CA1213332A - Welding and laying pipelines - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A pipe-welding assembly is provided in which single-pass welding of one pipe length to another is accomplished by gas lasers mounted to rotate around the axis of the pipes to weld the pipe ends together in the gap between two axially aligned spaced pipe clamps. Weld-testing units are similarly rotated around the pipe axis. The pipe-welding assembly is mounted on a gyroscopically-stabilised platform, which can be located on a pipe-laying land vehicle, or on a pipe-laying ship for laying pipe lines on the ocean bed. If the ship is equipped with a pipe feed tower, with the pipe-welding assembly positioned at the base of the tower and a drawbridge provided for elevating successive pipe lengths angularly into the tower, pipe laying can be performed in the "J" configura-tion. If the tower is mounted so that it can be inclined angularly into a position approaching the horizontal, and the pipe-welding assembly can be similarly rotated on its stablised platform, pipe-laying can be performed in the "S" configuration.

Description

3~32 This invention relates to the ~elding and laying of pipelines both on-shore ,nd a-t sea.
Convelltional iechniques in off-shore pipe-laying currently adopt the S curve corlfig-lration in ~.~hich the pil)e leaves the laying vessel ubstantially horizontally.
h'ith this confiyuration it is technically feasible to lay up to 30 diarneter pipe-lines in ~aters to a del,th of approximately lnO0 rretres i.e. 3 300 feet but -the problerlls increase as the depth increases. The maxirnum depth achieved we believe has been 1025 feet of ~ater.
Ilajor practical problerns arise at greater depths.
The stinger supporting the pipe as it leaves the vessel must be longer stronger and nlore buoyant. The necessary horizontal force to prevent pipe bucklillg increases and it bc-comes more difficult to create that horizontal force because of the reqllirellents on dynamic positionil-lg of the pipe-laying vessel. It is also r,ecessary to use stronger tensioning machines. ~ore specifically the suspended pipe in the S configuration has a dist.inct sag and overbend. To avoid buc~ling of the pipe as the pipe leaves the ranp and to ~c~duce tensioning forces the use of a stinger is indispensible even in shallo~ ater depths. The technical limits of this rl-lethod for deep water pipe-laying are deterrnined by the stinger size and the necessary horizontal compollellt of force ~Ihich must be .~

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generated by tfle propulsion system and transmitted to the pipe by a tensioner.
lhe technique of the J nlethod in ~^hich the pipe leaves the laying vessel substantially vertically can be used for laying pipe in deep water. I~ith this system a 34 diameter pipe can be laid in 1200 metres (3950 feet) of water and a 24 pipe can be laid in 3000 metres (9850 feet) of water. In such instances a dynamically positioned laying vessel can be used since only very low hori~ontal tensions are involved. Sub-surface pipe flotation is unnecessary and the equipment is not so sensitive to sea conditions. The J pipe-laying method thereFore has considerable advantages over the conventional S method that is currently used~ and it is an obJect of the present invention to rerlder it economically feasible.
According to one aspect o~ the invention there is provided a self-contained welding assembly in ~!hich single-pass girth welding of pipes is perfornled by coherent beam energy and particularly by one or more high power C02 gas lasers the ~hole assembly being mounted on a gyro-scopically-stabilised platform.
~ ccording to another aspect the invention provides a pipe-~lelding assembly mounted on a gyroscopically-stabilised platform a pipe feed tower also moullted on the platform to support and feed the pipe down the to~er for 13~3;~ ~

