WO1988009460A1

WO1988009460A1 - Anti-fouling covering for sub sea structures

Info

Publication number: WO1988009460A1
Application number: PCT/GB1988/000403
Authority: WO
Inventors: Thomas Christopher Arnott
Original assignee: Regal Technology (U.K.) Ltd.
Priority date: 1987-05-21
Filing date: 1988-05-20
Publication date: 1988-12-01
Also published as: DK454489D0; AU1785388A; GB8711996D0; DK454489A; BR8807514A

Abstract

The covering, comprises anti-fouling metal sheeting (13, 13', 20) which is adapted to enclose the surface (11) of a sub sea structure, and which has corrugations (14). The sheeting is in the form of a strip (13) which is transversely corrugated and is adapted to be spirally wound onto the structure. It is copper or copper-nickel. The process for applying the covering (13, 13', 20) to a tubular sub sea structure (11) comprises the steps of coating the surface to be protected with an elastomeric anti-corrosion material, applying the sheeting (13, 13', 20) of anti-fouling metal to the elastomeric material to enclose the structure to be protected, applying a pressure of the area of the sheeting to provide a restricting force thereto and vulcanising the elastomeric material. As the sheeting is corrugated the corrugations (14) allow movement of and changes in the circumference of the elastomeric coating to be accomodated during and after the vulcanisation process without undue stress on the bond between the coating (12) and the metallic covering (13, 13', 20). The sheeting (13, 13', 20) is corrugated such that the corrugations (14) extend longitudinally or substantially longitudinally of the structure (10). The sheeting may be in the form of several individual strips wound transversely onto the structure. The anti-corrosion material may be an epoxy resin which is cured chemically after the metallic sheeting has been wound onto the structure. The structure to be protected is normally an offshore structure but may be a structure for use in deeper waters.

Description

ANTI-FOULING COVERING FOR SUB SEA STRUCTURES.

This invention relates to a covering to protect tubular sub sea offshore structures from fouling by marine organisms particularly offshore structures and to a process for applying the covering.

Marine fouling of offshore structures by marine organisms, the most troublesome being mussels, normally occurs in depths of 20 to 100 feet and involves the operators of these structures in expensive cleaning processes. It also involves higher than necessary costs of the structures due to additional steel required to accommodate increased weight and high wave loadings due to increased dimensions of the members. It is known that copper or copper and nickel prevents the growth of marine fouling due to emission of copper ions.

Copper or copper-nickel sheeting applied directly to the steel surfaces is affected by what is known as a switching off effect or earthing and prevents the emission of copper ions from the surface of the metal. It is necessary to have an insulation material between the steel and the copper. This can be achieved by the use of elastomers or epoxies.

Certain parts of offshore structures are protected from the effects of corrosion by elastomer coatings vulcanised and bonded to the steel surfaces. This also provides a good interface for cupro nickel sheet metal. Various methods have been attempted in the recent past to provide the best technical and economical solution to apply anti-fouling material to tubular steel members. Two systems which have found merit and have been used are:-

(a) forming two half shells of copper-nickel which are prepared and attached to the elastomer coating and bonded in position.

(b) by copper-nickel wire mesh supported in a matrix of elastomer or epoxy, or copper granules bonded to the surface of rubber and which is applied in sheet form to the anti-corrosion coat on the tubular member. The coated pipe is then placed in an autoclave where temperature cross-links the elastomer anti-corrosion coat and forms a bond to the steel and also the anti-fouling material.

System (a) is very Labour intensive as only relatively short lengths of half shells of copper -nickel can be applied at one time and cannot be applied to anything other than straight lengths of pipe.

System (b) is expensive due to the high cost of manufacturing the anti-fouling material mesh or granule.

Attempts have been made to apply to copper-nickel sheeting to a tubular section (pipe) by preparing it in a narrow w i d t h approximately 75mm to 100mm wide wound on a reel and winding it in a spiral manner continuously over the full Length of the pipe. This process was discounted as unsuccessful owing to the different expansion and contraction factors between elastomer and copper-nickel. Following the vulcanisation process which is normally carried out at temperatures between 110º and 170º C the concentration of the elastomer being greater than the contraction of cupro nickel exerted high stress to the chemical bond between elastomer and copper-nickel either causing disbondment or a buckling effect of the copper- nickel cladding.

An object of this invention is to obviate or mitigate the aforementioned disadvantages.

According to one aspect of the present invention there is provided a covering to protect tubular sub sea structures from fouling by marine organisms, and covering comprising anti-fouling metal sheeting which is corrugated.

Preferably, the metallic sheeting is in strip form which is corrugated transversely and is copper or copper- nickel.

According to another aspect of the invention there is provided a process for applying the covering to a tubular sub sea structure to protect said structure from fouling by marine organisms, said process comprising the steps of coating the surface to be protected with an elastomeric anti-corrosion material, applying a sheeting of anti- fouling metal to the elastomeric material to enclose the structure to be protected, applying a pressure of the area of the sheeting to provide a restricting force thereto and vulcanising the elastomeric material, characterised in that the sheeting is corrugated whereby the corrugations allow movement of and changes in the circumference of the elastomeric coating to be accommodated during and after the vulcanisation process without undue stress on the bond between the coating and the metallic covering.

