APPARATUS

Abstract: There is described a pig suspension system adapted to fit a pig shaft (2) and comprising a plurality of wheels (8) characterised in that the wheels (8) are concentrically mounted and individually connected to a circumferentially acting biasing means.

Description: APPARATUS This invention relates to a novel apparatus for use in connection with pipe cleansing and monitoring systems. In particular the invention relates to a novel suspension system for use in relation to pipeline pigging apparatus, for pipes ranging in diameter from as small as 6 inches (15.24cm) to as large as 56 inches (142.24cm), although the system could fit into pipes of any diameter. The invention also relates to a pig comprising the suspension system and to a method of cleaning or monitoring a pipeline. Both subsea and land pipelines for the transportation of various products are subjected to frequent internal cleaning and inspection. This process, known as "pigging", is effected by inserting a "pig" into the pipeline. The "pig" usually comprises a longitudinal shaft upon which is mounted at least one sealing disc and at least one guide disc, more normally a pair, comprising a sealing disc and a guide disc, is situated at each end of the shaft. In a dewatering, RFO (ready for operations) or cleaning pig, the diameter of the sealing disc is such that it creates a positive interference between the inner walls of the pipe and the outer surface of the sealing disc. Motion is induced in the pig vehicle due to the flow of the product, e.g. oil or gas, in the pipeline against the sealing disc. Thus, the pig progresses along the pipeline, the sealing disc scraping the sides of the pipe wall causing a sealing, cleaning and scouring motion. Such pipeline pigs are used in commissioning and decommissioning fuel pipelines and cleaning pipelines in use, e.g. production pipelines. Pipeline cleaning technology up to this point has relied upon a pig unit consisting of discs connected by spacer rings via their longitudinal axis. The weight of the pig is supported on "hard" guide discs or, alternatively, individually sprung wheels, whilst the cleaning is carried out by "soft" sealing discs. Inspection pigs operate along similar lines, but because there is no necessity to scrape the internal walls of the pipe, other than to effect propulsion inspection pigs can be mounted on individually sprung wheels. They usually comprise a longitudinal shaft provided with one or more guide discs and are propelled in a similar fashion to a cleaning pig. An inspection pig will also be provided with monitoring equipment, for example, gauging discs, odometer wheels, or n.d.t. (non destructive testing) measuring equipment to enable the detection of structural flaws in the pipes. Such monitoring equipment is well known to those skilled in the art. However, both types of pig currently used suffer from the disadvantage that they cannot be run concentrically down a pipeline. For cleaning pigs this can result in uneven wear of the guide and/or sealing discs. Even with a wheeled pig, because, inter alia, the wheels are independently sprung, the weight of the pig will usually rest on a fraction of the wheels at any given time, for example, when the pig is travelling through a horizontal pipe, the lowest set of wheels will take most of the load. This will cause the pig to run off centre and cause uneven wear on the discs. To compensate for this "below centre line" running, up until now sealing discs have been manufactured with a considerable oversize on the outer diameter. This allows for off centre line running and wear and tear on the disc, but creates considerable friction between the sealing disc and pipe wall and results in a differential pressure that builds up across the sealing disc. This pressure differential is used effectively to 'drive' the pig, but when the friction is too great the differential pressure becomes unrealistically high. In fact, it can become so high that a phenomenon known as 'plugging' could occur. Thus, there has long been a desire to produce a pig which reduces wear and friction thereby increasing efficiency and increasing the pig's life span. A reduction in friction between sealing discs and pipe wall would result in a lower differential pressure, across the sealing disc, by which method the pig is propelled along the pipe. We have now surprisingly found a novel suspension unit which is suitable for use with a pig assembly and which overcomes or mitigates the aforementioned disadvantages. The suspension unit also permits the manufacture of a pig which is capable of functioning in multidiameter pipelines. Thus, according to the invention we provide a pig suspension system adapted to fit a pig shaft and comprising a plurality of wheels characterised in that the wheels are concentrically mounted and individually connected to a circumferentially acting biasing means. The biasing means is preferentially a circumferentially acting plate. The plate may be energised by any conventionally known plate biasing means, e.g. a hydraulic or pneumatic activator. The plate biasing means may comprise any conventionally known type of piston, such as a hydraulic piston. However, a preferred