~elding and laying and means for inclining the to~er about a pivotal mourlt-ing at its base bet~een a vertical or near vertical position in wnich J configu1^ation pipe-laying can be performed and a position approaching the horizontal in which S configuration pipe-laying can be perforrlled.
A dra~bridge may be provided that lies substantially hori20ntally to recei~e the pipe lengths one at a tirne and can be raised about an end pivot on the stabilisecl platform to lift each pipe length into the pipe feed tower.
l~igh po~er C02 lasers provide the rapid ~/elding capability needed to rnake this variable mode pipe-laying technique economically feasible. I!elds ~ith ~all thicknesses up to 17/19 mm. on 30 pipe have been undertaken and have rnet the internatiollal API Standard 1104 a complete girth ~eld be;ng made in a single pass at one station.
In the preferred arrangenlent the ~elding lasers are rnounted to rotate around the pipe joint and non-destructive ~eld-testing probes can also be mounted on the same being rotating assembly the ~elds/made and tested in one pass under computer control ~ith substantially instantaneous read-out of the weld quality.
To enable the ~elding assembly to ~eld pipes passing througll vertically hol^izontally or at any intermediate inclination there is preferably a ~eld table car~ying the ~elding equipnlent ~hich is mounted on the stabilised .~

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- platforln -ror rotation through 9G about a hori,orltal axis.
Such a ~eldir,g assemt)ly can be ~ ployed nCJt Ollly on a sc-a-gGing v(ssel arrcr,ged for pipe-laying in b()~i~ the S and J configurations but also on a yessel laying pipe only in tl-,e S configllraticln or only in the J
configuration. Ful-tllerr)ore by mountillg the asselllbly on a land veilicle suitable for ~-Gugh terrairl ovcrlarld pipr-laying can be ca~l-ied out~
Arrangcrlerlts according to the invention will now be descriiJed in rcre detail ~ith refct~ence to tne accGml-anying drawi ngs .
In the drawings:
Figure 1 is a pictorial view o-f a pipe-laying ship according tn the invention Figure 2 is a side elevation of the ship partly broken away Figure 3 is a plan view of the ship Figure 4 is a cross-section on the line 4-4 of Figure 1 - Figure 5 is a side elevation partly in section of a pipe-welding assembly Figure 6 is a diagrammatic plan of the base of the assernbly of Figure 5 Figure 7 is a further side elevation of the pipe-welding assembly showing the base in section on the line 7-7 of Figure 6 and Figure 8 is a pictorial view of a pipe-laying land vehicle according to the invention.

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A deep water pipe-laying vessel is shown in Figures 1 to 4. The vessel is of tl~in-hull catamaran design and has an overall l ength of approximately 900 feet a beam of 160 feet and a draught of approxill;ately 30 feet. The vessel 5 has a displacement tonnage of approximately 70,noo tonnes a pipe-carrying capacity of approY~imately 25 000 tonnes and a cruising speed of approximately 20-24 knots.
The ship s deck area is divided into pipe-prepara-tion regions 11 and a pipe-1aying region 12. In the pipe-10 preparation regions pipes each approximately 40 ft inlength withdrcwn from a pipe storage hold 13 are elevated mechanically in succession by an elevator 14 to a transfer area 20 through which they are delivered by a walking beam station conveyor 16 to a pipe end preparation/15 where both ends 15 of each pipe are machined true. Each pipe is then fed from the pipe end preparation station 15 across the deck by the walking beam conveyor 16 to a primary welding station 17 at which a C02 laser 18 welds four sections of pipe end to end making a total pipe length 19 of 160 20 feet the pipes being shifted endwise for the ~.elding operation on a roller conveyor by a ram 21. The four-section pipes 19 are then shifted transversely by a walking beam conveyor 22 on to a roller conveyor 23 that ccnveys each pipe length end~ise along the deck to a primary 25 testing station 24 at which X-ray testing of the welded ,.

