WO1995031669A1

WO1995031669A1 - A method of laying a pipeline

Info

Publication number: WO1995031669A1
Application number: PCT/GB1995/001051
Authority: WO
Inventors: Murray Lachlan Dick; Stewart Risk; David Grenville Barnes; Herbert Gary Newbury
Original assignee: Subsea Offshore Limited
Priority date: 1994-05-13
Filing date: 1995-05-10
Publication date: 1995-11-23
Also published as: GB2302381A; GB2302381B; CA2190252A1; GB9623807D0; AU2414295A; NO964817D0; BR9507722A

Abstract

A method of laying a pipeline comprises the steps of providing a number of lengths of pipe (162) to be coupled together to form the pipeline. Co-operating connector formations (1, 2) are provided on each adjacent end of the pipes (102) to be coupled together. A first pipe (102) is positioned at a location and a second pipe (102) is positioned adjacent to the first pipe (102) in end-to-end relationship with the first pipe. The respective connector formations (1, 2) on the adjacent ends are brought into contact with each other and a force applied to the connector formations (1, 2) to form at least one of the connector formations. The connector formations (1, 2) are then made together by causing relative movement between the first and second pipes (102) in a direction substantially parallel to the longitudinal axes of the pipes (102), and the force is subsequently relaxed to couple the connector formations (1, 2) together.

Description

"A Method of Laying a Pipeline"

This invention relates to pipeline laying, and relates more particularly but not exclusively to methods for laying subsea pipelines and for coupling an end of a pipeline to a subsea structure.

Various procedures have been used conventionally for the laying of subsea pipelines. For example, in the case of pipelines of 2-3 kilometre length, it has been common practice to deploy spools (pipeline sections having a length of about 70-80 metres) from a surface vessel to the seabed and there to couple successive spools by bolting together spool-end flanges. However, in the case of pipelines having a diameter of about 36 inches (about 91 centimetres), typical flange bolts have a diameter of about 3-3-4 inches (about 75-90 millimetres) and a weight of about 100 kg. This makes connection by an underwater remotely operated vehicle (ROV) difficult, and therefore requires the use of divers for extended periods at each joint. The use of bolts to join the spool pieces is also relatively time consuming and therefore costly in terms of diver time and the cost of diver support vessel time. Despite the difficulties of making up flanged pipe joints underwater, and the need for components (bolts, etc) additional to the joint components (flanges) integral with the pipe, relative rotation of successive pips sections is not necessary (beyond minor adjustment for mutual angular alignment) . Well-established screw connectors enable pipes to be mutually connected in a mechanically secure and fluid-tight manner but require extensive relative rotation of successive pipe sections, which is impracticable in the laying of underwater pipelines. Welding together of pipe spools avoids the need for relative rotation and for separate components, but requires the use either of skilled welders or of sophisticated welding machinery, and produces joints which are not inherently separable.

In accordance with a first aspect of the present invention there is provided a method of laying a pipeline, the method comprising the steps of providing a number of lengths of pipe to be coupled together to form the pipeline, providing a cooperating connector formation on each adjacent end of the pipes to be coupled together, positioning a first pipe at a location, positioning a second pipe adjacent to and in end to end relationship with the first pipe, bringing the respective connector formations on the adjacent ends into contact with each other, applying a force to the connector formations to deform at least one of the connector formations, mating the connector formations together by causing relative movement between the first and second pipes in a direction substantially parallel to the longitudinal axes of the pipes, and subsequently relaxing the force to couple the connector formations together. Typically, the method is repeated for each of the adjacent lengths of pipe which are to form part of the pipeline.

In accordance with a second aspect of the invention, a method of coupling an end of a pipeline to a structure, comprises the steps of providing the end of the pipeline and the subsea structure with co-operating connector formations, bringing the connector formation on the end of the pipeline into contact with the connector formation on the structure, applying a force to the connector formations to deform at least one of the connector formations, mating the connector formations together by causing relative movement between the end of the pipeline and the structure in a direction substantially parallel to the longitudinal axis of the pipeline, and subsequently relaxing the force to couple the end of the pipeline to the structure.

