity base, resulting in reduced lengths of flexible risers

Initial studies have demonstrated that this is a viable alternative to conventional riserinstallation techniques.

TOWHEAD STRUCTURES - SUMMARY

Contain manifold to tie-in bundle into otherpipelines

e.g flowlines and water injection linesTowhead may also contain ancillaryequipment

e.g. SubSea Isolation Valves (SSIVs)Gravity based structure or piled in positionCan pre-install flexible risers

Any questions?

A towhead structure is fitted to each end of the bundle. It contains the tie-in points(such as flanges or clamps) and equipment that enable the lines within the bundle tobe connected to other lines when located on the seabed.

BUNDLES 153

TOWING METHODS

TOWING METHODS

There are four primary methods of towingsingle pipelines or bundles to their requiredlocation:

Bottom towOff-bottom towControlled depth tow (CDT)Surface tow


BOTTOM TOW

Bundle pulled along the seabed, usually withsome buoyancy tanks attachedUsed in Gulf of Mexico, where lengths up to10 km long have been installedSeabed along route must be flat with noobstructionsAny pipeline crossing must be protected

Bottom tow:• The bundle is pulled along the seabed, usually with some buoyancy tanks

attached, by one or more towing vessels• Has been primarily used in Gulf of Mexico• Need for accurately surveyed tow corridor with no obstructions• Suitable for deep water applications when minimal bundle weight is required• Crossing of third party pipelines a major problem

BUNDLES 155

OFF-BOTTOM TOW

Suitable when the seabed is relatively evenand there are only a few crossings required

BuoyancyTransponder

Towing vessel

Chain ballast

Towheadstructure

Off-bottom tow:• The bundle is 2 to 3 metres clear of the seabed with ballast chains maintaining

contact with the seabed• Suitable when the seabed is relatively even and there are only a few crossings

required• Towed by one or two towing vessels. Trail tug only required for final positioning• Slower installation than Controlled Depth Tow (CDT) and bundle usually

designed to be heavier to provide stability• Bundles can be positioned in curve by placing concrete blocks


CONTROLLED DEPTH TOW

Traditional method used in the North Sea

Leading TugTrailingTug

ChainBallast

Towhead

Controlled depth tow:• As for the off-bottom tow, but the tension in the bundle is increased by using a

tow and trail tug. As the speed of the tow increases, the hydroplane effect of thechains causes the bundle to rise in the water column and ‘fly’

• Traditional method used in the North Sea• In deeper water, the bundle is in a catenary shape. Towheads are typically 20 to

30 metres below the surface and lowest point of the bundle 20 to 50 metres abovethe seabed

• Most third party pipelines operators request 15 to 20 metres of vertical clearancewhen the bundle is being towed over their line

• Average speed of the tow is about 4 knots• The bundle starts the tow in off-bottom mode and is returned to this

configuration, by reducing speed and tension, for the final positioning in the field

BUNDLES 157

TOW CONFIGURATION FOR CDT

Trail Tug Tow Tug

Ballast chains

Transponders

TowheadTrailhead

Command vessel EscortVessel

A typical configuration during Control Depth Towing (CDT):

The vessels involved are:

• Tow Tug - typically an anchor handling vessel with a bollard pull of up to 200tonnes and a towing winch with a load monitoring system

• Trail Tug - typically an anchor handling vessel with a bollard pull of about 60 to100 tonnes and with a towing winch with load monitoring system that is riggedover the bow of the vessel

• Escort Vessel (warning vessel) - usually a fishing boat acting as a warning vesselduring transportation of the bundle to the field

• Command Vessel - usually a DP vessel equipped with ROV facilities, deck crane,deck space for anchor blocks and flooding spread. Survey equipment willinclude surface positioning package, acoustic positioning package and telemetrylinks


SURFACE TOW

Not normally used in open sea conditionsDependent upon environmental conditionsCareful control needed whilst loweringbundle to the seabed at the end of the tow

Surface tow:• The bundle is towed on the surface of the water with or without additional

temporary buoyancy tanks• Not normally used in open sea conditions• Very dependent upon environmental conditions• Assessment of fatigue in tail end of pipeline for long tows through waves• Careful survey/tug control involved in lowering bundle to the seabed at the end of

the tow

BRITANNIA BUNDLES VIDEO

BUNDLES 159

This video shows the two 7.5 km (5 mile) long bundles for the Britannia developmentbeing assembled onshore, then launched and towed into position.

TOWING METHODS - SUMMARY

Towmethod Advantages Disadvantages

Bottomtow

• Minimum bundleweight

• Accurate seabedsurveys

• Permission forcrossings

Off-bottom

tow• Install bundle in curve

• Accurate seabedsurveys

• Permission forcrossings

ControlledDepthTow

• No issues withcrossings or surveys

• Bundle towed belowwave affected zone

• Requires accuratecontrol of tension inbundle

Surfacetow

• Simplest towingconfiguration

• High risk of fatigue• Requires calm

conditions

Any questions?

The advantages and disadvantages of the four methods of towing bundles are shownin the above slide.


INSULATION & HEATINGSYSTEMS

INSULATION SYSTEMS USED FOR BUNDLES

High temperatures and low OHTCs (lessthan 1 W/m²K (0.176Btu/ft2/hr/°F)) required

Possible systems are:Low density polyurethane foamMicroporous silicaMineral or Glass woolSyntactic polyurethane (SPU) and Polypropylene(PP)

BUNDLES 161

LOW DENSITY POLYURETHANE FOAM

LDPUF is injected into theannulus between theflowline and the steelsleeve pipeIt is suitable fortemperatures up to 160°CIt transfers thermalexpansion loading fromflowline to sleeve pipe(compliant structure)

Polyurethane foaminsulated flowline insleeve pipe

FBE coatedcarrier pipe

EXAMPLE

MICROPOROUS SILICA

Around the flowline in moulded tile or fabricquilt formEncased in steel sleeve pipe (pipe-in-pipe)Suitable for temperatures up to 1000°CConcentric spacers required toaccommodate loose fit flowline within sleevepipeTo reduce cost, it is used in conjunction withalumina silicate microspheres to givecompliant structure


MINERAL/GLASS WOOL

Applied to flowlines in half shell assembliesand then encased in steel sleeve pipe (pipe-in-pipe)Suitable for temperatures up to 400°CThermal conductivity higher than LDPUFMust be kept dry in sleeve pipe withconcentric spacers

SPU & PP

Syntactic polyurethane (SPU) andPolypropylene (PP)Water resistant materials that can resist highcompressive loads induced by thehydrostatic head with minimal creepSuitable for temperatures up to 150°CCan be used in deepwater applicationswithout a sleeve pipeHigh material cost (≈ £2000/m3)

BUNDLES 163

HEATING SYSTEMS IN BUNDLES

Bundles can incorporate active heating systems to prevent formation of hydrates orwax plugs.Three systems are available:

• A direct heating system with an electric cable attached to the outside of theinsulated flowline

• Hot water circulation incorporating heat-up and return flowlines within thebundle

• Circulating hot water through a closed loop within the bundle, utilising a singleflowline and the annulus of the insulated carrier pipe

The latter system is used on the Britannia flowline bundles and is shown above.

Waste heat from the platform is used to heat portable water in the bundle up to 90°c.The system is designed to be heated up to operational requirements from coldallowing production to start within a 24-hour period.


INSULATION & HEATING SYSTEMS - SUMMARY

InsulationCarrier pipe protects insulation materials fromhydrostatic pressure and seawater ingressTherefore, wider range of insulators available

Active heating systemsElectric cablesHeated flowlines

Any questions?

The carrier pipe of a bundle enables the use of a wider range of materials to insulatethe flowlines as it protects them from hydrostatic pressures and seawater ingress.

Active heating systems may also be incorporated into the bundle to maintain theflowline temperatures to acceptable levels.

BUNDLES 165

RE-USABLE & DEEPWATERBUNDLES

RE-USABLE & DEEPWATER BUNDLES

On marginal, short term field developments,conventional one-off bundles may not beeconomically viableAbility to decommission and reposition anexisting bundle at a subsequent fieldlocation at the end of the first fields lifeEconomic production life can be attractive tothe Operator

There are two concepts:

1. A conventional bundle with a ballast water line that is flooded for long-termstability and emptied during repositioning• It has more steel than conventional bundles• Pig launchers and receivers for ballast pipe built into the towhead

2. A flat pack bundle with the central carrier flooded for stability and emptied duringrepositioning• It depends on particular flowline configuration• Future tie-ins to flowlines made easier• Simple pig launcher and receiver at each end of central carrier pipe• Limited protection to flowlines


Re-usable bundles are in the region of 5 to 10% more expensive than conventionalbundles, but the cost of repositioning in a similar field is 40% to 50% of the originalinvestment. They can be recovered to an onshore facility for refurbishment andlength adjustment, or for decommissioning at the end of their useful life.

Major problems are the long term integrity of the ballast chains and their connections,and the re-floating of the towhead structures.

DEEPWATER BUNDLES

Main problem is preventing carrier pipe fromimploding in deep water. Alternativemethods include:

Pressurise conventional bundle in trimming areabefore towPressurise conventional bundle at pre-determinedtemporary parking areas during towDecant nitrogen from flowlines into carrier during towBottom tow “wet” bundles into positionInstalling flowlines in a flat-pack configuration

Pressurise in trimming area:• Overcomes onshore safety issues• Suitable for water depth of up to 800m• If bundle rises during remainder of tow, it could explode

Pressurise at parking areas:• Difficulties transporting and transferring nitrogen at sea• Need to re-trim bundle• If bundle rises during the remain of the tow, it could explode

Decanting nitrogen into the carrier pipe:• Valve technology to automatically release nitrogen into carrier at various depths

exists• Effectiveness dependent upon ratio of flowline volume to carrier volume• No additional mass being added, therefore no need for re-trimming• Can be effective in water depth of up to 1200 m

Bottom tow “wet” bundle:• Being done on Girassol• Suitable for bottom towing only• Difficult to cross over obstruction or uneven seabed

Need expensive syntactic buoyancy and insulation

BUNDLES 167

GIRASSOL PROJECT

The bundles consist of a 30” diameter outer steel carrier containing two 8” diameterproduction lines enclosed in syntactic foam. The foam was specially developed forthe project to insulate the flowlines from the high seabed pressure (130 bar at a waterdepth of 1,300 metres) and a very low temperature (3°c). The carrier is allowed to‘free flood’ and is used to protect the flowlines and transfer the installation loads.These bundles are each between 1,100 to 2,900 metres long.

The bundles were fabricated in Angola and bottom-towed over a distance of 220kilometres on the seabed, with depths ranging from 0 to 1,300 metres.


FLAT PACK BUNDLES

Carrier pipe filled withmacrospheres or kerosene

Flowlines

Flat pack bundles with macrosphere buoyancy:

• Macrospheres with various depth ratings packed into carrier pipe prior to thelaunch

• Carrier pipe allowed to ‘free flood’ during tow to field• Bundle positioned on seabed by flooding flowlines• Macrospheres recovered by pumping water and pigging carrier pipe

Flat pack bundles with low density filled buoyancy pipe:

• Kerosene or similar is contained in plastic buoyancy pipe and pressurecompensated

• Kerosene can be transported, injected into buoyancy pipe and recovered afterdeep water installation

• After initial investment, buoyancy pipe and kerosene can be re-used many times

BUNDLES 169

RE-USABLE & DEEPWATER BUNDLES - SUMMARY

Re-usable bundlesViable for short-term field developmentsIssues

Long-term integrity of ballast chainsRe-floating towhead structures

Could return bundle to shore for refurbishmentDeepwater

Concerns regarding collapse of carrier pipePressurise with NitrogenFlood carrier

Any questions?

Bundles may become economically viable if they can be reused. However, it isnecessary to consider during the design phase the issues regarding the long-termintegrity of ballast chains and re-floating of the towhead structures. A possible optionis the return of the bundle to shore for refurbishment.

Deepwater bundles have an additional concern regarding the high hydrostaticpressure exerted on the carrier pipe. Two methods can be used to help the carrierpipe withstand this high external pressure; one is to internally pressurise the carrierpipe with Nitrogen, the second is to allow the carrier pipe to flood.


ADVANTAGES OF BUNDLES

MERITS OF BUNDLE SYSTEMS

Land based fabricationFully pre-commissioned prior to installationAll flowlines and umbilicals within oneconfined corridor and protected withincarrier pipeComposite structureTrenching not requiredProduct temperature can be controlledduring production cycleFlexibility in installation schedule

Land-based fabrication:• Ideal for exotic steels• Advanced insulation systems• Liner insertion

Fully pre-commissioned prior to installation - can save a great deal of offshore time.

Flowlines and umbilicals in one corridor:• Saves congestion of seabed, particularly when multiple developments are

involved• Carrier protection can save rock dump and mattressing

Composite structure - prevents any tendency for upheaval buckling of hightemperature flowlines

BUNDLES 171

No trenching - cost savings, particularly in difficult soil conditions

Temperature control - active heating systems can prevent hydrate formation

Flexibility - installation not dependent upon availability of a particular vessel

FLOW-LAY

FLOW-LAY

Developed by Land and Marineas part of a Shell cost-saving initiativeUsed successfully for Gullane Outfalls

24in x 650 m and 10in x 1200 mOffers major cost savingsContact [email protected]

The Gullane outfalls were constructed at Kvaerner’s Methill yard, to the east ofEdinburgh by Land and Marine Project Engineering Ltd, and floated across the Firthof Forth using 400 mm and 450 mm standard HDPE pipe as a carrier.

Launch tow and installation tension loads were no more than 30 tonnes.


FLOW-LAY

Surface towFlowline slungbelow buoyancyReusable HDPEpipe as carrierInstalled bycontrolled floodingof lineCarrier strapsreleased

Coated flowline

ReusableHDPE carrier

Fabric strapwith quick

release

The system is similar in some respects to ‘flatpack’ bundles in that the buoyancy islocated above the flowline. However, with Land and Marine’s Flow-Lay system, thebundle is towed at the surface and the carrier is recoverable for reuse.

FLOW-LAY INSTALLATION

Buoyancy floats to surfaceand is recovered in sections

Straps released

Touchdown positioncontrolled usingtension of tow tug

Flowline filled fromsurface throughtowhead valvingTouchdown

monitoring

Flooded portion of flowline

A pig is used to ensure that the flooding can take place in a controlled manner.

The important difference in Flow-Lay is that with modern methods of touchdownsurvey monitoring, the flowline can be positioned exactly when combined with real-

BUNDLES 173

time control of the flooding and tow tug positions. All three vessels are in directcommunication with each other. The tow tug can be moved either port or starboardto correct any lateral current on the pipeline.

The flowline is then released and the buoyancy floats to the surface with the strapsattached. Polyethylene is slightly less dense than seawater.

GULLANE OUTFALL FLOW-LAY VIDEO

The video shows installation of the Gullane outfall. This short length of pipelinedemonstrates that the new Flow-Lay system can be used for installation of flowlines.

Two lines were installed: a long 10in x 1200 m outfall with a shorter 20in x 650 mstorm water bypass line. For this particular installation, a midline tie in was used toconnect the two lengths of 10in. However, the system is designed to installcontinuous lengths of flowline up to 10 km.


ADVANTAGES OF BUNDLES - SUMMARY

Fully pre-commissioned prior to installationCompact design4 methods of towingVarious insulation systemsActive heating systemsRe-usable bundles‘Specials’ for deepwater service available

Any questions?

The main advantage with bundle systems is that they can be fabricated and pre-commissioned onshore, prior to installation. The controlled onshore environmentenables a greater assurance in the quality of the fabrication at lower costs than incomparison with offshore commissioned systems.

Bundles are fabricated with several pipelines contained within a single carrier pipe.The compact design has advantages in that multiple pipelines can be installed at onceusing minimal space on the seabed.

There are four installation methods; on and off-bottom towing, controlled depth towand surface towing.

Bundles can also incorporate integral active heating systems to maintain producttemperatures during production.

Depending on the integrity of the bundle at the end of the field life, it may be possibleto re-use the bundle on other field developments.

Standard bundle designs are usually not sufficiently strong to be used for deepwaterapplications. However, ‘special’ bundles have been developed for deepwaterapplications. They may utilise internal pressurisation or flooding of the carrier pipeto enable it to withstand the hydrostatic pressures associated with deepwater.

BUNDLES 175

BUNDLES AND TOWED INSTALLATION - SUMMARY

You should now:Know what bundles areKnow their track recordUnderstand bundle design and fabricationKnow what towhead structures areKnow the towing methodsUnderstand insulation & heating systemsKnow about re-usable and deepwater bundlesKnow the advantages of bundles

Any questions?

We have addressed the following:

• What bundles are and their track record• Considerations in bundle design• The 2 alternative procedures for the beach located fabrication of the bundles• The 4 primary methods used to position and install the bundles offshore• Insulation and heating systems for bundles• Re-usable and deepwater bundles• Why bundles are selected for some projects

FLEXIBLES

FLEXIBLES 179

EXPECTATION

EXPECTATION

Understand difference between flexible andrigid pipeKnow what flexibles are and where they areused

Three types of flexibleUnbonded flexiblesUmbilical cablesBonded hoses

Understand installation techniques

We examine the methods of installation of flexibles. By flexibles we mean “non-rigid” pipes and cables for which there are three main types:• Unbonded flexibles• Umbilical cables• Bonded hoses

First of all, we summarise what flexibles are and how they are used. More detail onthis is contained in the “Overview” course. The crucial difference between flexiblesand rigids is that the flexibles can be bent to tight radii without damage. Withdynamic designs they can be repeatedly flexed without fatigue.


FLEXIBLES - AGENDA

IntroductionUnbonded flexiblesUmbilical cablesBonded hoses

WHAT IS AN UNBONDED FLEXIBLE?

Suggestions please

Pipe made fromplastic layers andsteel windings

An unbonded flexible is a pipe made out of layers of plastic and steel windings whichare free to move (slightly) relative to each other. The construction of a flexible is indiscrete layers, each with a particular function:

FLEXIBLES 181

• The carcass prevents collapse of the (plastic) pressure sheath due to pressurebuild-up in the steel windings;

• The pressure sheath contains the fluid within the pipe and offers the corrosionresistance;

• The pressure vault comprises interlocking wires wound with a large helix angle.This resists the pressure hoop stresses whilst still being able to flex;

• The double armour layers are torque-balanced outer steel layers with a low helixangle. They resist the tensile loads and offer impact resistance;

• The external sheath keeps out the seawater.