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joints takes place. Satisfactory pipe--lengths are transferred transversely by a ~alking beam conveyor 25 to a coating station 26 at which the pipes are pro~ectively coated by a pipe-coating unit 27 and thence to a storage area 28.
S Any pipe length that fails in the X-ray testing continues endwise on the roller conveyor 23 -to a repair area 29 from where a separate roller conveyor 30 returns it after repair to the walking bearn conveyor 25 for coating.
From the storage area 28 the pipes descend -in succession down a sloping beam conveyor 31 on to a drawbridge 32 which can be raised about a for~ard end pivot for ti^ansferring the pipe to a pipe feed tower 34 wilose angle of tilt is infinitely variable about a pivot 33 from 10 to the hori20ntal up to 90 i.e. vertical. At an inclination of 10 or somewhat more pipe-laying can be undertaken in the S configuration in in-shore shallow waters using adjustable stingers 35 3~ designed to accommodate varying angles of inclination and disposed inboard in between the catamaran hulls 10 of the vessel the whole system being completely autornatic. Between vertical and 30 from the vertical pipe-laying from the tower can take place in the IJI configuration. In consequence pipe-laying can be undertaken in both deep and shallow waters with the same vessel and without the need to make expensive off-shore ties.

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The drawbridge 32 is raised and lowered by jacking legs 37 and the inclination of the tower 34 is chanoed by a duplex jacking system 38. Each pipe length arriving on the drawbridge is located endwise by a swing end stop 39 and clamped to the drawbridge by swing arlns. On rais-ing of the drawbridge to transfer the pipe to the tower 34 the pipe is received in a central vertical conveyor system 40 in the tower and its upper end is received in a pipe clamp 41 at the top o~ the tower. The drawbridge clamps are released and the end stop 39 withdrawn and the drawbridge can then be lowered to receive the next pipe length.
With the tower vertical the pipe length 19 constrained by the vertical conveyor system 40 of the tower is suspended from the pipe clamp 41 at the top of the tower directly over a self-contained automatic pipe-welding assembly 42 within the tower base. The pipe clamp 41 also con,prises a pipe loweril-lg rnechanism which then lowers the pipe 19 vertically until it is within the welding assembly 42 with its lol~er end ready to be welded to the upper end of the already completed pipeline 43. The completed pipeline 43 leaving the vessel vertically under the to~er between the catamaran hulls 10 is clamped near its upper end by a pipeline slip and hold mechanism 44 located centrally below the tower the terminal end of the thus clamped pipeline 43 lyjng within the welding assembly 42 ready to be ~elded to 0 ~ 3132 the lower end of the rext pipe length 19. The assembly 42 within the base of the tower comprises not only high power C2 gas lasers to accornplish the welding but also X-ray weld-testing equipment and a pipe coating unit for applying the final protective coating to the welded pipeline joints after the welds have been made and tested. I!hen the weld connection between the upper end of the cornpleted pipeline 43 and the lower end of the next pipe length 19 has been made the pipe clamping and lowering mechanism 41 lowers the whole pipeline 43 until the new pipeline end lies within the welding assembly 42 ready for connection to the next pipe length. The pipeline slip and hold mechanism 44 then clamps the pipeline while the clamping and lowering mechanism 41 releases the upper end of the new pipe length 19 and returns to the top of the tower ready to receive the next pipe length elevated by the drawbridge 32.
The pipe feed tower 34 drawbl^idge 32 welding assembly 42 and slip and hold mechanism 44 are supported on a cornputer-linked gyroscopically stabilised platform 45 that remains dynamically level as the vessel moves according to sea conditions up to Force 8. Therefore the tower if vertical remains vertical and the weldirlg process is unaffected by the motion of the ship. Pipe-laying is possible at a faster rate than by the techniques employed hitherto; a pipe joint can be made approximately every eleven to t~elve minutes.

