Pipeline Repair Equipement

Pipeline & Gas Journal/April 2001/pipelineandgasjournalonline.com

hen Sonsub Inc., Houston, agreed to developequipment to meet deepwater subsea pipelinerepair needs for a consortium consisting of ShellDeepwater Producing Inc. (SDPI), EquilonEnterprise and Coral Gas Transmission, theyknew they faced some challenges. Even thoughSonsub had designed, built and tested a complete

Diverless Sealine Repair System (DSRS) for the 667-mile Trans-Mediterranean (Transmed) pipeline a number of years ago, Shell’srequest required customized solutions.

For example, the following were provided by Shell as require-ments for performing deepwater subsea pipeline repairs in2,000(+) meter water depths:

1. Locate the damaged area and identify the pipe cut locations.Depending on the type of pipeline damage, this may includecircumferentially measuring the pipeline diameter to verifythe area to be cut is concentric.

2. Lift the pipeline off the seabed using H-frames allowing fullaccess around the pipeline.

3. Cut the pipeline as required and pull the damagedpipe aside.

4. Remove concrete and FBE coating (if applicable) from thetwo free ends of the pipeline to provide a clean smooth areafor the Pipeline Termination Assembly (PTA) grip & seal typeconnector to grip over the outside of the pipeline ends.

5. Perform an end preparation operation on the end of thepipeline to cleanup any burrs that may be left from cuttingthe pipe.

6. Install the PTAs over the two pipeline ends.

7. Perform metrology, fabricate and install a “U” Jumper or deep“M” shaped jumper as is typically performed on offshore con-struction projects.

Initially, Shell believed that the best approach would be to per-form as much of the deepwater pipeline repair work aboard a sur-face vessel. This meant the pipe would be cut subsea, the endsrecovered and transported to the surface vessel and then theprocess of neatly cutting the pipe ends, coating removals and thefitting of PTAs would be performed on the vessel. The PTAs, con-figured with elbows and vertical facing collet connectors, wouldthen allow the final part of the work to be performed using a “U”Jumper or deep “M” shaped jumper.

While this idea was being developed, Shell realized thatin some cases a bottom repair would be necessary, as apipeline crossing may not permit a pipeline section to beremoved and returned to the surface. Furthermore, as thetools began to develop, it became apparent that this couldbe beneficial to their base repair scenario since it meantsmaller vessels reduced risks associated with recoveringpipe ends from the seabed and later ensuring the PTAs landwith the correct orientation when setting the pipe backdown. Additional tasks of measuring the pipe diameter, cut-ting the pipeline, preparing the ends and then removing therespective coatings required ROV intervention, therefore,Sonsub’s extensive experience in the design and delivery ofROV operated tooling systems was required.

Deepwater Repair Solution

Pipeline Repair Equipment For2,000(+) Meter Water Depths

By David S. Cox, Sonsub Inc., Houston, TX

Caliper Tool

Concrete Removal Tool

Dramond Wire Cutter


Diamond Wire Cutting Module

To assist in this deepwater endeavor,Sonsub either modified current tooling orestablished new tooling technology. Oneexample of where Sonsub had a headstart was to borrow from the previouslybuilt and tested Sonsub Diamond WireCutting Module (DWCM).

The DWCM uses a cutting elementthat is a special diamond-coated wireformed into a closed loop. The wire runsin a cutting arm that is made up of anarc-shaped tubular frame that houses ahigh-speed traction pulley with its motoron its upper part. This pulley, plus thetwo free pulleys at the two ends of theframe, serves as a support for the dia-mond wire. One of the two free pulleysis mounted on a hydraulic actuatedcylinder that is used to provide constanttension on the wire.

The cutting arm is joined to aclamping module that consists of a setof hydraulic clamp arms that keep themachine secure to the pipe during thecut. It is built from a rigid structure,supporting four moving arms operatedby hydraulic cylinders. The upperstructure and the mobile arms are sup-plied with reduction kits profiledaccording to the diameter of the pipeto be clamped.

Prior to its use, extensive testing wasneeded. This included cutting the testpipe under significant bending loads aswell as cutting concrete weight coatedpipes and pipe-in-pipe sections. Theoperation had to be performed efficient-ly and consistently without user inter-vention. Ultimately, the tool proved tooffer excellent performance when cut-ting through 14-inch pipe with a 1½-inch thick weight coat in less than 40minutes during testing.