Preferably, the cooperating connector formations may comprise a male and female sections of a connector which may be of a type known as a "snap connector". Typically, the snap connector may a Hunting Merlin S (trade mark) connector marketed by Hunting Oilfield Services.

For the purposes of the present invention, a "snap connector" is a connector for mutually detachably coupling two pipes or the like without the permanent use of additional major components (ie possibly including one or more seal rings but omitting bolts or keys or clamps and the like, and disregarding temporarily utilised tools, jigs, and other aids to assembly/disassembly) , the snap connector functioning by mating of two mutually interfering formations, one being respectively formed on each pipe (or other articles to be so joined), one or both of these formations being temporarily elastically distorted during the mating process temporarily to lie in a substantially non-interfering configuration with respect to the other formation.

Preferably, the force applied to the connector formations may be provided by fluid pressure applied to the connector. Typically, the fluid may be a hydraulic fluid.

Preferably, the relative movement between the first and second pipes is generated by a movable clamp device which engages with each of the first and second pipes and draws the adjacent ends of the first and second pipes towards each other. Typically, the clamp device is fluid operated, for example by hydraulic fluid.

Preferably, a remotely operated coupling module is used to effect coupling of the lengths of pipe and/or coupling of the end of the pipeline to the structure.

Said pipeline may be a subsea pipeline, with part or all of said route lying on the seabed. Laying of said pipes may be carried out by a floating vessel which may also serve to transport unconnected pipes to laying locations therefor.

Preferably, in the second aspect, the structure is fixed and typically may be a subsea structure, such as a wellhead, manifold, riser base or other subsea structure to which a pipeline is to be coupled. Examples of a method of laying a pipeline in accordance with the invention will now be described with reference to the accompanying drawings, in which:-

Fig. 1 is a longitudinal section in a radial plane of a snap connector; Figs. 2, 3, and 4 are successive stages in the mating of a snap connector; Figs. 5, 6 and 7 are successive stages in the de-mating of a snap connector; Fig. 8 is a plan view of a sea-going vessel for pipeline installation in accordance with the present invention; Figs. 9, 10, 11 and 12 are successive steps in the method of pipeline installation in accordance with the present invention; and Figs. 13 to 30 show schematically successive steps in the method of connecting an end of a pipeline to a subsea wellhead.

Referring first to Fig. 1, this is a section through one side of a made-up snap connector 10 comprising a box 1 and a pin 2. Facing circumferential surfaces of the box 1 and pin 2 are formed with interengaging formations in the form of circumferential teeth 4. It is to be noted that the teeth 4 are purely circumferential and not helical, ie they can not be screwed together.

In order to force the toothed portions of the box 1 and the pin 2 mutually apart such that the connector 10 can be disassembled, hydraulic fluid is pumped and high pressure through a port 6 in the skirt (see Fig. 6). This pressurisation radially separates the respective toothed formations 4, and by applying axial forces through circumferential grooves 5 (see Fig. 7) the connector 10 can be pulled apart.

When the connector 10 is in its made-up configuration (Fig. 1), fluid tightness is assured by metal-to-metal seals 3 which are vented during make-up by pressure relief ports 7. If necessary or desirable, seal rings (not shown) can also be incorporated to augment sealing.

Fig. 1 shows only the connector 10 and not the two pipes to which the box 1 and the pin 2 would be respectively connected by circumferential fusion welds (not illustrated) applied around the welding bevels 8.

Fig. 2 shows the connector 10 in its initial stage of being made-up, with the pin 2 stabbed into the box 1 until the respective toothed formations 4 collide (being in an undistorted shape) .

In Fig. 3, hydraulic pressure is applied from an injector 12 through the port 6 to force the toothed skirts radially apart, and at the same time, clamp jaws 14 engage the grooves 5 in that the box 1 and the pin 2 can be pulled together, resulting in the made-up connector configuration shown in Fig. 4.

Making-up of the connector 10 is reversible, de-mating of the box 1 and pin 2 taking place in a reverse sequence of the Fig. 2-4 operations, and is separately illustrated in Figs. 5, 6 and 7.

