Cleaning pig

Abstract: A pipeline pig for pigging a fluid transportation pipeline, especially one in which a cable or other line is permanently deployed, comprises on a central tubular shaft (10,24) an array of radial-bristle planar brushes (12,14) which are spaced apart in planes normal to the axis of the shaft (10,24) by spacers (16), and in some cases by groups of sail cloth diaphragms (18) secured between spacers (20). The brush bristles (22) comprise resilient plastics filaments (preferably nylon) coated with an abrasive material such as carborundum, and have a radial length such that when the pig is inserted in a pipeline, the bristles are deflected and curved rearwardly so that a substantial part of each bristle lies in contact with the internal surface of the pipeline. The leading end of the pig may comprise a deflector cone (50) to facilitate passage of the pig past a cable deployed in a pipeline. The sail cloth diaphragms (18) may be provided with radially extending pleats (62).

Description: This invention relates to fluid transportation pipeline systems for transporting bulk liquids or gases over substantial distances, and to a means for 'pigging' the pipelines of such a system. By 'pigging' is meant the passing of a 'pig' through a pipeline between pig entry and exit hatches whereby to accomplish any one or more of the following tasks: (i) to scrape from the internal surface of the pipeline material which has been deposited on (dirt or other foreign bodies) or otherwise developed at (rust or scale) the internal surface of the pipeline; (ii) to gather up and expel loose rust or scale lying in the pipeline; (iii) to gather up and expel (swab out) contaminants, such as water, lying in the pipeline; and (iv) to separate and provide an interface between different fluids flowing in a pipeline, as for example, between a product such as oil, and a purging water flow, or between a liquid product and a purging gas flow. Known pigs commonly comprise at least two resilient cup-shaped diaphragms mounted at axially spaced positions on a central shaft or mandrel. Each such diaphragm is impervious to the liquid flowing in the pipeline, and has an annular skirt portion that is intended to contact and rub against the internal surface of the pipeline, thereby to scrape from that surface material that has become deposited or is lying thereon. It is also known to provide, on such pigs, brushes for scrubbing the internal surface, sometimes in conjunction with the afore-mentioned impervious diaphragms. Such brushes have commonly comprised a circumferentially-spaced array of longitudinally aligned individual brushes; alternatively, an axially-spaced array of disc-shaped, radial bristle brushes. In one prior disclosure (patent specification US-A-1,165,455 - SCHLEMMER) it has been proposed to use a pig having a series of disc-shaped brushes (with radial bristles) spaced axially apart on a central shaft, which brushes were caused to flex rearwards on entering a pipe of smaller diameter. That pig also included at respective end and central positions on the shaft respective disc-like diaphragms providing fluid-tight sealing of the pig when moving in the pipe. Each such diaphragm comprised a pair of abutting canvas discs each having radial cuts for facilitating flexure of the diaphragm when entering the pipe. The radial cuts in the respective discs were angularly staggered relative to one another so as to prevent undue by-passing of the pig by the propelling fluid flowing in the pipe. In another prior disclosure (German patent specification DE-B-1,170,973 - HEEREN ET AL) it has been proposed to provide on the respective ends of a reversible cleaning device, intended for cleaning heat exchanger cooling tubes, respective conical end members for deflecting water present in the cooling tube radially outwards towards the internal surface of the cooling tube so as to scour and thereby clean that surface. In our European patent application EP-A-0 294 243 and EP-A-0 294 244, there is disclosed the concept of, and a method of, deploying within (instead of alongside) a fluid transportation pipeline, for transporting bulk liquids or gases, an electrical or other cable or line for transmitting data, control or other signals which need to be transmitted from one location on a pipeline system to another such location. The presence in a pipeline of such a cable or line presents a problem in that the conventional forms of cleaning pigs cannot be used except with substantial disadvantages. In particular, (a) the resilient fluid sealing diaphragms would be subjected to excessive deflection and distortion, so that pipeline fluid could undesirably by-pass the pig, and so permit mixing of different fluids that are to be kept separate by the pig, and (b) those diaphragms would be subjected to excessive and uneven wear, and possibly the development of grooves in their peripheral surfaces. Moreover, the use of a conventional pig could damage, or even destroy, such a cable or line at any position in the pipeline where such cable or line crosses the path of the pig. According to a first aspect of the present invention there is provided a pipeline pig comprising: (a) a central shaft; (b) a plurality of similar disc-shaped, radial bristle brushes carried transversely at