WO1997017567A1

WO1997017567A1 - Coating of pipe joints

Info

Publication number: WO1997017567A1
Application number: PCT/GB1996/002657
Authority: WO
Inventors: Ernest Coutts
Original assignee: Nicc Limited
Priority date: 1995-11-04
Filing date: 1996-11-01
Publication date: 1997-05-15
Also published as: AU7321096A; GB9522646D0

Abstract

There is provided a procedure and an arrangement for coating a bare joint (10) between two pipes (12, 14) otherwise coated with a pipe-coating (16, 18). The procedure and arrangement involves providing two pipes (12, 14) precoated with a pipe-coating (16, 18) and a shell (20, 22) formed in two semi-cylindrical sections, substantially or entirely made of the same material as the pipe-coating (16, 18), wherein the shell (20, 22) is subsequently fused to said pipe-coating (16, 18) to form a shroud for the joint (10). The procedure further involves injecting an infill material to fill a void which initially exists between the pipes (12, 14) and the shell (20, 22) once fusing has taken place, through the use of a vent hole (28, 30) and a fill hole (28, 30). In addition there is provided a procedure for forming a sleeve (20, 22) for use in the previous procedure and arrangement, which is intended to shroud the joint (10).

Description

"Coating of Pipe Joints"

This invention relates to procedures and arrangements for coating of pipe joints, and relates more particularly but not exclusively to procedures and arrangements for forming polypropylene coatings around bare-metal joints in polypropylene-coated pipes.

Polypropylene is a material which has recently found its place in the pipeline coating market. The new coating offers many advantages over those previously used, namely, superior insulation properties, resistance to fatigue induced by external pressure/temperature, and excellent abrasion resistance.

Whilst "mill coating" of the pipes is generally a straightforward operation, the problem of how to provide a homogenous retrofittable coating during the laying of the pipes has given rise to a host of attempts using csemical bond techniques which do not provide an adequate bond to the parent coating. The only way to achieve this bond is to physically fuse polypropylene to the coating using heat. A site- applied coating by way of injection moulding via specially "tailored to suit" moulds would in theory work, but the practicalities do not suit the "pipelay spread" environment. The procedure of site-applied injection moulding has major drawbacks, as follows:-

A. The immobile nature of the capital equipment required to carry out the injection moulding operation and the associated purchase costs. B. The requirement of expensive dedicated moulds for each contract and their maintenance. C. The site-applied joints are hot and dangerously semi-cured as they are fed with the pipe along a series of rollers, guides and other pipe-handling equipment. This gives rise to the likely disbonding or damaging of the joint coatings. D. The operational speed as a result of "C" during pipelay operations is drastically affected because of the requirement for forced cooling of each joint. E. The mobilising of highly trained operatives and the associated costs.

The present invention provides procedures and arrangements which obviate or mitigate the above disadvantages.

According to a first aspect of the present invention there is provided a method for coating a bare joint between two pipes otherwise provided with a pipe- coating the method comprising the steps of; providing a shell dimensioned to shroud the joint, the shell formed of a shell material which is compatible with the pipe-coating material of the pipe-coating; fitting the shell around the joint in contact with the pipe-coating on either side of the joint; and fusing selected parts of the shell to the pipe-coating provided on the pipes.

The shell may be principally or entirely composed of a material which is selected to be csemically substantially identical to the material of the pipe- coating and which may also have the same physical form. The shell and the pipe-coating may both be principally or entirely composed of polypropylene.

The shell may be constituted by two or more shell components each formed as a length of arcuate material, the shell components collectively forming a substantially cylindrical shroud for the joint.

Fusing of selected parts of the shell to the pipe- coating may be undertaken by locally melting mutually contacting parts of the shell and of the pipe-coating. Where the shell is constituted by a plurality of shell components, these components are preferably mutually fused along lines of mutual contact to form a unitary shroud, such mutual fusing of shell components preferably being carried out contemporaneously or simultaneously with fusing of the shell to the pipe- coating. Fusing is preferably carried out by highly localised heating.