A new DWCM was then built for Shellbased on the proven design, but modifiedto operate on a wide range of pipe sizesfrom 8 to 36 inches. It was also configuredto work on vertical members (such as ris-ers); if ever required.

Concrete & FBE Removal

Once the pipe is cut using theDWCM, the removal of concrete weightcoat and Fusion Bonded Epoxy (FBE)may be required depending upon waterdepth of the pipeline. The Concrete andFBE Removal tool (CFRT) representedthe most significant set of challenges ofall the pipeline repair equipment. Thefirst challenge concerned removingconcrete up to 4½ inches thick as wellas removing the FBE coating withoutdamaging the pipeline. Sonsub and oth-ers had developed a variety of toolsover the past few years utilizing high-pressure water jets or similar abrasivetechniques. However, these techniquesare inefficient and often require longhoses from the surface to provide suffi-

cient power at the nozzles to performthe removal work. It seemed that amechanical means of performing theremoval operation would be more ben-eficial as long as it could perform thework without the potential for damag-ing the pipeline.

For assistance with this challenge,Sonsub called on Comax L.C., a Utah-based company specializing in themechanical removal of surface coatings.Together with Sonsub, a series of testswere performed to prove that themechanical techniques were feasible.Consisting of two main components,the first comprised a series of diamonddisk blades, similar to those ordinarilyused for cutting concrete, which wereplaced adjacent to each other with aspacer in between to hold the blades ¼-inch apart. When cut into the weightcoat, it left a series of grooves in theconcrete that caused the remaining con-crete to fall off the pipe when impact-ed by the tool head.

The second component was a cylin-drical brush arrangement where each ofthe large “bristles” had a tungsten car-bide tip (diamond tips were used on thefinal tool). The brush is strong enoughto remove concrete (if any remains afterthe diamond disk head has been used)but will also efficiently remove anyremaining FBE coating from the pipe.The brush leaves a clean finish thatremoves no more than 0.01-inch of thesteel surface from the pipe, somewhatsimilar to that of grit blasting.

Having proven the concept wouldwork, Sonsub set about creating a fullsized system to utilize on pipe sizesfrom 12 to 36-inches with up to 4½-inch of steel reinforced concreteweight coating (i.e. max OD of 45inches). The system had to provide aconcrete removal rate of 1,250in3/hour as well as remove up to 6feet of weight coat from each of thetwo free pipe ends. This requires over50 hp of hydraulic flow from the ROVto sustain the rate of removal. Giventhat the work may be done with a 75horsepower ROV of opportunity,careful consideration was given onhow this could be achieved. As withall of the tools, the operations wereall to be performed without recoveryof the ROV or tools until the job iscompleted.

In order to meet all of Shell’s strin-gent requirements, it was determinedthat existing Sonsub designs could notbe simply adapted to hold the cuttingheads. Due to the reasonably largeweight of the two cutting heads andthe low rotation speeds required,Sonsub devised a new system for rotat-ing the tool heads. This new systemwas lower in complexity than previoustools, but still maintained the failsafeaspect of being able to recover the sys-tem no matter what malfunctionoccurred. This cutting head simply

uses a rope, wrapped around a motor-ized capstan with a series of sheavesand rope guides, to rotate a “C” shapedplate up to 400º around the pipeline.The two cutting heads were designedas independent systems that could bemounted at different circumferentialpositions on the “C” plate, which thenallows for a simple adjustment for dif-ferent pipe sizes.

The body of the tool, while lookingquite different, was functionally thesame as that for the DWCM. It providesfour hydraulically operated clamp armsto hold the tool onto the pipeline whilethe concrete and FBE removal operationis taking place. This frame, however,requires an additional subsea system,which consists of a slide arrangementthat allows the front tooling assembly tomove up to three feet along the pipelinewithout the entire tool having to be relo-cated along the pipeline after each passaround the pipe.

Once the tool was assembled, theprocess of optimizing its operation wasa time consuming task. As the tech-nique was new, establishing the bestparameters was not always straightfor-ward. On a couple of occasions some“improvements” to such things as rigid-ity of the rotate head actually turnedout to be backward steps as we learnedthe most efficient means for breakingoff the concrete after the diamond diskhead had performed its cut. By opti-mally removing concrete with the dia-mond disk head, we could then reducethe amount of work that the “brush”head had to do, leaving it for theremoval of the FBE only.