piston is a spring loaded piston. Alternatively, the plate biasing means may simply comprise a coiled torsion spring. The spring or pistons may be mounted either internally or externally. The suspension system will preferably comprise a plurality of wheels wherein each wheel is mounted radially in a wheel mounting. The wheel mounting is preferably located in a cylinder, the cylinder being connected to an end plate. The end plate is axially mounted on the pig shaft and therefore the plane of the plate is perpendicular to the pig shaft, the end plate thereby being coplanar with the discs of the pig. The wheel and wheel mounting are free to slide within the cylinder. The external end of the wheel mounting is connected to a wheel , whereas the internal end of the wheel mounting is connected to a rotatable disc. The rotatable disc is mounted against one face of the circumferentially acting plate. Preferably, the internal side of the wheel mounting is connected to the rotatable disc via a pivotally mounted connecting rod. A second end plate is positioned against the other face of the rotatable disc, thus the disc is supported, sandwiched between two end plates. The end plates are constructed so as to be able to be load bearing, i.e. will accept radial load. A first end of the biasing spring is attached to the end plate, a second end is attached to the rotatable disc. Thus, in operation, the plurality of wheels are all connected either directly or indirectly, to the rotatable disc and therefore the wheels will move in unison. According to the invention we provide a pig suspension system adapted to fit a pig shaft and comprising a pig body provided with a plurality of wheels characterised in that the wheels are concentrically mounted and individually connected to a circumferential biasing means, each wheel being linked to a connecting rod, the distal end of the rod being linked to a rotatable disc, wherein the rotatable disc is spring loaded against a stationary end plate. As previously mentioned, one significant advantage of the suspension unit of the invention is that it provides centre line running of the pig. The wheel loading can be varied depending upon, inter alia, the nature and tuning of the suspension system. The connecting rod geometry may also be tuned to gain near constant wheel loading. Thus, in the case of a spring loaded disc, the spring rate may be varied depending on each application. If the weight of the pig changes, through, for example adding parts, then the springs can be tuned which will modify the spring rate. Centre line running is achieved when the pig is running at or near a horizontal attitude, because there is a force applied by each wheel. The sum total of these forces, being greater than the weight of the pig, centralises the pig and enables it to run on the centre line of the pipe. In a further preferred embodiment, the wheel mountings of the wheel assembly are offset from the axis of the pig shaft. This enables the wheel assembly, and hence the pig, to rotate whilst travelling down a pipe. This has the advantage that there is an evening out of the length of time any wheel experiences maximum load and, more importantly, it minimises and evens out the wear on the sealing discs. The degree of offset may be varied depending upon the application of the pig, but, for example, the suspension unit may be offset between 1° and 3° of the pig shaft axis and preferably 2° of the pig shaft axis. The number of wheels provided in a suspension unit of the invention may vary depending upon the size and weight of the pig. In a preferred embodiment a pig will be provided with at least two wheel assemblies comprising the suspension unit of the invention, e.g. a front and a rear set. Although, for articulated pigs more than two sets may be used. Although each set may comprise any number of wheels preferably supported by up to eight wheels may be used in any set, although this number may be varied according to the dimensions of the pig. All the wheels in a single assembly are preferably connected to an appropriate piston although it is within the scope of the invention that some of the wheels may be conventionally mounted. The wheels are generally arranged so that any wheel is mounted with another wheel on the opposing side of the shaft. Alternatively, if an odd number of wheels is used then the wheels may be arranged asymmetrically. However, in a preferred embodiment a pig is provided with two sets of wheels, substantially one at either end of a pig shaft. We have found it particularly advantageous when operating a pig with at least two wheel assemblies to have the wheels of one assembly offset from the plane in which the wheels of a second assembly operate. By the term wheel it is intended to encompass conventionally known wheels, rollers, spheres, etc. and other known alternatives. The connecting rod used in the suspension system of the invention may incorporate a turnbuckle. According to a further feature of the invention we provide a pipeline pig comprising a suspension unit as hereinbefore described. The novel wheeled pig is advantageous in that, inter alia, in all spheres of operation it retains the centre line, unlike conventionally