Subsequent to fitting of the shell around the joint, and preferably also subsequent to fusing of selected parts of the shell to the pipe-coating provided on the pipe, a filling material may be injected between the shell and the underlying pipe, preferably such as substantially to fill the void initially existing between the joint and the shell. According to a second aspect of the present invention there is provided apparatus for coating of pipe joints, the apparatus comprising; a shell dimensioned to shroud the joint, the shell being formed of a shell material which is compatible with the pipe-coating material of the pipe-coating, the shell being constructed or adapted to fit around the joint in contact with the pipe-coating on either side of the joint; and further comprising fusing means for fusing selected parts of the shell to the pipe- coating provided on the pipes.

The shell may initially be in the form of two or more shell components each formed as a length of arcuate material, the shell components collectively forming a substantially cylindrical shroud for the joint. The shell is preferably initially in the form of two semi- cylindrical lengths. The inside diameter of the shell may be substantially equal to the outside diameter of the pipe-coating provided on the pipes on either side of the bare joint, and the length of the shell is preferably greater than the separation of material- coated portions of the pipe on either side of the bare joint such that the shell is ultimately lap-jointed to the pipe-coating.

The shell may be principally or entirely composed of a material which is csemically identical to the material of the pipe-coating and which may also have the same physical form. The shell may be principally or entirely composed of polypropylene.

The fusing means preferably comprises ohmic heating resistors located adjacent to or in contact with the selected parts of the shell that are to be fused to the pipe-coating. The ohmic heating resistors may be in the form of wire or tape located on or set into the parts of the shell to be fused to the pipe-coating, for example on the bore of the shell at longitudinally opposite ends thereof and (in the context of the plural-component shell) along the abutting longitudinal edges of the shell components.

The shell may be provided with at least one fill hole and at least one vent hole whereby a filling material may be injected between the shell and the underlying pipe after fitting of the shell around the joint.

According to a third aspect of the invention there is provided a method of forming a sleeve, the method comprising the steps of; winding a composite of polymeric fibre and initially molten polymer around a mandrel to form a mass of polymer; cooling the mass to form a solid shell; and providing local heating means on or adjacent to those parts of the shell which will subsequently contact the pipe-coating provided on the pipes.

The polymeric fibre may be a polypropylene cloth which may be woven. The fibre may be coated with an extruded sheet or film of molten polypropylene. Strands of fibre may be arranged to extend from the inner face of the shell components to provide a key for material subsequently injected under the shell.

The formed shell may be longitudinally divided into two or more shell components, and the local heating means extended to longitudinal edges of these components.

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, wherein:-

Fig. 1 is a longitudinal elevation of a bare-metal joint between polypropylene-coated pipes; Fig. 2 is a perspective view of the joint of Fig. 1, in the process of being shrouded by two shell components; Fig. 3 is a perspective view of the shell components of Fig. 2 with their integral ohmic heating elements; and Fig. 4 is a perspective view of the layout of the heating elements of Fig. 3.

Referring first to Fig. 1, this shows a welded joint 10 formed between and mutually joining two metal pipes 12 and 14 which may, for example, form part of a land pipeline or a submarine pipeline. The pipes 12 and 14 present bare metal in the immediate vicinity of the joint 10, but are otherwise respectively coated with layers 16 and 18 of polypropylene for the purposes of thermal insulation and corrosion protection. Welding of the joint 10 requires that the polymeric coating be removed from the pipes 12 and 14 in the immediate vicinity, but the protective function of the coating requires the subsequent restoration of an integral coating over the joint 10.

Fig. 2 shows a preliminary stage in restoration of the coating around the joint 10, comprising the steps of providing two matching semi-cylindrical polypropylene shell halves 20 and 22, locating the shell halves on either side of the joint 10, and subsequently clamping the shell halves 20 and 22 tightly together by suitable clamps (not shown) . The shell formed by the shell halves 20 and 22 is dimensioned in terms of its bore (internal diameter) and overall length to be a tight overlapping fit on the coatings 16 and 18 on either side of the joint 10, with the longitudinal edges of the shell halves 20 and 22 in firm mutual contact.

