GB2273543A - Pipe cleaning pig - Google Patents

Abstract

A pipe cleaning pig (10) comprises an elongate carrier body (11) on which a set of scraper plates (12) are mounted along its length. At least some of the scraper plates have outwardly extending scraper fingers which are resiliently deformable and which are circumferentially spaced apart from each other to define gaps therebetween to allow fluid flow between the upstream and downstream sides of the pig. Each scraper plate comprises a star shaped disc (15) having radially outwardly extending teeth or fingers (16) which define generally V shaped gaps or recesses (17). Further, when received from one end of the pig, the fingers prevent a substantially continuous scraper edge. <IMAGE>

Description

PIPE CLEANING PIG This invention relates to a pipe cleaning pig.

As is well known in the art of pipeline technology, so-called "pigs" are used for a variety of different purposes within pipelines, such as for cleaning, maintenance or monitoring purposes, and usually they are driven along a pipeline by the medium which is being conveyed along the pipeline.

In the extraction of underground hydrocarbons, pipelines are used to convey the hydrocarbons from the wellhead to treatment plants, and in the case of extraction of hydrocarbons from below the seabed e.g. in the North Sea, the pipelines run along the seabed to an on-shore treatment plant. The extracted hydrocarbons usually comprise gas / oil mixtures, and over a period of time waxy deposits build-up on the walls of the pipeline and which must be scraped clean on a regular basis.

There are known cleaning pigs which have an external diameter substantially the same as the internal diameter of the pipeline to be cleaned (without waxy deposits) and having external scraping surfaces which scrape the walls of the pipeline clean while being driven along the pipeline by the pressure head of the conveying fluid behind the pig.

However, this is liable to scar or score the metal wall surface of the pipeline, and the close fit of the rigid pig can be a problem in successfully cleaning, and negotiating by-pass ports which are usually provided at intervals along a pipeline for various purposes.

A further problem with the close fitting cleaning pigs is that they create a piston effect with the wall of the pipeline, and while the fit of the piston within the pipeline will not be absolutely gas tight owing to variation in pipeline cross section, there will tend to build-up behind the pig a substantial gas pressure head by reason of the usual presence of gaseous hydrocarbons in the fluid mixture being conveyed along the pipeline. Although the pig does not have completed sealed contact with the wall of the pipeline, any leakage paths generated are not normally sufficient to prevent the build-up of gaseous pressure behind the pig, or to allow significant dissipation of this pressure, and this is a serious drawback to satisfactory operation of the pig.

The invention therefore seeks to provide an improved pipe cleaning pig which is able to carry out effective wall cleaning of the pipeline, but in such a way as to allow gas to pass between the upstream and downstream sides of the pig.

According to the invention there is provided a pipe cleaning pig which is movable along a pipeline by the fluid medium to be conveyed by the pipeline in order to clean the wall of the pipeline, said pig comprising a carrier body, and a plurality of scraper plates mounted along the length of the carrier body and having radially outer scraping edges for engaging the wall of the pipeline as the pig is conveyed along the pipeline, in which: at least some of the scraper plates include outwardly extending scraper fingers which are resiliently deformable and which are circumferentially spaced apart from each other to define gaps therebetween to allow fluid flow between the upstream and downstream sides of the pig; and, the fingers of successive scraper plates are angularly off-set relative to each other in such a way that, when viewed from one end of the pig, the radially outer ends of the fingers of the scraper plates present a substantially continuous wall scraping edge.

Therefore, a cleaning pig according to the invention is able to carry out an effective wall cleaning action, in view of the substantially continuous scraping edge presented by the combined arrangement of the fingers of the successive scraper plates, and which will usually be slightly oversized relative to the pipeline diameter so as to make resilient scraping contact with the wall of the pipeline, but in which by reason of the gaps between adjacent fingers of each plate gas flow passages are defined between the upstream and downstream sides of the pig. These gaps may also allow any debris scraped from the walls of the pipeline to be dispersed into the fluid conveying medium.

In a particularly convenient arrangement, each scraper plate comprises a star-shaped disc which is readily mounted on the carrier body, and having generally V-shaped gaps or recesses defined between adjacent fingers of the star shape and with the tips of the fingers of each disc forming part of the overall scraping edge provided by the set of discs mounted on the carrier body, as viewed in end view. Thus, the spaces between the tips of the fingers of the leading disc are filled by the tips of the fingers of the angularly off-set following discs.

Preferably, each finger has a hardened or wareresistant rigid tip portion, with the remainder of the finger being made of suitable resiliently deformable material e.g.

polyurethane or other suitable elastomeric material, and preferably also the remainder of the disc also is moulded from the same material.

One embodiment of pipe cleaning pig according to the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a schematic side view of a pipe cleaning pig for use in scraping clean the wall of a pipeline; and, Figure 2 is a front view of one of a set of star-shaped scraper discs mounted on the pig shown in Figure 1.

