GB2339876A

GB2339876A - Pipeline pig

Info

Publication number: GB2339876A
Application number: GB9915773A
Authority: GB
Inventors: Walter Robert Suttie
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-07-07
Filing date: 1999-07-07
Publication date: 2000-02-09
Anticipated expiration: 2019-07-07
Also published as: GB2339876B; GB9915773D0; GB9814579D0

Description

2339876 Pipeline pig The invention relates to a pipeline pig, that is to

say to a device which can be used to clean the interior surfaces of pipelines in the process industry. Such a device can also be used to provide a moving seal to separate different fluids or substances being pumped through a pipeline.

Pipeline pigs are usually made at least in part of a resilient material and of spherical or cylindrical form. When a cleaning operation is to be carried out, the pigs are generally propelled through the pipelines concerned under gas or liquid pressure, and, being slightly oversize initially, that is to say each being made of a diameter slightly greater than the bore diameter of the pipeline through which it is to be traversed, they clean the pipelines to a standard largely dependent upon the condition of the pipelines and the condition of the pigs and their fit within the pipelines concerned.

Pipeline pigging apparatus for reclaiming product which would otherwise be degraded or wasted by being drained or purged from the pipeline is increasingly being employed in process industries. The reasons for this include recent legislation limiting the production of waste together with other environmental considerations, cost of disposal of waste (including increased water charges) and also operational considerations, for example to reduce downtime resulting from removal of waste product from pipes which are to be used for conveying a different product, and the introduction of more stringent quality control measures. In pipework installations where there is a substantial length of pipeline between a product store and a production machine using the product, a considerable cost saving can be made if the product in the length of pipeline can be reclaimed on completion of a production run; this can be a particularly important consideration in those installations where frequent changes of product are made.

If used in the foodstuffs manufacturing or pharmaceutical industries in particular, a vitally important requirement is that the apparatus, including the pigs, should be able to be cleansed to a very high standard in a short space of time.

According to the inventiono there is provided a pipeline pig of generally cylindrical form and provided with a plurality of resilient discs which project radially outwards of a central body part, the outside diameter of said discs being such as to provide an interference fit in the bore of a pipeline for which the pig is intended, the resilient discs being sufficiently closely spaced that when acted upon by a pressure appropriate for propelling such pigs along a pipeline the radially outermost portions of the discs will become dished to such an extent that peripheral portions of adjacent discs will contact each other for mutual support. The resilient discs will preferably be provided in two spaced apart groups located towards the opposite ends of the pig, and in this case the discs in each group of discs will be at least three in number.

In an arrangement where the spacing of an adjacent pair of discs is roughly equal to the thickness of the discs, the distance by which said discs project radially from the central portion of the pig may be at least twice the thickness of the discs having regard also to the resilience of the material of which said discs are made. The material of which the discs are made may be between 50 Shore A and 80 Shore A hardness and preferably between 60 Shore A and 70 Shore A hardness.

The pig may have been formed by the threading of the resilient discs and of spacers between said discs onto a bolt extending axially of the pig and in this case the head of the bolt, and a nut engaged with a threaded end length of the bolt, will preferably be shrouded within respective nose pieces located at opposite ends of the pig.

Alternatively, the pig may have a moulded body part, said body part having grooves towards its opposite ends which accommodate repective moulded disc units each comprising a sleeve element moulded integrally with a plurality of the resilient discs. In a still further construction, the pig may have a moulded body part and groups of the resilient discs moulded integrally with said body part.

The body part of the pig may incorporate at least one magnet capable of revealing the location of the pig within a pipeline as it reaches or passes the location of a detection apparatus.

In the accompanying drawings, which illustrate particular embodiments of the invention,:- Figure 1 is an axial section through a pipeline pig embodying the invention, Figure 2 is an end view, Figures 3 and 4 are views which show the pig travelling first in one direction and then the other through a pipeline, and Figures 5 to 8 illustrate other constructions of pig which embody the invention.

Referring now to Figures 1 and 2 of the drawings, the pipeline pig there illustrated is of generally cylindrical shape, being formed by a plurality of resilient discs 10 (in this case made of polyurethane) and a body po rtion constituted mainly by spacers 12 which separate adjacent pairs of discs, the outside diameters of the spacers being somewhat smaller than the outside diameters of the discs 10. As shown, the resilient discs are provided in two spaced apart groups located towards the opposite ends of the pig, the discs in each group of discs being four in number. Also as shown, the pig has been formed by the threading of the resilient discs and of spacers between said discs onto a bolt 14 extending axially of the pig. In addition to the spacers 12 which separate the adjacent pairs of discs in the two spaced groups of discs, there is a further spacer 16 which separates said two spaced groups. The head of the bolt 14, and a nut 18 engaged with a threaded end length of the bolt, are shrouded within respective nose pieces 20,20 located at opposite ends of the pig. The nut 18 is securely located on the bolt by means of split pin 22 inserted through a diametrical hole in the threaded end length of said bolt.