Fig. 3 shows ohmic heating elements 24 and 26 pre- fitted in the shell halves 20 and 22 respectively, to lie along one longitudinal edge of each shell half, and around the semi-circumference of the bore at each end of each shell half. The heating elements 24 and 26 extend along each shell half 20 and 22 on a "once- through" basis, and beyond each half shell at both ends as pigtails or flying leads for subsequent temporary connection to a power supply, as detailed below. The layout of the heating elements 24 and 26 is depicted in Fig. 4.

The heating elements 24 and 26 may each comprise a single strand of a suitable ohmic alloy (eg a nickel alloy) or (as schematically depicted in Fig. 3) as braided ribbons containing multiple strands of alloy wire.

In Fig. 3, the shell halves 20 and 22 are shown slightly separated for clarity, but they will in fact be tightly clamped together at the time that the heating elements 24 and 26 are connected to a suitable source of electric power. Electrical energisation of the heating elements 24 and 26 (either simultaneously or sequentially, and at a suitable power level) will cause them to heat up by ohmic conversion of electric power directly into heat, thereby causing localised melting of the mutually contacting portions of the shell halves 20 and 22, and of the underlying pipe coatings 16 and 18. After a suitable interval, power to the heating elements is switched off, and the elements are allowed to cool to ambient temperature. The polypropylene in the localised volumes around the heating elements resolidifies, thereby fusing together the contacting masses and forming a unitary solidified sleeve around the joint 10.

The interior of the fused-in-place sleeve will be hollow around the joint 10. This hollow may optionally be filled with a suitable material, placed in the hollow by injection. Each of the half shells 20 and 22 may have a respective hole 28, 30 drilled or otherwise formed in it, either subsequent to fusing or preformed with the original shell. The lower one of the holes 28, 30 will serve for injection of the filling material while the upper one of these holes will serve as a vent during injection.

Forming of the shell will now be discussed, by way of further example.

While the concept of a segmented outer shell is of primary importance, there is considerable difficulty in producing the segments (preferably half shells). The obvious method of using extruded pipe falls down on two main counts:

1 the size of the pipe required is beyond the normal capacity of extrusion lines. 2 the variety of sizes required and the volume of any one size makes tooling costs high in relation to turnover.

Other production methods, such as casting (which has problems with tooling costs and the probability of blow holes) and forming from thick sheets (which have problems of molecular memory causing a tendency to straighten under the influence of heat and time) , all appear to have problems in practical usage.

The proposed method of creating a spiral of woven polypropylene cloth coated with a layer of molten polypropylene, wrapped round a mandrel to form a solid tube, overcomes the problems.

The cloth is pre-woven in bulk and is coated with extruded molten polypropylene sheet or film. It is then wrapped round a mandrel which may be of any size. The only tooling required to alter the dimensions is a relatively inexpensive mandrel which may or may not have special features included on its surface.

Because of the laminar construction, which may use pre- stretched tape in the cloth, the shell segment is very stable and does not distort significantly during subsequent processing.

It is possible to have a network of fibres protruding from the inner layer which could be used to key to any material used as an infill between the shell and the inner pipe.

A slot(s) or cut(s) may be formed in the inside of the segment(s), leaving a thin section parallel to the axis of the segment. The cloth in this thinned section forms a hinge, allowing the segment to open along this axis. This would allow a segment of greater than a half section to be fitted over the pipe. The slot could subsequently be filled with a plastic material to restore the strength of the segment.

In summary, the present invention utilises pre-formed modular segments (as detailed above) where the unique method of their manufacture allows a variable "shell" thickness to be produced if required without the need for moulds. The segments are pre-wired along each jointing area face using electrical welding elements in the form of tapes. The "shells" are fitted around the "field joint" area and compressed and held in position using a special clamping device.

The tape ends are clamped in the sequence as in the diagrams accompanying this text, ie Figs. 3 and 4, via a simple electronic control unit which varies electrical current to the welding tapes. The unit houses a series of control components such as transformers, variable input/output regulators, a timer device and an automatic cut-out. The fusion/timer sequence is set and the unit is then energised creating a "welded field joint" encapsulation.