WHERE ARE UNBONDED FLEXIBLES USED?

JumpersIntegral flowlinesDynamic risers

JumperWellManifold

J tube onfixed

platform

FPSO

Flowline

Dynamicriser

Integral flowline

Three main uses for unbonded flexibles are• Jumpers: short (say 30m) lengths which act as spoolpieces to connect one piece

of equipment to another (a well to a manifold in the diagram above), or areconnected to a pipeline instead of a rigid spool to make the tie-in faster.

• Flowlines: even though they are more expensive to manufacture, becauseflexibles can be installed and tie-in quickly, they can be cost effective as staticflowlines. This is particularly so if they can be pulled into a J-tube and made updirectly to the manifold, such that the riser and jumper are integral with theflowline.

• Dynamic risers: the original reason for developing flexibles was for dynamicapplications such as risers where the pipe needs to connect a static point on theseabed to a moving point on the vessel.


WHO MAKES UNBONDED FLEXIBLES?

TechnipLe Trait, FranceRio de Janeiro, Brazil

WellstreamPanama City, USANewcastle, UK

NKTKalundborg, Denmark

There are three main players in the market for high pressure unbonded flexible pipemanufacture.

Their allegiances are:• Technip was formerly Coflexip;• Wellstream is part of the Halliburton group;• NKT is partly owned by Stolt Offshore.

Web addresses are:www.coflexip.com/flexibleswww.halliburton.com/BRES/BRES_wellstreamwww.nktflexibles.com

FLEXIBLES 183

WHAT IS AN UMBILICAL?

Multifunctional cablePowerChemical injectionControl

Hydraulic (HP/LP) or electricalData

Electrical or fibre optic

An umbilical is multifunctional cable. It has numbers of components twisted togetheras shown in the picture. Diameters are up 250mm. The twisting allows the umbilicalto be reeled to small radii (say 2m) without damaging the internal components.

The functions include:• Provision of electrical power, often high voltage, through insulated copper cores• Chemical lines (such as methanol injection, downhole chemicals) typically in a

nylon hose with Kevlar reinforcement. An alternative is a duplex hose, for whichfatigue during manufacture and installation needs to be considered. These caneven feature larger tubes (say 50mm diameter) to carry production duringextended well testing.

• Hydraulic and electrical control lines are similar to the above, but on a smallerscale

• Data lines can be similar to the electrical control lines, typically in quads, or canbe fibre optic. The latter are normally placed in the centre of the umbilical tominimise bending and axial strains


OTHER COMPONENTS OF UMBILICALS

Armour wiresSheaths

Woven - gas releaseSolid

FillersSpares

Twin layerhelically-wound

armour wiresOuter sheath

Plasticfillers

Other components of an umbilical include:• Armour wires to give protection and tensile strength. These are generally

protected from corrosion using a galvanised coating;• Extruded sheaths, typically of polyethylene, to contain the bundle and exclude

water. The alternative, woven sheaths permit gas permeating from hoses to bereleased along the whole length of the cable rather than at one end at theplatform;

• Low cost, soft plastic fillers are used to fill the interstices between the varioustubes to keep the umbilical round.

Sometimes spare cables or hoses are included to improve the packing. It is easier topack a bundle of seven wires (6+1) together than just five.

FLEXIBLES 185

WHO MAKES UMBILICALS?

Duco (Technip group)Nexans (formally Alcatel)Oceaneering MultiflexKvaerner Oilfield Products

These are the main players in the market for umbilical manufacture. Key web sitesare:

www.technip.comwww.oceaneering.comwww.kvaerner.com/oilgas

Their allegiances are:• Duco is partly owned by Technip-Coflexip• Oceaneering is partly owned by Halliburton


WHAT IS A BONDED HOSE?

Vulcanised rubber hose with wire or nylonreinforcement

Bonded hose are made from rubber with helical wire or nylon reinforcement. Theyare manufactured by winding layers of rubber and reinforcement onto a mandrel andthen heating the hose in an oven to vulcanise the rubber, thus bonding all the layerstogether.

This process can produce large diameter lines (up to 36”) of modest pressure rating(say 30 bar) but in short lengths (say 20 m). Bonded hoses are robust, fatigueresistant, and flexible. These characteristics lend them to use on single pointmoorings (SPMs) for both the floating section pictured about, and riser from theseabed.

FLEXIBLES 187

TYPICAL USE OF BONDED HOSES

Single pointmooring buoy

Subseamanifold andvalve

Anchor cable

Floating hoses

Controlumbilical toSPM and valve

Tanker rail hosesY pieceGoose neck

swivel Strengthenedtail hose

Riserhoses

Tanker mooring wire

The above diagram illustrates two typical uses of bonded hoses.

The first is to connect a PLEM (pipeline end manifold) to the underside of the SPM(single point mooring). An SPM is a large anchored buoy to which an oil tankermoors. The tanker will swing around the SPM to face into the weather. Therefore,the SPM incorporates a swivel joint such that the risers and moorings are not twistedby the weather vaning.

A second use for bonded hoses is to connect the SPM to the tanker. In this casefloating hoses are used, and are secured to the SPM gooseneck. The tanker picks upthe free end and connects to it. Sometimes the tanker is not able to lift the largediameter hose, so a wye and two smaller hoses are added for the connection.


WHO MAKES BONDED HOSES?

DunlopTaurusCeboPhoenix BeattieRB Pipetech

There are many manufacturers of bonded hoses world wide.

Installation can be undertaken by both international and local contractors since thereis no need for specialist barge plant.

INTRODUCTION - SUMMARY

This section has introduced:unbonded flexiblesumbilicalsbonded hoses

in terms of what they are,where they are used,and who makes them.

Any questions?

Three types of ‘flexible’ are used by the offshore industry:

• Unbonded flexibles for jumpers, flowlines and dynamic risers

FLEXIBLES 189

• Umbilicals for grouping together electrical and hydraulic control lines, chemicallines and data transfer cables.

• Bonded hoses for large diameter and low-pressure applications where fatigue is aconcern, i.e. risers and floating sections attached to Single Point Moorings.

FLEXIBLES - AGENDA


Load-out

The overall installation process for unbonded flexibles is simpler and faster than forrigid S-lay and J-lay, in that it does not include the element of fabrication. It is moreakin to reeling.

The process is illustrated in the next few slides, focussing on:• Loading the pipe onto the vessel• Pipelaying and the control of the lay tension and minimum bend radius• Pull-ins to J-tubes and to make first and second end connections to subsea

equipment• Installation methods for flexible risers


LOAD OUT OF RISERS AND JUMPERS

Where risers and jumpers are sufficiently short, they may simply be loaded on a reelin the factory, and the reel placed on the installation vessel. The reels may also betransported by a supply vessel if more cost effective than having the installationvessel return to port to pick them up.

LOAD-OUT OF FLOWLINES

Longer lengthsDirect from factoryto ship’s holdAdjacent to quaysideSailing time to site

FeaturesCatenary forspeed toleranceTurning carousel

For larger lengths, the assembled flexible flowline is wound off its reels in thefactory, over a conveyor belt, channels or roller system, onto the vessel and into thecarousel as shown above. The carousel is normally in the vessel hold and rotates

FLEXIBLES 191

slowly to wind the flexible on. Note the man “walking the reel” to make sure the linepacks down properly.

This means the yard needs to be adjacent to the quayside. Sailing times for the vesselto site need to be considered.

Note the catenary in the cable as it is being wound on. This gives it some tolerance tovariations in the speeds of the carousel and reel without pulling tight.

STORAGE ON CAROUSEL

Flexible end fitting Flexible end fitting

Replaceableinner guide(different radiusfor different pipediameters)

Another shot of a carousel, this time showing how the end fittings are held away fromthe windings at the side.

Note the stiffer end fittings and the replaceable inner guide; this varies in size to suitthe particular flexible’s minimum bend radius (MBR).


PIPE ROUTING CHANNEL

The loadout operation is reversed during offshore pipelay with the flexible beingrouted along channels and roller systems to the tensioners.

Pipe lay

INSTALLATION METHODS

J-lay method of installationTower through moonpool (deep)Chute at side (shallow)Curved stern (shallow)

Choice dependent onbending with tension limit

CHUTE

TOWER

FREEBOARD

Sag bend

Tensioner

TouchdownResidual lay tension

High tension

Low backtension

There are two main methods of installing flexible pipelines.

FLEXIBLES 193

For shallow waters, (say <300m) the pipeline runs through the tensioner and over acurved chute or freeboard (stern of vessel). This means that it is subject to the weightof the lay curve as it goes over the chute or freeboard. There is a limit on thecombination of bending and tension that a given design can withstand. If this isexceeded, then the vertical lay system will be needed.

For deeper waters, the vertical lay system tensions the flexible in the vertical, so thatit is not both bent and tensioned at the same time. The flexible is at a low backtension from the carousel as it curves into the vertical.

Near the seabed in the sag bend and at the touchdown the three methods are similar inthat it is necessary to have enough horizontal force on the pipe to avoid reaching theminimum bending radius. Normally, this horizontal force (also known as the residuallay tension) will be kept to a minimum so that the line can be laid is tight plan curves(say 100-200m radius compared to 10 times that for rigids) with the minimum ofspanning.

VERTICAL LAY TOWER

Vertical lay tower is patented by Coflexip StenaOffshore under European Patent N° 0,478,472

Tower on CSO Wellservicer


TOWER SCHEMATIC

Plan view of cruciformtensioners

Tensioners

Moonpool

GrippersPipe

Two further points on the tensioners. It is necessary to ensure that the flexibles passthrough the tensioners without either shearing (and therefore tearing) the plastic outersheath, or crushing/ovalising the steel internals.

To avoid shearing the outer sheath, the tensioners are long: perhaps three sets of 6mlong. This means that the shear stresses are distributed over a large enough surfacearea.

To avoid crushing the internals the grippers are provided at 3 or 4 locations aroundthe circumference (as shown in the diagram above) rather than just the two normallyused for tensioning rigid pipe. This makes the loading more even, and the pipe lessprone to ovalisation.

FLEXIBLES 195

SEAWAY CONDOR

Horizontal carousel Tower Chute

As a further example, the Seaway Condor is pictured above, showing an above-deckcarousel, lay tower, and a side chute.

TENSIONER ON SUNRISE 2000

Pipe passes overfreeboard

A more traditional tensioner setup is pictured above on the Sunrise 2000. This hasfour units in line. Each unit has two caterpillar tracks gripping the pipe top andbottom. The pipe passes along the tensioner and then over a curved freeboard at thestern of the vessel.


WHO INSTALLS UNBONDED FLEXIBLES?

NORTH SEAStolt Offshore

Seaway Condor Falcon

Subsea 7FennicaRegalia

Technip-CoflexipSunrise 2000Deep Blue

GULF OF MEXICOCaldiveGlobal IndustriesHorizonJ Ray McDermottOceaneeringSaipemStolt OffshoreTechnip-CoflexipTorch

Above is a list of companies with the capability of installing unbonded flexibles.

A comprehensive list is published as a poster from time to time by OffshoreMagazine. This is focused on the Gulf of Mexico and details all the pipelay andtrenching contractors together with measures of their equipment and capabilities. It isavailable for the cost of the postage. The contact is [email protected]

PERFORMANCE COMPARISON WITH S-LAY

FLEXIBLE LAYPARAMETER S-LAY12 km/dayLay rate 4.5 km/dayYesSailing time No483 mm (19in)Max diameter 1524 mm (60in)Yes (end fittings)Integral connections NoNormallyTrench Sometimes

FLEXIBLES 197

The above table seeks to point out the main differences between flexible lay and rigidS-lay.

A strong influence on the cost of a pipeline is in the offshore installation vessel time.For flexibles, the installation and tie-in times are fast compared to S-lay, but thevessel may have to sail to port to reload for longer lengths.

Flexibles are limited in diameter to the “flowline” rather than “trunkline” range dueto the mechanics of design and manufacture. This pushes the S-lay barges moretowards the trunkline market, leaving the flexibles and reel-lay vessels to compete onthe flowlines.

In areas subject to demersal fishing, the flexibles will need to be protected, and assuch it is normal to trench them following laying. Rigid lines may not need to betrenched if they are both stable and sufficiently stiff to resist trawl gear impact andpullover.

J tube pull

Barge Jacket

J tubebellmouth

J-TUBE RISER INSTALLATION

Wire fed through J tubeFlexible section drawn inFlowline attached and laid normally

Plug in placeFlanges and anodes

Flowlinesection

attached

Riser section

Flange

Winch

Pull head

Plug

Dropped object protectionand bend restrictor

We have looked at the loadout and pipelay of flexibles and are now moving on to thepull-ins, starting with J-tube pulls.

A J-tube is a steel tube pre-installed onto a rigid jacket. As the name implies it hasthe shape of a J, and can be used for pulling in future flexibles or umbilicals. It isnormally 2-3 times the flowline diameter, and has shallow curves of about 80diameters radius.

The following steps are taken during J-tube pull-in, and are shown in the a video(courtesy of Stolt Offshore).• First a wire is passed through the J tube at the jacket end and brought aboard the

barge. A pulling head is attached to the flange of the riser section of flexible, andis connected to the draw wire. The winch on the jacket then pulls the end of the


flexible from the barge. The riser portion is of a different design to the remainderof the flexible.

• At the correct point along the flexible, a plug is positioned which will eventuallyseal the bottom end of the J tube.

• The longer length of the main flowline section is attached to the trail flange of theriser section, along with anodes to prevent corrosion.

• As these larger diameter flanges and plug move off the drum, the tensioners areopened up to permit them to pass through. The tension from the flexible istemporarily held at the barge using a strop, which is cross-banded around thepipe.

• The barge then moves away, laying the flexible as normal.

STOLT J-TUBE INSTALLATION - VIDEO

This video shows the installation of a flexible line spooled from a reel. It shows theflexible being spooled from the vessel for a J-tube pull-in initiation. The key pointsto look for are:

• The pull-in head. This is fixed to the start of the flexible on the reel and then to acable that travels up through the J-tube to a winch on the topside. When theflexible has been lowered to the seabed, the winch draws the flexible up throughthe J-tube.

• The split drum on the reel. The smaller section of the reel contains the flexiblethat will be pulled up inside the J-tube riser. The larger section contains the mainflexible that will be used to lay away from the vessel.

• The connection of the two types of flexible. The make-up of the flanges on theend of the J-tube flexible and start of the main flexible is shown. The flanges aresimple bolted flanges. Either side of the flange connection, anode are clampedon.

• The passage of pipe through the tensioner. Also shown is the method of passingthe flange connection through the tensioner with the use of a braided webbingstopper to temporarily hold the tension in the flexible. (Note that stopper cannothold the full tension capacity of the flexible)

FLEXIBLES 199

End pull-insFIRST END PULL-IN2

1 Well

M a n i f o l d

Installation vessel

T h e f i r s t e n d w i l l t y p i c a l l y b e p u l l e d d o wn t h r o u g h t h e w a t e r c o l u m n b y a p r e -

i n s t a l l e d c a b l e a t 1 , a n d w i l l b e p u l l e d i n d i r e c t l y t h r o u g h a p u l l e y t o m a t e w i t h i t s f i r s t e n d c o n n e c t i o n a t 2 .

T h e k e y p o i n t i s t h a t t h e r e i s n o s l a c k t o t a k e u p , a n d n o n e e d f o r s p o o l p i e c e s t o t a k e

o u t p i p e l i n e e x p a n s i o n ( w h i c h i s a v o i d e d a s p a r t o f t h e d e s i g n o f t h e f l e x i b l e ) s o t h e p i p e i s p u l l e d d i r e c t l y i n t o t h e s t r u c t u r e . T h e m a k e - u p c a n b e d o n e w i t h f l a n g e s o r d i v e r l e s s c o l l e t c o n n e c t o r s .

F l e x i b l e p i p e l a y w i l l t h e n p r o c e e d , t o t h e s e c o n d e n d .


SECOND END PULL-IN

4

3

At the second end, because the end fitting is pre-installed, a configuration to absorbslack is needed (NB to be too short would be hopeless and unthinkable).

The normal approach is to lay past the second structure in a curve, and then toconnect wires across and winch the end in. The wire can either be via a pulleyarrangement to the surface as shown above, or can be to an ROV winch on thestructure.

Not only does this method have to take out any slack, it also has to capture and alignthe second end flange which will not always approach at the right angle. This taskcan be done with divers and tuggers, or as part of diverless connection systems indeepwater. These are described in our “Overview course”

FLEXIBLES 201

Riser installation

FLEXIBLE RISER OVER ARCH - INITIATION

Deploy clump and archLay flexibleInstall clamp on riser

Arch

Clump weight

Clamp

A typical installation sequence for a flexible riser running over an arch and up to anFPSO in a lazy S configuration is as follows:• The clump weight and arch are pre-positioned. This involves transport by barge

to site, and assembly of the arch to clump weights by chains or wires. Normallythe clump weight is lifted into the water and secured to the vessel whilst the archis then lifted into the water. Then the pair is lowered into place.

• The clump weight could be a gravity base structure resting on the seabed, or itcould be a lighter structure latched to a pre-installed piled template.

• The flowline installation vessel would lays the flowline towards the arch, andattaches a clamp at the position required to rest on the midpoint of the arch.


FLEXIBLE RISER OVER ARCH - LAYDOWN

Lay over archDeploy bend stiffenerLay down on seabed

Clamp engagestop of arch

• Guided by an observation ROV it lays the flexible over the arch, engaging theclamp in a cow horn receiver. This secures the riser in the correct position.

• The bend stiffener is deployed, and the flexible laid onto the seabed. Thelaydown wire is released by ROV and the lay vessel is then complete.

FPSO

FLEXIBLE RISER OVER ARCH - CONNECT

FPSO picks up riserLatches bendstiffenerConnects riser end

Turret

• When the FPSO arrives and moors it attaches a wire to the riser end, and winchesit under the turret

• The bend stiffener is latched (remotely) on the underside of the turret

FLEXIBLES 203

• The flexible is pulled further into the vessel and a dry connection made on theturret. (The turret allows the vessel to weather vane without twisting up themoorings and risers).

The riser configuration is then complete.

UNBONDED FLEXIBLES - SUMMARY

Flexible flowlines are stored on carouselsand laid through tensioners.

