GB2205143A

GB2205143A - Joining pipes together

Info

Publication number: GB2205143A
Application number: GB08810798A
Authority: GB
Inventors: John Maurice Houlder
Original assignee: HOULDER OFFSHORE Ltd
Current assignee: HOULDER OFFSHORE Ltd
Priority date: 1987-05-07
Filing date: 1988-05-06
Publication date: 1988-11-30
Also published as: GB8810798D0; GB8710778D0

Abstract

A pig is used in connection with the welding together of two pipes, provides a circumferential gap between the clamps at the join. This allows welding material to extend completely through the join to form a strong bond. The pig may be moved to the desired join by travelling along one pipe and may be provided with sensing means for sensing the physical properties of the wall of the pipe within which it travels so as to detect the join. The sensing means may control the travel of the pig to locate the pig accurately at the join so that the welding operation can take place. <IMAGE>

Description

JOINING PIPES TOGETHER A pipeline is generally formed by welding together lengths of pipe and it is important that the two ends of adjacent pipes should be accurately shaped and accurately aligned during the joining operation. It has previously been proposed to shape and hold such adjacent pipes in position by means acting on the exterior of the pipes, but the present invention is concerned with acting on the interior of the pipes by means of a pig. A pig is a body which can be moved along the bore of a pipe for various uses, such as transporting a camera along the pipe for inspection purposes.

An example of a pig for use in welding together pipes is disclosed in British Patent Specification 2165788. The pig in this specification performs the functions of aligning the ends of the pipeline as well as drawing the pipes together to form a closely butted joint, and so has considerable length. This has the disadvantage that it is difficult to pass the pig round bends in the pipes when moving it from one end of the pipeline to the required position.

The present invention is concerned only with alignment of the ends of the pipes and holding them to the correct shape, the function of bringing the pipes together axially being no concern of the present invention and being left to apparatus on the exterior of the pipes.

As stated above, it is important not only that ends of pipes to be welded together should be aligned, but also that they should be held in the correct shape (such as circular) during the welding process. The clamps however are located close to the ends of the pipes in order to hold the ends both aligned and in the correct shape during the welding operation. According to this aspect of the invention, there is provided a pig for use during the welding together of two pipes, the pig fitting within the pipes extending across the join and being provided with clamping means for engaging the pipes to be joined at the end region of each pipe, but leaving a gap between the extreme end of each pipe and the clamping means.

Another problem encountered in the use of a pig in the welding together of pipes is that of accurately locating the pig within the pipe since the pig is hidden by the pipe and so cannot be located visually. It is possible to measure the distance travelled by the pig from a control line towed behind the pig and extending out of the entry to the pipe, but in pipes of considerable length, this method is subject to error. Although it is possible to locate a pig electromagnetically, the present invention in another aspect provides a pig with sensing means for sensing the physical properties of the wall of the pipe within which it travels, so as to detect a join between adjacent pipes and thereby control the positioning of the pigacross the join so that clamping means on the pig can clamp both pipes thereby aligning them and holding them in correct shape.

Although it may be possible for the clamping means to correct the shape of the pipe simply by forcing all the clamps located around the internal circumference of the pipe to the same radial distance, a more sophisticated shape control apparatus can be provided by providing individual measuring elements of the clamping means around the internal circumference of the pipe and providing sensing means for sensing the radial position of each element of the clamping means when in contact with the pipe in its uncorrected position and responsive to the sensing means to apply a pressure to each element in relation to the sensed position so as to correct the pipe wall position.

An example of the invention will now be described with reference to the accompanying drawing which is a perspective view of a pig for aligning pipes.

The pig 10 is generally cylindrical in shape but is of reducing diameter towards both ends in order to allow passage of the pig through curved pipes. At the mid-region there are provided two rows 11, 12 of eight clamping rams, the rams of each row being equidistantly spaced around the circumference of the pig, leaving a small gap 13 between each row of rams 11,12. At one end of the pig is a radiation source 15, such as of gamma rays, for use in testing the weld made at a join in the pipeline. Adjacent the radiation source is a driving mechanism including extendible driven wheels 16 for engaging the internal surface of the pipe to drive the pig along the length of the pipe. At the other end of the pig is provided a main computer 17 and a remote control unit 18 including programs for operating the computer 17 and spring loaded trailer wheels 19.Rechargeable electric batteries are located in the central region of the pig for operating the computer 17 and for energising a hydraulic pump 21 for operating the clamps 11,12 and the extension of the driving wheels 16. An electric motor (not shown) is provided for driving the wheels 16 themselves.

In the central region of the pig, there is provided a sensor (not shown) for sensing the physical properties of the pipe wall immediately adjacent to it. The pig is set in motion down the pipeline by means of the driving wheels 16 until the sensor senses a discontinuity in the wall of the pipe, indicating that the pig has reached a join in the pipeline which is to be welded. The sensor causes the pig to stop with the two rows of clamps 11, 12 equidistantly spaced from the join of the pipes. The rams are extended into contact with the end regions of the pipes and sensing devices, such as potentiometers, provide an electrical output representing the extension of each element of the clamps, which output is fed to the main computer which calculates the pressure to be applied to respective elements in order to force the ends of the adjacent pipes into aligned circular shapes.These pressures are then fed to the respective elements of the clamps and the process continues until the computer registers that the pipes have been forced to their desired shape. While the ends of the pipes are held in correct shape and alignment, welding takes place from outside the pipeline, the gap 13 between the two rows of clamps being left free of clamping elements to allow the welding operation to take place and weld material to pass into the bore of the pipes without danger of welding the clamping elements to the pipe, but the gap 13 between the rows of clamping elements is sufficiently small that the end region of the pipes to be welded are accurately held in the desired shape.

After completion of the welding operation, the wheels 16 drive the pig so as to align the radiation source with the newly formed weld, and sensors on the exterior of the pipeline use the transmitted radiation to detect any flaws in the weld. After the weld has been tested as satisfactory, the pig can move under its own power or can be forced by fluid pressure within the pipeline to another location.

Claims

CLAIMS:

1. A a pig for use during the welding together of two pipes, the pig fitting within the pipes extending across the join and being provided with clamping means for engaging the pipes to be joined at the end region of each pipe, but leaving a gap between the extreme end of each pipe and the clamping means.

2. A pig for use during the welding together of two pipes, the pig comprising sensing means for sensing the physical properties of the wall of the pipe within which it travels, so as to detect a join between adjacent pipes and thereby control the positioning of the pig across the join so that clamping means on the pig can clamp both pipes thereby aligning them and holding them in correct shape.

3. A pig as claimed in claim 1 or claim 2, wherein the clamping means comprises a plurality of elements and means for sensing the radial position of each element of clamping means when in contact with the pipe in its uncorrected position and means responsive to the last-mentioned sensing means to apply pressure to each element in relation to the sensed position so as to urge the pipe wall towards a desired shape.

4. A pig for use during the welding together of two pipes substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.