GB2223290A

GB2223290A - Pig for pipeline operations

Info

Publication number: GB2223290A
Application number: GB8921100A
Authority: GB
Inventors: Michael Garton
Original assignee: INT TESTING AND COMMISSIONING
Current assignee: INT TESTING AND COMMISSIONING
Priority date: 1988-09-29
Filing date: 1989-09-18
Publication date: 1990-04-04
Also published as: GB8921100D0; GB8822900D0

Abstract

A pig for use in pipeline operations includes two sealing devices spaced apart along a body (11). Each sealing device includes two flat annular flexible elements (15), lying side by side. Each element (15) has a radial slit, and the slits of the two elements are angularly separate from one another. Within the body there is a spring-loaded seal expansion arrangement including two cams 19 and a plurality of radial pins (22) which are thrust outwardly into engagement with the elements (15). The pig can be inserted into the end of a pipeline and the seal expansion arrangement is then triggered to expand the seals. <IMAGE>

Description

PIG FOR PIPELINE OPERATIONS This invention relates to a pig for use in pipeline operations.

Pigs are frequently used in the commissioning of undersea pipelines. For example, where a joint has to be made in an undersea pipeline during installation thereof, it is conventional practice to seal the ends of the pipes before joining with inflatable stoppers and these stoppers have to be cleared before the pipeline can be commissioned. Conventionally this involves filling the pipeline from both ends with suitably treated water and then propelling a pig through the pipeline from one end to the other using further treated water to drive the stoppers from the pipeline. This involves using a very large quantity of treated water (approximately double the total capacity of the pipeline) and, as the water treatment is expensive, the cost of treated water alone is considerable.Moreover, the energy cost in pumping in the treated water to propel the pig from one end of the pipeline to the other can also be very considerable and the time taken for the complete operation is excessive.

The present invention resides in part in the realisation that much of the above-mentioned costs and time can be saved if the pig is not propelled from one end of the pipeline to the other but installed, before joining the pipes, at the joint. The distance through which the pig must be propelled is therefore significantly reduced, thereby lowering water-treating, pumping energy and time-related costs significantly.

It is one object of the present invention to provide a pig suitable for an operation as defined above.

A pig in accordance with the invention comprises a body and a pair of expandable sealing devices mounted at spaced positions on said body, each of said sealing devices comprising a pair of flat annular flexible members each of which is radially slit at one position to permit expansion thereof, said flexible members lying side by side with their radial slits angularly spaced from one another, and axially movable means within the body for simultaneously expanding the flexible members into contact with the interior of a pipe.

Preferably, each flexible member has a metal spring member bonded to its interior surface, which acts to maintain the external diameter of the flexible member at a minimum.

The axially movable means may comprise a pair of conical or pyramidal cam members attached to a rod extending axially of the body, the assembly of the rod and cam members being spring-loaded axially, and catch means, releasable from the exterior of the body, preventing axial movement of the assembly.

An example of a pig in accordance with the invention is shown in the accompanying drawings in which: Figure 1 is an axial section through the pig; Figure 2 is a transverse section on line A-A in Figure 1; Figure 3 is a diagram showing the relative orientation of expandable, flexible members forming part of the pig, and Figure 4 is a diagram illustrating the manner in which the pig is utilised.

The pig shown comprises a body tube 10 which has a flange 11 at each end. Two annular blocks 12 are bolted to these flanges respectively, the external diameter of each such block 12 being less than the external diameter of the flanges 11. Two end members 13, 14 have flanges 13 14a of the same external diameter as the flanges 11, bolted to the respective blocks 12. Each block 12 and the flanges between which it is situated provides an outwardly directed seal locating groove.

Each such groove locates a sealing device comprising a pair of flat annular flexible members 15. Each such member is bonded to an internal spring member 16 and is slit radially at one position 17. The spring member acts to hold the flexible member 15 in a retracted condition with the slit 17 closed, but the slit 17 allows radial expansion of the member 15, the slit 17 opening as flexible member is expanded. An annular disc 23 is located between each pair of members 15 to provide smooth sliding surfaces and to improve the sealing performance.