Pipe End Preparation

After the concrete and FBE has beenremoved from the pipe, the end mustbe cleaned up to ensure that the con-nector seals, or future pigs in thepipeline, cannot be damaged by burrsleft over from the DWCM. Sonsub ini-tially proposed a tool that had beendeveloped for its own DSRS. This toolincorporated a central mandrel thatcentered the tool in the pipeline. Whilesuitable for providing high quality sur-face finishes, Shell really only requireda tool that could cleanup the end of thepipe, rather than provide a machinefinish. Additionally, the tool did notlend itself well to working on all sizepipelines (8- to 36-inch). This waswhen Sonsub conceived an EndPreparation Tool (EPT) that would be a“one-size-fits-all” tool. It’s simplicityand the low cost meant that it offered aperfect solution for Shell.

The EPT is operated via two hot stabsfrom the ROV IHPU and is positionedonto the end of the pipe by the ROVmanipulator. As with all of the tools dis-cussed in this article, the system isdesigned to be deployed to the sea floorin a single, combined ROV tool deploy-


ment frame, and then moved into placeand operated by a work class ROV ofopportunity.

The concept of the tool is that, ratherthan using a central mandrel to hold thetool in place, the tool grips with three (3)rollers on the wall of the pipe. Two of therollers are on the outside of the pipe, withthe third on the inside. Rotation aroundthe pipe is accomplished using ahydraulic motor connected to the two topdrive rollers.

To install the tool onto the pipe ahydraulic cylinder is operated to swingthe bottom roller open. This allowseasy access for the ROV manipulator toinstall the tool onto the pipe edge. Thecutting head is rotated at high speed bya second hydraulic motor and consistsof a grinding wheel head that is mount-ed on two sliding rods that allow a lin-ear motion towards and away from thepipe end. The cutting head achievesthe end preparation in just one passaround the pipe by utilizing the factthat the grinding wheel head wears toconform to the profile of the pipe endas it cuts. This allows both the insideand outside corners of the pipe to becleaned simultaneously. The EPT cancomplete a 20-inch pipeline end prepa-ration in approximately three minutes,

and is so small that it does not requirebuoyancy.

Other ToolsSonsub provided a number of other

tools and equipment for the pipelinerepair spread. One example is an IHPUpackage, capable of supplying 50 GPM at2,000 psi that could mate to any workclass ROV of opportunity. This tool pro-vided the API 17H hot stabs as well as aSonsub design high flow hot stab for theoperation of all of the tools. Anotherexample is a caliper tool capable ofmeasuring pipe diameters up to 36 incheswith a measurement accuracy of betterthan 1/8-inch on the diameter.

The FutureThe future of pipeline repair holds

further possibilities for improvementand cost optimizations. One of the pos-sibilities is the use of Sonsub’s Brutussystem, a horizontal, rigid spool con-nection system capable of economicallyconnecting rigid spools to flowlines orsubsea structures. Although normallyused in construction projects (such asthe recently completed Norne &Heidrun development in the North Sea),it could easily be used for pipelinerepairs. Rather than connecting PTAs to

the pipe ends, as Shell has prepared for,the connection could be performedwithout any subsea structure whatsoev-er. Using grip and seal connectors (orsimilar) welded to a horizontal spoolpiece, Brutus can directly connect thespool straight to the cut ends of thepipeline. This means very little hard-ware is required to be stored, a reduc-tion in the number of connectors in therepair, as well as the added benefits ofa horizontal connection which canavoid hydrate or wax plugs that verticaljumpers are more prone to cause. P&GJ

David S. Cox joined Sonsub more thanten years ago. Originally in Australia(with over 2 years as EngineeringManager for the Asia Pacific Region), healso worked in Norway, Aberdeen,Scotland and spent a year in France. NowManager of Intervention Systems atSonsub’s Houston office, Cox has extensiveexperience in the design and operation ofremote intervention systems. He earned anhonors degree in Mechanical Engineeringfrom the University of Newcastle, Aus-tralia, and a postgraduate Diploma ofComputer Science from Curtin University,Australia. Cox also holds a Fitter & TurnerCraftsman Certificate.

Deepwater Repair Solution

Pipeline Repair Equipement

Documents

Transcript of Pipeline Repair Equipement