GB2139303A - Protecting pipe joints - Google Patents

Abstract

A method of protecting joints between steel pipes of a pipeline to be laid underwater, wherein a sleeve (10) of rubber or other suitable material and of preformed shape is press fitted around the joint by a machine press. The sleeve material or materials are selected to provide an inner surface of the sleeve which bonds to the steel, as by flowing under the applied pressure into the surface pores thereof, and to provide an external surface which is resistant to corrosion by salt water. <IMAGE>

Description

SPECIFICATION Rotecting joints in a pipeline for under water use This invention relates to a method of protect ing joints between steel pipes which are to form an underwater pipeline, to a sleeve means and to a machine for use in carrying out said method.

Conventionally, pipelines for carrying oil and gas and the like are formed by jointed steel pipes. For underwater use, the pipes are wrapped in concrete to protect the pipes from corrosion by salt water. The ends of the pipes to be jointed, as the pipeline is laid, as from a pipelaying barge, project from the concrete wrapping. The projecting pipe ends are com monly welded to form a sealed joint, but this joint then remains to be protected from corro sion. For this purpose a mastic asphalt is usually applied around the joint wholly to cover the steel between the concrete wrappings of adjacent pipes. This asphalt protection is applied using an inexpensive metal former to retain the soft asphalt while it sets, and the pipeline is laid underwater in this condition, with the metal formers still in place.

Amongst other disadvantages of the conventional method is one that the metal formers tend to detach and partly disintegrate with time, leaving metal fragments, often of rough and jagged nature, on the seabed.

These metal fragments are a hazard to any subsequent underwater work in the vicinity including trawl fishing and the like.

An object of the present invention is to provide an improved method of protecting joints in a pipeline to be laid underwater.

According to the invention, there is provided a method of protecting joints between steel pipes which are to form an underwater pipeline, according to which a preformed sleeve means is pressed by a machine press into position around the joint, the sleeve means being made orie or more materials presenting an inner surface which will bond to steel under the applied pressure and presenting an outer surface which will be resistant to corrosion by the water wherein the pipeline is to be laid.

In a preferred method, a sleeve means formed in two arcuate parts is employed, said sleeve means being formed of rubber or of plastics material having an inner lining of rubber. The two part sleeve means is press fitted together around the joint by a machine press, thereby to form a complete sleeve wholly encasing the joint between adjacent pipe wrappings.

Due to the existing temperature of the joint immediately subsequent to welding, about 90 to 110 degrees Centigrade, and under the applied pressure, the rubber inner surface of the sleeve is softened and flows into the surface pores of the steel pipeline at the welded joint therein, whereby the sleeve is permanently bonded into position to form a reliable seal against ingress of salt water which would otherwise corrode the joint.

A method of protecting pipe joints in accor- dance with the invention will now be exemplified making reference to the accompanying drawing, wherein the single figure shows one possible construction of sleeve means for use in the method.

In Fig. 1, the reference 10 generally denotes a sleeve means having two arcuate parts 12 and 14.

The sleeve parts can be press fitted together to interlock through hole and peg fittings 16.

The enlarged head of the pegs and the matching enlarged base of the holes will be apparent from secondary Fig. 1A.

The sleeve 12. 14 is made of a rubber selected to soften and flow at a temperature of about 100 degrees Centigrade.

Alternatively, the sleeve may have an outer skin of a selected material which does not substantially soften at a temperature of about 100 degrees Centigrade and which is corrosion resistant to salt water and an inner softenable skin of a selected rubber or possibly a selected nylon, being a material which will bond with steel under pressure, with or without heat.

In the preferred method, a pipeline is being formed of concrete wrapped steel pipes hot welded together and laid from a sea-going barge.

A sleeve 12, 14 as shown in Fig. 1 is applied around each joint immediately after the latter has been hot welded, whilst the steel remains hot. It is applied by means of a machine hot press, for example of an impact type, having two relatively movable formers which engage around the two parts of the sleeve and press fit them together around the joint. Under the elevated pipe temperature and the preselected applied pressure, the inner surface of the sleeve softens and flows into the surface pores of the pipe permanently to bond the sleeve into position, whereat it forms a seal for preventing ingress of salt water which would attack the steel.

The sleeve is preformed of an internal diameter to match the external diameter of the pipeline, a thickness to match that of the concrete wrapping, and a length to fill the space between the concrete wrappings of adjacent pipes. The sleeve may be slightly expanded or compressed in the longitudinal direction during the pressing and bonding operation.

