GB2469519A - A pipeline J-lay apparatus having two erector arms for loading pipe sections - Google Patents

Abstract

A J-lay apparatus comprises a pipeline laying tower, and two erector arms 28 for loading the tower alternately, each erector arm comprising a pipe holder / cradle 38, each pipe holder and erector arm moving in sequence to alternately move a section of pipe 48 from a horizontal lower position to a position C aligned with the launch axis in an upper area of the tower. Both erectors / loaders preferably rotate to swing the pipes into place. A welding station 52 on the tower welds consecutive segments / lengths of pipeline. The holders may be provided with relatively movable clamps. Each pipe-feeding erector may also have gearing for lowering and withdrawing an internal expanding clamp, for use during welding. The expanding clamp is inserted into the pipe sections prior to loading on the launch tower. The J-lay device is ideally mounted at the stern of a marine vessel, and may be configured to receive pipe form a reel for S-laying.

Description

I

Marine Pipe Laying, and Apparatus for use therein This invention relates to an improved pipe laying apparatus, and to a method and vessel using the apparatus. The invention relates in particular to the provision of "J-lay" apparatus as an auxiliary provision on a vessel equipped for laying continuous pipeline from a storage reel or on-board production line.

BACKGROUND TO THE INVENTION

In conventional J-lay apparatus, two or four pipe lengths are prepared at deck level as a stalk and erected into a J-lay tower by an erector. The stalk is then aligned with the previous stalk and welded, followed by any necessary treatment and testing of the welded joint. An internally expanding clamp is used to ensure alignment of the joint to be welded; this clamp is suspended on a wire and positioned by a reel which is located, together with a clamp garage, at the top of the J-lay tower.

In early forms of J-lay, pipe was erected and welded in single lengths.

However, this limited laying speed and it became usual to operate with double-joint or quad joint stalks. Even if single lengths are used as a starting material, more than one stalk can be prepared in parallel at deck level. Therefore, increasing the stalk length in the J-lay operation achieves increased laying speed, but at the expense of requiring a higher tower and larger erector.

A further feature of conventional J-lay systems is that the line is supported by a movable table at the foot of the tower. When a stalk has been added, it is necessary to take the weight on a winch or the like, move the table aside, lower the pipe, and reposition the table.

The present invention finds particular, although not exclusive, application in vessels having a tower provided with tensioners which is used at times for launching pipe which has been plastically bent and subsequently straightened. This may occur where the pipe is supplied from a storage reel, or where the tower is used as part of a steep S-lay system supplied from a deck firing line. When operated in this way the vessel can achieve relatively high laying speeds (much higher than J-lay), and without interruptions. However, when a riser section of the pipeline is reached, it is undesirable to use pipe which has undergone plastic deformation as this reduces fatigue life which is important in an unsupported catenary. This has been dealt with in the past by switching to conventional J-lay, but this has necessitated a separate J-lay apparatus, even a separate vessel, or an excessive amount of additional equipment in the main laying arrangement.

SUMMARY OF THE INVENTION

The present invention, from one aspect, provides a J-lay apparatus comprising: a tower for receiving successive lengths of pipe and welding each length received to a suspended pipe at a welding station to form a continuous pipeline along a launch axis; an erector apparatus for moving lengths of pipe from a generally horizontal orientation in a lower work area into a position aligned with the launch axis in an upper area of the tower; and in which the erector apparatus comprises: first and second erector arms each mounted for movement to move the erector arm between a lower and an upper position; each of the erector arms being provided with a respective pipe holder; the erector arms and pipe holders being moveable in sequence to alternately erect lengths of pipe from the lower work area to an upper area of the tower and position the pipe length in alignment with the launch axis.

Preferably, each of the pipe holders is adapted to accommodate a single pipe joint. The single pipe joint is suitably less than 20 meters in length, preferably in the range 10-15 meters.

The invention thus allows single pipe joints to be erected onto a relatively short J-lay tower, or a tower which has only a short length available for J-lay purposes owing to the presence of devices such as tensioners, while providing a reasonable operating speed by the use of two erector arms alternately.

Each pipe holder may be mounted for movement relative to its respective erector arm, the respective pipe holder moving relative to its erector arm in order firstly to receive a length of pipe and secondly to position the pipe length in alignment with the launch axis.

The required motion of the pipe holder may be provided by each pipe holder being connected to its erector arm by a transverse arm which is mounted for pivotal movement about substantially the erector arm axis.