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Also the vessel can be reloadcd with pipes by lighter barges coming alongsi'de the fresh pipes being lo~ cred directly into the rnain holds of the vessel ~!ithout affecting the laying progralllrlle.
Figures 5 6 and 7 sno~ the ~elding asser,lbly 42 rnounted on the platform 45. The platform 45 is dynalrlically supported from a deck ~ell by means of a ring of twenty hydraulic piston-and-cylil-ldcr units 46 serlsors 47 being provided to Inonitor the arlgular relationship of the platform and the deck A ~eld table 52 is n-io~nted on the platfGrm 45 by mearls of bearings 48 ~!hich perlnit the ~eld .able to rotate about a horizontal axis through 90 to match the inclination of the pipe feed to~er. Drive rllotors49 acting throllgh ~oim reduction yearboxes 50 rotate the ~eld table h~draulic disc bra~es 51 being provided to arrest and hold the table in any chosen arlgular position The ~eld table 52 I~as a central aperture in ~!hich is disposed a lo~er pipe clarp 53 sur~r)orted from the ~eld table by brackets 55 and operated by hydraulic c)~l irlders 54.
In axial alignment ~!ith and spaced a short distance above the lo~er pipe clamp 53 there is an ur)l'er pipe clamp 56 carried froln the ~ eld table on mounting arlllS 57 and operated by hydralilic cylinders 58. The pipe ends to be ~ elded are clamped in the upl)er and lo~ er clanlps 56 53 in such manller that the joint to be ~elded lies in the gap 59 bet~een the clarnps and the ~elding is accomplished by two 20 Kh~ C2 9aS lasers 60 diametrically opposed and mounted on the \-eld table by means of a slew ring 61 that enables thern to rotate through 180 around the pipe joint in â plane at right angles to the common axis of the clarnps 56 53. The slew ring is driven by a hydraulic motor 62 and extra support is provided for the lasers 60 by wheels 63 rullning on a track 64 on the weld table. ~.nnular guides 65 for the laser heads are provided on the pipe clamps 56 53 to ensure alignrnent of the lasers with the pipe joint weld line.
Also mollnted to rotate with the lasers 60 are two diametrically opposed ~eld testing heads 66. ~ormally the welding of a joint will be accomplished in one 180 pass;
but if the test units indicate a weld fault then another welding pass is carried out. Different si~es of pipe can be accommodated by changing the clarnping segments 68 in the pipe clamps 56 53.
To ensure true positioning of the platform during dynamic levelling three alignrnent units 69 are provided at 120 interYals around the platform each cnrlsis-ting of a bracket under the platform carrying rollers 70 that engage a part-spherical guide surface 71 supported in the deck well.
In addition the supporting piston-and-cylinder units ~6 are connected at their ends to the platform and the deck respectively by spherjcal joints. Four sc~ew-jacks 67 3;Z ~