The resultant polypropylene joint can be utilised to act as a stand-alone coating or as a carrier void for a variety of csemical infill composite components, which can be facilitated by the addition at manufacture of injection and vent ports in the segments (see Fig. 3).

The installation sequence is as follows:-

A Clean bare metal of all contaminants, oil etc. B Prepare ends of pipe at field joint area by simple scraping to remove oxidised layer. C Apply anti-corrosion coat to bare metal up to the ends of the metal/coating interface. D Apply segments, position and clamp in place. E Fit welding/control unit leads to fusion tapes, set the weld/fusion time (this can operate automatically), and energise the unit. The joint is thereby fusion bonded to the mill coat and the segments fuse together also. F If required, the inner surfaces of the shell may be pre-treated to provide a key or tie coat for csemical infill products placed via injection or by other means. They may also have a pre- assembled bonded insulation layer added at segment manufacture.

The fusion-based joint-coating system described above offers great benefits to the pipelaying market by way of its simplicity, economy and its practicality especially where laybarge or reelship installation of offshore pipelines is required. The capital plant costs are low and the cost of maintenance is likewise. Minimal training is needed for operatives and repeatability of joint quality is controlled by the fusion unit.

Modifications and variations in the above described exemplary embodiments can be adopted without departing from the scope of the invention.

Claims

1. A method for coating a bare joint (10) between two pipes (12, 14) otherwise provided with a pipe- coating (16, 18), the method comprising the steps of; providing a shell (20, 22) dimensioned to shroud the joint (10), the shell (20, 22) being formed of a shell material which is compatible with the pipe-coating material of the pipe-coating (16, 18); fitting the shell (20, 22) around the joint (10) in contact with the pipe-coating (16, 18) on either side of the joint (10); and fusing selected parts of the shell (20, 22) to the pipe-coating (16, 18) provided on the pipes (12, 14) .

2. A method according to Claim 1, wherein said shell (20, 22) is principally or entirely composed of a material which is selected to be csemically substantially identical to the pipe-coating material of the pipe-coating (16, 18) and which has the same physical form.

3. A method according to either Claim 1 or 2 wherein said shell (20, 22) and said pipe-coating (16, 18) are both principally or entirely composed of polypropylene.

4. A method according to any preceding claim wherein said shell (20, 22) is constituted of two or more shell components (20, 22).

5. A method according to Claim 4, wherein each shell component (20, 22) is formed as a length of arcuate material, the shell components (20, 22) collectively forming a substantially cylindrical shroud for the joint (10).

6. A method according to either Claim 4 or 5 wherein the components (20, 22) are mutually fused along lines of mutual contact to form a unitary shroud.

7. A method according to any preceding claim wherein said fusing of selected parts is undertaken by locally melting mutually contacting parts of the shell (20, 22) and of the pipe-coating (16, 18).

8. A method according to Claim 6, wherein said mutual fusing of said shell components (20, 22) is carried out contemporaneously or simultaneously with fusing of selected parts of the shell (20, 22) to the pipe-coating (16, 18).

9. A method according to any preceding claim, wherein said fusing selected parts of the shell (20, 22) to the pipe-coating (16, 18) is carried out by highly localised heating.

10. A method according to any one of Claims 6 to 9 , wherein said mutual fusing is carried out by highly localised heating.

11. A method according to any preceding claim wherein the shell (20, 22) is formed by first forming a sleeve (20, 22), by winding a composite of polymeric fibre and l h initially molten polymer around a mandrel to form a mass of polymer; cooling the mass to form said shell (20, 22); and providing local heating means (24, 26) on or adjacent to those parts of the shell (20, 22) which will subsequently contact the pipe- coating (16, 18) provided on the pipes (12, 14) .

12. A method according to any preceding claim wherein a filling material is injected between the shell (20, 22) and the pipes (12, 14) to substantially fill a void initially existing between the pipes (12, 14) and the shell (20, 22), subsequent to the fitting of the shell (20, 22) around the joint (1°) and subsequent to the fusing of the selected parts of the shell (20, 22) to the pipe-coating (16, 18) provided on the pipes (12, 14).