Fig. 8 is a plan view of a sea-going work vessel 100 carrying pipe spools 102 consisting of pipes prefabricated into integral lengths of about 75 metres. Each pipe spool 102 has a snap connector box (1, Fig. 1) at one end and a snap connector pin (2, Fig. 1) at the other end, though these are not visible in Figs. 8- 12 because of the scale.

The vessel 100 also has a derrick crane 104 by which individual ones of the spools 102 are lifted from the deck of the vessel 100 and controllably deployed to the seabed 200 as shown in Fig. 9.

Fig. 9 illustrates the first step in laying a pipeline along a predetermined route by deploying pipe spools 102 successively to the seabed 200 and there joining them end-to-end by means of the snap connectors detailed above with reference to Fig. 1, according to the connector make-up procedure shown in Figs. 2-4. Figs. 10, 11 and 12 respectively show steps 2, 3 and 4 of the pipeline installation method.

The pipeline installation steps are described in greater detail below:

Work Method Summary

70-80m long spools 102 will be deployed to the seabed .200 from the crane vessel 100. The spools 102 will be connected on the seabed 200 using hydraulic snap connectors. Divers will assist during spool deployment and connector make up.

Outline Method Statement

1. Lower and flange up tie-in spool 102 to base structure (not shown) . (Alternatively this tie-in spool will be installed at a later stage, after the pipeline is installed and tested) .

2. Lower second spool 102 (Fig. 10). Locate using guide wires and stabbing guides. Set spool 102 on seabed 200. Note that male and female stabbing guides on first and second spools respectively are deployed with the spools. Divers will connect airbag - tensioned guide wires into male stabs as spool is held approx. 5m off bottom.

3. Position Pipe Handing Frame (PHF) 210 over first spool 102 at breakover point.

4. Position two further PHFs 210 over second spool 102 and raise to working height (Fig. 10). PHFs 210 to have roller-type pipe clamps to allow longitudinal pipe movement.

5. De-rig stabbing guides.

6. Lower and position connector make up unit 220 (Fig. 11). Unit 220 will be deployed in purpose-designed frame. Unit 220 will be clamped around pipe ends and will be located on circumferential rims. After pipe ends are pulled together, hydraulic pressure applied in the radial direction between the male and female connector sections will separate these sections just sufficiently to allow them to be pulled further together to snap into place to form a permanent connection.

7. De-rig connector make up tool 220 (Fig. 12).

8. Lower next spool as in 2. above. 9. Shift the two PHFs furthest from end of pipeline to new location on the last spool. New locations to be marked with lines painted on spools. Raise spool to working height.

10. Repeat steps 5, 6 and 7.

11. Repeat steps 8 through 10 for each spool until required pipeline length is installed.

Note: Where seabed conditions are suitable, a bellhole may be excavated at each connection location as an alternative to use of Pipe Handling Frames.

Figs. 13 to 30 show the successive steps in the procedure of coupling a pipeline (or flowline) 20 to a subsea wellhead 21. The end of the pipeline 20 is provided with a snap connector formation 22 and a pull- in head 23. The wellhead 21 is a conventional wellhead and a flowline hub 24 to which the pipeline 20 is to be connected is provided with a debris cover 25 and a snap connector formation 26 to co-operate with the formation 22 on the pipeline 20.

In order to carry out the subsea operation a remotely operated vehicle (ROV) 27 is utilised. The ROV 27 (see Fig. 13) pulls down a mounting base 28 on the wellhead 21, connects the guide wires 30 and mini guide posts 31 onto the mounting base 28 and removes debris cover 25 from the flowline hub 24.

As shown in Fig. 14, the next stage is for a flowline pull-in and connection tool 29 to be run down the guide wires 30 to land on the guide posts 31 and mounting base 28. The tool 29 includes a winch 35 on which a winch rope 32 is wound.

As shown in Fig. 15, the ROV 27 collects the termination of the winch rope 32 from its stowed position within the tool 29.

As shown in Fig. 16, the ROV 27 moves towards the pipeline 20, reeling the winch rope from the tool 29 and as shown in Fig. 17, attaches the winch rope termination to the pull-in head 23 on the pipeline 20.