are provided to lock the platform against movement when necessary e.g. for maintenance and in sea conditions too rough for pipe-laying.
As can be seen in Figures 2 to 4 the operations in 5 the regions 11 are carried out on a ~orking deck level 72 above the main deck 73 under cover these areas being roo-red over as at 74. On leaving the covered regions 11 to enter the region 12 which is at main deck level the pipes 19 pass through a flexible exit door 79 on to the sloping 10 beam conveyor 31.
The stingers 35 36 used ~hen laying pipe -in the S
configuration are not only adjustable to suit different to~ler and pipe inclinations but also are dynamically adjustable automatically to accommodate the motions of 15 the vessel due to sea conditions. One stinger 35 forward of amidships is pivotally mounted under the deck at its aft end as at 75 for angular movement in the vertical plane.
The bo~ stinger 36 is pivotally mounted at 76 near its ~aft end for angular rnovement in the vertical plane on a ¦20 carriage 77 that is able to travel fore and aft along the hold floor a piston cylinder unit 78 being provided for raising and lo~ering the for~lard end of the stinger relatively to the carriage 77.
Since the laser ~elding assembly 42 on its dynamically 25 stabilised platform is a self-contained unit essentially .
, 3Z ~3 the sarne assembly can be employed in other situations. Thus~
although in the example so far described the pipe-laying vessel is arranged to lay pipeline in both the S and the J' configurations -the same assembly including if desired the tower 34 and the dra~bridge 32 can be elnployed on a vessel designed only for laying pipe in the J confiyuration at great depths or a vessel designed only for laying in the S' configuration in comparatively shallow wdters. It is therefore convenient for the welding assembly on its platform to be readily demountable from the vessel so that - it can be ernployed on a different vessel e.g. a barge.
The C02 gas lasers employed are preferably of the type developed at the Culham Laboratory of the United Kingdom Atomic Energy Authority. They have essentially no optics and are brought close to the work to be welded so that there is no significant beam attenuation.
The same welding assembly 42 can indeed also be used in the laying of pipelines on shore. Figure 8 shows a vehicle for laying pipeline overland in the S configuration for which purpose the weld table 52 is rotated relatively to the platform 45 through 90 from the position shown in Figures 5 to 7 so as to be able to rnake welded joints in pipe passing through the welding assembly horizontally. The pipe-laying yehicle is essentially a large flat truck 80 supported on large-diameter wide-tyred twin wheels 81 at 33;~ 0 its front and rear ends and also at the centre. The wheel sets have independent suspensions such as to enable the vehicle to traverse difficult terrain and are independently hydraulically driven and steered. At -the front of the vehicle there is a control room housing generators with a ~ crane 82 alongside embodying a motion-compensating system for loading pipe lengths from transport trucks on to a pipe storage area 83 of the vehicle immediately behind the crane.
From this storage area the pipe lengths are fed to the welding assembly 42 which i5 mounted toward the rear oF the vehicle. Assistance over difficul-t terrain is given by crawler tracks 84 underneath the region of the vehicle that carries the welding assembly which tracks can be raised out of contact with theground when not required.
As before the platform of the welding assembiy is gyroscopically levelled so that the motions of the vehicle do not adversely aFfect the pipe-laying operation. The area of the vehicle occupied by the welding assembly 42 is roofed over as at 85 so that the welding is performed under cover. In this instance on cornpletion of a welded joint the whole vehicle moves forward a sufficient distance to bring the next joint to be ~elded into the welding assembly.
As in the case of the ship-borne system the welding and pipe-laying can be fully automatic and computer-controlled.
Changes in pipe diameter can be quickly accommodated and 3~ ~

consistent weld 4uality is achieved. The computer read-out gives subs-tantiallyimrnediate indication of the we1d quality and if any fault shows up it can 4uickly be removed by the performance of a second welding pass. ~lany 5 rnodifications of the arrangements described are of course possible without departing from the scope of t~le invention.
Thus different numbers of welding lasers can be employed and in a welding assembly intended for work largely or wholly on horizontal pipe laid in the 'S' configuration 10 it may be preferred to mount the lasers for rotation around the joints on a "ferris wheel" assernbly instead of in the manner shown in Figures 5 to 7. Air suspension instead of hydraulic suspcnsion can be employed for the ~elding platform. And the X-ray weld-testing probes may be replaced 15 or supplemented by ultrasonic or other types of non-destructive test probe if desired.
h'hen laying pipeline in cold conditions a pre-heating facility can be employed to warm the pipes to an acceptable temperature prior to welding. Facilities for grit-blasting 20 the pipes prior to application of the protective coating can also be proYided.

Claims (5)

1. A pipe-welding assembly comprising a platform, two axially-aligned spaced pipe clamping means mounted on said platform with a gap therebetween to hold two pipe lengths with their ends in juxtaposition in the gap for welding, and at least one laser welding head mounted on said platform to rotate about the axis of said pipe lengths held in said clamping means with the laser beam constantly directed into said gap between said clamping means to produce an annular weld joining said pipe lengths.

2. The assembly according to claim 1, further comprising a weld table rotatably mounted on said platform to rotate about a horizontal axis, said pipe-clamping means and said laser weIding head being mounted on said weld table to rotate therewith.

3. The assembly according to claim 1, comprising an angularly spaced plurality of laser welding heads to rotate about said axis thereby to produce a complete annular weld in less than one complete rotation.

4. The assembly according to claim 3, further comprising weld-testing units mounted to rotate with said laser welding heads.

5. The assembly according to claim 3, wherein the laser heads are CO2 gas lasers.