GB2265433A - Articulated pig system for pipelines - Google Patents

Abstract

The invention relates to a pig system for use in pipelines, consisting of at least two identical tubular bodies or wagons (12, 14) arranged in line, each of which has strong, flexible ring-shaped cups (16, 18, 20, 22) fitted to its outer wall. The wagons (12, 14) are in contact with one another at their adjoining ends and are connected mechanically by means of flexible elastic coupling (38) which runs coaxially through the inner chambers of the two wagons, which is fastened into bushes 40 and which exerts opposing tensile forces to the wagons, which tend to push the adjoining ends together. Said coupling (38) is in the form of a tubular sheath or umbilical cord with flexible tubing or conductors passing through the middle, carrying electrical, hydraulic and air power from one wagon to the other. <IMAGE>

Description

ARTICULATED PIG SYSTEM FOR PIPELINES The present invention relates to an articulated pig system designed to enable modification, maintenance and inspection work to be carried out in pipelines, particularly those used for the conveyance of oil products.

Pipelines (e.g. oil and gas) used for the conveyance of liquid or gas products over long distances, require attention for modifications and for maintenance work, such as cleaning and inspection. Sometimes for instance, such lines have to be modified to connect them to other production systems, in addition to which such lines require regular cleaning or inspection to detect any corrosion or other faults which are likely to interfere with the flow of products.

This task is accomplished by pigs, which are inserted into the lines at release points and propelled under hydraulic or pneumatic pressure generated by the product being conveyed in the line.

The pigs currently in use usually feature a tubular metal body with flexible, wear-resistant cups made from materials such as polyurethane or ethylene polytetrafluoride. These are ring-shaped cups fitted at the front and rear of the body, as shown in the transverse sectional diagrams. The external diameter of these rings is approximately equal to the internal diameter of the pipeline in which the pig is fitted. The result of this is that, as the pig moves along, the cups form a seal and, hence, provide motive power. Where necessary, these cups also provide support for the pig and perform a scraping action along the line. Supporting castors may also be fitted around the entire tubular body in order to make it easier for the pig to move along the line.

Provided that such pigs are used in linear routes without any branches, they are extremely efficient, but where there are ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ secondary lines which diverge from the main pipeline, the seal may be broken as the pig crosses the junction, where there is a break in the continuity of the main pipeline. This means that if the tubular body is not long enough, the cups at the leading end will not have made contact with the section of the main pipeline downstream from the junction by the time the cups at the rear lose contact with the section of the main pipeline upstream from the junction.

This is a problem which can, obviously, be tackled by ensuring that the pig is long enough, but if it becomes too long, there is a risk that it will become jammed at points where there is a bend in the pipe.

Attempts have already been made to tackle this difficulty by manufacturing pigs with at least two tubular bodies or wagons which are short enough to negotiate bends in pipelines, these wagons being connected together by a ball-type or rod and cardantype coupling which allows the two wagons to pivot in relation to one another.

There is, however, one major drawback with this type of pig: in order to ensure that such coupling mechanisms have adequate fatigue strength and that they are able to withstand the bending moments to which they are exposed, (which are due, mainly, to the presence of welds along the full length of the pipeline and to the need to cross junctions), they have to be of a design which is mechanically very robust. This means that the ends of the wagon have to be strengthened and that the rod has to be manufactured as a bulky and heavy item. However, the weight of this articulated coupling then exerts considerable pressure upon the cups or supporting castors and this tends to cause them to wear out prematurely.

Patents US-A-2 281 918 and SU-A-801 904 give details of pigs which can deal with these drawbacks inasmuch as each of these documents deals with the type described in the preamble to Claim 1.

In patent US-A-2281918, the elastic coupling unit consists of a spring the length of which, when completely at rest, is less than the combined lengths of the two wagons, the ends of this spring being anchored at the outer ends of the wagons, whereas in patent SU-A-801904 the elastic coupling consists of non-extending cable the ends of which are attached to extending elastic devices.

It will be appreciated that no strengthening is required to be carried out on the wagons, neither does the weight need to be increased, where the cable or spring coupling method is used to connect them. This means that no moments or forces will be created such as are likely to cause the cups or support castors to wear out prematurely.