13. Apparatus for coating of pipe joints (10), the apparatus comprising; a shell (20, 22) dimensioned to shroud the joint (10), the shell (20, 22) being formed of a shell material which is compatible with the pipe-coating material of the pipe-coating (16, 18), the shell (20, 22) being constructed or adapted to fit around the joint (10) in contact with the pipe-coating (16, 18) on either side of the joint (10); and further comprising fusing means for fusing selected parts of the shell (20, 22) to the pipe-coating (16, 18) provided on the pipes (12, 14).

14. Apparatus according to Claim 13 wherein the shell (20, 22) is initially in the form of two or more shell components (20, 22) each formed as a length of arcuate material, the shell components (20, 22) collectively forming a substantially cylindrical shroud.

15. Apparatus according to either Claim 13 or 14, wherein the shell (20, 22) is initially in the form of two semi-cylindrical lengths (20, 22).

16. Apparatus according to any one of Claims 13 to 15 wherein the inside diameter of the shell (20, 22) is substantially equal to the outside diameter of the pipe-coating (16, 18) provided on the pipes (12, 14) on either side of the joint (10) .

17. Apparatus according to any one of Claims 13 to 16 wherein the length of the shell (20, 22) is greater than the separation of the portions of the pip on either side of the bare joint (10) provided with the pipe-coating (16, 18) such that the shell (20, 22) is ultimately lap-jointed to the pipe-coating (16, 18) provided on the pipes (12, 14).

18. Apparatus according to any one of Claims 13 to 17, wherein said shell (20, 22) is principally or entirely composed of a material which is selected to be csemically substantially identical to the material of the pipe-coating (16, 18) and which has the same physical form.

19. Apparatus according to any one of Claims 13 to 18 wherein said shell (20, 22) and said pipe-coating (16, 18) are both principally or entirely composed of polypropylene.

20. Apparatus according to any one of Claims 13 to 19 wherein said fusing means comprises ohmic heating resistors (24, 26) located adjacent to or in contact with the selected parts of the shell (20, 22) that are to be fused to the pipe-coating (16, 18) .

21. Apparatus according to any one of Claims 13 to 20 wherein said ohmic heating resistors (24, 26) are in the form of wire or tape located on or set into the parts of the shell (20, 22) to be fused to the pipe-coating (16, 18).

22. Apparatus according to any one of Claims 13 to 21 wherein said ohmic heating resistors (24, 26) are located on the bore of the shell (20, 22) at longitudinally opposite ends.

23. Apparatus according to any one of Claims 13 to 22, wherein said ohmic heating resistors (24, 26) are located along the abutting edges of the shell components (20, 22) .

24. Apparatus according to any one of Claims 13 to 23 wherein said shell (20, 22) is provided with at least one fill hole (28, 30) and at least one vent hole (28, 30) whereby a filling material is injected between the shell (20, 22) and the pipes (12, 14) after fitting of the shell (20, 22) around the joint (10).

25. A method of forming a sleeve (20, 22), the method comprising the steps of; winding a composite of polymeric fibre and initially molten polymer around a mandrel to form a mass of polymer; cooling the mass to form a solid shell (20, 22); and providing local heating means (24, 26) on or adjacent to those parts of the shell (20, 22) which will subsequently contact pipe-coating (16, 18) provided on the pipes (12, 14).

26. A method according to either Claim 11 or 25 wherein the polymeric fibre is a polypropylene cloth which is woven.

27. A method according to any one of Claims 11, 25 or 26 wherein the fibre is coated with an extruded sheet or film of molten polypropylene.

28. A method according to any one of Claims 11 or 25 to 27 wherein strands of the fibre are arranged to extend from the inner face of the shell components (20, 22) to provide a key for the material subsequently injected under the shell (20, 22).

29. A method according to any one of Claims 11 or 25 to 28 wherein the formed shell (20, 22) is longitudinally divided into two or more shell components (20, 22) and wherein the local heating means (24, 26) extends to the longitudinal edges of these shell components (20, 22).