First end connections are pulled straight in,second ends need to absorb slack

Risers can have complex procedures to getthem into the correct configuration

Any questions?

The main operations for installing unbonded flexibles are summarised above. Thevarious riser configurations require unique installation procedures which can becomequite complex to implement.


FLEXIBLES - AGENDA


LAYING METHODS

Similar installation method to flexiblesThrough simpler tensionerOver chute or freeboard

Trenched insame operationDuplex different

fatiguevee trenches

Umbilicals are laid in much the same manner as flexibles, generally over a curvedchute with axial loads being supplied by tensioners. Because the umbilicals cangenerally withstand higher crushing and shear loads then flexibles, the tensioners canbe simpler as shown in the picture above.

FLEXIBLES 205

For protection, many umbilicals are simultaneously laid and trenched (see‘Trenching’ section for details). This then governs their lay rate at perhaps 5 km/daycompared to 100-200 km per day for non-buried telecoms cables.

Umbilicals containing duplex tubes have some different points to watch:• The duplex can be subject to low cycle high stress fatigue, so its chemistry and

amount of fatigue loading during manufacture and installation have to becarefully controlled.

• Such umbilicals tend to be about 150mm diameter, and too stiff to go through thecable ploughs without introducing another cycle of yield and restraighten.Therefore, they have been laid into pre-made Vee trenches, and adjacent totrenched pipelines.

SMD CABLE ENGINE

Cable wound5 x around drumDrum frictionWraps shifted laterallyUsed for deep water14 mm to 150 mm dia

If a cable is wound five times around a drum, then there are enough friction losses tohold any tension applied to the cable.

However, if the drum is a simple one, the cable will spool right off one edge.

This cable engine keeps the position of the five wraps constant relative to the edgesof the drum enabling the whole length to be laid without conventional tensioners.

It is capable of supplying 40 t at a payout rate of 2 to 4 m/s (4-8 knots). It can beused for 14 mm lightweight cable up to 150 mm armoured cable.


STAB PLATES

Hydraulic terminationsQuick releaseNo loss of hydraulic fluidBalanced pressure design

Electrical connectionsConcentric circlesocket arrangementROV attach/detach

Strength clampLocator pins

At the subsea ends of umbilical cables, it is normal to have a quick make/breakconnection socket known as a stab plate. This needs to have different types oftermination for each of the components making the cable.

The hydraulic connections are often snap fittings, which are pressure balanced toreduce the makeup forces. On opening, this ensures that there is no loss of hydraulicfluid.

Electrical connections require similar considerations and are designed to ensure thatno corrosion can occur at the contacts over the design life of the system. Since thesefittings are exposed to seawater, these are often of proprietary design using provenmaterials.

Different forces are needed to connect these hydraulic and electrical sockets. Thismeans that the connectors are balanced, often in the form of concentric circles.

In order that the unit is attachable/detachable by an ROV, it is normal to have acentral strength clamp device. To ensure the correct mating of each socket, locatorpins are also fitted around the circle.

FLEXIBLES 207

UMBILICALS - SUMMARY

Umbilicals follow similar lay techniques toflexibles. Most are simultaneously laid andburied.

Any questions?

Umbilicals are often installed by unwinding from drums. The process of installingthem on the seabed is similar to that undertaken to install unbonded flexibles. Theyare often buried to ensure greater protection.

FLEXIBLES - AGENDA



BONDED HOSE MANUFACTURE

Tapered mandrelEnd flangesDouble hosesVulcanisation Smooth lining

Rubber

Reinforcement

Integralbuoyancy

Fabric UV shield

Bonded hoses are manufactured as follows:

• A release fluid is first applied to the mandrel. The mandrel appears to becylindrical, but is in fact very slightly tapered in order to be able to remove thefinished hose.

• Hoses are built up starting with a smooth lining layer. Further layers of manmadefabric and rubber are wound onto the mandrel. Helical wire reinforcement isbonded in to resist external or internal pressures. Buoyant layers are also woundon and the whole is protected with an outer fabric layer to protect againstultraviolet degradation.

• In some instances, the hoses can be manufactured in a double skin. This providessome degree of protection against rupture.

• The hose is then vulcanised in an autoclave. This means these hoses aremanufactured in a batch process, rather than the continuous winding constructionof the unbonded flexibles or umbilicals.

FLEXIBLES 209

FLANGES

Earthing strapPrevents spark discharge at vessel

Tanker endsButterfly valveBlank flange

The flanges normally have electrical continuity straps attached to prevent sparks fromstatic electricity build-up. This is because fluid flow through the hose induceselectrical currents in the strengthening wires. By attaching an earthing strap at theflanges along the hose string and ensuring continuity within each hose, this risk canbe eliminated.

The end hoses which are used to connect to tankers will be terminated with abutterfly valve. This is lighter than other types of valve. A blank flange will also befitted with a lifting lug to aid lowering and retrieval of the hose.


BONDED HOSE DEGRADATION

MECHANISMSUV degradationWave motion wear and fatigueWhip action at ends

MITIGATIONChange-outsSpecial design at endsHoses rotates in string

The surface buoyant hoses are subjected to wave and current action for their wholeoperational life. The hoses are freely streamed from the buoy in the direction of thecurrent, but the waves may be moving the hose at a different angle. This leads towear and fatigue on the hose. Together with the degradation in the rubber due toexposure to ultra violet light, it means that hose life is limited to a few years.

The end hoses of a string are generally of a different reinforced design to account forthe whip action and extra bending moments at the ends. They need regular inspectionand the position of standard hoses in a string may be rotated to extend theiroperational usage (in a similar manner to tyres being rotated onto different wheels ofa car).

FLEXIBLES 211

SPM RISER HOSE INSTALLATION

Riser installedbefore floating hose

PLEMBend prevent wearPulley

Riser floodedPulled downWinch on barge

Shallower watersDiver connected

PLEM bend


GIRASSOL SPM ON BARGE

This shows the SPM buoy being loaded out atop a barge, and during installationduring adjustment of the chain tensions.

Note the large amount of buoyancy in order to provide support for the anchor chainsin 1.3 km depth of water. The top section rotates. The gooseneck pipe is to the LHside in both photographs.

FLOATING HOSE INSTALLATION

SPM installedStrings built up at slipway in harbourFloated out with tugs

Standard hosesSpecial flexible

end hoseSpecial strong

end hose

Butterfly valve& blank flange

Remove blank flangeDiver connected to buoyTemporary clump weight

FLEXIBLES 213

Hoses are generally assembled into the string on a slipway in an adjacent harbour.There may be as many as a dozen in the full string. At the ends, the special hoseswill be attached depending on whether flexibility or strength is required.

Since the hoses are empty, they will generally float higher in the water than they willduring service when filled with product.

Blank flanges are fitted to the ends and small tugs float the string out the SPM buoy.

The blank flange is removed from the first end. The floating section can be easilyattached to the gooseneck using divers, which is level with the correct height the hosewill eventually float at. This may mean that the hose has to be temporarily weighteddown at that end.

BONDED HOSES - SUMMARY

Bonded hoses are made from rubber inbatches and deployed in short lengths,typically on SPMs

Any questions?

The main use of bonded hoses is on Single Point Moorings (SPMs). They arerelatively cheap and ideal for surface applications due to their high fatigue resistance.


INSTALLATION OF FLEXIBLES - SUMMARY

Flexibles can be bent to tight radii andwithstand fatigue loadsThree types of flexible

Unbonded flexiblesUmbilical cablesBonded hoses

Installation - reel-lay or tow-out

Any questions?

Flexibles are designed to allow them to be bent to tight radii and withstand the fatigueloads associated with offshore applications. Dynamic design is a particularconsideration for riser designs.

There are three types of flexible design, each with unique applications:

• Unbonded flexiblesTypically used for seabed flowlines, jumpers and dynamic risers

• Umbilical cablesUsed to supply hydraulic and electrical power for controls and communications toseabed equipment.

• Bonded hosesDesigned to withstand high fatigue loading, they are typically used in the splash zoneto connect Single Point Moorings (SPM) to shore-based loading facilities. They mayalso be used to connect the SPM to the Pipeline End Manifold (PLEM).

Installation methods for flexibles depend on the type of flexible. Dynamic risers andumbilicals are generally reeled onto spools at an onshore spoolbase and then unreeledat the installation site. Bonded hoses for SPM applications are usually fabricated onshore and towed out to connect to the SPM.

REEL LAY

REEL LAY 217

EXPECTATION

EXPECTATION

Know the principles of the reel-lay processReview the main reel-lay contractors, theirvessels and the reel-lay marketAppreciate some special considerations tobe made if using the reel-lay method

Piggyback pipe, plastic lined pipe and pipe-in-pipeKnow what to consider if conducting atechnical analysis to predict pipe responseto the reeling process

Here we introduce the reel-lay method of pipeline installation. The reel-lay method ispresented together with the equipment involved. The main contractors to offer thereel-lay service and their vessels are briefly reviewed. A discussion of the reel-laymarket is presented, giving typical performance and cost values. Some of theconsiderations required for the installation of special pipe systems using the reel-laymethod are examined. These systems being piggyback pipelines, plastic lined pipeand pipe-in-pipe. Finally, the considerations required if conducting a technicalanalysis of pipe response to loads imparted during the reel-lay process are detailed.


WHAT IS REEL-LAY?

WHAT IS REEL-LAY?

Reel-lay is the process where rigid or flexible pipe is spooled from a drum, passingthrough tensioners a J-lay tower and then laid over a ramp to the seabed. It has theadvantage that the majority of the pipe joints can be welded, tested and coated at anonshore facility where joint integrity is easier to control than if welding offshore.The welded section of pipeline is then wound onto the hub of a spool which maybepermanently located on the lay vessel or subsequently loaded on by crane.

The lay vessel then sails along the pipeline route and the pipe is spooled from thereel, straightened, passed through the tensioners in the J-lay tower and laid to theseabed under a constant tension with a lay curve having the catenary configuration.

REEL LAY 219

OVERVIEW OF REEL SHIP LAYOUT

ALIGNER

MAIN REELUPPER STRAIGHTENER

TENSIONERS

PIPE CLAMP

LOWER STRAIGHTENER

UPPER TENSIONER

The main components of a reel ship are shown, much simplified, in the above figure.These include:

Reel - The pipe stalks are mechanically wound on the reel ready for laying.

Stern Ramp - This is where the straightener and tensioner are situated. The ramp isvertically adjustable and also acts as a level-wind system to guide the pipe intouniform layers on the reel during spooling.

Straightener - This device straightens the pipe by reverse bending as it comes off thereel, ready for laying.

Tensioner - This hold the weight of the pip-string when it is reeled off the stern of thevessel on to the seabed.


REELING HISTORY

Operation PLUTO -PipeLines Under TheOceanEarly 1960’s when bargeU-303 fitted with 50ft reelfor Gulf of MexicoIn 1970 the RB-2 was firstpurpose-built vesselApache, first reel ship,built in 1979

The reeling installation technique was first used during World War II to lay a pipelineacross the English Channel from the Isle of Wight to France to supply fuel to theinvasion army. A number of these lines were laid across the Channel, fabricated fromsteel or lead with a liner.

During the 1960’s, a flat-top barge was converted for reel installation use in the Gulfof Mexico. At that time, offshore pipeline design and construction had already comeof age, and specialised pipelay barges were active in the Gulf of Mexico, SoutheastAsia and the Persian Gulf, while bottom pull installations of more than 30 km lengthhad already been accomplished.

In 1970, a new-build vessel, the RB-2, was constructed by Fluor Ocean Services.This was renamed the Chickasaw by Santa Fe and is currently owned by GlobalIndustries.

In 1979, Santa Fe designed and built the Apache reel ship which, due to its steeplyinclined ramp, could lay pipelines in 600m water depth.

Now there are more than 25 vessels internationally which are equipped (or suitable tobe equipped) with designated or modular Reel-Lay equipment.

REEL LAY 221

WHAT IS REEL-LAY? - SUMMARY

Pipeline is welded onshoreSpooled onto a reel at the loading dockLay vessel carries reel to locationPipe unspooled and laid onto seabed undertension

Minimal offshore welding means increasedlay rates

Any questions?

Reel-lay is a pipelay method where the pipe string is welded onshore and thenspooled onto a reel. The lay vessel transports the reel to the installation location andunspools the pipestring, laying the pipe on the seabed under tension.

The main advantage of the reel-lay system is the minimisation of offshore welding.This enables greater assurance of welds as they can be tested onshore and an overallincrease in layrate in comparison with S-lay and J-lay techniques.


REEL LAY PROCESS

REEL-LAY PROCESS

Pipe spooled onto reelPipe-lay initiation/start-upPipe spooled from reel

Pipe straightenedAnodes attachedPipe laid onto seabed

Pipe-lay termination/lay down

The key stages in the reel-lay process are as follows:

1. At an onshore spoolbase, the sections of pipe are welded together intoapproximately 500 m long pipe ‘stalks’. These stalks are then stored on racks andawait the arrival of the lay vessel for spooling. Once the vessel is docked, each stalkis then spooled onto the vessel reel, with a single weld required to connect successivestalks. The stalks will be reeled on and held on the reel at a required constant tension.

2. The lay vessel sails to the start of the pipeline construction route and performs apipe-lay initiation or ‘start-up’. This requires that one end of the pipe on the spool islowered to the seabed, whilst the required tension is maintained to prevent bucklingin the sagbend of the lay curve. Usually, the process will utilise a dead man’s anchoror pile to provide a point of fixity on the seabed. A length of cable is attached oneend to the point of fixity and the other end to a start-up head welded onto thebeginning of the pipeline on the reel. The vessel then lays away from the point of

REEL LAY 223

fixity with the cable providing a means of obtaining the required tension in the pipeas it is lowered to the seabed.

3. Normal reeling then takes place as the vessel lays the pipe along the constructionroute. As the pipe is spooled from the reel. It is straightened by a four-point rollersystem. The straight pipe then passes down through the tensioner system. Oncethrough the tensioners the anodes can then be attached. The pipe then is laid down tothe seabed through the catenary lay curve.

4. At the end of the pipe route, the termination or ‘lay down’ of the end of the pipe isperformed. This is basically the reverse process to that undertaken for start-up. Acable is attached to a lay down head that is welded to the pipe end. The cable is fedthrough an abandonment and recovery winch that lowers the lay down head to theseabed. During lay down, tension is maintained in the cable to prevent sagbendbuckling.

CSO EVANTON SPOOLBASE SCHEMATIC

1000m (3280 ft)

The above figure shows the layout of the Evanton spoolbase.

Key to features:

1. Pipe Storage Area2. Pipe Welding, NDT & Field Joint Coating facility3. Pipe ‘Stalk’ Storage Racks4. Pipe ‘Stalk’ Load Out Causeway5. Pipe ‘Stalk’ Tie-in Facility6. Reel Ship


SPOOL-SITE PREPARATION

Permanent sitesTemporary sitesBoth sites contain:

Welding stationsNDT stationField joint coating stationDock or jetty for reel vesselAccess for construction materials

The spool site is where the pipe spools are fabricated and reeled on to the vessel.Fabrication entails welding the pipe-joints together, non-destructive testing (NDT) ofthe weld and then covering the weld with anti-corrosion coating. The process isknown as field-jointing (See the S-Lay section for more details).

There are two types of spool site; permanent and temporary. There are a fewpermanent spool sites located throughout the world in areas where there is a highdensity of oil and gas development e.g. the North Sea and the Gulf of Mexico.

Temporary spool sites are constructed in areas where there is a requirement for a longpipeline (greater than one trip), and the pipeline location is distant from a permanentspool site.

Both types of spool site have to fulfil the following criteria:

• Area on coastline located close to offshore pipelay location• Flat level area for spool construction, 1.5 to 2.5 km in length, 200 m wide• A water depth and approach water sufficient to manoeuvre and moor vessel• Access for the delivery of pipeline construction equipment

REEL LAY 225

REELING-ON

N° of trips requiredBending strain of pipe onreelLength/weight limit of reelReel packing arrangementStress in pipe due tospooling

Reeling-on is the task of loading the reel with the pre-welded pipe stalks at the spool-site.

The analysis tasks include calculating:

• Bending strain in the pipe during the reeling operation• Reel-packing arrangement or the amount of pipe that can be carried on the reel,

based on either the weight or length limit• Stresses in the pipe and loads on the rollers due to the spooling operation


START UP - INITIATION

Anchor installationAttach head and rigging

Apart from the reeling-on operations and the lay-curve stresses, most of the aspectscovered are also applicable to S and J-Lay installation methods.

The are a number of different options that are used for start-up, which are normallydependent on the type of pipeline being installed.

Pipelines starting at subsea locations can be initiated using a dead man anchor(DMA) or diverless latch, depending on the surrounding infrastructure. The use of aDMA can be restricted due to having a structure in the way. Normally the DMAneeds to be between 200m and 400m from the start-up target box, this distancedepends on the water depth. A diverless latch requires less space but is installed on apile or clump-weight with a sheave.

Pipelay is initiated by a start-up head (a pipe piece with a pad-eye and flood and ventvalves), which is welded to the first joint before reeling begins. The start-up headnormally contains one or more pigs to dewater the pipeline after hydrotest.

Other start-up techniques are J-tube pulls and pull ashore, which are discussed inmore detail later.

REEL LAY 227

START-UP PROCEDURE

Target box

Start-uphead

CablePile or

dead mananchor

Pipeline

Vessel lay direction

The various start-up elements are modelled in the pipelay analysis; i.e. the latch ordead man anchor, the wire, the start-up head and eventually the pipe-string and vesselequipment, including the rollers and tensioners.

This configuration is then analysed with the start-up head in various places along thecatenary to obtain:

• Top and bottom tensions• Stresses in the pipe string• Loads on the rollers

Another activity can be to prepare start-up locations for pipelines, either by placinganchors or mattresses to keep the pipeline up above soil level.


