GB2368034A

GB2368034A - Welding Pig

Info

Publication number: GB2368034A
Application number: GB0020133A
Authority: GB
Inventors: John Spraggon
Original assignee: Pipeline Engineering and Supply Co Ltd
Current assignee: Pipeline Engineering and Supply Co Ltd
Priority date: 2000-08-17
Filing date: 2000-08-17
Publication date: 2002-04-24
Also published as: GB0020133D0

Abstract

A pipe sealing unit in the form of a welding pig consists of two modules, a welding unit (10) and a sealing unit (20), and is used in the welding of two sections of pipe (1, 2) together along a weld joint (5). Each unit (10, 20) comprises a body (11) and a pair of inflatable disc seals (12). The body (11) is commonly manufactured from carbon steel. The disc seals (12) incorporate a number of disc portions (12a) which are commonly manufactured from polyurethane. The invention provides a seal which is at least as effective as those provided by welding spheres, but which also is easily removable from the pipeline by pigging.

Description

WELDING PIG

The present invention relates to the field of welding, and in particular to the sub-sea welding of pipeline components.

At present, sub-sea welding of pipeline components is most commonly carried out within a hyperbaric welding habitat on the seabed. Hyperbaric welding requires that the areas at the ends of the pipes bordering the weld joint are sealed. Such sealing means are necessary due to the fluctuating pressure within the welding habitat caused by the surface sea swell.

Because of the hyperbaric conditions, the gas contained within the pipes is at high pressure. Without the use of such sealing means, a pressure drop within the habitat caused by sea swell can cause the high pressure gas within the pipe to escape via the partially closed weld joint into the lower pressure area of the habitat outwith the pipe. This causes the molten metal at the weld joint to blow out, leaving large craters which must be repaired, or in some cases requiring the whole

weld to be cut out and re-welded. This escape of pressure is commonly known as a"blow-back".

Until now, the most common method of sealing the ends of the pipes has been to use inflatable welding spheres within the ends of the pipes, as can be seen in Figs. l (a) and l (b). The usual method of hyperbaric welding is to have the two sections of pipe 1,2 positioned on the seabed and then to insert and inflate first welding spheres (not shown) in each of the pipes 1,2. Second welding spheres 3,4 are then inserted into the ends of the pipes 1,2 but are not inflated. The hyperbaric chamber is then positioned over the joint where the two pipes 1,2 meet and is pressurised. The second spheres 3,4 are then inflated-usually by divers-to create a double seal in each pipe 1,2. With the double seal, the pipes can then be welded together along a weld joint 5 without fear of a blow-back.

Although the welding spheres 3,4 are effective in creating the seal at the ends of the pipes 1,2, one drawback of using the spheres 3,4 is when it comes time to remove them from the pipes 1,2. The most common way of removing the spheres 3,4 is to push them out of the pipe using gas or water from direction A, which is more commonly known as"pigging". However, pigging requires high pressure and as the pigging pressure increases, the unstable welding spheres can twist and lock in the pipe, as shown in Fig. l (b). This in turn gives rise to excessive pigging pressures. Furthermore, pipeline features such as junctions or valves can present potential problem points where the spheres can get

caught. Until now, the time and cost implications of these drawbacks have been accepted due to the spheres' ability to prevent blow-back.

However, it is an aim of the present invention to provide an apparatus for use in hyperbaric welding environments which provides a seal which is at least as effective as those provided by welding spheres, but which also is easily removable from the pipeline by pigging.

According to a first aspect of the present invention, there is provided a pipe sealing apparatus, said apparatus comprising first and second modules, each of said modules comprising a substantially rigid body portion and at least one first annular seal.

Preferably, each of said modules comprises a pair of first annular seals. Preferably, said each of said first annular seals is inflatable.

Preferably, said first module further comprises a second inflatable annular seal. Preferably, said second inflatable seal has a heat resistant coating.

Preferably said first seals are inflated with water.