axially-spaced positions on said central shaft; (c) a plurality of circular, planar diaphragms of a woven fabric material carried transversely on said central shaft and disposed between and spaced from selected brushes; and (d) means for securing the said brushes and diaphragms on said central shaft; wherein said pig is characterised by: (e) a resilient conical member secured on said central shaft at its lead end, said conical member having a peripheral rim portion disposed adjacent to and facing peripheral parts of the foremost brush, for adapting said pig said pig for use in a fluid transportation pipeline having an electrical or other signal transmitting cable or line deployed therein. The pig may also include adjacent the rearmost brush a resilient cup-shaped member having a rim portion facing rearwards away from the rearmost brush. According to one preferred feature of the present invention, the brushes are arranged in axially-spaced pairs, and the brushes of each such pair are spaced axially apart by at least one diaphragm. According to another preferred feature of the present invention, each diaphragm is formed with a plurality of radial pleats spaced circumferentially around the diaphragm thereby to allow the diaphragm to closely and sealingly engage the cable as the pig is propelled along the pipeline by the fluid pressure downstream thereof. According to another preferred feature of the present invention, the brushes and diaphragms have a diameter such that on movement of the pig into and along said pipeline the brushes and diaphragms are flexed rearwardly at their peripheries by movement of the pig in the pipeline. Preferably, the brush bristles are preformed to a shape conforming substantially to that adopted by them when the pig is moving through the pipeline. According to another preferred feature of the present invention, the brush bristles comprise filaments of a resilient plastics material, preferably of nylon. Advantageously, the brush bristles carry a coating of an abrasive material, preferably of carborundum. The central shaft may be hollow and sealed at its ends so as to provide a predetermined buoyancy for the pig. Such hollow central shaft may incorporate magnetic means for facilitating magnetic sensing of the pig in the pipeline. Pigs according to the present invention have the advantage that their brushes and woven fabric diaphragms are able to accommodate the presence of a cable in a pipeline without impairing the cleaning efficacy of the pig, and without substantially reducing the sealing ability of the pig or causing damage to the pig components. According to a second aspect of the present invention, a method of pigging a fluid transportation pipeline in which an electrical or other signal transmitting cable or line is deployed comprises introducing into, propelling through, and extracting from the pipeline a pig according to the said first aspect of the present invention. One pipeline pig, and various modifications thereof, all according to the present invention, will now be described by way of example and with reference to the accompanying diagrammatic drawings. In those drawings: Figure 1 shows a side elevation of the pig before its entry into a pipeline; Figure 2 shows a diametral cross section through a shaft or mandrel assembly on which an array of bristle brushes, woven fabric diaphragms and spacers is to be assembled to produce the pig shown in Figure 1; and Figure 3 shows in end view a pleated form of fabric diaphragm for use in the pigs of the Figures 1 and 2. Referring now to the drawings, the pig there shown comprises a shaft or mandrel assembly 10 on which is carried a tightly clamped array of axially spaced pairs of brushes 12, 14. The respective pairs of brushes are spaced apart by polyurethane spacers 16. Between the brushes of each such pair is clamped a single diaphragm 18, or a group of two, or three, diaphragms 18, of a sail cloth material. Interposed between each brush 12, 14 and the adjacent component (a diaphragm, or group of diaphragms 18, or a spacer 16) is a plastics foam washer 20. Each such brush comprises an array of carborundum-coated, nylon filaments which radiate from a central support (not shown) and constitute the 'bristles' 22 of the brush. The shaft assembly 10 comprises a central aluminium tube 24 having secured to the leading end thereof, by welding, a chamfered flange (not shown). At the trailing end of the tube is secured a screw-threaded, flanged, aluminium plug 28. Carried within the tube 24 is an array of disc magnets 30, secured in position within the tube by a clamping plate 32. A central shaft 34 extends through the tube 24, the magnet assembly 30, 32, and the associated plug 28, and carries outboard of the plug 28 a handling plate 36 which carries a handling ring 38. The shaft assembly 10 is secured together, after first threading on to the tube 24 the respective brushes 12, 14, the respective groups of diaphragms 18, and the respective spacers 20, and the respective spacers 16, by applying a nut 40 to the screw-threaded end of the central shaft 34, and locking the nut by means of a split pin 42. The pig is intended to move through a pipeline in the direction indicated by the arrow 44 shown in Figure 1. After passing a first time through a pipeline, the brush bristles