J-TUBE PULL

Start-uphead

Cable

Pipeline

J-tube

Topsidewinch

J-tube plug

This method of pipe lay initiation is used when pipe lay commences from an offshoreplatform that is fitted with a J-tube riser. It is a means of installing the riser and thenbeing able to lay the pre-connected flowline/pipeline in a single operation. It canonly be used for initiation and not for termination, as the vessel must lay away fromthe platform to maintain the required tension in the lay curve. The key stages in theJ-tube pull procedure are:

1. Cable lowered from topside down through J-tube to the seabed.2. Cable recovered from seabed, then brought up to the lay vessel and attached to thestart-up head of the pipeline.3. The vessel remains stationary whilst the winch on the topside pulls the cable backthrough the J-tube. With the cable connected to the start-up head and the vesselstationary, the pipe is then pulled off the spool at the required tension.4. The winch draws the pipe from the vessel down to the seabed and into the bell-mouth of the J-tube riser.5. Winching continues with the pipe being drawn up through the J-tube to therequired level for connection to the topside processing equipment.6. Once in position, the vessel commences laying away from the platform in thenormal reeling mode.

REEL LAY 229

NORMAL PIPELAY

Installation contractor checks the stressesin the lay curveControls the stress in the straightening andsag-bend to within code allowablesThe sag-bend stresses are controlled byvarying the pipelay tension

The installation contractor will check the stresses in the lay curve, and from this willdetermine the optimum pipelay settings (these cannot easily be adjusted once pipelayhas commenced) and the tension to apply for a given water depth. The lay curve hastwo areas where the stresses are checked during the installation analysis - theoverbend and the sagbend. This is known as the static analysis.

As the overbend is a controlled curvature (the shape of the pipe is controlled by theroller settings on the ramp), the equivalent stress factor is 0.96.

As the sagbend is an uncontrolled curvature (the shape of the pipe cannot beaccurately controlled), the equivalent stress factor for this region is 0.72.

After the static analysis has optimised the lay curve, a dynamic analysis is undertakenbased on the vessel operating characteristics or RAO’s. This checks the most highly-loaded node in the analysis for increases due to the movement of the vessels underenvironmental loading. This gives the highest sea-state that installation can beundertaken.


STRAIGHTENERS

Pipe is straightenedprior to passing throughtensioners4 point bending

Straighteners

Rigid pipe is plastically deformed when reeled onto the spool at the onshorespoolbase as it bends about the spool hub. This plastic deformation must berecovered before the pipe can be passed down through the lay curve, as anypermanent bending in the pipe can significantly reduce the critical stresses forsagbend buckling of the pipe at the touchdown location on the lay curve. Therecovery of the plastic bending deformation is usually achieved by a four point rollerbending system, known as a straightener, positioned at the top of the J-lay tower.

ANODE ATTACHMENT

Cannot be pre-installedon reeled pipeClamped on as pipegoes down rampThermite welding usedfor continuity lead topipe steel connection

REEL LAY 231

The anodes are attached at the workstation on the ramp to the pipeline entering thewater.

They are composed of two half-shells which are clamped around the pipeline. Acontinuity lead is welded to the pipe steel using the thermite welding process.Thermite welds are critical for the performance of cathodic protection systems andthe weld metal is composed of copper oxide and aluminium.

For reel installation, the speed of this task has a significant effect on the layrate,because the welds cannot be pre-installed on the reel and the vessel must be stopped.On S and J-Lay vessels this is not the case, as the task is less critical.

VALVES AND IN-LINE STRUCTURES

Pipe clamp

Valve orin-line structure

Welds

Seabed

Tensioners

Straightener

Valves must be installed as the pipeline is being laid.

The vessel is stopped and the pipeline is clamped in position on the ramp. The pipe isthen cut and the reel moved back, thus creating a gap for the valve to be inserted.Once the valve has been welded into position, the welds checked with NDT and fieldcoatings have been applied, the clamp is removed and the lay process continues.


WEATHER CONSTRAINTS

Consider three aspects:Operational limit of vesselBending of pipeline

Pipe and vessel motionVertical and lateral loads

Fatigue limit of pipe/weldsWave motion causes fatiguein pipe stringIf vessel stops the fatigue isconcentrated in one place

Change in bend radius

WaveMotion

The construction operation is dependent on sea-state during the installation window.This is why, in the North Sea, most offshore construction takes place during thesummer months. Areas with less severe weather conditions have constructionwindows that extend almost throughout the year. This is the situation in the Gulf ofMexico (although there is a hurricane season that can hinder offshore operations).

For semi-sub lay-vessels, the limiting sea-state is dictated by the loads on the stingerand rollers as the pipe moves up and down relative to the vessel. If the vessel stopsmoving, the limiting sea-state is dictated by the fatigue limit of the pipe/weld at thelocation of highest bending stress (the fatigue limit of the weld is a function of thelargest allowable weld defect).

For ship-shaped vessels, such as the Apache, the limit is normally an operational one;i.e. safe working cannot be contained above that limit, which is lower than the limitfor semi-sub vessels. The wave height limit for the Apache is around 2.5m,depending on wave direction, period etc. The wave height limit for Deep Blue is4.0m (significant wave).

Thus, semi-subs have a longer working window in locations such as the North Sea, orare the only vessels that can work in environmentally severe regions.

REEL LAY 233

LAY DOWN

Lay down head attachedAbandonment and recovery (A&R) winchused to lower pipeline to seabedAnalysed in opposite way to start-up

Target box

Lay downhead

Cable

Pipeline

Vessel lay direction

Recoverybuoy

A&R winch

The lay down operation occurs at the end of pipelaying, at the end of a spool orbecause of weather conditions.

A lay down head (a joint of the same diameter pipe with a lifting eye) is attached tothe last pipe-joint by either flange or welding. The A&R winch is then connected tothe lifting eye and the end of the pipe is lowered to the seabed. Additionally, alocation buoy or transponder may also be attached to the lay down head. Mattressesmay be placed on the seabed in the location of the lay down head to prevent it fromsinking below the mudline.

Abandonment is the operation in which pipelay is stopped and, if required, the pipe iscut and lowered to the seabed. As with lay down, an abandonment head is welded tothe pipe-string to which the A&R winch is attached and then the pipe is lowered. Inmost cases, the A&R winch cable is left connected to the abandonment head to easethe recovery operation.

Recovery is the reverse of the abandonment procedure. The pipeline is picked upfrom the seabed using the A&R winch and pulled up to the vessel ramp. Theabandonment head is then cut off, the pipe bevelled and re-welded to the remainingspool on the reel and pipelay carries on as before.


TECHNIP REELING - VIDEO

This video shows the capabilities of the ‘Apache’ rigid pipe reel-lay vessel. operatedby Technip. It discusses the following aspects of reel-lay from the Apache in moredetail:

The welding, testing and joint coating of pipe joints to form the pipeline section to bereeled are undertaken at an onshore spoolbase. The onshore facility can provide amore controlled environment for welding and testing and so joint integrity can beensured at a lower cost than if performing offshore welding of joints. Technip havethree permanent spoolbases in the world. One on the west coast of Scotland atEvanton, one in Norway and another in Brazil. However, temporary spoolbases canbe constructed around the world as required.

In 1995, the Apache vessel underwent an upgrade that provided the vessel with amain permanent single reel capable of carrying 2000 tonnes (2205 ton) of 406 mm(16 in) diameter pipe. This is the equivalent of 10 km (6.2 mile) of 406 mm (16 in)pipe or 24 km (14.9 mile) of 254 mm (10 in) pipe. It also carries two smallerauxiliary reels for smaller diameter pipe. The pipe on these smaller reels can beinstalled in parallel or on “piggy-back” with the main pipeline being laid. Theupdated configuration has been used to install pipe to a depth of 1400 m in offshoreBrazil.

REEL LAY 235

REEL LAY PROCESS - SUMMARY

Pipe reeled onto spoolPipe-lay initiation/start-upPipe reeled off spool

Pipe straightenedAnodes attachedPipe laid onto seabed

Pipe-lay termination/lay down

Any questions?

The reel-lay process has been summarised in the previous slides. The main stages inthe process are:

1. Pipe joints are welded to form longer stalks at an onshore spool base2. The stalks are welded together as they are reeled on to the spool on the lay vessel3. At the start of the lay route, the start of the pipe is lowered to the seabed using theinitiation method. An anchoring point is made on the seabed, a cable is attachedbetween the anchor and the start-up head on the pipe, the cable is held under tensionand the pipe is reeled to the seabed under the required tension.4. For normal pipe lay, the pipe is reeled from the drum, passes throughstraighteners, then through the tensioner, then anodes are attached. The pipe is thenlaid to the seabed through a J-lay type catenary lay curve5. The end of the pipe is lowered to the seabed in a reverse process to initiation


REEL-LAY MARKET & VESSELS

MAJOR REELING CONTRACTORS

Stolt OffshoreSubsea 7TechnipGlobal IndustriesJ.Ray McDermottTorch Offshore, Inc

A list of the major installation contractors operating reel barges is given above. Mostcontractors have the ability to use more than one installation method.

Due to the boom and bust nature of the industry, and more companies chasing fewerjobs, there has recently been a number of joint ventures, mergers and takeovers.

REEL LAY 237

GLOBAL INDUSTRIES: CHICKASAW

‘Chickasaw’

The Chickasaw, shown above, with its horizontal reel measuring 275 x 80 x 20 feet,can reel pipe up to 12-inch diameter and is now equipped with DP and a 4-pointmooring system.


GLOBAL INDUSTRIES: HERCULES

‘Hercules’

The modular reel that can be added will take 7500 t, making it the largest capacityreel barge in the world.

Type of vessel: Multifunction Derrick/Lay bargeDimensions: 445 x 140 x 25 ftRange of Pipe Diameters Handled: 2 to 60 in. (18 in Reel lay)Stations: Welding, 7; Other, 2Welding Method(s) Used: Automatic and manualPipe Installation Method(s) Used: Reel/S-layMinimum Pipelaying Water Depth: 45 ftMaximum Pipelaying Water Depth: 8,000+ ftMooring Station Keeping System: DP/8-point mooringLifting Capacity: 2 000 tonReel Capacity: 7 500 ton

REEL LAY 239

TECHNIP: APACHE

‘Apache’

A purpose-built reel ship designated by Santa Fe. The Apache was designed to lay upto 16in and its first installation projects were in the North Sea in August 1979. Sheunderwent a major upgrade in 1995 and her current characteristics are as follows:

Dimension: 122.9 x 23.34 x 8.69 mPropulsion & DP: 8 thrusters and 2 controllable pitch propellersMain reel: 25 m diameter, 2000 t capacity (100 km x 4in pipe to 8km x 16in pipe) Maximum tension - 180t with tensionersAuxiliary reels: Capacity 320t and 200t for piggyback lines orumbilicalsAccommodation: 100 persons


TECHNIP: DEEP BLUE

‘Deep Blue’

The Deep Blue is a large purpose-built ultra deepwater pipelay and subseaconstruction vessel that became fully operational in 2001. She can lay flexible pipeup to 16 inch ID and rigid lines up to 18 inch diameter from her main reel in waterdepths down to 2500 metres. In addition, she incorporates a J-Lay system enablingpipe up to 30 inch OD to be laid in similar depths.

Her key features are as follows:

Dimensions: 206.5 x 32.0 x 17.8mPropulsion & DP: 8 thrusters (34,000 HP)Main reels: Capacity 5000t (2 reels)Maximum rigid pipe diameter: 18 inchMaximum flexible pipe diameter: 16 inch IDTensioning capacity: 550tTransit speed: 13 knotsAuxiliary equipment: 2 workclass ROV’s, Hydrotesting systemAccommodation: 120 persons

REEL LAY 241

STOLT: KESTREL

‘Kestrel’

The reel has been designed to be lifted off and replaced. This enables a very quickturn-around. The reel can be skidded onto the vessel berthed at a jetty (not at sea) butit results in a higher centre of gravity than a reel lower in the hold.

Type of Vessel: Reel/Pipelay shipDimensions: 98 x 25 x 5.3 mYear Built: 1976Range of Pipe Diameters Handled: 3 to 12 in. flexible, 6 to 12 in rigidStations: Welding, 1; Other, 1Pipe Installation Method(s) Used: Reel-LayMinimum Pipelaying Water Depth: 10 mMaximum Pipelaying Water Depth: 100 mMooring Station Keeping Method: DP


REEL-LAY PERFORMANCE & COSTS

Currently up to 18in pipe diameter - DeepBlue and HerculesThick seamless pipe needed to avoidbuckling on the reel (D/t<22)Maximum pipelay depth to date 2165 m -Skandi Navica1.25 km/hr installation rate - Need toconsider time to return to spool base formore pipeVessel costs about US$200k per day

The major advantages that the reel lay process offers are fast lay rates and relativelycheap vessel costs.

However, there are numerous constraints in the use of the technique. The maximumpipe diameter is limited because of the problem of buckling using the current size ofspool. This means the technique is of more use for pipes that will be used as flowlinesrather than trunklines. Similarly, concrete coated pipe cannot be wound onto a reeland so the pipes must be thicker (a requirement for reeling anyway).

There is also a volume and weight limitation as to how much pipe can be taken pertrip, although long lines can be assembled using a number of trips.

REEL LAY 243

REEL-LAY MARKET & VESSELS - SUMMARY

Vessel typesPrincipally barge and mono-hull

Advantages of reel-layRelatively fast lay rates and cheap vessel costs

Disadvantages of reel-layLimitations on diameter - buckling concernsLimitations on quantities of pipe carried per trip

Any questions?

Reel-lay vessels are generally converted barges or mono-hull ships. The reel-laytechnique has advantages over other installation techniques in that the pipe can beinstalled relatively quickly and the day rates of the vessels are relatively cheap.Disadvantages of the reel-lay technique are limitations on diameter and the amount ofpipe that can be transferred to the construction location in each visit.


SPECIAL CONSIDERATIONS

PIGGYBACK PIPELAYING

Reduced installation costImproved operational reliabilityCuts maintenance timeSingle trenching operation

Typical examples:Britoil - AmethystArco - WellandHamilton Bros - Ravenspurn

For the past 15 years or so, the practice of installing two or more pipelines in oneoperation has become an established practice in North Sea offshore oil and gasprojects. The practice commonly known as “piggyback”, reduces installation costsand improves operational reliability and cost maintenance time. For example, ROVinspection of a dual-pipe system becomes a single operation.

A saddle assembly typically comprises EPDM rubber spacer/support block, Kevlarstrap and metallic tensioner.Straps can also be metallic banding; e.g. nickel alloy 625 with a crimp of the samemetal type.Selection of the strapping used is governed by the arrangement and number ofpipelines, stresses incurred during the laying operation, operational life requirement,type of coating of main flow line pipe, type of installation vessel and method ofassembly.

REEL LAY 245

Internal water corrosion protectionMedium density Polyethylene (MDPE) liner

Joint make-up is time consumingFeasible if reeling as only 1 joint per 500 m string

PLASTIC LINED PIPE

CRAWeldPE

Carbon steel pipe

Cap

Tension

Steel pipe stringPE pipe

Swagelining die

When steel pipe is to be carrying significant amounts of water, then internal corrosionbecomes an issue. This is a particular concern for water injection flowlines with longservice lives. One solution is to use a medium density Polyethylene (MDPE) linerpipe, inserted into the steel pipeline that seals the steel against contact with the water.

The process of lining the steel pipe with the MDPE liner is known as Swagelining,this process is illustrated above. It requires that the MDPE liner has an outerdiameter slightly larger than the inner diameter of the steel pipe. The liner is thenpulled through the steel pipe under tension. The tension reduces the diameter of theliner enough for it to pass through the steel pipe. Once pulled through, the tension isreleased and the liner attempts to return to its original diameter. This then creates atight fit between the liner and the steel pipe.

To connect two sections of lined pipe together then the connection is made asillustrated above. Two short sections of pipe made from a corrosion resistant alloy(CRA) are welded to the end of each steel pipe joint. A larger diameter cap is thenplaced and welded over the whole joint. The two sections of MDPE are thenpositioned to ensure the water contents will only contact the CRA pipe sections.

The make-up of the joints for plastic lined pipe is a time consuming process, whichmakes the process uneconomical if using the S-lay or J-lay methods. Reeling has theadvantage that the pipe strings are fabricated onshore in 500 m (1640 ft) lengths. It isthen possible to swage line these long pipe strings in a single activity onshore, priorto reeling the string onto the spool. This then means only one joint is required foreach 500m pipe string. It then becomes viable to use plastic lined pipe for reelingoperations.

This type of lined pipe has been used on the Foinaven field for the water injectionflowlines. The field is west of the Shetland Isles at a depth of between 396 m (1300ft) and 607 m (2000 ft). The depth meant that the water injection flowlines wouldhave to survive their required 25 year service life without maintenance. Developmentof the field began in 1996 and 15 km (50000 ft) of 254 mm (10 in) pipe and 2.8 km


(9300 ft) of 203 mm (8 in) PE lined pipe were installed by reeling from the Norliftvessel.

Deepwater flowline issuesInsulationHydrostatic collapseCost of weldingpipe-in-pipe systems

Reeling difficultiesCannot recover all plasticstrain for flowlineBulkheads and spacersmust withstand largebending stresses

PIPE IN PIPE

Flowline InsulationSpacer or bulkhead

Carrierpipe

Pipe-in-pipe system

Spiral buckle arrestorinvestigated by CSO

If a subsea flowline is to transport untreated product in a deepwater field then theflowline must be designed to consider the following. The high operating internaltemperatures and cold external temperatures require high performance insulation toprevent the formation of wax hydrates. The high hydrostatic pressure will require theuse of buckle arrestors to eliminate the need for excessively thick pipe walls toprevent hydrostatic collapse. A pipe-in-pipe design is able to utilise highperformance foam insulation (e.g. Rockwool) in the annulus, which is protected fromwater absorption by the outer pipe. The pipe-in-pipe also incorporates spacers andbulkheads within the annulus that act as centralisers and buckle arrestors.

The reeling process is suited to pipe-in-pipe installation because of the savings onwelding costs over the S-lay and J-lay processes. Due to the design of pipe-in-pipesystems and the cost of welding offshore, it is not effective to conduct welding of twopipes for every single joint as would be required by the S-lay and J-lay installationmethods. Therefore reeling has been used for the installation of several pipe-in-pipeprojects, including the Statoil Gullfaks pipe-in-pipe in offshore Norway, theEnterprise Cook pipe-in-pipe in offshore UK and the BP Nile pipe-in-pipe offshoreGulf of Mexico.

However, savings made from reduced welding costs should be offset against theissues associated with reeling pipe-in-pipe designs. One issue is the recovery of theplastic bending strains generated during reeling. During reeling, the outer pipe is incontinuous contact with the reel, straighteners and aligners, which enables strains tobe controlled. However, displacements are transmitted to the inner pipeintermittently at the location of spacers or bulkheads. This results in variations in thecurvatures applied to the inner pipe and makes it impossible to straighten completelythe inner pipe in the straighteners. This will have implications for allowable sagbendbuckling stresses at the bottom of the lay curve.

