WO1986001751A1

WO1986001751A1 - Pipeline pig

Info

Publication number: WO1986001751A1
Application number: PCT/NO1985/000055
Authority: WO
Inventors: Per Storesund
Original assignee: Per Storesund
Priority date: 1984-09-17
Filing date: 1985-09-17
Publication date: 1986-03-27
Also published as: AU4809385A; NO843686L; EP0195797A1

Abstract

A pipeline pig comprises a body (2) provided with means (3) for positioning the pig in a pipeline (1). The body (2) will permit the fluid transported in the pipeline to flow through the pig without creating a substantial pressure drop. The pig is provided with a turbine (8) driven by the fluid flow therethrough, the turbine in turn driving wheels (16) biased against the pipeline wall. The power transmission may be accomplished by a pump (11) driven by the turbine (8), the pump output in turn driving hydraulic motors (14) connected to the wheels (16). An hydraulic cylinder (17) connected to the pump (11) may be used for biasing the wheels (16) against the pipeline. The drive system is preferably reversible, so that the pig may move both with and against the fluid flow in the pipeline. The pig may carry instrumentation for checking the condition of the pipeline, and power to this instrumentation may be provided by a generator driven by the turbine (8). Both the instrumentation and the reversing mechanism may be controlled by acoustical signals or an electronic computer included in the pig.

Description

Pipeline pig .

Pipeline pigs are used for variety of purposes in the construction, operation and maintenance of pipelines for the transport of e.g. hydrocarbons. One very important function is testing submerged or buried pipelines for leaks, corrosion, erosion or other damage since pipelines of this type are not readily accessible from the outside. For these pur¬ poses the pigs may carry advanced equipment for performing and registering various measurements and a power source, normally in the form an electric battery. Most conventional pigs of this type comprise an elongate body and one or more disks or cups at each end, the peripheral parts of the disk or cups being made of flexible material and fitting snuggly within the pipeline so that the pig will be carried along with the fluid flow in the pipeline. Thus, the pig cannot be controlled after it has been launched from one end of the pipeline, and at the other end a rather elaborate pig trap and sluice must be arranged for recovering the pig, preferably without damage to its advanced equipment. Some submerged pipelines extend for hundreds of kilometers between pumping stations and it is clearly inefficient to send a pig all that distance if, for instance, only the section of the pipeline closest to one or both of the end points needs checking. Furthermore, if the entire distance is to- be controlled, it may be difficult to pack the pig with sufficient batteries to last all the way. In some underwater pipeline systems reco¬ very of the pig is not possible in a conventional manner. In such systems, therefore, double parallel pipelines have been contemplated for returning the pig. This, of course, adds considerably to the cost and operational difficulties of the pipeline system. Instead of scraper cups or the like that will make the pig move along with the flow in the pipe¬ line, another type of conventional pig is moved by means of a cable attached to the pig. This cable normally also acts as an umbilical cord transmitting power and signals between the pig and the launching station. However, such pigs have rather short operational distance due to the limited length of the umbilical cord and, furthermore, handling of the umbilical cord is difficult.

A rather specialized type of pig, particularly intended for cleaning purposes, is known from US-PS No. 2 596 571. This pig comprises a main body fitting with a small clearance inside the pipeline so as to be carried along with the fluid flow. The casing has a number of axial passages which will permit some fluid flow through the pig, this flow being directed to impinge on the vanes of a turbine supported -for free rotation in the main body. The turbine is provided with an excentric weight so that when the turbine rotates, the excentric weight causes an unbalanced rotating force which will set the entire pig vibrating in order to improve its cleaning capabilities and reduce the risk of it getting jammed by sediments in the pipeline. In other pigs of a similar type the turbine is made to drive a cutting or cleaning head mounted for rotation with respect to the body of the pig. Also this type suffers the dis¬ advantages of not being controllable after launching and requiring special equipment and operating proce¬ dures for recovery.