known pigs. Thus, as a consequence, it reduces and evens out the wear on the discs and increases efficiency. Thus, in one aspect of the invention, conventionally used discs may be included in the pig system. Such discs usually comprise substantially circular polyurethane discs, "hard" guide discs being used to support the pig and "soft" sealing discs to scrape the inner surface of the pipe. It is an especially advantageous feature of the present invention that a pipeline pig using a centre line suspension system can operate at a minimal differential pressure and high efficiency. The differential pressure is preferably between 0.2 and 0.5 bar, more preferably between 0.2 and 0.4 bar, e.g. 0.3 bar. It is well understood in the art that if a pipeline pig should stall inside a pipeline that increased pressure may be applied in the direction of flow in order to restart movement of the pig. , The pressure applied can be high and it is essential that the sealing disc of the pig be designed so that the increased pressure will not cause it to "flip" forward and create bypass of the driving medium, resulting in complete loss of driving force. The pressure at which the sealing disc commences to flip is known as the "flip pressure". The flip pressure, for those versed in the art, is normally stated to be a multiple of the differential pressure. For example a flip pressure of times 10 is common. It is a feature of this invention that when comparing it to conventional high interference/high differential pressure pig designs, a much higher multiple of flip pressure to differential pressure can be achieved. This results in the benefit of either the sealing disc being able to withstand a higher flip ratio multiple (thereby reducing the likelihood of flipping and stalling) and/or the ability for the drive disc to be of lighter construction as the quoted example of the XI 0 multiplier will result in a lower absolute flip pressure value which, in a multi- diameter pipeline application, will give it the ability to fold more easily when entering the lesser diameter. Thus according to a yet further feature of the invention we provide a pipeline pig as hereinbefore described which may operate with a flip pressure of 5 bar or less when desirable. The flip pressure is preferably between 2 and 5 bar, more preferably between 2 and 4 bar, e.g. 3 bar. In a further embodiment of the invention two or more pigs may be coupled together. Such a coupled pig is advantageous in that, inter alia, it aids in progression of the pig over any voids in the pipeline, such as a WYE connection or TEE connection. The pigs may be coupled in any conventional manner, e.g. by a ball joint and shaft, enabling one pig to be rotatable relative to the other. According to a further feature of the invention we provide a method of cleaning a pipeline which comprises passing a pig as hereinbefore described down the pipeline, at least once. According to the invention we also provide a method of detecting a defect in a pipeline which comprises a measuring pig as hereinbefore described down the pipeline, at least once. . The pig of the invention is especially suitable for use as a measuring pig. Optionally a pig of the invention may be adapted so as to act as a cleaning pig and a measuring pig simultaneously. The pig and/or the suspension system of the invention is especially advantageous in that the suspension system may comprise a very short axial length. Thus, units of the suspension system may be built up as modules. Such a modular arrangement is especially suited to use in a measuring pig. Units of the suspension system may be arranged at either end of the pig with measuring equipment housed between. In a further alternative embodiment, the pig of the invention may be provided with conventional detector systems, for example gauging discs, odometer wheels, thus enabling the pig to be used as a detector pig and enabling the manufacture of semi- intelligent cleaning pigs . The invention will now be described by way of example only and with reference to the accompanying drawings in which, Figure 1 is a longitudinal suspension system, partially cut away, and Figure 2 is a side view of a suspension system of the invention. Referring to Figures 1 and 2 together, a pig assembly (1) comprises a pig shaft (2), or alternatively a bore through which a shaft may be mounted, about which is axially mounted .end plates (3 and 4). The end plate (4) is provided with cylindrical wheel housings (5). In each of the wheel housings (5) is located a. wheel mounting (6), the external end (7) of the wheel mounting (6) is attached to a wheel (8). The internal end (9) of the wheel mounting (6) is pivotally attached to a connecting rod (10) about a pivot (11). The distal end (12) of the connecting rod (10) is connected about a pivot (13) to a rotatable disc (14). The rotatable disc (14) is sandwiched between the end plates (3 and 4). Angular movement is restricted by engagement of pin (18) in slot (19). The rotatable disc (14) is spring loaded with a spring (15). End plate (3) is provided with means for engaging with the end (16) of the spring (15) and the free end (17) of the spring (15) engages with the rotatable disc (14).

