Device for moving a pig through a conduit, such as a pipeline

A pig towing device is adapted for movement through a conduit having bends and open T intersections. The pig has a front leading cup and a rear trailing cup adapted to seal with the conduit for propelling the device through the conduit. The leading and trailing cups are spaced apart a predetermined distance to maintain the seal with the conduit as the pig towing device negotiates past the open T intersections. The pig towing device has a flexible body interconnecting the front leading cup and the rear trailing cup. The flexible body is urged normally into a straight position extending along a central axis thereof to maintain the front leading cup and the rear trailing cup spaced apart by the predetermined distance. The flexible body has predetermined limited flexibility permitting it to bend relative to the central axis as the pig towing device negotiates through the bends in the conduit.

FIELD OF THE INVENTION

The present invention relates to pipeline pigs and, in particular relates to a pig towing device.

BACKGROUND OF THE INVENTION

Devices known as pigs are commonly passed through conduit, such as pipelines, in order to service or inspect the pipeline. A pig may contain the necessary servicing or inspection equipment or may draw other devices behind it. In pipelines for conveying fluids, the pig is commonly driven along the pipeline by the flow of the pipeline fluid. To achieve this, the pig is usually fitted with two spaced apart flexible or expandable cups that are attached to a rigid body of the pig and extend outwardly to the interior of the conduit wall. The cups are adapted to provide a sufficient seal in the pipeline permitting the pig to travel at the speed of the pipeline fluid.

In many instances, the pig comprises more than one section with a towing section having an elongated rigid body supporting the expandable cups. The towing section or device pulls other inspection devices through the pipeline. These other inspection devices may also clean the pipeline.

In some instances, pigs may become stuck in pipelines due to bends in the pipeline that have a radius equal to the diameter of the pipeline. In these instances the pig is too long and straight to negotiate the bend in the pipeline. In other instances the pig may become stuck because it loses its seal with the conduit due to openings in the pipeline wall that are larger than the length or distance between cups of the pig. These openings occur where the conduit has intersections with other pipes. These intersections are referred to as full bore T's and Y-connections. In particular the full bore T intersection occurs when a conduit intersects the pipeline at 90 degrees. The pig must be designed to negotiate past both bends and intersections in the pipeline which two factors have opposite requirements for the pig. Clearly a longer pig works better to maintain a seal with the pipeline as it negotiates past open T intersections. On the otherhand, a shorter pig is able to negotiate past bends in the pipeline. Consequently, pipelines having both the bends and intersections can increase the risk of a pig becoming stuck in the pipeline making the pipeline “unpiggable”.

At the present time pig towing devices have collapsible multi diameter flexible cups which allow for movement of the cups relative to each other and the axis of the rigid body of the pig towing device to permit the pig towing device to negotiate slight bends in the pipeline. One such pig having a multi diameter flexible cup is disclosed in more detail in my U.S. Pat. No. 6,381,797 issued May 7, 2002. Even so, the multi diameter cups of the pig towing devices must still be spaced sufficiently far enough apart so as to allow each one of the cups to maintain a seal with the conduit as the pig negotiates past intersection openings in the pipeline wall. That is, the cups must be of spaced apart a sufficient distance to permit the trailing cup to push the leading cup via the rigid interconnecting body past the intersection and then permit the leading cup to drag the trailing cup via the rigid interconnecting body past the intersection so that the pig towing device does not become stuck in the pipeline. However, the length of the rigid elongated body interconnecting the two cups still restricts negotiation of the pig towing device around tight bends or curves within the pipeline.

Accordingly, there is a need for the development of a pig towing device which is able to negotiate past intersections within the pipeline as well as being able to negotiate through curves or bends in the pipeline.

SUMMARY OF THE INVENTION

The present invention relates to a pig towing device for moving through a conduit, such as, for example, a pipeline where the conduit has bends and open T intersections. In accordance with the present invention the pig towing device has at least a front leading cup and a rear trailing cup adapted to seal with the conduit for propelling the device through the conduit. The leading cup and the trailing cup are spaced apart a predetermined distance whereby at least one of the leading and trailing cups is adapted to maintain the seal with the conduit as the pig towing device negotiates past the open T intersections. The pig towing device has a flexible body interconnecting the front leading cup and the rear trailing cup. The flexible body is urged normally into a straight position extending along a central axis thereof to maintain the front leading cup and the rear trailing cup spaced apart by the predetermined distance. The flexible body has predetermined limited flexibility permitting it to bend relative to the central axis as the pig towing device negotiates through the bends in the conduit.