Accordingly, it is an object of the present in¬ vention to provide an improved pipeline pig which will at least partly overcome some of the drawbacks and disadvantages of conventional pigs.

According^'to the invention, a pipeline pig is provided, comprising a body provided with means for positioning same in a pipeline and propulsion means utilizing a pressure differential across the pig to propel the pig along the pipeline, said body having at least one generally axial passage to permit at least some flow therethrough of the fluid transported in the pipeline, said body further comprising rotat- ably supported means drivable by said flow for con¬ verting hydrostatic energy in said fluid into mechanical energy, the invention being characterized in that said rotatably supported means is coupled to at least one driving means being engagable with the inside of the pipeline for driving the pig along the pipeline.

With this arrangement the pig according to the invention will be able to move both against and with the fluid flow in the pipeline and stop wherever wanted. By making the drive mechanism reversible, it is possible to launch the pig from one point and make it return to the same point through the same pipeline after accomplishing its mission. The energy conver¬ ting means may also be used to supply energy to instrumentation carried by the pig. Since all energy required may be taken out of the pipeline flow, there is no limit to the distance the pig may travel. Further advantageous features of the invention are defined in the dependent claims and are explained in greater detail 'in conjunction with the following description of the exemplifying embodiment shown in the appended drawing. The drawing shows a side elevation, partly in section, of a pig according to the invention situated inside a pipeline, with some parts broken away.

The pipeline is designated 1. The pig com¬ prises a body 2 consisting generally of a piece of pipe having an external diameter somewhat smaller than the internal diameter of the pipeline 1. The body 2 is provided with wheels 3 supported for rota¬ tion and limited radial movement in wheel wells 4 and biased towards the inside of the pipeline 1 by means of a spring 5. Thus, the wheels 3 will keep the body 2 of the pig centered in the pipeline. Inside the body 2 radial webs 6 support a

5 housing 7 shaped generally like a drop in order to represent the least possible flow resistance. The nose of the housing is a turbine 8 with vanes 9. The turbine is mounted on the input shaft 10 of a hydrau¬ lic pump 11.

•in In conjunction with the rear wheel wells 4 brackets 12 are arranged forming supports for pivot- able arms 13. Each arm 13 carries an hydraulic motor 14 (shown in broken lines), on the output shaft 15 of which a drive wheel 16 is mounted. The drive wheels it 16 are forced against the pipeline wall by means of a hydraulic cylinder 17 with piston rods 18. The cylinder 17 is hydraulically connected to the pump 11 by means of lines 19. The motors 14 are also connected (not shown) .to these lines, e.g. through

20 internal passages in the cylinder 17 an-d pis-ton rods 18.

In operation, the pipeline fluid will be flowing through the body 2 of the pig, e.g. from the left to the right in the drawing. This flow will be

25 impinging on the vanes 9 so as to drive the turbine 8 in rotation, thus also rotating the input shaft 10 of the pump 11. Hydraulic fluid under pressure will flow from the pump to the cylinder 17, so that the piston rods 18 will force the wheels 15 against the

30 pipeline wall. Hydraulic fluid from the pump will also flow to the motors 14 for rotating the wheels 16. The direction of rotation of the wheels 16 may be such that the pig will move from ^"the right to the left in the drawing, i.e. against the direction of

35 flow in the pipeline. The hydraulic motors 14 being reversible, the direction of rotation of the wheels may be changed by simply switching the flow direc¬ tion through the motors, thus making the pig move in the opposite direction, i.e. the same as the pipeline flow.