Claims: Claims 1. A pig suspension system adapted to fit a pig shaft and comprising a plurality of wheels characterised in that the wheels are concentrically mounted and individually connected to a circumferentially acting biasing means. 2. A pig suspension unit according to claim 1 characterised in that the biasing means is a circumferentially acting rotating disc. 3. A pig suspension unit according to claim 2 characterised in that the biasing means is a spring. 4 A pig suspension unit according to claim 1 characterised in that each of the plurality of wheels is mounted radially in a wheel mounting. 5. A pig suspension unit according to claim 4 characterised in that the wheel mounting is located in a cylinder, the cylinder being connected to an end plate. 6. A pig suspension unit according to claim 5 characterised in that the wheel mounting is linked to the end plate via a connecting rod. 7. A pig suspension unit according to claim 6 characterised in that the connecting rod also comprises a turnbuckle. 8. A pig suspension unit according to claϊm 5 characterised in that the end plate is axially mounted on a pig shaft. 9. A pig suspension unit according to claim 5 characterised in that the rotatable disc is mounted against one face of the end plate. 10. A pig suspension unit according to claim 8 characterised in that a second end plate is positioned against the other face of the rotatable disc. 11. A pig suspension unit according to claim 8 characterised in that the second end plate is also provided with means for engaging with the fixed end of each piston, whilst the free end of each piston engages with the rotatable disc. 12. A pig suspension system adapted to fit a pig shaft and comprising a pig body provided with a plurality of wheels characterised in that the wheels are concentrically mounted and individually connected to a circumferential biasing means, each wheel being linked to a connecting rod, the distal end of the rod being linked to a rotatable disc, wherein the rotatable disc is spring loaded against a stationary end plate. 13. A pig suspension system according to claim 11 characterised in that the wheel mountings of the wheel assembly are offset from the axis of the pig shaft. 14. A pipeline pig comprising a suspension system according to claim 1. 15. A pipeline pig according to claim 14 characterised in that the pig is provided with at least one sealing disc and at least one guide disc and a centre line suspension system, which pig has a high dewatering efficiency. 16. A pipeline pig according to claim 14 adapted to be a measuring pig. 17. A pipeline pig provided with at least one sealing disc and at least one guide disc, and a centre line suspension system according to claim 1, which pig has a flip pressure of 5 bar or less. 18. A pipeline pig according to claims 14 or 17 characterised in that the pig is coupled to at least one other pig. 19. A method of cleaning a pipeline which comprises passing a pig according to claim 14 down a pipeline, at least once. 20. A method of detecting a defect in a pipeline which comprises a measuring pig according to claim 16 down a pipeline, at least once. 21. A pig suspension system substantially as hereinbefore described with reference to the accompanying description and drawings.

Inventors: SMITH STEVE, SYKES SIMON, SMITH, STEVE, SYKES, SIMON
Applicants: FTL SEALS TECHNOLOGY LTD, SMITH STEVE, SYKES SIMON, FTL SEALS TECHNOLOGY LIMITED, SMITH, STEVE, SYKES, SIMON
Application year: 2001
Main classification: B08B9
IPC codes: B08B9