In one form of the invention, each of the erector arms is mounted for rotational movement about a horizontal axis so as to move an outer end of the erector arm spaced from the pivot axis between a lower position adjacent the lower work area and the upper position. Each pipe holder in this case may suitably be mounted to its respective erector arm for rotational movement about a horizontal axis and for rotational movement about the longitudinal axis of the erector arm.

Each of the pipe holders may be provided with clamps for holding the pipe length, the clamps being moveable with respect to the pipe holder for translating the pipe length axially into abutment with a preceding length for welding. This allows each of the pipe lengths to be positioned on the launch axis and then brought into abutment with the upper end of the suspended pipe.

The new pipe length may be brought into precise alignment with the previously welded pipe by any suitable means. Preferably an internal expanding clamp is used for aligning pipe at the welding station, and each of the pipe holders is provided with a winch and cable adapted to engage and move the clamp.

Another aspect of the invention provides a pipelay vessel including the J-lay apparatus defined above.

In a preferred form, the tower is provided with a straightener and tensioners for use in laying continuous pipe from a reel or by steep S-lay.

The straightener may be retractable from the J-lay tower for operation in J-lay mode.

The tower may be located at the stern of the vessel, the vessel also including a firing line located at deck level on a fore-and-aft axis for producing continuous pipeline, a lower diverter positioned to divert said pipeline upwardly, and an upper diverter positioned to receive pipeline form the lower diverter and deliver it to the launch axis of the J-lay tower.

This arrangement gives great flexibility of operation.

The vessel may alternatively or additionally include one or more storage reels positioned to receive pipeline from the lower diverter and to supply pipeline to the upper diverter, there preferably being two storage reels located one either side of the firing line at a shallow angle to the firing line axis. This increases the modes of operation available from the vessel.

From a further aspect, the present invention resides in a method of operating a J-lay apparatus in which pipe lengths are supplied to a tower for welding, the pipe lengths being supplied alternately by first and second erector arms.

Each pipe length is may be a single pipe joint. The single pipe joint is suitably less than 20 meters in length, preferably in the range 10-15 meters.

In one embodiment, each pipe length is raised and aligned with a launch axis of the tower, and is then moved axially into abutment with a preceding pipe length for welding.

The pipe length may be aligned precisely with the preceding length by means of an internal expanding clamp.

In one embodiment of the method, each pipe length is rotated in a vertical plane while being raised and then moved bodily horizontally into the launch axis.

The vessel may include one or more storage reels positioned to receive pipeline from the lower diverter and to supply pipeline to the upper diverter, as mentioned above.

In a further aspect, the invention provides pipe handling apparatus for J-lay operations, wherein a moveable erector arm is provided for transferring successive lengths of pipe into a pipe laying tower, and wherein gear for lowering and withdrawing an intended alignment clamp is mounted on the moveable erector arm rather than being fixed on the tower.

This feature is beneficial in the dual-arm arrangements set forth above, but may also be beneficial in other arrangements.

In an embodiment where the erector arm is provided with a pipe holder moveable relative to the erector arm, the gear for handling the internal clamp may be carried on the pipe holder.

The gear for handling the internal clamp may comprise a winch and/or a garage for the clamp, positioned so as to be above the pipe length when erected into the pipelaying tower.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which: Fig. 1 is a side elevation of a pipelay vessel, including an apparatus embodying the present invention; Fig. 2 is a plan view corresponding to Fig. 1; Fig. 3 is a stern view corresponding to Fig. 1; Fig. 4 is a side elevation showing an elevator apparatus embodying the invention, positioned at the stern of the ship; Fig. 5 is a plan view corresponding to Fig. 4; Fig. 6 is a stern view corresponding to Fig. 4; Fig. 7 is a diagrammatic perspective view illustrating the operation of the elevator and erector apparatus; Fig. 8 is a side elevation of a modified form of ship; Fig. 9 is a plan view corresponding to Fig. 8; Fig.10 is a section on the line A-A of Fig. 9; and Fig. 11 is a stern view corresponding to Fig. 8.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Referring to Figs. ito 3, a ship 10 has a firing line 12 on which pipe lengths are assembled and welded into continuous pipeline 14, as is well known per se. The pipeline 14 may be launched at a shallow angle over a stern stinger (not shown) using tensioners i6. In deep water, the pipeline 14 may be launched by being passed around a lower diverter i8, and an upper diverter 20 to a tower 22 provided with a straightener 24 and tensioners 26. Suitable forms of straightener and tensioner are well known in the art. In the present embodiment, the diverters 18 and 20 are in the form of wheels of 30m diameter, but other forms of diverter may be used such as arcuate sections of moving tracks or rollers.