REEL LAY 247

SPECIAL CONSIDERATIONS - SUMMARY

Piggyback linesCan lay additional lines connected to the mainflowlineReduced installation costs

Plastic lined pipeEconomically viable for reeling operations

Pipe-in-pipeSavings on welding cost as carried out onshoreDesign issues on recovery of plastic bending

Any questions?

Some special considerations that require further design if to be installed using thereel-lay technique are summarised above.


TECHNICAL ANALYSES

CUMULATIVE STRAIN

Cumulative strain degrades fractureresistance of materialRequirements for cumulative plastic strain

≤ 0.3%: No additional requirements

0.3% to 2.0%: Engineering Criticality Assessment (ECA) - determine material fracture toughness

required to tolerate largest weld flaws

> 2.0%: Additional material tests to determinecharacteristic strain resistance (DNVsupplementary requirement P)

Cumulative strain occurs when the pipe is reeled-on and then reeled-off the spool andstraightened. When plastically deforming pipe beyond 0.3% cumulative plasticstrain, an engineering criticality assessment (ECA) must be performed. The criteriafor additional requirements for cumulative strain are shown above. The criteria mayrequire additional testing to determine the fracture toughness of the material andwelds. The tests may require fracture assessment to BS7910 level 3. Additional testsmay include crack tip opening displacement (CTOD) tests on specimens of the weld.This test will be usually based on the largest weld defects allowed by the weldingspecification.

REEL LAY 249

IMPLICATIONS

Implications of cumulative strain areLower fatigue resistance

Defects grow

Increased strain hardeningIncreased strengthIncreased brittleness

The implications of excessive cumulative strain are a reduced resistance to fatigue.The reduced fatigue resistance results in the growth of defects through cyclic loading.This is a particular concern for the growth of cracks and defects that most commonlyoccur in the welds. Cumulative strain also increases the brittleness of the pipe andwelds. This can lead to brittle fracture of a pipe sections undergoing minimalincreases in plastic deformation.

Reeling gives large plastic strainsSection (tangential) stiffness definesresistance to bucklingMain factors affecting section stiffness

D/t and YS/TS ratios

LOCAL BUCKLE

Elas

tic

YSTS

TS

Plas

tic

Stress

Strain

Reelhub

Local buckle

Pipe

Reel hub

NTension

CompressionA

Plastic

Elastic


Reeling of pipe causes large plastic strains due to the large applied bending moments.Plastic strains will be largest when the pipe must be deformed around the highestcurvature which occurs when the first reel is made around the hub of the spool.Subsequent layers of pipe reeled onto the hub will undergo smaller, but stillsignificant plastic strains.

At high curvatures, the plastic deformations may be large enough to cause apermanent local buckle, or kink, in the compressed section of the pipe. The ability toresist this local buckling is related to the section stiffness of the pipe. The sectionstiffness if governed by both geometric and material properties. The section stiffnessprovided by the geometry of the pipe is dependant on the D/t ratio. The sectionstiffness provided by the material is the ratio of the yield stress (YS) to the tensilestress (TS). As the pipe is entering the plastic range of material response, then thelower the YS/TS ratio, the more resistant to local buckling the pipe material will be.

MATERIAL / DIMENSIONAL TOLERANCES

Section stiffness may differ betweenadjacent pipe joints

Causes discontinuities and strain concentrationsSection stiffness variations due to

material propertiesdimensions

Strain concentrationmay give local buckle

Occurring at pipe jointReelhub

Stiffer pipe joint Weaker pipe joint

Localbuckle

Material and dimensional tolerances may result in the sectional properties beingdifferent between adjacent pipe joints that are welded together and then spooled ontothe reel. Bending of the connected pipe joints having different sectional propertieswill result in there being strain concentrations occurring at the pipe joints. The strainconcentrations can become significantly large and cause a local buckle at the pipejoint.

To prevent local buckles occurring it becomes important to ensure tighter toleranceson dimensional and material properties than would usually be required for otherinstallation methods, such as S-lay and J-lay.

REEL LAY 251

STRAIN CONCENTRATION

Curvature

Moment Stiffer pipe

Weaker pipe

Curvatureof reel

Resultant curvature inweaker pipe

Momentrequiredto reel

The above figure illustrates the occurrence of strain concentrations in terms of theload-deflection response of two adjacent pipe joints with differing sectionalproperties being reeled. For the applied moment required to reel the pipe about thecurvature of the drum there will need to be equilibrium of the moment through theweld joining the two different pipes. This equilibrium then requires that the weakerpipe will have a greater curvature than the stiffer pipe. This difference in curvatureresults in a strain concentration at the weld and may be extensive enough to result in alocal buckle.

COATINGS

Stiff coatings with gaps across field jointsWill amplify strainconcentrations at joints


Coatings applied to the pipeline may have significant section stiffness properties ifthey are thick and stiff. If gaps are left at the field joints then bending of the pipe as itis laid may result in strain concentrations at the field joints. This problem isparticularly associated with the J-lay and S-lay of pipe when concrete coatings areapplied. Although concrete coating is not used in the reeling process, it has beenfound that high performance external insulation coatings required for reel-lay mayhave a sufficient section stiffness to amplify the strain concentrations at the fieldjoints. This amplification may not be sufficient to cause local buckling, but can causetearing and failure of the coating at the joint locations.

MITIGATION

Specify:Low thickness fabrication tolerance (D/t ratio)Low variation in yield stressLow YS/TS ratioApplying a high and steady back tension duringreeling

Similar problem for girth (hoop) weldsOver match weld properties to avoid excessive strainin weld

To mitigate against the risk of local buckles occurring during the reeling process thenit will be necessary to specify the following to the pipe manufacturers:

• Low thickness fabrication tolerance. A tighter manufacturing tolerance on thewall thickness will be required to ensure joints have similar D/t ratios

• Low variation in yield stress. Usually a minimum yield stress will be specified.For reeled pipe it may be necessary to specify a maximum as well.

• Low yield stress (YS) to tensile stress (TS) ratio. Materials should be selectedwith relatively large differences between yield and tensile strengths. In generalthe higher strength materials have lower ratios.

• High and steady back tension should be applied when reeling. A higher tensionwill generally limit the difference in curvature between two pipe joints as they areadjacently reeled onto the drum. This has been found to be one of the easiestremedies available to reduce the risk of pipe buckling during reeling.

These methods for improving the resistance to buckling during reeling form the basisfor DNV’s supplementary material requirements for reeling, as detailed in the DNV2000 pipeline design code. More detailed information is available in the reference:

Crome, Tim; “Reeling of pipelines with thick insulation coating, finite elementanalysis of local buckling”, OTC, Houston, 1999

REEL LAY 253

REELING TENSION

R

Rreel

T

thickness coating2

is tensionmax giving radius, Minimumreel on radius bending

thickness wallnominaldiameter outside

261

modulusplastic stress yieldminimum specified

momentplastic where

33

=

++=

==

=

⋅−−=

=

=σ

⋅σ==

coating

coatingreelmin

wall

wall

P

y

PyP

t

tDRR

RtD

))tD(D(

Z

ZM

RMT P= Tension

Rmin

The above equations show how to calculate the minimum reeling tension in order toensure that the pipe yields to the radius of the reel.

The reeling tension is the tension between the main reel and tensioner during pipespooling. If it falls below the minimum, the pipe will not spool tightly onto the reel.Conversely, an excessive tension would act to crush the inner layers of pipe. It istherefore controlled during spooling, with the maximum tension being required at thestart of spooling, reducing as the reeling radius increases.

The maximum nominal bending strain is calculated for the neutral axis of the pipe onthe reel. Therefore:

R = Radius of hub of reel + (Diameter of pipe/2) + coating thickness

Before the pipeline is installed, the residual strain is removed in a procedure whichapplies a reverse curvature to the pipe by means of pre-determined roller settings.This is undertaken by the straightener.


IMPLICATIONS

Crush inner pipe layer on reel

Large amounts of stored energyUncontrolled release is a significant threat to life

Reelingtension

Reaction forces actingto crush pipeReeling

tension

Care should be taken to ensure that the back tension applied to the pipe when beingreeled is not sufficiently high as to crush the pipe layers beneath. The tension willcause reaction forces that will be applied to the top and bottom of each pipe in thevarious layers. The reaction forces will be a maximum on the layer of pipe closest tothe reel hub. Depending on the pipe specifications and the amount of back tensionapplied, these forces can become large enough to crush the lower layers of pipe.

Another problem is that the reel must be held under tension throughout the reeling-on, transport to site and reeling-off processes. The amount of stored energy in thelarger reels can be massive and failure of a section that maintains this tension canresult in the uncontrolled release of this energy. When this occurs, the pipe willuncontrollably spool itself off the wheel in a similar manner as an unravelling clock-spring. If this occurs on the vessel then there is a significant danger to the lives ofcrew. For this reason, additional precautions should be taken when operating reeledpipe. These include limiting access of crew to areas that are at risk from spoolingpipe and possibly including bumper type ‘structures’ to protect equipment andbuildings that could be damaged.

REEL LAY 255

OVALISATION

Dmin

Dmax

( )

thickness wallt)/2 (D radius pipe Mean

radius Reel ratio Poissons

pipe of nOvalisatio where

122

2

=−==

==υ=

⋅

υ−=

trR

f

tRrf

reel

reel

reelreel

Definition of ovality

Equation

minmax

minmax

DDD-DOvality

+=

The definition of ovality above is taken from BS8010 Part 3 section C.1.2. Pleasenote that there is an alternative definition in DNV OS F101 which is about twice this,i.e. the difference in diameters over the nominal diameter. So it is important to knowwhich you are using, and to make sure that the equations are consistent.

This slide shows the ovalisation equation as defined by Brazier on elastic tubes,which is a conservative estimate in the plastic region.

This equation does not give the final ovality value for the installed pipe as someroundness is regained during the straightening operation.


IMPLICATIONS AND MITIGATION

ImplicationHydrostatic pressure greater on flatter sides of pipeLead to collapse in deep water

MitigationTight fabrication tolerancesCare when handling

DminDmax

Ovalisation of the pipe can significantly reduce the pipes ability to withstandhydrostatic pressures, which is a particular problem for pipes installed in deepwater.When the pipe is ovalised, the hydrostatic forces are larger over the flatter side of thepipe due to the relatively larger surface area. This difference in applied external loadover the pipe circumference results in moments within the pipe that tend to increasethe ovalisation. The feedback loop can lead to a rapid collapse of the pipe. With thecollapse occurring at one point along the pipe, it is then very likely it will propagatealong the pipe until there is a significant change in pipe section (e.g. a bucklearrestor) or applied pressure (lower water depth).

To prevent external collapse, then tighter fabrication tolerances are required to ensurethere is limited and acceptable tolerance on the pipe diameters after manufacture.Also care is required when handling the pipe to ensure it cannot be ovalised. Thisbecomes a significant issue when the pipe is reeled onto the drum as ovalisation canoccur from the bending of the pipe and the crushing that results from the tension, asdiscussed previously.

REEL LAY 257

FINAL OVALISATION

Cyclic loading tests by Kyriakides - bendthen re-straightenRecovers approx 75% of bending ovalisation

( )75.01−⋅= reelfinal ff

When reeling pipe that is at risk of hydrostatic collapse due to ovalisation, then it isdesirable to know the ovalisation that will remain in the pipe once it has been reeled-off the drum. Research into this subject has been conducted by Kyriakides (seereference below) who studied the bending and re-straightening of pipe. He found thatfor pure bending, approximately three-quarters of the maximum ovalisation can berecovered.

Kyriakides, S and Yeh, M. K. (1985), “Factors Affecting Pipe Collapse” EngineeringMechanics Research Laboratory, EMRL Report No 85/1, A.G.A Catalogue No.L51479 Department of Aerospace Engineering and Engineering Mechanics, TheUniversity of Texas at Austin.


TECHNICAL ANALYSES - SUMMARY

Need to have ability to accurately estimatethe following

Cumulative strain build-upPotential for local bucklingRecoverable ovalityCrushing

MitigationsImprove tolerances on materials and pipe geometryReel onto spool under high back-tension

Any questions?

Analysis methods are required to enable accurate prediction of the pipe response tothe high degree of bending required in reeling operations. Of principal concern willbe the following design issues:

• Build-up of cumulative strain. Generated during reeling on and off the spool.• Local buckles in the pipe wall. A result of the large bending strains.• Amount of ovality recovered. Maximum allowable ovality is required to ensure

no collapse under hydrostatic pressure.• Ability to withstand the crushing pressures generated when reeling the pipe onto

the spool under a high back-tension.

To mitigate against the above design issues we need tighter control on themanufacturing tolerances of reeled pipe, in particular the tolerances on materialproperties and geometry. Reeling the pipe onto the spool under high tension canprevent high stress concentrations which will also alleviate some of the above issues.

REEL LAY 259

REEL LAY - SUMMARY

You should now:Know the principles of the reel-lay processReview the main reel-lay contractors, their vesselsand the reel-lay marketAppreciate some special considerations to be madeif using the reel-lay method

Piggyback pipe, plastic lined pipe and pipe-in-pipe

Know what to consider if conducting a technicalanalysis to predict pipe response to the reelingprocess

Any questions?

Here we have introduced the reel-lay method of pipeline installation. The reel-laymethod was presented together with the equipment involved. The main contractors tooffer the reel-lay service and their vessels were briefly reviewed. A discussion of thereel-lay market was presented, giving typical performance and cost values. Some ofthe considerations required for the installation of special pipe systems using the reel-lay method were then examined. These systems being piggyback pipelines, plasticlined pipe and pipe-in-pipe. Finally, the considerations required if conducting atechnical analysis of pipe response to loads imparted during the reel-lay process weredetailed.

LANDFALLS

LANDFALLS 263

EXPECTATION

EXPECTATION

Understand the basics of landfallsConsider methods and equipmentReview shore and offshore pullsUnderstand the process of directionaldrillingReview performance capabilities fordifferent methods

We describe what landfalls are, followed by a look at why they should be difficultareas, a review of examples within UK waters is made.

The differences between the operations and equipment required for an ashore pull andoffshore pull are studied, as well as the alternative of directional drilling. Thebenefits of directional drilling are considered, together with its performance underdifferent soil conditions.


INTRODUCTION

What are landfalls?Why are they difficult areas?Number of landfalls in the UK

12 sites46 landfalls

Landfalls are the installation of a trunk line from the inshore limit of the offshorelaying vessel to the onshore tie-in point above high water line. The length can varyfrom 1km to 5km, depending upon the location and the selected laying vessel.

Why are they difficult areas?• Most landfalls are located in environmentally sensitive areas such as sand dunes,

winter lochs, with rare plant species, wildlife and birds.• Engineering problems associated with unstable cliffs, extensive erosion and

difficult soil conditions. (The pipeline often requires deep excavation for long-term stability).

• Shallow water makes marine operations difficult at exposed locations.

Landfalls in UK waters: (to 2003)Shetland Islands 4Orkney Islands 1Nigg 1St Fergus 9Cruden Bay 2 (1 replacement)Teeside 2Easington 6Theddlethorpe 4Bacton 12 (includes 1 interconnector)Point of Ayr 1Barrow-in-Furness 2South West Scotland 2 (interconnectors)Twelve sites 46 landfalls

Three methods of landfall installation are considered in this section. There are othermethods, as outlined below, but these are not discussed in detail for the reasonsgiven:

LANDFALLS 265

• pulling ashore from a first-generation laybarge using an anchor wire around asheave block on the beach. This method is not considered appropriate forexposed UK waters.

• installing the landfall in a rock tunnel. This method is unique to Norway andeach project tends to be site-specific.


PULL ASHORE

PULL ASHORE INTO COFFERDAM

A trunk line being pulled ashore atEasington from the laybarge Castoro Sei

Note the following points:• The dune excavated to give access to the beach and construction area for

cofferdam.• Sheet piled cofferdam installed between low water line and point where invert of

pipeline is above high water on its final profile.• 2 no 200 tonnes capacity linear winches to give a total pull of 400 tonnes.• the marine trench for the pipeline between the low water line and the inshore

limit of the lay barge (more or less 1 km) was pre-dredged in clay to give 2.5metres of cover on the beach.

• Prior to the start of the lay, the wires were attached to the pulling head on the pipeand the lay barge moved astern to tension the system.

• The lay barge then produced the pipe which passed down the stinger until 3 or 4lengths lay on the seabed. The barge and the pipe were then pulled towards theshore a similar distance, with the tension being maintained.

LANDFALLS 267

• The laying sequence was then repeated until there was sufficient pipe on theseabed to provide resistance and enable each length of pipe to be pulled, with thewinches, towards the landfall as it was welded on to the line.

• After the pipe pulling was completed, the lay barge continued towards the fieldand the dredged trench was back-filled with pre-excavated material.

• At the landfall, a pig launcher and test end were welded on to the line for the finalcommissioning of the pipeline. The cofferdam was extracted and the dunereinstated. The dune was stabilised using gabions at the toe and the vegetationlayer was replaced and planted with marram grass that had been conserved fromthe excavation.

WINCH SITE LAYOUT

DunesBack anchorage

Cofferdam

Linear winches

Reel windersPower packs

Control cabin

Pipein trench‘Static’ pulley

on skid

Pull ashore

Beach

HW

M

LWM

Tie-in location

The above diagrammatic representation of the main items on a winch site shows:• the pipe brought in within a dredged trench offshore (up to low water mark)• a cofferdam between high and low waters to prevent the sand from the beach

filling the trench in this area• dunes cut through to permit the pipeline to reach the tie-in point set safely above

the high water level• pair of pulling wires connected to the pipeline using a non-rotating pulley on the

pulling head and skid• pair of linear winches• pair of reelwinders set behind the winches to gather the wires• sheet pile back-anchorage


LANDFALL AT EASINGTON VIDEO

Particular points from the video:

• 2 linear winches, each with a capacity of 200t, reaved to give total pull of 400t• maximum winch speed 6m/min• laybarge involved in landfall works for 3 to 4 days• budget cost, excluding laybarge - £3 to £4 million

PULL ASHORE - SUMMARY

Trench excavated through shore lineCoffers installed to keep trench dryLinear winches installedWinches connected to pipe pull-head on layvesselWinches pull pipe ashore from vesselTrench backfilledLand reinstated

Any questions?