By providing a flexible body portion between the cups that is normally urged into a straight position extending along its central axis, the pig is adapted to maintain the cups spaced apart a sufficient distance for the pig to negotiate past open T intersections in the conduit. Further, by having a predetermined limited flexibility, the flexible body is able to bend about its central axis and negotiate through bends in the conduit. The predetermined limited flexibility also prevents the pig from “jack-knifing” the trailing cup relative to the leading cup resulting in the pig becoming stuck in the conduit.

In one embodiment, the flexible body has a first tension means, a flexible compression sleeve means, and a second tension means. The first tension means is connected with both the front leading cup and the rear trailing cup for transferring drag forces from the front leading cup to the rear trailing cup. The flexible compression sleeve means surrounds the first tension means and is sandwiched between the front leading cup and the rear trailing cup for transferring compression forces from the rear trailing cup to the front leading cup. The second tension means is operably connected with one of the first tension means and the flexible compression sleeve means to provide a predetermined tension load that normally urges the flexible body into its straight position extending along the central axis and to limit bending of the flexible body relative to the central axis.

In one embodiment, the rear trailing cup has a first central aperture and the first tension means has a threaded end portion that extends through the first central aperture. The second tension means comprises a compression spring surrounding the threaded end portion and a nut like connector secured to the threaded end portion for engagement with the compression spring. The nut is rotated about the threaded end portion to compress the compression spring against the rear trailing cup thereby providing the predetermined tension load to the first tension means.

In one embodiment, the flexible compression sleeve means comprises a plurality of compressible metallic disk elements stacked adjacent to each other. Each of the compressible metallic disk elements has a central opening throughwhich the first tension means extends whereby relative movement between the compressible metallic disk elements allows the flexible body to bend relative to the central axis.

In another embodiment the second tension means comprises a resilient sleeve of predetermined density adapted to surround the first tension means and spread the first and second cups apart to impart the predetermined tension load onto the first tension means. In this embodiment, the flexible compression sleeve means comprises a series of spaced apart metallic disk elements secured in surrounding relation with the second tension means whereby the spacing between the metallic ring elements limits the bending of the flexible body.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to pipeline pigs and, in particular relates to a pig towing device.

Referring toFIGS. 1 to 3and5athrough5d, there is shown the pig towing device10for moving through conduit12. The pig towing device10has a front leading cup14and a rear trailing cup16separated by a flexible body18. The front and rear cups14and16are multi diameter cups. That is the cups14and16are adapted to flex relative to the inside diameter “Dp” of the conduit12. This is accomplished by each of the cups14and16having a central portion or hub20to which pivotal levers22are pivotally connected and have at their end a roller24for engaging the inside wall13of the conduit12. The levers22are further provided with brackets26which holds the disk shaped cup portion28of the cups14and16. The levers22are urged outwardly to bring the rollers24into engagement with the inside wall13of the conduit or pipeline12and provide a sufficient seal between the cups14,16and the inside wall13of conduit12. A more detailed description of the multi diameter cups can be found in my U.S. Pat. No. 6,381,797 issued May 9, 2002. The cups28, in response the fluid flowing through the pipeline12engaging the cups, propel the pig towing device10along the pipeline12in the direction shown by arrow32(SeeFIG. 1).

The flexible body18interconnects the front leading cup14and the rear trailing cup16. The flexible body18normally extends straight along its central axis34that extends through the flexible body18and the cups14and16. The flexible body18maintains the cups14and16a predetermined axial distance “D” apart. The distance “D” is chosen to permit the pig10to negotiate past the open T intersections200in the conduit12.

InFIG. 3, the flexible body18is shown to have a first tension means40in the form of a chain having links41. It should be understood that this first tension means40may alternatively be a wire rope. The flexible body18also has a flexible compression sleeve means42surrounding the first tension means40. In this embodiment, the sleeve means42comprises a series of metallic disk elements60which are described in more detail hereinafter. InFIG. 3, some of the metallic disk elements60have been removed for illustrative purposes to show the chain links41of the first tension means40. It should be understood that the flexible compression sleeve means42extends between the cups14and16as shown inFIGS. 1 and 2. The first tension means40and the flexible compression sleeve means42are adapted to bend relative to the central axis34. The first tension means40normally extends along the central axis34and is attached to the front leading cup14at hub20and to the rear trailing cup16. The first tension means40transfers any drag forces from the front leading cup14to the rear trailing cup16. The flexible compression sleeve means42transfers compression forces from the rear trailing cup16to the front leading cup14.