The function of the diverters is to support and guide the pipe product while avoiding too small a radius of curvature. Nevertheless, the pipe suffers plastic bending while traversing this convoluted path. This bending is removed by straightener 28 prior to launch.

These arrangements are suitable for laying continuous pipeline on the sea bed. However, for sensitive installations such as steel catenary risers (SCR5) or hybrid risers, it is desired to avoid plastic deformration of the riser and a J-lay operation is preferred.

The ship 10 has a J-Iay arrangement incorporating the tower 22 and function including an erector apparatus which will now be described with particular reference to Figs. 4 to 6.

The erector apparatus includes port and starboard erector arms 28 each of which is pivotally mounted to a supporting tower 30 about a common, horizontal axis 32 for pivotal movement in a vertical plane. Axis 32 is at an elevated position which for the purpose of understanding its operation may be considered as half the height of the tower 20. The outer end of each erector arm 28 carries a transverse arm 34 pivoted about an axis 36 aligned with the erector arm 28. Each side arm 34 in turn carries a pipe holder 38 pivoted about a horizontal axis 40. A winch 42 and clamp garage 44 are mounted at one end of each pipe holder 38.

Port and starboard pipe elevators 46 are mounted near the base of the tower 30 and are operable to raise single lengths of pipe 48 from deck level to an elevated position, corresponding to the lowest position of pipe holder 38, as arm 28 pivots.

The various pivoting movements of the erector apparatus and the vertical movement of the pipe elevators 46 may be produced by any suitable actuators, such as hydraulic rams and motors and electric motors, which need not be described in detail. The ship is also naturally equipped with dynamic positioning systems, heave compensation and the like, which need not be described in detail here.

Fig. 7 shows the moving elements of the erector and elevator apparatus in schematic form, for ease of understanding. Referring now particularly to Figs. 4, 6 and 7, in use a pipe length 48 is placed on one of the elevators 46 and raised to the upper position (we shall use the starboard side as an example). The erector arm 28 is then moved (A) to position the pipe holder 38 horizontally beneath or beside the pipe length 48, and pipe length 46 is then transferred from the elevator to the pipe holder. This transfer can be implemented in a variety of ways. In the present example, the elevator is lowered to place the pipe length 48 on the pipe holder 38 where it is secured in position by clamps 50. Clamps 50 are mounted on carriages so that they may be translated a certain distance along the pipe holder. The erector arm 28 is then rotated upwardly, during which motion the pipe holder 38 is rotated with respect to the erector arm 28 during which the position indicated at B' in Fig. 7 is reached. Thereafter, as the erector arms 28 completes its upward rotation, the pipeholder 38 is then counter-rotated and finally the transverse arm 34 is rotated with respect to the erector arm 28 until the position indicated at C' in Fig. 7 is reached to deliver the pipe length 48 into the top of the tower 22.

In this position C' the pipe length 48 is aligned with the pipeline axis passing through the tensioners 26. It will be noted in Fig. 4 that the straightener 24 has been removed from the tower 22 for J-lay operation, or at least retracted. The clamps 50 holding pipe length 48 are then moved along the pipe holder 38 to bring the lower end of the pipe length 48 into abutment with the upper end of the existing pipeline at a welding station 52, and these are welded together. The pipeline is then paid out by use of the tensioners 26, ready for addition of another length.

Since independent elevators and erectors are provided at port and starboard sides, each length of pipe can be ready much sooner by alternating handling from side to side.

As illustrated in Fig. 7, the starboard arm 38 can be delivering a pipe length 48 to the tower 22, while the next pipe length 48' is being received from the elevator at the port side by the port side arm 28 and holder 38.

For each successive pipe length, the roles of the port and starboard apparatus are reversed.

Other work stations are provided along the length of the J-lay tower 22, in this example a non-destructive testing station 54 and a coating station 56.

The pipe length to be welded is preferably aligned by means of an internal expanding clamp (not shown) of a type known per se. Conventionally, this clamp would be handled by a winch operating from the top of the tower 22, with garage' space provided to accommodate the internal clamp above the new pipe section prior to insertion and after retraction from the pipe.

However, in the present embodiment the internal expanding clamp is moved by means of a winch 42 carried on the end of each erector arm 28, port and starboard. When a new pipe section has been welded and paid out, the clamp is exposed, just above the top of the suspended pipeline.