In this particular example, the material of which the resilient discs are made is of about 60 Shore A hardnes$.

A number of cylindrically shaped magnets 24 are located in respective holes in the spacer 16 and flanked by respective pairs of plugs 26,26.

Referring now to Figure 3, this shows that the outside diameter of each of the discs 10 is such that it is an interference fit in the bore of a pipeline for which the pig is intended. It can also be seen that the discs of each group of discs are sufficiently closely spaced that when acted upon by a pressure appropriate for propelling such pigs along a pipeline, in the direction indicated by the arrow, the radially outermost portions of the discs are dished to such an extent that peripheral portions of adjacent pairs of discs contact each other for mutual support. In Figure 4 it can be seen that when the direction of travel of the pig is reversed (by th e pressure of fluid now acting in the direction indicated by the arrow) the resilient discs are dished in the reverse manner.

Thus there is provided a pipeline pig of relatively simple construction which can be caused to travel in either direction along a pipeline without the need to remove it and turn it around. A further advantage of the pig just described is that the seal produced at the periphery of each resilient disc can compensate for wear as the pig travels along a pipeline. The pressure of fluid propelling the pig augments the initial sealing pressure produced by the resilience of the material of which the resilient discs are made, and the sealing pressure increases according to any increase in propulsion pressure.

Mainly for the sake of simple illustration, the resilient discs in Figures 1 to 4 are shown to be sharp edged, at least initially, but it will be understood that in service such sharp edged discs would very soon become rounded (and for this reason, in the foodstuffs and pharmaceutical industries in particular, manufacturers may prefer the discs to be of rounded edged form initially). However, whether of sharp edged or rounded form, it is found that the resilient discs of a pig embodying the invention will wipe clean the walls of a pipeline far better than a conventional pig of spherical or of a plain cylindrical form.

The fact that the resilient discs of each group of discs abut together for mutual support has allowed the use of individual discs which are relatively soft and floppy and this in turn has been found to result in a construction of pig which can be propelled by a relatively low propulsion pressure. For example, a conventional pig of three inches diameter may require a propulsion pressure of 30 p.s.i. whereas a pig embodying the invention, in the same pipeline, may well require only 10 p.s.i. propulsion pressure, the product being moved being the same in each case. A further advantage has been found to be that the pig can travel without difficulty around pipe bends of relatively small radius. In addition, a pig embodying the invention can be used without difficulty in pipelines which have suffered local deformation to an extent which would be likely to cause jamming of previous designs of pig or require excessive propulsion pressure to be used; it can also travel through convoluted hoses and pass without difficulty full bore branches in a pipeline through which it is travelling.

It will be understood that a pipeline pig embodying the invention can very easily be fitted with new resilient discs when the original discs eventually become excessively worn.

In Figures 5 and 6 there is illustrated a modified construction of pig having a one piece moulded body part 28 of generally cylindrical shape but having opposite ends of hemispherical form. A magnet 30 has been moulded into the body part at its central axis. Towards its opposite ends, the body part is provided with flat bottomed grooves 32, these accommodating respective moulded disc units indicated 34 which can be forced into position from the ends of said body part, as indicated in chain-dotted lines in Figure 5. Each disc unit is a moulded fitment comprising a sleeve element 36 moulded integrally with three resilient discs 38. As shown, the periphery of each disc is rounded in cross section, and changes of section where the discs merge into the sleeve element are rounded to avoid the formation of crevices or sharp corners.

The construction of pig just described may be particularly advantageous in certain circumstances. For example, the pig can be fitted with moulded disc units the hardness of which is selected according to the material or substance contained in a pipeline concerned. Because the pig is almost entirely devoid of crevices (and in fact entirely devoid of crevices or sharp corners between the resilient discs) it is thought that the pig will be able to be effectively cleaned by being sprayed, in situ, with cleaning fluid. When the peripheral portions of the discs have become worn, the disc units can be cut from the body part and new disc units fitted in place (and it will be understood that, in a variation of this construction of pig, one or both of the flat bottomed grooves of the body part could be fitted with two moulded disc units, one of these having discs different from the other, either being of a different hardness or being differently shaped - for example being sharp edged instead of rounded - or being differently dimensioned).