Referring now to the drawings, there is shown one preferred embodiment of pipe cleaning pig which is movable along a pipeline in order to clean the wall of the pipeline, and preferably being movable by the fluid medium which is to be conveyed by the pipeline, which may be, for example, a gaseous / liquid phase hydrocarbon mixture of the type derived from an underground reservoir of crude oil.

The pig is designated generally by reference numeral 10 and comprises an elongate carrier body 11 on which a set of scraper plates 12 are mounted along its length. The scraper plates 12 have radially outer scraping edges for engaging the wall of the pipeline as the pig is conveyed along the pipeline, and in the illustrated arrangement the set of plates 12 are arranged in two separate stacks, i.e. an upstream stack and a downstream stack, and which are spaced apart from each other along the length of the carrier body 11 by means of a spacer sleeve 13.

The scraper plates 12 of each stack are assembled together by bolts 14 or other suitable clamping arrangement, and evidently when any individual scraper blade becomes damaged or unduly worn, it is a simple matter to mount a replacement scraper plate.

At least some of the scraper plates having outwardly extending scraper fingers which are resiliently deformable and which are circumferentially spaced apart from each other to define gaps therebetween to allow fluid flow between the upstream and downstream sides of the pig. One scraper plate is shown in more detail in Figure 2, and comprises a starshaped disc 15 having radially outwardly extending teeth or fingers 16 which define generally V-shaped gaps or recesses 17 between adjacent fingers 16.

The scraper discs are mounted on the carrier body 11 in such a way that the fingers of successive scraper plates are angularly off-set relative to each other whereby, when viewed from one end of the pig, the radially outer ends of the fingers 16 of the scraper plates present a substantially continuous wall scraping edge. Thus, the fingers 16 each have radially outer tips presenting scraping edges 18, and the space 19 between successive edges 18 of the leading disc will be filled by the edges 18 of the fingers 16 of the successive discs of the set of discs mounted on the scraper body.

Accordingly, a cleaning pig according to the invention is able to carry out an effective wall cleaning action, in view of the substantially continuous scraping edge provided by the combined arrangement of fingers, and which will usually be slightly oversized relative to the pipeline diameter so as to make resilient scraping contact with the wall of the pipeline. However, by reason of the gaps between adjacent fingers of each scraper disc, gas flow passages are defined between the upstream and downstream sides of the pig, and which also may be helpful in dispersing debris scraped from the wall of the pipeline to be dispersed into the fluid conveying medium.

As shown in Figure 2, required degree of angular offset between success star-shaped scraper discs can be set by taking the fastening bolts 14 through different ones of preformed holes 1, 2, 3 formed in the disc.

Although not shown, preferably each finger has a hardened or wear resistant rigid tip portion, and with the remainder of the finger being made of suitable resiliently deformable material, such as polyurethane, or other suitable elastomeric material. Conveniently, the entire disc and finger portions are moulded from the same material.

The cleaner body 10 is preferably conveyed along the pipeline by the conveying fluid medium, although if required it can be propelled by other means, including being drawn through the pipeline.

Claims (6)

1. A pipe cleaning pig moveable along a pipeline by the fluid medium to be conveyed by the pipeline in order to clean the wall of the pipeline, the pig comprising a carrier body, and a plurality of scraper plates mounted along the length of the carrier body and having radially outer scraping edges for engaging the wall of the pipeline as the pig is conveyed along the pipeline, in which: at least some of the scraper plates include outwardly extending scraper fingers which are resiliently deformable and which are circumferentially spaced apart from each other to define gaps therebetween to allow fluid flow between the upward stream and downward stream sides of the pig; and the fingers of successive scraper plates are angularly offset relative to each other in such a way that when viewed from one end of the pig, the radially outer ends of the fingers of the scraper plates present a substantially continuous wall scraping edge.

2. A pipe cleaning pig according to claim 1 wherein each scraper plate comprises a star shaped disc which is readily mountable on the carrier body, and having generally V shaped gaps or recesses defined between adjacent fingers of the star shape, and with the tips of the fingers of each disc forming part of the overall scraping edge provided by the sets of discs mounted on the carrier body, as viewed in end view.

3. A pipe cleaning pig according to claim 1 or claim 2 wherein each finger has a hardened or wear resistant rigid tip portion, with the remainder of the finger tips being made of resiliently deformable material.

4. A pipe cleaning pig according to claim 3 wherein the remainder of the disc is moulded from the same resiliently deformable material.

5. A pipe cleaning pig according to claim 3 or claim 4 wherein the resiliently deformable material comprises polyurethane.

6. A pipe cleaning pig substantially as hereinbefore described with reference to the accompanying drawings.