A mechanism is provided within the body for expanding the flexible members 15 simultaneously. This mechanism comprises an axially extending rod 18 on which two conical or pyramidal cam members 19 are secured and so oriented that both taper axially in the same direction.

A powerful compression spring arrangement, actually comprising two separate coiled springs 20 in the example shown, urges the assembly of the rod and the two cam members axially. The end member 14 carries a catch element 21 of known kind which restrains the assembly of rod and cam members from moving to the right as viewed in Figure 1, thereby holding the springs 20 compressed. This catch element 21 is of the type which can be released by pulling out a central pin 211 enabling radially projecting detents 211 to be displaced inwardly.

The cam members 19 extend through the central openings in the blocks 12 and there are pins 22 slidably mounted in radial bores in these blocks. When the catch element 21 is released and the cam members move axially to the right, the flexible members 15 are expanded by the resulting outward radial movement of the pins 22. Two additional pins 24 radially slidable in bores in the blocks 12 engage in grooves in the cam members to prevent rotation of the latter.

Each pin 22 has a roller 22a, 22b mounted at opposite ends. The rollers 22a 22b at opposite ends of the pin have their axes perpendicular to one another and to the axis of the pin. Roller 22b at the radially outer end of the pin 22 has its axis parallel to the longitudinal axis of the pig. These rollers ensure efficient transmission of forces from the cams 19 to he flexible members 15.

Rotation of the pins in their bores is prevented by screws 22 which engage in longitudinal grooves in the respective pins.

The end member 13 is formed with a screw-threaded axial bore 13a for receiving a jacking screw used to push the assembly of rod and cam members to the left (as viewed in Figure 1) to prepare the pig for use.

Figure 4 shows the pig installed in one of two pipes 30, 31 awaiting the completion of an undersea joint. As shown the pig has been inserted into the tube 30 and the catch element released. Subsequently stoppers 32 have been inserted and inflated in the tube 30. There are also stoppers 32 in tube 31. Following completion of the joint, additional treated sea water is pumped into the longer of the two tubes 30 to displace the pig and the stoppers 32 towards the remote end of the pipe 31. The stoppers may move along the tubes 30, 31 ahead of the pig. If any of the stoppers burst and collapse, they will be pushed along by the pig itself.

Whilst the members 15 have been described as forming sealing devices, it is to be understood that the sealing action obtained is not necessarily a true hermetic seal.

Some leakage of propulsion fluid past the pig is tolerable and the pressure difference across the pig will still remain adequate to propel it.

The invention also resides in the method described above of clearing stoppers from an undersea pipeline joint.

Claims

1. A pig for use in pipeline operations comprising a body and a pair of expandable sealing devices mounted at spaced positions on said body, each of said sealing devices comprising a pair of flat annular flexible members each of which is radially slit at one position to permit expansion thereof, said flexible members lying side by side with their radial slits angularly spaced from one another, and axially movable means within the body for simultaneously expanding the flexible members into contact with the interior of a pipe.

2. A pig as claimed in Claim 1 in which each flexible member has a metal spring member bonded to its interior surface, which acts to maintain the external diameter of the flexible member at a minimum.

3. A pig as claimed in Claim 1 in which said axially movable means comprises a pair of conical or pyramidal cam members attached to a rod extending axially of the body, the assembly of the rod and cam members being spring-loaded axially, and catch means, releasable from the exterior of the body, preventing axial movement of the assembly.

4. A pig as claimed in Claim 3 further comprising a plurality of radially extending pins, radially displaceable by said cams and engageable with said flexible members.

5. A pig as claimed in Claim 4 in which each of said pins has a roller at each end, the two rollers on each pin having their axes perpendicular to one another and to axis of the pin, said rollers engaging the associated cam and the associated flexible member respectively.

6. A pig for use in pipeline operations substantially as hereinbefore described with reference to the accompanying drawings.

7. A method of clearing a pipeline comprising introducing a pig into the pipeline adjacent a joint of a pipeline before completion of the joint, completing the joint, and driving the pig to an end of the pipeline.

8. A method of clearing a pipeline utilizing a pig as claimed in any one of Claims 1 to 6.

9 A method of clearing a pipeline substantially as hereinbefore described with reference to the accompanying drawings.