Referring now to Figures 7 and 8, the pipeline pig there illustrated has a body part 40 and groups of discs 42 which have been moulded integrally with said body part, the opposite ends of the body part again being of hemispherical form. As shown, the periphery of each disc is again rounded in cross section and the changes of section where the discs merge into the body part are again rounded to avoid the formation of crevices or sharp corners. A pair of magnets 44,44 have been moulded at the central axis of the body part, these being spaced apart longitudinally of the pig.

The construction of pig just described may be found to be advantageous in several respects. For example, since it is entirely devoid of any kind of crevice or sharp corner in which bacteria could lodge, it is relatively easy to make biologically clean and is more likely to remain biologically clean throughout its working life in a pipeline. It is thought that such a construction of pig will be able to be effectively cleaned from time to time throughout its useful life by being sprayed, in situ, with cleaning fluid. When the peripheral portions of the discs have become worn, the entire pig will be discarded and replaced by a new one.

Various other modifications may be made. For example, the number of magnets located at the axis of the pig could be varied. Furthermore, the number of discs in each group of discs may be varied; indeed it may be preferred to provide the discs in a single group extending virtually along the entire length of the pig; in this case, the magnets in the Figure 1 and 2 construction could be located in apertures formed in one of the nose pieces, or there could be a magnet or magnets in each nose piece. Although the resilient discs of the pig described above have been said to be made of polyurethane they could be made of any material of a suitable resilience having regard to the substances with which they will come into contact.

The optimum number of resilient discs and their dimensions (having first determined their material specification and thus their hardness) in order to ensure that they may be deformed to the extent required to provide mutual support, as previously described, may be determined by trial and experiment. Suffice to say, in the pigs previously described and illustrated, in which the diameter of the body part is roughly 75% of the bore diameter of the pipeline in which the pig is to be used, the outside diameter of each resilient disc is roughly 7% greater than the pipeline bore diameter, and the thickness of each disc is roughly equal to half the distance by which its peripheral portion projects radially outwards from the body part. It is thought that the resilient discs should be between 50 Shore A hardness and 80 Shore A hardness and ideally between 60 Shore A hardness and 70 Shore A hardness. (A particularly poor quality pipeline, that is to say one having bends of relatively small radius and/or having significant local deformations, may require a pig with resilient discs as soft as 50 Shore A hardness).

Claims

1. A pipeline pig of generally cylindrical form and provided with a plurality of resilient discs which project radially outwards of a central body part, the outside diameter of said discs being such as to provide an interference fit in the bore of a pipeline for which the pig is intended, the resilient discs being sufficiently closely spaced that when acted upon by a pressure appropriate for propelling such pigs along a pipeline the radially outermost portions of the discs will become dished to such an extent that peripheral portions of adjacent discs will contact each other for mutual support.

2. A pipeline pig according to claim 1, in which the resilient discs are provided in two spaced apart groups located towards the opposite ends of the pig.

3. A pipeline pig according to claim 2, in which the discs in each group of discs are at least three in number.

4. A pipeline pig according to any one of the preceding claims, in which in an arrangement where the spacing of such pairs of discs is roughly equal to the thickness of the discs, the distance by which said discs project radially from the central portion of the pig is at least twice the thickness of the discs having regard also to the resilience of the material of which said discs are made.

5. A pipeline pig according to any one of the preceding claims, in which the resilient discs are between 50 Shore A hardness and 80 Shore A hardness.

6. A pipeline pig according to any one of claims 1 to 4, in which the resilient discs are between 60 Shore A hardness and 70 Shore A hardness.

7. A pipeline pig according to any one of the preceding claims, the pig having been formed by the threading of the resilient discs and of spacers between said discs onto a bolt extending axially of the pig.

8. A pipeline pig according to claim 7, in which the head of the bolt, and a nut engaged with a threaded end length of the bolt, are shrouded within respective nose pieces located at opposite ends of the pig.

9. A pipeline pig according to any one of claims 1 to 6, the pig having a moulded body part and said body part having grooves towards its opposite ends which accommodate repective moulded disc units each comprising a sleeve element moulded integrally with a plurality of the resilient discs.

10. A pipeline pig according to any one of claims 1 to 6, having a moulded body part and groups of the resilient discs moulded integrally with said body part.

11. A pipeline pig according to any one of the preceding claims, in which the body part of the pig incorporates at least one magnet capable of revealing the location of the pig within a pipeline as it reaches or passes the location of a detection apparatus.

12. A pipeline pig constructed, arranged and adapted to be used substantially as hereinbefore described with reference to and as illustrated by Figures 1 to 4, Figures 5 and 6, or Figures 7 and 8 of the accompanying drawings.