In contrast to conventional methods of pipe joint protection, the sleeve is preformed in its sleeve shape, and this shape is generally retained during pressing and bonding. In consequence, a former analogous to that used for retaining mastic asphalt during application and setting is not required.

The method of the invention is not limited to the form of sleeve means shown in Fig. 1, and various alternative constructions of sleeve are possible.

For example, the invention is also applicable to the sealing of flange jointed pipelines, for which purpose it may be formed in longitudinally split parts which fit together at stepped ends defining an internal annular recess in the sleeve for encasing the jointed flanges. Furthermore, in this case, the sleeve will generally be applied cold, for which purpose it may be made of a resin glue which will bond to the steel of the pipe joint under the applied pressure of the machine press.

Various other modifications are possible within the scope of the invention.

Claims (21)

1. A method of protecting joints between steel pipes which are to form an underwater pipeline, according to which a preformed sleeve means is pressed by a machine press into position around the joint, the sleeve means being made of one or more materials presenting an inner surface which will bond to steel under the applied pressure and presenting an outer surface which will be resistant to corrosion by the water wherein the pipeline is to be laid.

2. A method according to claim 1, wherein the sleeve means is formed in two or more arcuate parts which are pressed together to form a sleeving around the joint.

3. A method according to claim 1 or claim 2, applied to steel pipes jointed by welding, wherein the sleeve means is pressed into position whilst the welded joint remains hot.

4. A method according to claim 3, according to which the inner surface of the sleeve means is formed by a material which at the temperature of the pipe and under the applied pressure will flow into the surface pores of the steel in order to bond said sleeve means around the joint.

5. A method according to any of the claims 1 to 4, according to which the steel pipes are concrete wrapped except at their jointed ends, and the sleeve means has a thickness substantially to match the thickness of the concrete wrapping.

6. A method according to any of claims 1 to 5, according to which the sleeve means is weighted, as by the incorporation of steel plates encapsulated therein, to have a weight per unit length substantially to match the weight per unit length of the rest of the pipeline, including any wrapping carried by the latter.

7. A method according to any of claims 1 to 6, according to which the inner surface of the sleeve means is formed by rubber.

8. A method according to claim 7, according to which the sleeve means, except for any weighting means incorporated therein, is formed entirely of rubber.

9. A method according to claim 7, wherein the outer surface of the sleeve means is formed by a corrosion resistant plastics material.

10. A method according to any of claims 1 to 9, according to which the sleeve means is formed in two or more parts which interengage through interlocking fittings.

11. A method according to claim 10, according to which the two or more parts of the sleeve means are bonded together by a resin glue at such interlocking fittings.

12. A method according to claim 1 or claim 2, applied to steel pipes which are flange jointed, according to which the preformed sleeve means includes an outward annular recess within which the jointed flanges are encased.

13. A method according to claim 12, according to which the sleeve means is formed in longitudinally split parts which are sealed together generally in the plane of the jointed flanges.

14. A method according to claim 1 or claim 2 or claim 12 or claim 13, applied to cold jointed steel pipes, according to which the preformed sleeve means is formed of a material which is softened under externally applied heat and/or the applied pressure to effect the bond with the steel.

15. A method according to claim 14, according to which the sleeve means is preformed of resin glue or the like.

16. A method according to any of claims 1 to 15, according to which the sleeve means is pressed into bonding relationship with the steel by a machine press which applies a preselected bonding pressure for causing the inner surface of the sleeve means to soften and flow into the surface pores of the steel whilst generally retaining the preformed shape of said sleeve means.

17. A method according to claim 16, according to which the machine press applies an impact bonding pressure to the sleeve means.

18. A sleeve means for use in the method of any of claims 1 to 17, comprising two or more parts which press fit together to form a complete sleeve, the inner surface of the said sleeve comprising a material to bond with steel under the applied pressure and the outer surface of said sleeve comprising a material which is corrosion resistant in the presence of salt water.

19. A machine press for use in the method of any of claims 1 to 17, comprising formers for enclosing the parts of a sleeve means having two or more parts positioned around a pipe joint in a steel pipeline and for applying a preselected pressure to such sleeve means to cause the inner surface of the sleeve means to soften and flow into the surface pores of the steel so as to bond the sleeve means around the pipeline.

20. A method of sealing joints in a steel pipeline to be laid underwater, substantially as hereinbefore described.

21. A sleeve means substantially as hereinbefore described with reference to the accompanying drawing.