Preferably, said second seal is inflated with a gas.

Most preferably, said gas is air.

Preferably, each of said first and second modules further comprises pressure monitoring means.

Preferably, said pressure monitoring means is an

annulus port located on the body portion of each module.

Preferably, said body portion is steel. Most preferably, said body portion is carbon steel.

Alternatively, said body portion may be polyurethane.

Preferably, said first seals are polyurethane.

Alternatively, said first seals may be rubber.

According to a second aspect of the present invention, there is provided a method of welding first and second pipes together, said method comprising the steps of: positioning said first and second pipes so that first ends of said pipes face each other; inserting first and second modules into each of said first ends of said first and second pipes respectively, each of said modules comprising a substantially rigid body portion and at least one first annular seal, and wherein said first module has a second annular seal, said second seal being inflatable; positioning said first module in said first pipe so that said second seal protrudes from said first end of said first pipe; inflating said first annular seals so as to provide a fluid tight seal between said modules and an inner surface of said pipes; drawing said pipes together until said first ends of said pipes define a joint; inflating said second seal so that said joint between said first ends of said pipe is sealed by said second seal;

welding said pipes together along said joint ; and pushing said modules out of said pipes under high pressure.

Preferably, each of said modules has a plurality of first annular seals. Most preferably, each of said modules has a pair of first annular seals. Preferably, said first annular seals are inflatable.

Preferably, said second inflatable seal has a heat resistant coating.

Preferably said first seals are inflated with water.

Preferably, said second seal is inflated with a gas.

Most preferably, said gas is air.

Preferably, said pressure monitoring means is an annulus port located on the body portion of each module.

Alternatively, said body portion may be polyurethane.

Preferably, said first seals are polyurethane.

Alternatively, said first seals may be rubber.

A preferred embodiment of the present invention will now be described, with reference to the accompanying drawings, wherein:

Figs. l (a) and (b) are drawings to accompany the description of the prior art ; and Fig. 2 shows a side elevation view of a welding pig according to the present invention.

The welding pig consists of two modules, a welding unit 10 and a sealing unit 20, and is to be used in the welding of two sections of pipe 1,2 together along a weld joint 5. Each unit 10,20 comprises a body 11 and a pair of inflatable disc seals 12. The body 11 is commonly manufactured from steel, usually carbon steel.

The disc seals 12 incorporate a number of disc portions 12a which are commonly manufactured from polyurethane.

Each disc seal 12 performs the same task as a prior art welding sphere 3,4 previously described and shown in Fig. l (a).

Both of the modules are required in order to affect a weld. The welding unit 10 is equipped with an inflatable seal 13, such as that described in British Patent Application No. 9910021.6, which when inflated expands a flexible, heat-resistant backing material against the underside of the weld joint 5. As a result, the volume of gas passing in the pipes 1,2 due to the hyperbaric welding environment is reduced to virtually zero, and therefore the possibility of blowback during welding is also reduced considerably.

The units 10,20 can either be deployed in the pipes 1,2 before going underwater, or else a diver or remotely

operated vehicle (ROV) may insert the units 10, 20 on the seabed. Once the units 10, 20 are installed in the pipeline, the disc seals 12 are inflated with water via a valve (not shown) on the body 11, normally to hold 2 Bar differential pressure. An annulus port (not shown) is provided on each unit 10,20 between each pair of disc seals 12 so that the pressure between the seals 12 can be monitored during deployment.

Once the units 10,20 are correctly installed in the two pipes 1,2 which are to be connected, the pipes 1,2 are drawn together so as to leave a 20mm gap between the weld faces of each pipe 1,2. An inflation lance (not shown) is then inserted into the inflatable seal 13 so as to inflate the seal 13. The weld faces of the pipes 1,2 are then drawn together to close the 20mm gap between the pipes 1,2, with the inflatable seal 13 expanded against the underside of the weld joint 5.