LANDFALLS 269

The main operations undertaken in the pulling ashore of a pipe from a lay vessel areoutlined in the above slide.


PULL OFFSHORE

PULL OFFSHORE

Point of Ayr landfall

This picture shows the construction site at Point of Ayr showing the 400 metre-longstrings being assembled.

Note the following points:• The extent of onshore construction area• The barrier fence between construction area and caravan park (6m high)• The start of the dune excavation• 4km of 20 inch gas line with two 3.5 inch piggybacks being assembled in 10

string lengths

LANDFALLS 271

PULL OFFSHORE

Point of Ayr at lowwater

This picture shows the landfall section at low water after the pipeline was pulled intoposition.

Note the following points:• The pull barge anchored beyond the sand bank• The pipeline lying on the beach with conveyors being removed• The extent of the dune excavation to allow access to the beach• The excavated faces of the dune and the stockpile of material coated with

biodegradable bitumen spray• Nursery area for the temporary storage of the vegetation

1. This pipeline was post buried to give 2 metres of cover using a trenching machine and land based excavators2. The sand dune was reinstated and the excavation in this SSSI area is no longer visible3. The construction site area has been re-graded and a number of lakes formed as part of a wildlife conservation area4. The Laybarge 1601 recovered the pipe end and continued to lay towards the offshore field

Additional facts:• The 1601 Laybarge needed 12m of water at low tide.• There was 6 months of work, independent of the laybarge• An 8km long access trench was dredged for the laybarge• Budget cost, include inshore trenching = £7 million


COMPARISON OF LANDFALL TECHNIQUES

PULL ASHORE PULL OFFSHORE

ADVANTAGES

• Small land area • Independent of laybarge

• Less onshore equipment • Landfall can be installed andtrenched in a separate season

• Less disturbance • Less risk of damage to otherpipelines

DISADVANTAGES

• Access for laybarge • Extensive land area required

• Time/cost of laybargeoperations

• Environmental disturbance

• Risk of standing time forlaybarge

• Pull barge requirements

PULL OFFSHORE - SUMMARY

In principle, same operations as pull ashoreHowever, pipe pull direction reversed

Pipeline can be constructed on landGreater assurance of weld quality

Requires much larger amount of land thanpull ashore

Any questions?

Pull offshore is effectively the same technique as pull ashore but the direction of pipepull is reversed. There is a pull barge upon which the winches may be installed,otherwise the winches may be installed on land and the pull vessel used as an anchorthrough which the winch cables are routed.

LANDFALLS 273

The main advantage of a pull offshore is that the pipe joints can be welded onto thestring in controlled conditions on land. Therefore, a greater assurance in weld qualitycan be achieved. The main disadvantage is that a greater amount of land is requiredfor this process compared to that needed for pull ashore.


DIRECTIONALLY DRILLEDLANDFALLS

DIRECTIONALLY DRILLED LANDFALLS

Main benefitsMinimum disruption to environmentMinimal third party disturbanceLess risk of flooding than with open cut methodNo maintenance as pipeline is installed atgreater depth

LANDFALLS 275

DIRECTIONALLY DRILLED LANDFALLS

The overhead shows the drilling rig site and the reel barge in position at a landfall sitein Northern Holland (plus an artist’s impression of the method).

DRILLING RIG

A typical directional drilling rig.


Horizontal directional drilling is now established as a method of installing pipelinesand cables under a range of obstacles and in a number of cases has replacedtraditional open cut techniques.

METHOD - DRILL PILOT HOLE

The process has 3 distinct stages:

• An initial pilot hole is drilled with a down-hole navigation package, relaying theposition and depth to the drilling crew

LANDFALLS 277

METHOD - PULL-BACK REAMER

• The diameter of the hole is increased using different types of reamers dependingupon the ground conditions

METHOD - PULL THROUGH PIPELINE

• When the hole is opened to a suitable diameter, the pipeline or cable is pulled intoposition

Drilling and hole-opening technology has advanced to cope with a wide range of soilconditions likely to be encountered. Rock, estuarine silts and clays, as well as less


cohesive materials, are now accepted as suitable for directional drilling. Groundtreatment processes can be employed to cope with gravel. In all cases, non-toxicdrilling fluids are used and the tailings from the drilling and hole-opening processesare returned to the surface to bunded storage areas for re-use or disposal.

Pipeline lengths over 1800 metres and diameters up to 1200 mm have beensuccessfully installed using this technique.

The main benefits associated with this method for landfalls are as follows:• Minimum environmental disturbance• Minimal third party disruption• Less risk of flooding than with open-cut techniques (particularly in Holland)• With pipeline installed at greater depth, there is no maintenance

There are various methods of constructing landfalls by directional drilling; theselection being dependant upon the location, the soils, the size of the pipe and theavailability of marine equipment.These methods are as follows:

• Drill from the shore and pull the trunk line ashore from a lay barge/reel bargeusing the drill string

• Drill from the shore and pull a sleeve pipe into the hole from either the offshoreend (sleeve pipe floated out) or from the onshore end using a separate pull barge

• Drill from shore and bottom-pull the trunk line out from the beach along theseabed. The trunk line will be positioned in line with the drilled hole and pulledback using the drill string

• Drill from either a barge or jack-up located offshore and pull the previouslyassembled trunk line directly into the hole. The offshore end of the trunk linewill then be recovered by a lay/reel barge and the lay to the field will commence

There are a number of risks associated with directional drilling that can make thefeasibility of the technique questionable in some instances. These include:

• The type of soils - are they uniform? Are there any fissures? What is theinclination of the rockhead?

• What are the risks associated with loss of drilling fluid, particularly at the break-out point on the seabed and at any fissures?

It is therefore essential to have extensive geotechnical and geophysical surveyinformation available, so that the contractor can fully assess the risks involved.

In addition to landfall construction, directional drilling can be utilised to installoffshore pipelines under environmentally sensitive and unstable sand bars orapproach channels to harbours, where large depths of cover are required. In theseinstances, the drilling is undertaken from one jack-up platform to another.

LANDFALLS 279

PERFORMANCE

Lengths up to 1800mDetailed geotechnical information requiredRisks associated with some soils androckheadLoss of drilling fluid

DIRECTIONAL DRILLING VIDEO


DIRECTIONAL DRILLING - SUMMARY

AdvantagesMinimal environmental damageMinimal third party interference and disruptionUndertaken from land or sea based constructionunits

DisadvantagesRequires good geophysical and geotechnicalsurveysNo post-installation maintenance of pipe

Any questions?

The main advantages and disadvantages of the directional drilling technique arehighlighted above. The primary advantage is the minimal damage to theenvironment, which in some locations may make this landfall method the only viableoption.

LANDFALLS - SUMMARY

You should now:Understand the basics of landfallsConsider methods and equipmentReview shore and offshore pullsUnderstand the process of directionaldrillingReview performance capabilities fordifferent methods

Any questions?

We have described what landfalls are, followed by a look at why they should bedifficult areas, a review of examples within UK waters was made.

LANDFALLS 281

The differences between the operations and equipment required for an ashore pull andoffshore pull were studied, as well as the alternative of directional drilling. Thebenefits of directional drilling were considered, together with its performance underdifferent soil conditions.

TIE-INS

TIE-INS 285

EXPECTATION

EXPECTATION

Know why tie-ins are necessaryUnderstand the processes for the three mainmethods of conducting a tie-in

Diver connection of flangesHyperbaric weldingDiverless installation of rigid spools and jumpers

Know the equipment required for these tie-inmethods

We start by introducing the concept of a tie-in and why subsea tie-ins are a necessaryactivity in field development. The three main methods of conducting a tie-in are;diver connection of flanges, hyperbaric welding and diverless installation of rigidspools and jumpers. The processes involved, the equipment and the advantages anddisadvantages of these methods are presented. Other methods of tie-in are covered inother modules presented in this course.


INTRODUCTION

WHAT IS A TIE-IN?

Connection of a pipeline to another facilityDone with spoolpieces or jumpersFacilities include

RisersManifoldsTreesTeesWyesSSIVs

Pipeline

Riser

Spoolpiece

Tie-in

Tie-in

A tie-in is the connection of a pipeline to any other facility. The tie-in of a platformor manifold to a newly laid pipeline will usually involve using sections of pipe knownas spools or jumpers to ‘bridge’ the gap between the two. Spools are designed toaccommodate expansion of the pipeline due to thermal effects. Jumpers are generallyflexible and are often longer than rigid spools.

Other subsea facilities which may require a tie-in with a pipeline include risers,manifolds, trees, etc. as listed above.

Three uses of “tie-in”:

• The connection itself, e.g. flange• The whole operation of putting in a spool• The connections of a 3rd party to an existing pipeline.

TIE-INS 287

Shallow waterLift to surface, complete and lower

Covered hereDiver-installed rigid spools, flanged and weldedDirect pull-in and deflect-to-connectDiverless jumpers and rigid spools

Covered elsewhereJumper, flexible riser and flowline pull-ins: FlexiblesSteel catenary risers and J-tube pulls: J-Lay

SCOPE

In shallow water (<100 m or 300ft), it is common to lift the pipeline to the surface,weld or flange connect the riser and then lower the whole structure back to theseabed. We will not detail this further.

This section addresses how divers install conventional rigid spools. It then coversboth flanged and hyperbaric welded make-up. Also covered are the various forms ofdiverless tie-ins, some utilising rigid spools, others flexible spools. Some diverlessconnections can also be made by pulling in the start-up end of the pipeline and usinga deflect-to-connect at the termination end.

There are several other types of tie-ins which are detailed in other sections of thiscourse. Flexible connection and flexible risers are covered in the Flexibles section..Steel Catenary Riser connections and J-tube pulling are discussed in the J-Laysection.


FLANGED CONNECTION BYDIVER

FLANGED CONNECTION BY DIVER

ProcessesMeasureFabricateLowerAlignBoltTestProtect

Safety assessment

The following slides outline the processes adopted by divers during the connection offlanges for tie-ins of rigid spools.

Initially the divers conduct metrology to determine the size of spool required for thetie-in. The spools are generally pre-fabricated onshore so that only the final weldsand leak test are needed offshore on the installation vessel. The spool is then loweredto the seabed and aligned with the two pipeline sections it is being tied into. Diversthen insert the bolts into the flanges and use bolt tensioners to do up the nuts andbolts. The whole pipeline is leak tested. Then the site is cleaned of equipment andany protection placed on the spools.

The following slides go through the above sequence in more detail.

TIE-INS 289

In all cases of diver work, a full safety assessment is needed especially whenoperating below a platform.

TAUT WIRE METROLOGY

Find distance and anglesbetween flanges

Attach gimbalsStretch wireAlign gimbalsRetrieve

V

300 mmL

Tension

Airbag

Spiritlevel Bull dog

clip

The taut wire system is a common method of conducting metrology to obtain spooldimensions performed by divers. Here is a description of one approach.

A standard bracket is fixed to two bolt holes of the connecting flanges at either end ofthe gap to be filled by the spool piece. Each bracket is adjusted using an attachedspirit level or ‘Bulls Eye’ to ensure that it is centred above the top of the flange, thusensuring that the protractor plate is level. The wire is attached and placed underconstant tension using an airbag of between 100 or 250 kg (220 or 551 lb) lift. Alarger bag would be used to increase the tension for longer spools. A bulldog clampis positioned on the wire by the diver at a standard distance, 300 mm (11.8 in) from areference point, which is used to determine the length of separation between theflanges. The 300 mm offset from the flange face allows for independent verificationwhen the wire is under tension. Therefore, when back on the vessel, and applying thetension again, the bull-dog is not hard up against a stop.

The horizontal angles of the wire to the faces of the flanges are read from theprotractors set onto the brackets. The vertical angle is measured at either end using aspirit level and offset from the wire. Once the known flange offsets are included,these measurements fully define the length of the spool and the required angles tohorizontal and vertical that the mating flanges need. A seafloor profile verificationmay also be made using a series of vertical offsets down from the wire to ensure thatthere are no seafloor obstructions.

With the wire length and protractors locked in position, the system can be stretchedapart and laid out so that the distance and angles of separation can be recreated on thevessel deck. The spool can then be fabricated to size. Achievable accuracy of thissystem on angles can be to within � 0.5° and distance of separation to within � 3mm (� 0.125 in) over a 20 m (66 ft) range. Taut wire metrology can typically beperformed by divers in one to two, 8 hour shifts.


DIVERLESS TAUT WIRE

Courtesy of NGI

Above is an example of diverless taut wire measurements:

• The ROV attaches the units to the flanges.• The units pull the wire taut and contains precision instruments to monitor the

length of wire and its inclinations.• The data on spool dimensions is transmitted to the surface via the ROV.• Accuracy is approximately ±10 mm (±0.4 in) over 20 m (65.6 ft)

The time taken to conduct diverless taut wire metrology can be around the same asthe diver assisted method. However, the cost of a dive spread is around £120k($192k) per shift whereas an ROV could be less than a tenth, approximately £12k($19.2k).

Although taut wire is still used, most metrology (90% – 95%) is now carried out byROVs using acoustic or other means. Both methods can achieve comparableaccuracy, normally better than ± 100 mm (± 3.9 in) in length and ± 0.5° in angle.

TIE-INS 291

LBL HYDROACOUSTIC POSITIONING

Transmitter on vesselReceivers on flangesLong BaseLine (LBL)Gives positionsrelative to vessel

Courtesy of Kongsberg Simrad

LBL AcousticPositioning

Hydroacoustic positioning has been used extensively for the positioning of subseastructures and seabed surveying. With increases in accuracy, the systems have beenadapted for use in subsea metrology.

The system works by emitting sounds from transceivers located on the vessel, onflange faces and at locations on the seabed. When a signal is received, a reply isemitted. Knowing the speed of the signals in the water and the time taken to receivea reply enables the distance to be calculated. From these measurements theautomated systems can then determine horizontal and vertical angles and lineardistances. Three transceivers are required for unambiguous definitions of position,four provide some redundancy.

The Long BaseLine (LBL) system is used to determine metrology relative to a vessel.The Short BaseLine (SBL) system gives measurements for metrology on the seabed.

Measurements using this system can be made in water depths up to 4000m (13200 ft)and accuracy can be less than 200 mm (7.87 in) and less than ± 0.3° in angle.Acoustic positioning devices are available from Oceanscan, DPS, Ashtead andSeatronics, amongst others.


INERTIAL METROLOGY

Laser ring gyroCarried by ROVDocking ports oneach flangeFive or sixjourneys betweenthe two dockingports

CDL MiniSpool on ROVCourtesy of CDLtd

Inertial metrology is a relatively new system for diverless measurements. The systemuses inertial navigation and topside processing software to make accurate subseameasurements without requiring any external sensors on the ROV. The inertialnavigator is attached to an ROV and flown between docking ports on each flange.The ROV is required to make the journey 5 or 6 times for the processing software todetermine the metrology. Typical accuracy is around 50 mm (1.97 in) over a 25 m(82 ft) linear distance.

FABRICATE SPOOL

Reproduce flange orientationPre-fabricate onshoreFinal welds offshoreHydrotest

L - shape

U - shape

Dog-legor Z - shape

TIE-INS 293

When the required dimensions are known from the metrology, the spool can be pre-fabricated on shore and shipped to site. Larger spool may need to be shipped insections and then welded together on the installation vessel. The spool undergoes ahydrotest on the vessel prior to installation.

Typical spool lengths are 15 to 30 m (approx. 50 to 100 ft); however, they may be aslarge as 100 m (approx. 330 ft). The limitation is generally on deck space, metrologyand lifting.2 point lift Beware of strut bucklingT

w

i

n

c

r

a

n

e

s

2

o

r

4

p

o

i

n

t

l

i

f

t

L

a

r

g

e

r

s

p

o

o

l

s

M

u

s

t

o

p

e

r

a

t

e

i

n

u

n

i

s

o

n

S

p

r

e

a

d

e

r

b

a

r

s

A

l

l

e

v

i

a

t

e

c

o

m

p

r

e

s

s

i

v

e

l

o

a

d

s

A

d

d

w

e

i

g

h

t

a

n

d

h

e

i

g

h

t

T h e s p o o l i s l o w e r e d t o t h e s e a b e d b y c r a n e . T h e l i m i t a t i o n o n l e n g t h f o r a s i n g l e

c r a n e l i f t i s u s u a l l y g o v e r n e d b y s t r u t b u c kl i n g c r i t e r i a . I f u s i n g a s i n g l e c r a n e a n d a

t w o p o i n t l i f t , t h e n t h e a n g l e o f t h e l i f t i n g w i r e s c a n r e s u l t i n a x i a l c o m p r e s s i v e l o a d s

b e i n g a p p l i e d t o t h e s p o o l . I f t h e s p o o l i s t o o l o n g o r t h e a n g l e s t o o s h a l l o w , t h e s e

compressive loads may become large e n o u g h t o c a u s e E u l e r b u c k l i n g o f t h e s p o o l .

S p r e a d e r b e a m s c a n b e u s e d t o a l l e v i a t e t h i s p r o b l e m . H o w e v e r , t h e y n e e d t o b e v e r y

s t i f f c o m p a r e d t o t h e p i p e , s o a r e u s u a l ly l a r g e I - b e a m s . T h e y a d d t h e i r o w n w e i g h t

a n d h e i g h t t o t h e l i f t i n g c o n f i g u r a t i o n .

T h e a b o v e d i a g r a m s a r e d e s i g n e d t o c l e a r l y d e m o n s t r a t e s t r u t b u c k l i n g w i t h a b e n t

s p o o l p i e c e . H o w e v e r , i t w o u l d b e m o r e c o m mo n t o h a v e a t h r e e o r f o u r l e g l i f t w i t h

a n L o r Z s p o o l . N e v e r t h e l e s s , t h e s e c a n a l s o i n d u c e c o m p r e s s i v e f o r c e s i n t h e s p o o l

i f a s p r e a d e r b a r i s n o t u s e d .

L a r g e r D S V s a n d M S V s h a v e t w i n c r a n e s al l o w i n g l o n g e r s p o o l s t o b e i n s t a l l e d . I f

u s i n g t w i n c r a n e s , t h e o p e r a t o r s s h o u l d a l w a y s w o r k i n u n i s o n t o e n s u r e l i f t f o r c e s a r e

a l w a y s a c t i n g t h e v e r t i c a l d i r e c t i o n a n d n o t t r a n s f e r r e d a x i a l l y i n t o s p o o l

c o m p r e s s i o n .