In the embodiment shown inFIGS. 2 and 3, the rear trailing cup16has a central aperture50and the first tension means40has a threaded end portion52(FIGS. 2 and 3) that extends from the chain links41through the first central aperture50(FIG. 1). In the embodiment ofFIG. 1, a tightening nut54is shown to engage the threaded end portion52. In the embodiment shown forFIGS. 2 and 3, the flexible body18includes a second tension means100in the form of a compression spring110surrounding the threaded end portion52. The compression spring110is shown to comprise a plurality of spring washers. It should be understood that any suitable compression spring may be used, such as, for example, a helical coil spring. The compression spring110is held over the threaded end portion52by the tightening nut54. As the nut54is rotated in a clockwise direction about the threaded end portion52, it engages the compression spring110compressing the compression spring110against the hub20of the rear trailing cup16. This causes the compression spring110to exert a predetermined tension load on the first tension means40. Hence the tightening nut54together with the properties of the compression spring110controls the tension load applied to the flexible body18. The predetermined tension load results in the urging of the flexible body member18into its normally straight position shown inFIGS. 1 through 3and limits the bending moment of the flexible body18relative to the central axis34as the pig10negotiates through bends in the pipeline12as shown inFIGS. 5ato5d. Of course, the nut54may be loosened to reduce tension load on the flexible body18and thereby increase bending moment of the flexible body18about axis34.

In the embodiments shown inFIGS. 1 through 3, the flexible compression sleeve means42comprises a plurality or a series of rigid of metallic disks elements60stacked adjacent to each other. Each of the disk elements60has a second central aperture or opening62through which the chain links41extend. Each of the disk elements60has an outside diameter “Dc” which is less than the inside diameter Dp of the conduit12. In the embodiment shown inFIG. 1, the disk elements60have radial end corners62that taper to provide an angled effect which facilitates flexing or bending between adjacent the disk elements60. It should be understood that adjacent disk elements60may also be beveled along their sides to permit the desired bending angle between these adjacent disk elements60. The amount of tension applied by the first tension means40by the compression spring110results in the compression of the disk elements60and hence limits the bending moment of the flexible body18.

Referring now toFIGS. 4A and 4Bthere is shown an alternative embodiment for the flexible body18. In both these FIGS., a portion of the flexible body18have been removed to better illustrate the components of the flexible body18. In this embodiment, the first tension means40comprises chain links41. The second tension means100comprises a unitary resilient body120. The unitary resilient body120preferably comprises a urethane material molded to the shape shown in the drawings and surrounding the first tension means40. The density of the body120of urethane controls the resiliency of the body120. The resilient characteristic of the body120together with the relative length of the body120to that of the first tension means40acts to spread the leading and trailing cups14,16apart and places a predetermined tension load on the first tension means40. In this embodiment, the flexible tension means42compresses a series of spaced apart metal ring elements130having a T shaped cross section across the ring. The stem of the T is connected with the resilient body120and the space150between the ring elements controls the bending angle of the flexible body18. In this embodiment, the ring elements130comprise two half sections140assembled to the resilient body120. The predetermined tension load limits the bending moment of the flexible body18, while the ring elements130and their mutually adjacent spacing150limits the bending angle. It should be understood that while the preferred resilient material is a urethane, any suitable plastic or rubber like material may be utilized.

Referring toFIGS. 5A through 5D, there is shown the movement of the pig towing device10of the present invention through back to back bends210in a pipeline or conduit12. As the pig towing device10negotiates the bends210in pipeline12, it is apparent that the leading cup14has changed its diameter to accommodate for the bends. Further, the flexible body18also bends around the central axis34. This bending motion is shown for the pig towing device to be in one direction inFIG. 5Aand as the pig towing device negotiates through the bend throughFIGS. 5A,5B,5C and5D the pig towing device will then start to bend in other directions as shown inFIGS. 5C and 5D. Attached to the pig towing device by wire78is a pig inspection section80which may be used to either clean the conduit or take ultrasound or magnetic resonance measurements to determine the integrity of the conduit wall of the pipeline12.

In the practice of the present invention, the leading cup14and the trailing cup16each maintain a seal with the inside surface of the pipeline12to propel the pig towing device10through the conduit12. Further, the trailing cup16is typically provided with openings that allow controlled amounts of fluid to pass through the trailing cup16and drive the leading cup14. These openings and this practice are well known in the art. As the leading cup14negotiates past on open T intersection200(seeFIG. 1) in the pipeline and loses its seal, the trailing cup16has sufficient pressure exerted by the fluid in the pipeline to push the leading cup14past the open T intersection200until the leading cup14once again seals with the inside surface of the conduit.

While the invention has been described in connection with what is presently considered to be a practical embodiment, it is to be understood that the invention is not limited thereto, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.