In this way, the welding of the two pipes 1,2 can be effected without any significant volume of gas being present in the pipe at the weld joint 5.

Once the welding operation is complete, the units 10,20 can be pigged out using conventional pigging method.

When they are pigged out of the pipes, the welding seal 13 remains inflated so that any debris in the pipes can be removed at the same time as the units 10,20 are removed. Thus, the units 10,20 perform in the same manner as standard utility pigs when they are being removed.

An advantage of the welding pig apparatus is that the seal components of the units can be removed from the body and either refurbished or replaced. This is in contrast to conventional welding spheres which must be replaced in their entirety when worn out.

It will be understood by those skilled in the art that the above represents only one preferred embodiment of the present invention, and that further embodiments are possible. For example, the body of each unit is preferably made from carbon steel. However, it would equally be possible to use a plastics material such as polyurethane for the body. Another embodiment may also use a material other than polyurethane for the disc seals, such as one of several types of rubber, such as Neoprene, Nitrile or Silicon.

These and other modifications and improvements can be incorporated without departing from the scope of the invention.

Claims

CLAIMS 1. A pipe sealing apparatus comprising first and second modules, each of said modules comprising a substantially rigid body portion and at least one first annular seal.
2. A pipe sealing apparatus according to Claim 1, wherein each of said modules includes a pair of first annular seals.
3. A pipe sealing apparatus according to Claim 2, wherein each of said first annular seals is inflatable.
4. A pipe sealing apparatus according to any preceding Claim, wherein each of said first annular seals is inflated with water.
5. A pipe sealing apparatus according to any preceding Claim, wherein said first module further includes a second inflatable annular seal.
6. A pipe sealing apparatus according to Claim 5 wherein said second inflatable seal has a heat resistant coating.
7. A pipe sealing apparatus according to Claim 5 or 6 wherein said second seal is inflated with a gas, preferably air.
8. A pipe sealing apparatus according to any preceding Claim, wherein each of said first and second modules further includes pressure monitoring means.
9. A pipe sealing apparatus according to Claim 8, wherein said pressure monitoring means is an annulus port located on the body portion of each module.
10. A pipe sealing apparatus according to any preceding Claim, wherein said body portion of each of said first and second modules is of steel, carbon steel or polyurethane.
11. A pipe sealing apparatus according to any preceding Claim, wherein said seals are of polyurethane or rubber.
12. A method of welding first and second pipes together, said method comprising the steps of : positioning said first and second pipes so that first ends of said pipes face each other; inserting first and second modules into each of said first ends of said first and second pipes respectively, each of said modules comprising a substantially rigid body portion and at least one first annular seal, and wherein said first module has a second annular seal, said second seal being inflatable; positioning said first module in said first pipe so that said second seal protrudes from said first end of said first pipe;

inflating said first annular seals so as to provide a fluid tight seal between said modules and an inner surface of said pipes ; drawing said pipes together until said first ends of said pipes define a joint; inflating said second seal so that said joint between said first ends of said pipe is sealed by said second seal ; welding said pipes together along said joint ; and pushing said modules out of said pipes under high pressure.
13. A method according to Claim 12, wherein each of said modules has a plurality of first annular seals.
14. A method according to Claim 12 or 13, wherein said second inflatable seal has a heat resistant coating.
15. A method according to any of Claims 12 to 14, wherein said first seals are inflated with water.
16. A method according to any of Claims 12 to 15, wherein said second seal is inflated with a gas, preferably air.
17. A method according to any of Claims 12 to 16, wherein the pressure in the seals is monitored by pressure monitoring means provided in each of said first and second modules.
18. A method according to Claim 17, wherein said pressure monitoring means is an annulus port located on the body portion of each module.
19. A method according to any of Claims 12 to 18, wherein said body portion of each of said first and second modules is of steel, carbon steel or polyurethane.
20. A method according to any of Claims 12 to 19, wherein said seals are of polyurethane or rubber.