Fixedflange

ROV

Support vessel moves using anchor spread

Spool pieceand spreader

Clump andsheave

Winchcontrolsposition

SPOOLPIECE PULL-IN

Lower spool to seabedKeep 5 m from locationUse vessel anchorsto manoeuvre

Crane held stationary toeliminate swinging

ROV monitorsposition of spoolpieceSheave on temporaryclump as hold-back

In the North Sea, the common method of fitting spool pieces is to lower them fromthe barge onto the seabed in a safe storage location some 5 m from the final position.

The vessel is then manipulated on the anchors to bring the ends of the spool together.The crane is not used because it induces swinging of the spoolpiece on the seabed.

The positioning is under the control of either divers or ROV operators, who ensurethat the flange ends do not clash. Divers may get help from a Tirfor to bring theflange ends together.

In some cases, additional control is provided by a wire from the barge through asheave fixed to a temporary clump anchor on the seabed holding the rear of the spoolpiece - as shown in the slide above.

TIE-INS 295

PLACE ON SEABED

Pull down

To vessel

Taut wire

To vessel

Guidepost and cone ROV visual guidance

Final alignment of the spool on the seabed can also be achieved in a number of otherways. These older methods are more common in shallow water where tidal currentsare low and the risk of impact between flanges are small.

• Taut wire systems are widely used and can be installed using diverless equipmentin deepwater. They involve attaching a stab to the existing pipeline on the seabedand a wire which is brought back to the surface by a buoyancy bag. The cable isfed through a cone on the spool and the spool is lowered to the seabed. Thecable then guides the cone to the stab, forcing the spool to the desired location.

• The pull down method uses a cable which is fed through a pulley installed on thepipeline and back up to the vessel. The cable is pulled towards the vessel,bringing the spool to the desired location.

• The simple guidepost and cone method involves lowering the spool to the seabedso the cone locates over the post. This obviously relies on the crane operatorhaving vision of process via diver or ROV. In stronger sea currents a divermaybe required to help manoeuvre the cone over the post.

• Another method utilises an observation ROV to give visual guidance of thelocation of the spool on the seabed.


HANDLING FRAME

Courtesy of Saipem

Courtesy of Oceaneering

A common method of alignment in both diver and diverless water depths is the use ofhandling frames. Following placement of the spool on the seabed, handling framesare placed over the spool. The spool is picked up into the frame which hashydraulically-controlled movement in three planes. The frame then manoeuvres thespool to the desired position for connection.

TIRFORS

Manual spool manoeuvringCrude alignment of flangesRatchet and levermechanism

Loose tail

Small handle used to take up slack

Large handle forheavy pull-in

Pipeline

Spool

TIE-INS 297

Tirfors have been developed for lifting or pulling heavy loads. Pictured above, theyhave levers to pull in a chain or wire, and ratchets to hold it. They can be used bydivers to manoeuvre spool pieces once they have been located on the seabed.

Heavy duty tirfors can pull up to 3.5tonnes (7700 lb).

Tirfors are known as Grip-hoists in the United States and Griefzugs in Germany.

FLANGE PULLERS

Flange alignmentHydraulic retractingcylinderDiver or ROVoperated

Wirecable

Rear jawassembly

Front jawassembly

Fixed adapters

Flanges

Adapterplate

Cable gripclamp

Courtesy of FASTORQ Bolting Systems

Flange Pullers are used to draw flange faces together. A cable is inserted through thethe corresponding bolt hole on each flange and a clamp fitted behind one of theflanges to provide a reaction force to the pulling force. The flange puller is thenlocated on behind the other flange. A hydraulic cylinder then retracts which drawsthe two flanges together. Two or more flange pullers may be required to ensure theflange faces are parallel when pulled together.

Flange pullers are also available for diverless operation by ROV. The typical pull-inloads generated by standard flange pullers are around 530 kN (60 US Tonf) andstrokes can be achieved of around 125 mm (5 in).


Flange welded to pipeSuppliers world-wideDesigned for widerange of

SizesPressure ratingsMaterial specification

Alignment concerns ifconnecting two weldedflanges together

WELD NECK FLANGES

Having aligned the spoolpiece on the seabed, the next step is to bolt up the flanges.

Bolted flange connectors are readily available in a wide range of sizes, pressureratings and material specifications from suppliers all over the world. Flanges arenormally manufactured in accordance with ASME B16.5 - Pipe Flanges & PipeFittings.

In spoolpieces there is often a significant bending load, in which case, flanges may beuprated to give additional strength e.g. putting a class 1500 flange in a class 900system.

Welded neck flanges are bolted flange connectors that are welded to the pipeline end.However, if used in isolation they may cause difficulties as they require the two pipesto be aligned exactly for the bolts to be inserted.

TIE-INS 299

Neck welded to pipeRing containing boltholes rotates 360°

Easier alignment ofbolt holesElimination oftorsional stresses

Common practiceConnect swivel ringto weld neck

SWIVEL RING FLANGES

Courtesy of Oil States

Swivel ring flanges allow a greater degree of flexibility in that the rotations of thetwo pipes to be tied-in do not need to be exact. The outer ring of the flangecontaining the bolt holes can be rotated. This eliminates the introduction of torsionalstresses in the pipeline and eliminate the need for control of pipeline orientation. It iscommon practice to make a single tie-in using a swivel ring flange and a weld neckflange.

RING JOINT

Connection of swivel and weld neck flanges

PipeWeld neck

flange

Pipe/flangeweld

Stud bolt Nuts

Swivel ring

Ring joint

Swivel ring flange


The above figure shows the ring joint in a connection between a weld neck flange anda swivel ring flange. Offshore, the gasket joint is a soft iron ring which can either beoval or octagonal in section. The ring joint is inserted into a recess in the two matingflanges and acts as a seal. As the bolts are tightened the ring is crushed against thewalls of the recess, thus creating the required seal.

Onshore, where maintenance is easier, other ring materials are often used, such asgraphite, EPDM or Teflon.

Note that although it is possible to buy swivel flanges which are similar in thicknessto the standard weld neck flange (as shown above), care needs to be taken that the fullmoments can be transferred. To achieve this, it would be normal for the swivel ismuch thicker than the standard flange (perhaps twice as thick - see Oil States onprevious slide).

ALTERNATIVE FLANGE TYPES

Compact flangesTaper-LokGrayloc

Courtesy of Taper-Lok

Courtesy of Grayloc

Clamping surface

Seal ring

Connectorhub

Seal ring lip

Rib

Clamp

This slide shows the Taper-Lok and Grayloc connectors which are alternatives to theANSI or API bolted flange type connectors. Both these alternative connectors arelighter in weight and smaller and have less bolts than standard flanges. They utilisemetal-to-metal seals which are self energising, using the internal pressure of the pipeto reinforce the seal. They are also available in the entire range of diameters,temperatures and pressures. They can accommodate 1 to 2° of misalignment. Evenso, they are seldom used subsea.

TIE-INS 301

ALTERNATIVE FLANGE TYPES

Morgrip

Courtesy of HydratightSweeney Ltd

Radial seals

Ball bearing

Tension bolt

spring

Large diameter Morgrip

The Morgrip connector enables weldless, high integrity mechanical pipe connection.The Morgrip consists of three main components, a centre housing and on either side aseries of gripping sections. The gripping sections hold a series of spring-loaded ballbearings positioned around their inner circumference.

The make-up procedure for the Morgrip is as follows. The pipes are prepared byremoving the surface coatings at the point of connection. The gripping sections arethen slid over each end of the two pipes along with the radial seals which fit intorecesses in the gripping sections. Then the centre housing is located over the pipejoint. Stud bolts are inserted through all sections around the circumference of thecoupling. The bolts are then tensioned which forces the ball bearings to press into theouter surface of the pipes, giving the required mechanical grip. Pipe ovality andsurface imperfections are compensated for by having the ball bearings actingindependently of each other. The bolt tensioning also causes the radial seals to becompressed against the outer surface of the pipes.

The Morgrip connector is available for pipelines from 12.7 mm (0.5 in) up to 914 mm(36 in nominal) diameter and an ANSI rating to 2500 lb. Modifications to thestandard design have been made to enable external pressure ports, corrosion inhibitorfacilities, fire protection, Tee connections, and ROV connection in deepwater.

The Morgrip is more costly than conventional flanges. However, it is ideal forrepairs, and can be cost effective for spoolpiece tie-ins where speed and minimumvessel time are important.


TENSION BOLTS

Hydraulic tensioners

Hydraulicinput port

Ram

Access to collar

Tommy barfor nut rotation

Nut-retainingcollar

Courtesy of Hydratight Sweeny

Once the flanges are aligned, the ring joint inserted and the bolts/nuts in place, thebolts are tightened evenly. This can be done manually by torque wrench, using asystematic pattern to pull the flange in evenly. This is still common practice topsides.However subsea, it is more common to use hydraulic tensioners.

The process for tensioning a bolt and tightening a nut is as follows:

• Screw nut and tensioner onto bolt. Initially the nut will be screwed down thethreaded bolt until it stops against the flange face. Then the hydraulic tensioningunit is also threaded onto the bolt until it also stops against the flange. The insideof the hydraulic tensioning unit is threaded to allow it to grip onto the bolt.

• Pressurise the hydraulic tensioning unit. Hydraulic pressure is applied to the unitwhich forces rams to push the top of the unit away from the flange, thusstretching the bolt. A pre-determined hydraulic pressure will be applied to givethe desired bolt tension.

• Wind down nut. The nut can then be wound further down the now extended boltto meet the flange again. A Tommy Bar may be required to assist in the turningof the nut.

• Remove hydraulic tensioning unit. The hydraulic tensioning unit can then beunscrewed from the bolt and taken away.

• Install flange protector. A flange protector will then be placed over the the flangeto prevent any foreign objects snagging on the flange

The photo shows the hydraulic tensioning units located on both sides of the flange onalternating bolts. This will be due to problems associated with the separation distancebetween each bolt being too small to fit the units all on one side.

TIE-INS 303

Spool protection coverswaiting at dock side

PRECOMMISSION

Clear away equipmentLeak testProtection

Flange protectorsRock guardTunnels

Courtesy ofKomtek AS

Thermal Insulation coversfor flanges on Girassol

The installed spool undergoes a leak test to ensure the integrity of the flanges. Dye isadded to the water inside the pipe to help find a leak visually should it occur.

Once tested, the site is cleared and any protection applied. For example:

• Flange protectors can completely encase the flanges for thermal insulation. Somejust fit over the bolts to prevent snagging.

• Rock guard or Uraduct may be placed around the spools (or indeed pre-installedon the vessel deck) to give dropped object protection.

• In rare cases, concrete tunnels may be placed over the spool.


DIVER FLANGE CONNECTION - SUMMARY

MeasureFabricateLowerAlignBoltTestProtect

Any questions?

The main activities performed for a diver-based flange connection are shown above.These activities and the equipment related to them have been described in greaterdetail within this section.

TIE-INS 305

HYPERBARIC WELDING

HYPERBARIC WELDING

Dry weld at ambient pressureDiver performs

Pipe preparationMetrologyAlignmentWeldingTestingCoating

An alternative to flanges is hyperbaric welding. A hyperbaric weld is one made in adry environment at ambient pressure. To do this a sealed habitat is lowered to theseabed and fitted around the joint of the two pipes being connected. The habitat isthen filled with gas at ambient pressure to create a dry environment. The diver, whois also a qualified hyperbaric welder, enters the dry habitat to weld together the twopipe ends.

The equipment and processes used in hyperbaric welding are explained in thefollowing slides.


HYPERBARIC SPREAD

This figure shows the hyperbaric chamber or ‘habitat’ - in this case being used for ahot tap rather than a spoolpiece.

The welds are being performed by divers in a Heliox atmosphere. The yellowlobster-back is the diver exit point though they normally enter from above.

HABITAT

TIE-INS 307

The pictures show a typical hyperbaric welding habitat. The clamps, located oneither side of the chamber, allow the two pipes being welded together to be fixed ontothe chamber and held rigid relative to each other.

PIPE PREPARATION

Diver prepares site for equipmentPipe ends cutCoating removal

Laydown headRiser end cap

Cut Cut

Excavate for chamber

The diagram shows a newly laid pipeline and riser prior to a tie-in by hyperbaricwelding. A diver will be required to remove the pad-eye, end caps and any coatingsready for the welding procedure. The seabed may also require excavation to enablethe hyperbaric chamber and handling frames to be located at the correct height.

METROLOGY AND SPOOL LOWERING

Metrology and spool fabricationApprox. 300 mm (1 ft) short

Lowered to weld site with handling frame

Handling frame

Spool


The diver undertakes metrology to determine the required size of spool. The spool isthen fabricated, shipped to site and lowered to the seabed on a handling frame. Thespool will generally be fabricated approximately 300 mm (1 ft) short to give the diverfreedom to manipulate the spool on the seabed.

CHAMBER POSITIONED

Hyperbaric chamber installed

Flooded hyperbaricchamber

Clamps

The hyperbaric chamber is then lowered to the seabed and located around the twopipes to be joined. The chamber is in two parts which sandwich the pipes betweenthe outer walls giving a sealed fit around the pipelines.

TIE-INS 309

PREPARATION FOR WELDING

Temporary plugs fitted in pipesChamber gas filledPipe ends re-cut for welding

Heliox gas

Plugs or hyperbaric pigs

Ends re-cut

Temporary plugs are inserted into each end of the two pipes. The plugs (orhyperbaric pigs) are inflated and provide a seal to prevent water in the pipes leakinginto the chamber. The chamber is then flooded with Heliox gas and the sea waterpumped out. The diver then enters the chamber and re-cuts the ends of the pipes togive the required bevel for the weld.

Handling frame manipulates spoolChamber clamps lock pipes in position

SPOOL ALIGNMENT

Frame manipulatesspool

Required separationfor welding


The diver operates the handling frame to move the faces of the two pipelines into thecorrect position for welding. The clamps on the outer walls of the habitat are alsoused to align the pipes.

WELDING

SafetyFume extractionGas supply

Unique proceduresWelder qualificationNDT and coating

Weld

The diver then welds the two ends of the pipe together. Safety concerns during thewelding stage include the extraction of welding fumes and re-supply of gas to ensurethe atmosphere remains breathable by the diver.

The procedures required for hyperbaric welding are different to those for welding onthe surface. Both the arc and the chemical reactions during a hyperbaric weld behavedifferently. Divers who conduct hyperbaric welding have to undergo unique andregular qualification tests before being allowed to work. Due to the difficulty ofhyperbaric welding and the cost of later repairs, it is also important that hyperbaricwelds are rigorously tested to be certain of their integrity.

After the weld is completed it is coated for protection, usually with a tape wrap whichis heat shrunk around the pipe.

TIE-INS 311

OTHER WELD PREPARATION

MetrologyFabricate and lower pup

Pup piece

The diver then exits the chamber and conducts metrology on the other end of thespool to be welded. A small pup-piece is then fabricated to the required size andlowered to the seabed.

RELOCATION OF CHAMBER

Temporary plugs fitted in pipesChamber gas filledPipe ends re-cut for welding

The chamber is flooded again with seawater, dismantled and relocated to the otherweld area. As before, plugs are fitted, the chamber flooded and the pipe ends re-cutfor welding.


FINAL WELDS

WeldingNDTCoating

The pup is welded into position, the welds are tested and the weld coating appliedcompleting the hyperbaric stage of the tie-in.

CLEAN UP AND PRECOMMISSION

Remove equipmentPig line to remove plugsHydrotest

After removal of the hyperbaric equipment, the line can be pigged to remove theplugs. Finally a hydrotest should be conducted to ensure the integrity of the overalltie-in.

TIE-INS 313

PROS AND CONS OF HYPERBARIC WELD

PROTie-in the same as rest of pipelinePerceived greater reliability

CONDepth limitation

Manual metal arc approx. 200m (656 ft)TIG in excess of diving depths

Diving time 2-4 weeks£3 to 5 million ($4.5 to 7.5 million)

A hyperbaric weld will generally take considerably longer than is required to makeup a mechanical connection. There are water depth limitations for hyperbaric welds,although welds are generally feasible within diver depths.

HYPERBARIC WELDING - SUMMARY

Install spoolInstall habitatPrepare pipe endsAlign pipesWeld pipeTest weldCoat jointSystem test and protect

Any questions ?

The main activities undertaken when conducting a hyperbaric weld for a tie-in areshown above. The hyperbaric welding method requires the installation of a habitat inwhich the diver can perform the welding and testing in a controlled and dryenvironment.


DIVERLESS TIE-INS

DEFLECT-TO-CONNECT AND VERTICAL STAB

Verticalstab loweredinto place

Deflect-to-connectrigid pipeline with buoyancy and chains

Pull-in wireSet down ofrigid pipe end

within tolerance

Risers on fixed platform

Deflect-to-connect can be used with the ends of rigid pipelines. Even large diametersup to 914 mm (36in) have been installed in this way.

Pipelay initiation must ensure that the end sits within a rigid target box. The weightof the pipe is minimised using buoys and chains. A wire pulls the end of pipe over tothe riser. The ends are finally connected using collets or clamps.

Care must be exercised when recovering the buoyancy modules, since without theweight of the pipe, they surface rapidly.

Vertical stab-in risers can be lowered down using barge or platform cranes. An ROVhelps guide the spool onto the ends of the riser and pipeline.

TIE-INS 315

FlangeSonsub ‘BRUTUS’Stolt ‘MATIS’

ClampINTEC ‘DMaC’Big Inch ‘RAC’Kvaerner ‘BBRTS’FMC ‘UTIS’

ColletOilstates ‘Collet connector’

DIVERLESS TIE-IN SYSTEMS

Bolted flange

Clamp

Collet

The three main connector types used by remote tie-in systems are bolted flange,clamp and collet.

The bolted flange connector requires a number of bolts to be inserted through boltholes located around the flange diameter. Nuts are then threaded over the bolts, thebolts are tensioned and the nuts tightened to fix the flanges together.

Clamp connectors require less nuts and bolts to be tightened, usually only two orfour. A connector hub is attached to the end of each pipe. Over these hubs are fittedtwo semi-circular clamps which are connected by the bolts. When tightening thebolts, recesses in the clamps cause the perpendicular forces of bolt tensioning to betranslated to axial force in the pipes which holds the two hubs together.