There is, however, a drawback with these types of couplings in that they do not allow information or a function to be conveyed from one wagon to the next. Such data transfers are necessary in a number of cases, particularly where a branch is being installed from the main pipeline. The usual procedure followed when installing a junction is, in the first instance, to fit separate plugs upstream and downstream from the site of the junction.

These plugs consist of single-wagon pigs each of which is fitted with one or more inflatable bags. When inflated, these bags form a leak-proof seal as they press against the interior lining of the pipeline. The plugs are also equipped with remote control facilities which enable them to be positioned, respectively, upstream and downstream from the site where the junction is to be made. A remote control signal is then sent to inflate the bags in such a manner as to shut off a section of the pipeline on either side of the junction site.

This site may then be opened up and a Y-junction may be welded into position, a procedure well known where this procedure is concerned.

It will be appreciated that since the two plugs are separate entities, each needs to be fitted with its own facilities for inflating the sealing bags with fluid and with its own remote control system. The plug needs to be long enough to house all this equipment but, as was explained above, a plug which is too long runs the risk of becoming jammed in bends in the pipeline.

Moreover, when fitted individually with all this equipment, such plugs are heavy and expensive.

Since this invention relates to a pig system as described in the characterising section in Claim 1, it is able to tackle this further drawback.

The sheathing thus acts as an umbilical cord which can carry instructions or power from one wagon to the other, which means that the equipment can be shared out between a number of wagons which can, therefore, be made relatively short. Each wagon can be given a specific function which serves all the other wagons as well, since instructions are transmitted along the umbilical cord. For instance, one of the wagons may be fitted solely with a gas bottle, which can then be used to inflate the bags on all the wagons.

The net result is a train of short wagons, either ordinary or carrying instrumentation, each of which has its own special function, with power or data instructions being transmitted from one wagon to another. Obviously, such a train, in which each function is present only once, is far lighter and more economical than the separate plugs used in the previous procedure.

The way in which this invention is constructed will now be described with the help of the appended drawings in which Figure 1 is an axial, sectional view of a twin-wagon pig system installed inside a straight pipeline; Figure 2 shows the pig system featured in figure 1, but in a curved section of pipeline; Figure 3 provides a larger-scale view of a detail from Figure 1; Figure 4 shows a train of wagons fitted with inflatable bags and Figure 5 is an enlarged sectional view along the V-V line in Figure 4.

With reference to Figure 1, the pig system 10 incorporates two identical tubular bodies or wagons 12,14 which should, preferably, be of a circular cross-section. Each of these wagons has two sets of scraper cups, one at either end, these being numbered 16, 18 and 20, 22 respectively. Each of the cups is formed of a ring-shaped disk, the exterior diameter of which is approximately equivalent to the interior diameter of the pipeline 24 in which the pig system is installed. The cups are manufactured from a material which is flexible, but wearresistant, such as polyurethane or ethylene polytetrafluoride.

These are mounted co-axially on the paired wagon, on ring-shaped boxes 26 fixed to the ends of the wagons. The sets of cups are held in position laterally by collars 28 , these being braced, in turn, by strengthening longitudinal spars 30 and cross-struts 32 The two wagons 12, 14 are set up in line with one another and are fitted at their adjoining ends with two stiff ring-shaped buffers 34, 36 . The wagons are kept in contact with one another along these buffers by means of an elastic coupling.

With the design illustrated in Figure 1, this coupling includes a flexible, non-extending cable 38 running coaxially along the cavity in the two wagons, with the ends fastened into cylindrical bushes 40. As the detailed view shown in Figure 5 illustrates, each bush is of the sliding type and is installed inside a cylindrical sleeve 42 which is fitted coaxially at the outer end of the wagon and passes, with some play, through an aperture 44 drilled in the centre of a transverse partition 46 which forms an integral part of the sleeve. An elastic component 48 resembling a set of Belleville washers is threaded onto the end portion of the bush at the back of the partition 46 , these washers being kept compressed between said partition and a nut 50 screwed onto the threaded end of the bush.There is a pin 52 which runs diametrically across the bush, the ends of this pin being accommodated easily in two oblong holes 54 drilled in the wall of the sleeve 42 diametrically opposite one another, in a longitudinal direction. A removable cap 56 gives access to the nut 50 to allow it to be tightened or slackened.