After this stage has been completed, the ROV 27 docks on a docking panel 33 on the tool 29 (see Fig. 18) and actuates a lock-down system to secure the tool 29 to the mounting base 28. The ROV 27 then deploys an eyeball video camera 34 to monitor the pulling in of the pipeline 20 to the tool 29.

The ROV 27 powers the winch 35 to pull the winch rope 32 and pipeline 20 towards a bell mouth 36 of the tool 29. The progress of the pipeline 20 is monitored via the eyeball camera 34 which is coupled to the ROV 27 (see Fig. 19). The winch 35 is powered via the ROV 27. As shown in Fig. 20, pulling in of the winch rope 32 and pull-in head 23 is continued until the pull-in head 23 is brought up against locking dogs within the tool 29. At this stage the eyeball camera 34 is recovered to the ROV 27. At this point the pipeline 20 is locked in position within the tool 29 by a tool 37. A pull-in head release tool 38 is connected to the pull-in head 23 and the release tool is actuated to free the pull-in head 23 from the pipeline 20. The pull-in head is transferred with the release tool 38 to the position shown in Fig. 22. The tool 29 then secures the pipeline 20 in position to make up the connector formations 22, 26, as shown in Fig. 23. A make up tool 39 is then positioned, as shown in Fig. 24 so that the end of the pipeline 20 abuts against the flowline hub 24. The make up tool 39 is then operated, as shown in Fig. 25 to make the connection and an annulus pressure test is carried out. The connector make up tool 39 is then released and the flowline hold down is retracted (see Fig. 26). The lower support roller and bell mouth section are also released. This permits the tool 29 to be recovered to the surface after the ROV 27 releases the module lock down system and undocks from the panel 33 on the tool 29 (see Fig. 27) .

After the tool 29 is recovered to surface, the ROV 27 releases the guide wires 30 so that the guide wires 30 may be recovered to the surface and then the ROV 27 is also recovered to the surface. This leaves the pipeline 20 coupled to the wellhead 21, as shown in Fig. 28.

If required, grout bags 40 can be installed to support the pipeline 20, as shown in Fig. 29.

An elevational view of the connected pipeline 20 and wellhead 21 is shown in Fig. 30.

Modifications and variations of the above-described embodiments can be adopted without departing from the scope of the invention.

Claims

1. A method of laying a pipeline, comprising the steps of providing a number of lengths of pipe to be coupled together to form the pipeline, providing a co- operating connector formation on each adjacent end of the pipes to be coupled together, positioning a first pipe at a location, positioning a second pipe adjacent to and in end to end relationship with the first pipe, bringing the respective connector formations on the adjacent ends into contact with each other, applying a force to the connector formations to deform at least one of the connector formations, mating the connector formations together by causing relative movement between the first and second pipes in a direction substantially parallel to the longitudinal axes of the pipes, and subsequently relaxing the force to couple the connector formations together.

2. A method of coupling an end of a pipeline to a structure, the method comprising the steps of providing the end of the pipeline and the structure with co- operating connector formations, bringing the connector formation on the end of the pipeline into contact with the connector formation on the structure, applying a force to the connector formations to deform at least one of the connector formations, mating the connector formations together by causing relative movement between the end of the pipeline and the structure in a direction substantially parallel to the longitudinal axis of the pipeline, and subsequently relaxing the force to couple the end of the pipeline to the structure.

3. A method according to Claim 2, wherein the structure is a subsea structure.

4. A method according to any of the preceding claims, wherein the pipeline is a subsea pipeline.

5. A method according to any of the preceding claims, wherein the co-operating connector formations together form a snap-type connector.

6. A method according to any of the preceding claims, wherein the force applied to the connector formations is provided by fluid pressure.

7. A method of laying a pipeline and subsequently connecting the pipeline to a structure, the method comprising carrying out the steps of Claim 1 and repeating the steps of Claim 1 until the pipeline is completed and subsequently carrying out the steps according to Claim 2 to couple the pipeline to the structure.

8. A method according to any of the preceding claims, wherein the lengths of pipe are transferred from a floating vessel to a location on the seabed prior to being coupled together to form the pipeline.