The winch cable of one erector apparatus (e.g. starboard) is then disconnected, and the erector arm 28 is removed to allow the other (port side) erector arm 28 to bring and align the next pipe length. Exploiting the presence of winches on the erector arms, rather than the tower, the winch cable for the new pipe length has already been passed through the pipe during preparation at lower level, as shown at 66 in Fig. 4, and is connected to the clamp once the pipe length has been erected into position.

The cable' in this case should be understood to include an umbilical structure, carrying power and sensing signals to and from the clamp, as well as supporting it mechanically.

The addition of pipe in single lengths allows the height of the J-lay tower to be reduced in comparison with double and quad arrangements, which permits the same tower to be used in a deep S-lay operation. However, adding single lengths in the J-lay mode would normally lead to an unacceptably low operating speed. In the novel apparatus invention, this deficiency is met by the provision of twin erector arms 28 which increases speed by allowing handling and preparation of the pipe lengths in parallel prior to welding. In particular, the next pipe length can be prepared, set up and handled while the preceding one is being welded, and can be ready to bring into place as soon as welding and paying out are complete.

In the embodiment described, the preparation can include pre-threading the cable for handling the internal alignment clamp, which saves time of course. Moreover, the clamp itself can remain close to the joint and does not have to be retracted and threaded the length of the new pipe section.

It will be understood that in the mode of operation just described a single clamp is used, which will only be required to be placed in a garage when no J-lay operations are occurring. Accordingly, it would be possible to provide a garage on one only of the erector arms.

It is equally possible to provide each erector arm with its own expanding clamp. In this case, after a length of pipe is welded the clamp of that erector arm is withdrawn into its garage. The clamp of the other erector arm, while the first arm is in the welding location, is positioned at the "lower' end of the pipe section with the cable threaded through the pipe section. This may be done while the pipe section is horizontal, by means of a line through the pipe section, or after the pipe section has been moved into a substantially vertical orientation, by means of gravity. The provision of two clamps may be of benefit in increasing the operating speed Figs. 8-1 1 show a modification of the ship 10, in which storage reels 58 are mounted on either side of the firing line 12 in such a way that pipeline produced from the firing line 12 can be passed round the lower diverter 18 and reeled up onto one of the reels 58, and pipeline 62 can be unreeled from a reel 58 and passed via the upper diverter 20 to the J-lay tower 22 for straightening and launching. Figs. 8 and 9 also show the in-use and transit positions of a stinger 64 which can be used for S-lay of pipe, for example in shallower water. The provision of the storage reels 58 increases the flexibility of use of the ship. Pipeline may be produced on the firing line 12 during transit and stored for future use. Alternatively, prefabricated pipeline may be loaded and reeled from a shore base. Use of two reels 58 located on either side of the firing line at a shallow angle to the longitudinal axis of the ship 10 allows fabrication and storage to be accommodated within a shorter overall length. The cost of bearings and the centre of gravity can be reduced, compared with a single, large reel.

The pipeline 60 or 62 may receive additional support and guidance during these operations by means of a column 68 which can be raised and lowered, for example by hydraulic rams. A guide yoke 70 is located at the top of the column 68 and can be slewed relative to the fore-and-aft axis to assist in guiding the pipeline to or from the appropriate reel 58.

Modifications may be made to the above embodiment within the scope of the invention. For example, the novel erector apparatus would be of use on a vessel equipped purely for J-lay, without a firing line and diverters.

Paying out of the pipeline could be by means other than tensioners, such as winches.

Although described with reference to a self-propelled monohull ship, the invention may equally be used with other forms of vessel such as a semi-submersible or a dumb barge.

List of parts ship 12 firing line 14 pipeline 16 tensioners (shallow lay) 18 lower diverter upper diverter 22 J-lay tower 24 straightener 26 tensioners (steep lay) 28 erector arm supporting tower 32 pivot axis of erector arm 34 transverse arm 36 pivot axis of transverse arm 38 pipe holder pivot axis of pipe holder 42 winch 44 clamp garage 46 pipe elevator 48 pipe length clamps (on pipe holder) 52 welding station 54 NDT station 56 coating station 58 reel (x2) pipeline (from firing line) 62 pipeline (from reel) 64 stinger 66 Winch cable 68 column guide yoke A erector arm position -intermediate B erector arm position -launch axis

Claims (7)