take up a permanently-set curvature intermediate their fixed and free ends, which curvature assists subsequent passes of the pig through a pipeline. By way of example, the initial diameter of the brushes 12, 14 is approximately 10-10.5 inches (254-267 mm) for entry into a pipeline having a nominal bore diameter of 8 inches (203 mm). The brush bristles have to be resilient and wear resistant, and strong enough to support the weight of the pig when in a pipeline. The plastics material chosen for the bristles must also be capable of receiving the wear resistant abrasive coating material. Not only does the abrasive material coating enhance the life of the plastics bristle filaments, but it also provides a good cleaning surface for removing debris from the internal surface of a pipeline. The shaft assembly may, if desired, be sealed to render the pig slightly buoyant in the pipeline fluid. The brush bristles may be pre-treated so as to render them flexed in the shape that they would otherwise achieve in the course of a passage through a pipeline. If desired, some of the sail cloth diaphragms may be omitted. The positioning of the sail cloth diaphragms between the brushes in the manner shown assists in maintaining the brushes in good shape for performing their intended functions. The leading end of the pig has affixed thereto a generally cone-shaped deflector 50 of polyurethane or other suitable resilient plastics material. The deflector has a rounded nose 52, and a substantially conical profile 54 which is shaped to safely sweep aside (without inflicting any substantial damage) any electric cable or other line which is deployed in the pipeline and happens to traverse the path of the pig, for example at a position in the pipeline where such a cable or line enters or leaves the pipeline. The said conical profile may have linear sides as illustrated, or sides which are outwardly slightly concave, or slightly convex, as indicated by chain-dotted lines. In order to facilitate retrieval of the pig from a pipeline, the deflector is provided with a series of circumferentially spaced indents 56 into which spring-biased pawls 58 carried within a retrieval cup 60 may expand on engagement of the retrieval cup with the deflector, whereby to positively engage the deflector and so enable the pig to be withdrawn from the pipeline with the retrieval cup. In order to enhance the flexibility of the sail cloth diaphragms, and so further facilitate the passage of the pig past an electric cable deployed in the pipeline, some or all of them may be formed with uniformly spaced, radially extending pleats as indicated in the Figure 5 at reference 62.

Claims: A pipeline pig (10) comprising: (a) a central shaft (24); (b) a plurality of similar disc-shaped, radial bristle brushes (12, 14) carried transversely at axially-spaced positions on said central shaft (24); (c) a plurality of circular, planar diaphragms (18) of a woven fabric material carried transversely on said central shaft (24) and disposed between and spaced from selected brushes (12, 14); and (d) means (16, 40, 42) for securing the said brushes (12, 14) and diaphragms (18) on said central shaft (24): wherein said pig is characterised by; (e) a resilient conical member (50) secured on said central shaft (24) at its lead end, said conical member having a peripheral rim portion disposed adjacent to and facing peripheral parts of the foremost brush (12), for adapting said pig for use in a fluid transportation pipeline having an electrical or other signal transmitting cable or line deployed therein. A pipeline pig according to claim 1, including adjacent the rearmost brush (14) a resilient cup-shaped member (48) having a rim portion facing rearwards away from said rearmost brush (14). A pipeline pig according to claim 1 or 2 wherein said brushes (12, 14) are arranged in axially-spaced pairs, and wherein the brushes (12, 14) of each such pair are spaced axially apart by at least one said diaphragm (18). A pipeline pig according to any preceding claim, wherein each said diaphragm (18) is formed with a plurality of radial pleats (62) spaced circumferentially around the diaphragm (18). A pipeline pig according to claim 3 or 4, wherein the brush bristles (22) are preformed to a shape conforming substantially to that adopted by them when the pig (10) is moving through the pipeline. A pipeline pig according to any preceding claim, wherein said brush bristles (22) comprise filaments of a resilient plastics material. A pipeline pig according to any preceding claim wherein said brush bristles (22) carry a coating of an abrasive material. A pipeline pig according to any preceding claim wherein said central shaft (24) is hollow and sealed at its ends. A pipeline pig according to claim 8, wherein said central shaft (24) incorporates magnetic means (30). A method of pigging a fluid transportation pipeline in which an electrical or other signal transmitting cable or line is deployed, which method comprises introducing into, propelling through, and extracting from said pipeline a pig (10) as claimed in any one of the preceding claims.

Inventors: KERSHAW CHRISTOPHER FRANK, KERSHAW, CHRISTOPHER FRANK
Applicants: NORTHERN TELECOM LTD, NORTHERN TELECOM LIMITED
Application year: 1988
Main classification: B08B9
IPC codes: B08B9