On assembly, the two wagons are lined up and brought into contact with one another through the buffers 34, 36 . The nuts 50 are tightened up in such a way as to apply a moderate tension in the cable 38 . This creates a coupling between the wagons which keeps them in contact with one another whilst allowing pivoting movements in one of the wagons relative to the other.

A pig system of this type is capable of negotiating bends in pipelines without any difficulty. In fact, as will be seen from Figure 2 , the wagons 12, 14 pivot in relation to one another through the buffers 34, 36 , which part to some extent.

Stretching along the axial vein situated between the partitions 46 associated with the sleeves 42 puts the cable 38 under greater tension, causing the Belleville washers 48 to become compressed and thereby causing a matching amount of stretch in the elastic coupling.

Wagons which make up pig systems may be fitted out in a number of different ways. For example, as may be seen from Figure 4, they may be changed into sealing plugs by fitting them with inflatable ring-shaped bags 72 . These bags are inflated with gas, e.g. from a bottle secured inside one of the wagons.

As has already been explained, one great advantage with this invention lies in the fact that separate bottles do not need to be fitted in each wagon, as was the case where pigs made up of wagons with ball- or rod-type couplings were concerned. A bottle in just one of the wagons can inflate all the bags. In order to achieve this in the manner described in this invention, the cable may be manufactured in the form of a flexible tube-type sheath or umbilical cord, as illustrated in Figure 5. Flexible tubing 76 can be threaded through this sheathing, delivering gas to the various bags 72 on the two wagons.

A similar approach may be used in fitting out the wagons with various instruments to fulfil a variety of functions, such as monitoring the interior lining of the pipeline for corrosion, taking photographs, driving and braking the pig system, etc...) all being controlled remotely by intelligent systems installed in the pig system. Here, once again, the full instrumentation does not have to be placed in all the wagons but functions such as the transmission of instructions also the transfer of information and of power and measurement data may be shared out amongst them, using the electrical conductors 78 inside the umbilical cord 38 Pig systems may, obviously, be made up of more than two wagons; where this is the case, a single umbilical cord will also be used to link these wagons, which are arranged end-to-end.

Claims (6)

1. An articulated pig system to modify, maintain and inspect pipelines, of a type consisting of at least two identical tubular bodies or wagons arranged in line and each fitted with ring-shaped cups on the outer wall giving an external diameter approximately equal to the internal diameter of the pipeline, there being a single point of contact between said wagons at adjoining ends and the wagons being linked mechanically by means of a flexible coupling which runs coaxially through the interior chambers of the two wagons and which applies opposing tensile forces which tend to push adjacent ends together, characterised in that said coupling is formed by a flexible, non-extending tubular sheath or umbilical cord, both ends of which are attached securely to spring devices which work under tension, fixed to the wagons, flexible tubing to transmit hydraulic or pneumatic energy from one wagon to the other, and/or flexible electrical conductors passing through said sheath or cord to transmit measurement data from one wagon to the other.

2. A pig system as described in claim 1, wherein the ends of said sheath and/or of the tubing and conductors are secured to spring devices which work under tension and which are fitted to the outer ends of the wagons.

3. A pig system as described in claim 2, wherein each end of said sheath and/or of the tubing is fastened into a bush on a sliding mounting inside a cylindrical sleeve fixed the outer end of one wagon, said sleeve passing, with some play, through an aperture made in the centre of a transverse partition and accommodating, on the part which protrudes behind the partition, spring devices such as Belleville washers, which are kept under pressure between the partition and a stop, the position of which may be adjusted by means of a nut screwed onto a threaded portion at the end of the bush.

4. A pig system as described in claim 3, wherein longitudinal movements of the sleeve are guided by a pin which runs diametrically across the sleeve and the ends of which are accommodated in two longitudinal oblong holes cut into the wall of the sleeve

5. A pig system as described in any preceding claim, wherein each wagon is fitted with at least one ring-shaped inflatable bag which is normally left empty whilst the pig system is moving along the pipeline and which may be inflated once the pig system has been moved to a given position, the bags on each wagon being filled under remote control with gas from a bottle located on one of the wagons, which is fed to said bags on the various wagons via tubing installed inside the umbilical cord.

6. An articulated pig system substantially as hereinbefore described with reference to the accompanying drawings.