1. CLAIMS1. A J-lay apparatus comprising: a tower for receiving successive lengths of pipe and welding each length received to a suspended pipe at a welding station to form a continuous pipeline along a launch axis; an erector apparatus for moving lengths of pipe from a generally horizontal orientation in a lower work area into a position aligned with the launch axis in an upper area of the tower; and in which the erector apparatus comprises: first and second erector arms each mounted for movement to move the erector arm between a lower and an upper position; each of the erector arms being provided with a respective pipe holder; the erector arms and pipe holders being moveable in sequence to alternately erect lengths of pipe from the lower work area to an upper area of the tower and position the pipe length in alignment with the launch axis.
2. 2. Apparatus according to claim 1, in which each of the pipe holders is adapted to accommodate a single pipe joint.
3. 3. Apparatus according to claim 2, in which the single pipe joint is less than 20 meters in length, preferably in the range 10-15 meters.
4. 4. Apparatus according to any preceding claim, in which each pipe holder is mounted for movement relative to its respective erector arm, the respective pipe holder moving relative to its erector arm in order firstly to receive a length of pipe and secondly to position the pipe length in alignment with the launch axis.
5. 5. Apparatus according to claim 4, in which the required motion of the pipe holder is provided by each pipe holder being connected to its erector arm by a transverse arm which is mounted for pivotal movement about substantially the erector arm axis.
6. 6. Apparatus according to claim 4 or claim 5, in which each of the erector arms is mounted for rotational movement about a horizontal axis so as to move an outer end of the erector arm spaced from the pivot axis between a lower position adjacent the lower work area and the upper position, and in which each pipe holder is mounted to its respective erector arm for rotational movement about a horizontal axis.
7. 7. Apparatus according to any preceding claim, in which each of the pipe holders is provided with clamps for holding the pipe length, the clamps being moveable with respect to the pipe holder for translating the pipe length axially into abutment with a preceding length for welding.

   8 Apparatus according to claim 7, including an internal expanding clamp for aligning pipe at the welding station, 9. Apparatus according to claim 8, in which each of the pipe holders is provided with a winch and cable adapted to engage and move the clamp.10. A pipelay vessel including the J-lay apparatus of any preceding claim.11. A vessel according to claim 10, in which the tower is provided with a straightener and tensioners for use in laying continuous pipe from a reel or by steep S-lay.12. A vessel according to claim 11, in which the straightener is retractable from the J-lay tower for operation in J-lay mode.13. A vessel according to any of claims 10 to 12, in which the tower is located at the stern of the vessel, the vessel also including a firing line located at deck level on a fore-and-aft axis for producing continuous pipeline, a lower diverter positioned to divert said pipeline upwardly, and an upper diverter positioned to receive pipeline form the lower diverter and deliver it to the launch axis of the J-lay tower.14. A vessel according to any of claims 10 to 13, including one or more storage reels positioned to receive pipeline from the lower diverter and to supply pipeline to the upper diverter.15. A vessel according to claim 14, in which there are two storage reels located one either side of the firing line at a shallow angle to the firing line axis.16. A method of operating a J-lay apparatus in which pipe lengths are supplied to a tower for welding, the pipe lengths being supplied alternately by first and second erector arms.17. The method of claim 16, in which each pipe length is a single pipe joint.18. The method of claim 17, in which the single pipe joint is less than meters in length, preferably in the range 10-15 meters.19. The method of any of claims 16 to 18, in which each pipe length is raised and aligned with a launch axis of the tower, and is then moved axially into abutment with a preceding pipe length for welding.20. The method of claim 19, in which the pipe length is aligned precisely with the preceding length by means of an internal expanding clamp.21. The method of any of claims 16 to 20, in which each pipe length is rotated in a vertical plane while being raised and then moved bodily horizontally into the launch axis.22. Pipe handling apparatus for J-lay operations, wherein a moveable erector arm is provided for transferring successive lengths of pipe into a pipe laying tower, and wherein gear for lowering and withdrawing an intended alignment clamp is mounted on the moveable erector arm rather than being fixed on the tower.23. Pipe handling apparatus according to claim 22, in which the erector arm is provided with a pipe holder moveable relative to the erector arm, and the gear for handling the internal clamp is carried on the pipe holder.24. Pipe handling apparatus according to claim 22 or claim 23, in which the gear for handling the internal clamp comprises a winch and/or a garage for the clamp, positioned so as to be above the pipe length when erected into the pipelaying tower.