It will be understood that the pump 11 and the hydraulic motors 14 may be replaced by electrical equivalents, i.e. an electric generator and electric motors. Furthermore, hydraulic and electric systems may be combined, particularly where electric power is needed for instrumentation (not shown) to be carried by the pig. It will also be obvious to the skilled person that the driving system may be purely mechani¬ cal, the rotation of the shaft 10 being transmitted to the wheels 16 through suitable shafts and gearing. Varying the speed and driving force of the pig may be accomplished in various ways, depending on the drive system. If mechanical, the gear ratio may simply be changed. If hydraulic, the pump may be of the variable capacity type being able to deliver higher pressure at lower flow rates. Also, the pitch angle of the turbine vanes 9 may be changed. - Means will normally be included in ^'the pig for controlling its movements and instrumentation. Such control means may in turn be controlled by acoustical signals, as is well known in the art, or by means of a programmable micro computer, which is also well known in the art. The pig may also include equipment for automatically reversing the direction of travel when the pig arrives at the end of the pipeline or encounters an obstacle which cannot be passed.

It will be understood that the embodiment shown in the drawing is schematic only and that the various component parts may be varied or modified by the skilled person without departing from the spirit of the invention and the scope of the appended claims. Thus, the body of the pig need not be constituted by an elongate cylinder with a diameter close to that of the pipeline, but may take various other ^"forms adapted to the purpose of the pig, e.g. so as to make it able to negociate bends in the pipeline. The drive wheels may be replaced by caterpillars, and the rotating motors may be replaced by linear motors moving the pig in a stepwise fashion. The pig may comprise more than one turbine, e.g. one for propel¬ ling the pig and another for producing power for the instrumentation and control circuitry. For redun¬ dancy, two or more turbines may be used for each of these functions. Furthermore, it will be under- stood that the invention may be employed with either gaseous or liquid fluids in the pipeline. If the pipeline and fluid are clean, the fluid may even be used as the working medium in a fluidbased energy transmission system.

Claims

C l a i m s:

1. A pipeline pig, comprising a body provided with means for positioning same in a pipeline and propul¬ sion means utilizing a pressure differential across the pig to propel the pig along the pipeline, said body having at least one generally axial passage to permit at least some flow therethrough of the fluid transported in the pipeline, said body furthermore comprising rotatably supported means drivable by said flow for converting hydrostatic energy in said fluid into mechanical energy, c h a r a c t e r i z e d in that said rotatbly supported means (8) is coupled to at least one driving means (16) being engagable with the inside of the pipeline (1) for driving the pig along the pipeline.

2. A pipeline pig according to claim 1, - c h a r a c t e r i z e d in that said rotatably ■ supported, drivable means (8) is coupled mechanically to said at least one driving means (16) .

3. A pipeline pig according to claim 1, c h a r a c t e r i z e d in that said rotatably supported, drivable means (8) is coupled to said at least one driving means (16) through a hydraulic pump (11) and a hydraulic motor (14) .

4. A pipeline pig according to claim 1, c h a r a c t e r i z e d in that an electric generator and an electric motor are included between said rotatably supported, drivable means (8) and said at least one driving means (16) .

5. A pipeline pig according to any of the pre¬ ceding claims, c h a r a c t e r i z e d in that said at least one driving means comprises a wheel (16) supported for limited movement with^" respect to said body (2), means (17, 18) being provided for biasing the wheel (16) against the inner wall of the pipeline ( 1) .

6. A pipeline pig according to any of the claims

1 - 4, c h a r a c t e r i z e d in that it com¬ prises instrumentation for controlling parameters of the pipeline (1), and a source of power for the instrumentation driven by said rotatably supported means ( 8) .

7. A pipeline pig according to any of the claims i - 4, c h a r a c t e r i z e d in that it comprises means for reversing the travelling direc¬ tion of the pig.

8. A pipeline pig according to claim 7, c h a r a c t e r i z e d in that it comprises means for .acoustically controlling said reversing means .

9. A pipeline pig according to claim 7, c h a r a c t e r i z e d in that it comprises a programmable computer for controlling said reversing means .

10. A pipeline pig according to claim 7, c h a r a c t e r i z e d in that it comprises means arranged to activate said reversing means if the pig encounters an insurmountable obstruction in the pipeline.