GB2040459A

GB2040459A - Pipeline Gauging Pig

Info

Publication number: GB2040459A
Application number: GB7942283A
Authority: GB
Original assignee: Pipeline Eng & Supply Co Ltd
Current assignee: Pipeline Eng & Supply Co Ltd
Priority date: 1978-12-07
Filing date: 1979-12-07
Publication date: 1980-08-28
Also published as: GB2040459B

Abstract

A pipeline pig (1) for the gauging of pipelines (17) comprises a gauge plate (11) which has a limited radial freedom of movement relative to the remainder of the pig. Spurious marking of the gauge plate is thereby reduced. The plate 11 is secured to an elastomeric centralising disc 10 and both fit loosely on a fixed sleeve 12 to give the radial freedom the plate 11 may be centralised by springs in lieu of or as well as by the disc 10. <IMAGE>

Description

SPECIFICATION Pipeline Gauging Pig This invention relates to a pipeline pig suitable for use in the gauging of pipelines.

Such pigs are used, for example, by a pipe laying contractor to prove to the purchaser of the pipeline that the inside of the pipeline is empty, free of obstruction and of the specified internal diameter. Gauging pigs comprise a gauging plate, in the form of a circular disc, the diameter of which is, for example from 90% to 97% of the diameter of the pipeline. In use, the pig is driven through a pipeline to be proved, for example propelled by compressed air. If the pig emerges at the other end of the run, and the periphery of the gauging plate is largely undamaged, the line is said to be proved.

It can, however, occur, when using a conventional gauging pig, that the pig will fail to prove a pipeline which does, in fact, meet the contract specification, owing for example to the pig becoming jammed in the pipeline at the entrance to a bend or the gauge plate being marked by the weld seam of the pipe or dents in the pipe which do not in fact reduce the diameter of the pipe to below the specified minimum. Such an "unfair" failure to prove a line can and often will convert an otherwise profitable contract into a loss for the contractor.

According to the invention, there is provided a pipeline pig for the gauging of pipelines, comprising a gauge plate which has limited radial freedom of movement relative to the remainder of the pig.

By virtue of the provision of the radially displaceable gauge plate, the likelihood of an "unfair" failure to prove a line such as discussed above is substantially reduced. Thus, for example, in the case of a weld protuberance on the pipe wall, the gauging plate will only be marked if the protuberance reduces the diameter of the pipe to less than the gauge plate diameter.

In a preferred embodiment, the gauge plate is mounted on a centralising member such as an elastomeric disc adapted to engage the wall of a pipeline and which also has limited radial freedom of movement relative to the remainder of the pig.

In a further preferred feature, the gauge plate is arranged at substantially the axial mid-point of the pig. Such an arrangement has an advantage over a front mounted gauge plate in avoiding marking of the plate at the entrance to a bend. In the case of a pig having a front mounted gauge plate, as is conventional in the prior art, when the pig enters the transition from a straight to a bend, the gauge plate will tend to follow the centre line of the straight portion, since the pig cups supporting the pig are still in that portion, whereas the gauge plate has entered the curve. This tends to cause marking of the circumference of the gauge plate on the outside of the bend. This effect is enhanced by the high velocities achieved by the pig which result in centrifugal forces which tend to throw the gauge plate into contact with the outside of the bend.In contrast, with a centrally mounted gauge plate, the gauge plate is maintained in axial concentricity with the length of pipe between the front and rear supports of the pig, which may for example be pig cups.

In the accompanying drawing, the sole Figure is a sectional side elevation of a preferred embodiment of a gauging pig according to the invention.

A gauging pig 1 comprises a steel tube 2 which has a steel nose member 4 welded to one end and is threaded at the outer end 3. Two hollow cylindrical body members 5, 6 each having an annular plate at each end have bolted to them elastomeric pig cups 7, 8 made, for example, of polyurethane. The pig cups 7, 8 may be of the type described and claimed in copending application No. 7922503.

A gauge plate assembly 9 comprises a centralising member in the form of a disc 10 made, for example of an elastomer such as polyurethane, bolted to a gauge plate 11, preferably made of steel or an aluminium alloy.

The centralising disc 10 and the gauge plate 11 are loosely mounted on a sleeve 12.

The sub-assemblies described above are assembled on the tube 2 in the manner illustrated in Figure 1, and a steel-nut 13 and a clamping disc 14 are screwed onto the thread 3. It will be noted that the length of the sleeve 12 is greater than the combined thickness of the centralising disc 10 and the gauge plate 1 whereby the sleeve 12 is rigidly clamped between the body members 5, 6, and a small clearance is provided between the disc 10 and plate 11 and the faces 1 5, 1 6 of the respective body members 5, 6. The disc 10 and plate 11 are thus radially movable relative to the remainder of the pig, such radial movement being limited by the difference between the diameter of the apertures through the disc 10 and plate 11 and the outside of the sleeve 12.

The pig 1 is shown as being situated in a pipeline having an inside surface 17, the inside diameter of the pipeline corresponding to the diameter of the gauge plate 11. The elastomeric pig cups 7, 8, and the elastomeric disc 10 have, however, been represented in their relaxed state.

When the pig is placed in a pipeline, its weight will be carried by the flange portions 1 8 of the cups 7, 8, the sealing lips 1 9 being flexed to lie on the inside wall of the pipe. The disc 10 will flex to engage the wall of the pipe and retain gauge plate 11 coaxially of the pipe.

It will be appreciated that various modifications of the described embodiment may be made within the scope of the present invention. thus, for example, the gauge plate could be arranged behind the centraiising disc in the direction of movement of the pig.

In addition, over a long run, excessive wear of the centralising disc can occur. Although gauging would continue satisfactorily, a worn centralising disc will increase the likelihood of spurious no-go gauge marking. This problem can be overcome, for example, by the use of a steel centralising disc.

Alternatively, centralising springs may be used to centralise the radially movable gauge plate, instead of or in addition to the centralising disc.

Claims

1. A pipeline pig for the gauging of pipelines, comprising a gauge plate which has limited radial freedom of movement relative to the remainder of the pig.

2. A pig as claimed in claim 1, wherein the gauge plate is mounted on a centralising member adapted to engage the internal wall of a pipeline and which also has limited radial freedom of movement relative to the remainder of the pig.

3. A pig as claimed in claim 2, wherein said centralising member is an elastomeric disc.

4. A pig as claimed in any preceding claim, wherein the gauge plate is arranged at substantially the axial mid-point of the pig.

5. A pig as claimed in any preceding claim, comprising a pig cup at at least one end thereof adapted to sealingly engage the internal wall of a pipeline.

6. A pig as claimed in any preceding claim, wherein the gauge plate is an annular member surrounding a fixed member arranged axially of the pig, a clearance being provided between the inside diameter of the gauge plate and the outside diameter of said fixed member.

7. A pig as claimed in any preceding claim, wherein spring means are provided to bias the gauge plate into a position coaxial with the remainder of the pig.

8. A pipeline pig for the gauging of pipelines, substantially as herein described with reference to the accompanying drawings.