Collet connectors use a series of collets or ‘fingers’ positioned around thecircumference of a connecting hub on the pipe end being connected. A sleeve ispushed over the collets which forces them to pivot and lock behind a rim on theconnecting hub which holds it in position.

The slide above provides a summary of the diverless connection systems available forvarious types of tie-in. The following slides will discuss in more detail diverlesssystems.


PRINCIPLES OF DIVERLESS TIE-IN

Remote connection of two flanges or hubsRequire aligning

Initial alignmentTo bring flanges/hubstogether

Final alignmentTo make up seal

UtiliseROVs - to lift and carryCables and winches - to drag

Especially for larger forces at second end

Wellheador manifold

ROV

Support vessel

Flexible

Divers can only operate in limited water depths to a maximum of around 200 m (656ft). However, fields are being developed at greater depths which has led to a need forremote systems that can conduct tie-ins without diver assistance. A diverless tie-in isthen the connection of a hub on a newly installed flowline, spool or jumper to anexisting hub or flange located on the seabed. The existing hub may be fitted on awellhead or manifold or maybe at the end of a pre-laid pipeline. The main problemfaced when conducting a diverless tie-in is the remote alignment of the two hubs.

Most diverless systems separate the alignment of the hub into two separate tasks;initial alignment and final alignment. The initial alignment requires that the hubs arebrought into close enough proximity for equipment to perform their final alignment.Final alignment requires the hubs are precisely aligned so that the seals are engagedand the hub or flange can be permanently made-up. Initial alignment generallyrequires the ability to apply large loads to align the axes of the hubs or flanges.Loads may be generated by bending pipes to align the pipe axes. Final alignmentthen will generally require the hubs or flanges only be moved axially.

ROVs are an essential component in the systems used to conduct diverless tie-ins.They can be used to monitor other equipment on the seabed, carry tooling or used toperform the initial alignment themselves. Winches and cables are also used toperform the initial alignment by attaching them to the various components beingmanoeuvred on the seabed. Additional force is often needed for the second end ofrigid spools to bring flanges into alignment.

TIE-INS 317

BRUTUS FLANGE CONNECTION SYSTEM

Sonsub BRUTUSModular pipeline pull-in, alignment and connection

Flexible and rigid pipe connectionConnector independent

Bolted flange provenHorizontal tie-inUp to 609.6 mm (24 in) diameterDepths to 3000 m (9843 ft)

For deepwater tie-ins, Sonsub Ltd have developed the BRUTUS modular pipelinepull-in, alignment and connection system known as BRUTUS. Rigid pipe connectionwith bolted flanges was the preferred connection method. However, the fullydeveloped system has been adapted to give the option of making tie-ins withflexibles and the use of mechanical connectors.

The deign philosophy for the BRUTUS tie-in system was that all tools would haveneutral weight in water and could be installed and operated by a standard work classROV. Also the BRUTUS system would not require a termination skid (or tie-inporch) which is contrast to the MATIS system. The principal connector type wasbolted flanges, but the system has since been modified to allow the implementation ofother connector types such as clamp, collet and MORGRIP.

The final system is capable of making tie-ins of bolted flange connectors on rigidpipelines with diameters up to 609.9 mm (24 in) in water depths up to 3000 m (9843ft).


THE BRUTUS SYSTEM

Axial force and alignment tool (AFAT) Reaction Force Tool (RFT)

Docking probes

Spoolflange

Docking probe receptacles

thrustcollar

The Axial Force and Alignment Tool (AFAT) is the active alignment tool which useshydraulic cylinders to enable the tool to pull a newly installed spool or connectingpipe towards the existing pipe and align the flanges. For pull-in, two longitudinalcolumns with docking probes are located on the port and starboard sides of the tool.Hydraulic cylinders on the AFAT extend these probes to locate and lock intoreceptacles on the Reaction Force Tool (RFT).

Two clamps on the AFAT at the front and rear grip the spool or pipe. Each clampcan slide horizontally and vertically to deflect the pipe and enable the final flangealignment. The pull-in and alignment forces and speeds are controlled accuratelyusing pressure relief valves, flow control valves, pressure gauges and pressuretransducers to give a digital readouts and control from the topside.

The RFT is a passive tool that provides the reaction forces for the pull-in andalignment forces generated by the AFAT. The philosophy of the RFT is that itminimises the need for permanently installed subsea equipment such as pipe endtermination sleds or other tie-in porch structures. At the front of the RFT is a thrustcollar. This collar is clamped around the pipe and is flush against the rear of thepipeline flange. The collar is designed to transmit the axial forces generated duringpull-in to the rear of the pipe flange.

The AFAT and the RFT are both free flooding and neutrally buoyant. They are alsolowered to and recovered from the seabed on deployment frames. On top of bothtools is an interface which allows mechanical docking of an ROV, hydraulic hot stabso the ROV can input hydraulic power to the cylinders and electrical sockets to allowthe ROV to input electrical power for the remote operation of the hydraulic cylindervalves, cameras, lights and sensors.

TIE-INS 319

THE BRUTUS SYSTEM

Bolt Insertion andTensioning Tool (BITT) Nut Magazine (NM)

The Bolt Insertion and Tensioning Tool (BITT) and the Nut Magazine (NM) make upthe flange connection tooling. As with the AFAT and RFT, both are neutrallybuoyant and are lowered and recovered from the seabed on deployment frames. Theyboth have an ROV interface structure on the top so that they can be picked up by theROV and the ROV can provide power and communications.

The BITT is constructed from an aluminium frame which is designed with a housingthat hinges to open and close around the pipe diameter. The BITT contains a boltmagazine and a tensioner magazine. The bolt magazine consists of studs with pre-installed nuts contained in geared sockets which are driven by motors that rotate thenuts. The tensioner magazine contains bolt tensioners that can tension the bolts oncethey are located in the bolt holes and nuts have been threaded on from the NM. Turncounters are provided to record the rotation of the nuts and stroke and pressure metersare used to monitor the stud tensioning. Also fitted to the BITT is the seal insertiontooling which consists of a seal holder fitted on a motor driven lead-screw whichlowers the seal ring into the required position.

The NM is of a similar construction as the BITT and contains a split magazine whichlocates around the pipe diameter. The magazine contains nuts within geared socketswhich spin the nuts onto the bolts once the bolts have been inserted through theflange bolt holes by the BITT.

The alignment of the BITT bolts and the NM nuts is done with four alignment pins onthe BITT. These pins extend from the BITT into receptacles on the NM. The nut,bolt and tensioner magazines along with the swivel neck flange can then rotate sothey align with the bolt holes on the weld neck flange.


DEPLOY REACTION FORCE TOOL

RFT flown to positionClamped onto subsea structure export pipe

RFT

ROV

Spool

Structure flange

Subseastructure

The following slides show the tie-in procedure for connecting a rigid spool to asubsea structure and an export pipeline. Initially the spool is deployed to the site andthe spool and pipeline termination end are raised to the required height using a seriesof H-frames. The AFAT and RFT are then lowered to the seabed on deploymentframes. An ROV docks with the RFT and transports it to the export pipe on thesubsea structure. The RFT is lowered onto the export pipe behind the flange so thethrust collar is flush against the rear of the flange. The ROV then activates thehydraulic clamps on the RFT to fix the RFT to the subsea structure export pipe. TheROV then undocks from the RFT and flies back to the deployment frame to pick upthe AFAT.

TIE-INS 321


close proximity. This deflection of the spool is the pull-in stage of the connectionprocedure. Then the ROV activates the cylinders which move the clamps on theAFAT either horizontally or vertically to perform the final axial alignment of the twoflanges.

DEPLOY NUT MAGAZINE

NM flown to positionClamped onto subsea structure export pipe

Flanges aligned

NM

The NM and the BITT are then lowered to the seabed on deployment frames. TheROV disconnects from the AFAT and connects to the NM, then transporting it tobehind the flange of the subsea structure but infront of the RFT. The hydrauliccylinders on the NM are activated to close the nut magazine around the pipediameter.

TIE-INS 323

BOLT INSERTION & TENSIONING TOOL

BITT flown to positionClamped onto spool

BITT

The ROV disconnects from the NM, flies to the BITT, picks it up and transports it tothe spool piece. The BITT is lowered onto the spool pipe behind the flange andinfront of the AFAT. Again hydraulic cylinders are activated that close the split boltand tensioning magazines around the pipe diameter of the spool piece.

MAKEUP BOLTED FLANGE

Bolts pushed into bolt holes & tensionedNuts threaded on and tightened

Nuts

Bolts

Bolt magazinemoves forward

The BITT aligns the bolts with the bolt holes on the swivel neck flange on the spooland inserts them through the holes. The seal is then inserted into the recess in theflange. Alignment pins extend from the BITT to the NM locking the two together for


rotations about the pipe axis. The magazines and swivel neck flange are then rotatedto align with the bolt holes on the fixed flange. The BITT activates cylinders whichpush the bolts through the bolt holes of the fixed flange and into the NM. The nutson the NM are spun down the thread of the bolts until they are flush against theflange. Tensioner jacks and nut motors on the BITT are activated which close theflange gap. The nuts on the BITT are then rotated to be flush with the spool flangewhile the bolts are under tension. The tension is released and the flange connection iscomplete.

The ROV then manoeuvres the tools for the tie-in of the spool to the export pipelineand the same procedure is repeated. After the flange connection is complete the ROVmoves all tools back to their respective deployment frame and the frames and ROVare recovered to the surface. The tie-in is then tested.

BRUTUS VIDEO

The video shows the connection procedure for the BRUTUS system. It gives anoverview of the system and a breakdown of the individual tools; the AFAT, RFT,NM and BITT. An animation shows the sequence for the tie-in of an export pipelineto a subsea structure using a rigid spool with bolted flange connectors. Also shown inthe video is the land trial at Sonsub for tie-ins on the Norne-Heidrun project, showingthe connection procedure with inserts of footage from an actual tie-in on the project.

TIE-INS 325

BRUTUS CASE STUDY

Statoil Norne-Heidrun projectWinter 20007 horizontal tie-ins400 m (1312 ft) depth406.4 mm (16 in) diameter pipeFlexible and rigid pipeTaper-Lok flanges

The BRUTUS system has been successfully used on the Statoil Norne-Heidrunproject for 7 horizontal tie-ins of 406.4 mm (16 in) diameter pipe in a water depth of400 m (1312 ft). These tie-ins included:

• One flexible riser to export riser base tie-in• One rigid line to export riser base tie-in• Two rigid line to spool piece tie-ins• Three spool piece to manifold template tie-ins.

For these tie-ins, Taper-Lok flanges were used to allow 100% of the studs to betensioned at once which reduced the operational time required by the system tocomplete the tie-ins.


THE DMaC SYSTEM

DMaC components

Dockingporches

Flexiblejumper

Pullhead

ROV

Pull-in tool

Courtesyof INTEC

ModularManifold

Clampconnectors

Dockingprobes

The DMaC system has three main components; a pull-in tool, a pullhead, dockingporches and clamp connectors. The Pull-In Tool (PIT) is an ROV controlled andtransported system which contains two cable winches, docking probes and cableanchors. It also has a facility enabling it to connect to a pullhead on the flowlinebeing connected. The ROV inputs electrical and hydraulic power into the PIT andthe PIT is neutrally buoyant to allow the ROV to transport it about the tie-in site.

A pullhead is fitted to the flowline or umbilical end prior to installation on the seabed.The pullhead contains an outboard connecting hub, seal plate, gaskets and aprotection cover. The upper surface of the Pullhead is an interface which enablesconnection to the PIT, the lower surface is a skid that can be dragged across theseabed. The internal pipe configuration through which product will flow is designedto allow pigging.

On the subsea structure, to which the tie-in is being made (e.g. christmas tree ormanifold), a lightweight pull-in porch facility is fitted prior to installation. The porchfacility allows the PIT to lock into it with two receptacles for the docking probes.The receptacles can be shared to allow for a more compact size of porch facility.These receptacles interface with the PIT and provide the anchor point for the cablewinches. Also on the subsea structure is a pre-installed clamp assembly which fixesthe connecting hub located on the subsea structure to the connector hub on the newflowline.

The DMaC tie-in system has been used extensively in the North Sea and was thediverless connection method of choice for BP during the development of theirSchiehallion and Foinaven fields. These developments required the construction offive DMaC tooling systems and they were used to make the tie-ins of all the infieldflowlines and umbilicals. The water depth of these fields ranges from 400 to 550 m(1312 to 1804 ft). At present over 600 DMaC diverless tie-ins have been completedand the average connection time has been reduced to 7 hours (deck-to-deck). Thistime being the duration between deploying the PIT and its recovery back on thevessel deck.

TIE-INS 327

DEPLOY EQUIPMENT

Equipment lowered to seabedROV transports PIT to manifold

Subsea manifoldPIT

ROV

Docking porches

Clamp

Docking probe

The following slides detail the tie-in of an export flexible flowline to a subseamanifold using the DMaC tie-in system. The DMaC clamp connector and pull-inporches will have been fitted to the subsea manifold prior to the installation of themanifold. There will also be a DMaC pullhead fitted to the end of the flexibleflowline before it is lowered to the seabed.

The DMaC Pull-In Tool (PIT) is lowered to the seabed on a deployment frame. AnROV is deployed and connected to the interface on the PIT. The PIT is then flownfrom the deployment frame towards the subsea manifold. The ROV manoeuvres thePIT so that the docking probes on the PIT are inserted into the docking porchesinstalled on the manifold. Once in position cable anchors connected to the PIT areanchored into the docking porches on the subsea manifold.


RELEASE WINCH CABLE FROM PIT

PIT cable winches releasedROV transports PIT back to Pullhead

Export flowlinePullhead

cables

ROV

PIT

The cable winches on the PIT are set to ‘freewheel’ and the ROV releases the cableanchors on the docking probes from the PIT. The ROV manoeuvres the PIT back tothe Pullhead. During this operation, the cable is fed from the PIT.

PULL-IN

PIT connects to PullheadWinch retracts to pull-in flowline

Pullhead connected to PIT

Flowlineconnector

hub

The PIT is lowered over the Pullhead and they are locked together. The ROV thenstarts to reel in the winches on the PIT which draws in the cable and causes thepullhead to be dragged across the seabed towards the fixed manifold structure. Thisis then the ‘Pull-in’ phase of the tie-in completed.

TIE-INS 329

HUB ALIGNMENT

PIT probes re-located in docking porchesFinal hub alignment from clamp make-up

PIT

Pullhead skid

Flowline hub located in clamp

Clamp

Docking porch

As the free cable length is wound in, the docking probes on the PIT become re-located in the docking porches of the manifold. When the cable is fully retracted, thedesign of the system is such that the flowline connector hub is located 400 mm awayfrom the inboard hub to allow for final inspection. The hubs are brought together bythe stroking of the docking probes. Final alignment and sealing of the hub thencomes from clamp-make up, which is performed by tooling on the ROV. The ROVthen disconnects the PIT and return it to the surface for retrieval. The tie-in is thencomplete.


DIVERLESS COLLET CONNECTOR

Oilstates HydroTechDiverless collet connectors

Rigid and flexible spools and jumpersHorizontal and vertical tie-insROV operableUp to 1067 mm (42 in)diameter pipeDeepest diverless tie-in

1615 m (5300 ft)

ROV hot stabports

External and retrievablehydraulic cylinders

Diverless Collet

The Oilstates HydroTech diverless collet connectors have been developed foroperation by ROVs in diverless environments. These connectors are commonly usedfor final hook up of subsea production systems. Hard or flexible pipe jumpersbetween pipeline end manifolds and other manifolds or production trees. Also thecollet connectors have been used for diverless repair of deepwater flowlines.

The collet connector design has been adapted by Oilstates to give the followingvariations:

• Horizontal stab with retrievable actuator• Vertical stab with retrievable actuator• Vertical stab with integral actuator• Vertical stab and hang-over for first end make-up and pipe layaway.

To date the HydroTech diverless collet systems have been used in 140 connections inwaters around the world. They also currently hold the world depth record for adiverless pipe connection of 1615 m (5300 ft).

TIE-INS 331

COLLET CONNECTOR ASSEMBLY

Collet connectorprepared for receiptof connecting hub

Collets open Connector

hub

Sealingsurface

recessed

The following slides show the connection procedure for assembly of a colletconnector. The initial step is to have the collets in the open position ready to receivethe connector hub (attached to the connecting pipeline). The sealing surface is withina recess to ensure it is not damaged during the connection process.


Connecting hub insertedinto collet jaws

Ring seal

The hub is pushed into the collet jaws to the required position. As it does so, theprofile aligns the hub.



Cylinders extendedJaws close aroundconnector hub

Collet pivot

Drive ring

Hydraulic cylindersextended

Back-up springs

The hydraulic cylinders force a drive ring up against the collets. The collets hingeabout a pivot and lock behind the hub. The force of the collets acting on the hub alsoenergises the metal ring seal and applies an axial force to the hub faces.

Springs provide a passive back-up locking force in case of failure of the cylinders thathold the drive ring in place.

DIVERLESS TIE-INS - SUMMARY

Diverless tie-in systems use three types ofconnectors

FlangeClampColletExample given of a diverless system for each type

Other systems availableUniquely designed for different operationalparameters

Any questions?

TIE-INS 333

There are three types of connector that have been utilised for diverless tie-in systems;flange, clamp and collet. Flanges are made-up with bolts whose axes are parallel tothe pipe axis. Clamps have bolts with an axis normal to the pipe axis. Collets usehinged-jaws located around the hub circumference to grip the two connector hubs andforce them together.

Unique diverless tie-in systems have been developed and are available for use witheach of these connector types.

TIE-INS - SUMMARY

You should now:Know why tie-ins are necessaryUnderstand the processes for the three mainmethods of conducting a tie-in

Diver connection of flangesHyperbaric weldingDiverless installation of rigid spools and jumpers

Know the equipment required for these tie-inmethods

Any questions?

We started by introducing the concept of a tie-in and why subsea tie-ins are anecessary activity in field development. The three main methods of conducting a tie-in are; diver connection of flanges, hyperbaric welding and diverless installation ofrigid spools and jumpers. The processes involved, the equipment and the advantagesand disadvantages of these methods was presented. Other methods of tie-in arecovered in other modules presented in this course.

offshore pipeline construction volume one

Documents