In addition the corrugation effect allows the metallic anti-fouling covering to reduce its area and transfer the moulding pressure to the elastomeric coating. The anti-fouling metallic strip is preferably 75mm to 100mm wide and 1mm to 2mm thick in a continuous length long enough to cover the tubular structure to be protected. The strip is processed through a corrugating machine to produce an approximate 1mm to 2mm profile corrugation, and the corrugated strip is formed into a reel. The size of the corrugations can be varied depending on the diameter of the tubular member to be covered. Before it is applied to the elastomer coating, the strip is chemically or mechanically cleaned and a bonding agent applied to the contact surface.

According to a further aspect of the invention there is provided a tubular sub sea structure having an anti-fouling covering applied to a surface to be protected, said surface being pre-coated with an anti-corrosion material and said anti-fouling covering comprising sheeting of an anti-fouling metallic material, characterised in that said sheeting is corrugated. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of part of a tubular sub sea structure having an anti-fouling protective covering in accordance with the present invention; Fig. 2 is a side elevation of the anti-fouling protective covering of Fig. 1 passing through a corrugating machine;

Fig. 3 is a plan view of Fig. 2;

Fig. 4 is a side elevation of part of tubular sub sea structure having a covering in accordance with a modified arrangement; and

Fig. 5 is a perspective view of part of a covering according to another embodiment.

Referring to the drawings. Fig. 2 illustrates a protected tubular marine, i.e. sub sea structure 10 in this embodiment, a covered pipe 11 and it is shown with portions cut away for clarity. Other tubular structures, such as legs or jackets may be similarly protected.

The structure 10 comprises a Length of steel pipe 11 the outer surface of which is completely coated with an anti-corrosion material 12 and then totally encapsulated with a strip of anti-fouling metallic material 13 such as copper or copper-niekeI. The strip is applied in a spiral manner by hand or machine while rotating the coated pipe.

The strip 13 is pre-corrugated to provide transverse corrugations prior to being wound onto the coated pipe (for example by passing through a corrugating machine 15).

Also, the metallic corrugated strip is chemically or mechanically cleaned and a bonding agent is applied thereto before it is wound onto the coated pipe 11.

When the strip is wound spirally onto the pipe 11, the corrugations 14 run longitudinally or substantially Longitudinally of the pipe. The anti-corrosion coating 12 may be an epoxy resin which after the metal strip has been wound into the pipe, is cured chemically in a manner known per se in the art. Preferably however, the anti-corrosion coating is an elastomeric material. Once the strip has been wound onto a pipe coated with an elastomeric material, a temporary covering, not shown is wrapped around the metallic covering, e.g. a nylon tape applied at high pressure, e.g. 70 - 120 Kilos to provide a restricting force, over the full length of the metallic covering, and thereafter the elastomeric material is vulcanised at, for example 110º to 170º C to form an elastomer. On completion of the vulcanisation process the temporary covering can be removed.

During vulcanisation, the elastomer flow fills the corrugations and on cooling the differential in contraction of the elastomer and metal covering is accommodated due to the weakness and the even deformation of the metal covering. On contraction of the elastomer the deformation of the metal covering is therefore evenly distributed.

The elastomeric bond so formed can now accommodate the differing rates of contraction and expansion of the elastomer 12 and anti-fouling strip 13 by virtue of the corrugations 14. Furthermore the elastomer vulcanised within the corrugations 14 will protect the anti-fouling strip 13 from impacts.

In an alternative arrangement. Fig. 4, the metal covering is in the form of a series of transversely corrugated strips 13' each of which is wound transversely round the structure such that the sides of adjacent strips abut or overlap, and the corrugations run longitudinally of the structure.

In a further embodiment. Fig. 5, the metal covering comprises two or more shell portions 20, (only one of which is shown). They locate around the structure and are longitudinaIly corrugated so that the corrugations run longitudinally of the structure.

While the protective covering is particularly suitable for offshore structures it can also be applied to structures intended for use in deeper watess.

Claims

C L A I M S .

1. A covering to protect tubular sub sea structures (10) from fouling by marine organisms, comprising anti-fouling metal sheeting (13, 13', 20) adapted to enclose the surface (11) of the structure, characterised in that said sheeting is cor ruga ted (14).

2. A covering according to claim 1, characterised in that said sheeting is in the form of a strip (13. 13') which is transversely corrugated.

3. A covering according to claim 1 or 2, characterised in that the sheeting (13) is adapted to be spirally wound onto the structure.

4. A covering according to any one of claims 1 to 3, characterised in that the sheeting (13, 13', 20) is copper or copper-nickel.

5. A process for applying a covering (13, 13', 20) to a tubular sub sea structure (11) to protect said structure from fouling by marine organisms, said process comprising the steps of coating the surface (11) to be protected with an elastomeric anti-corrosion material (12), applying a sheeting (13, 13', 20) of anti-fouling metal to the elastomeric material (12) to enclose the structure to be protected, applying a pressure of the area of the sheeting to provide a restricting force thereto and vulcanising the elastomeric material, characterised in that the sheeting, is corrugated whereby the corrugations (14) allow movement of and changes in the circumference of the elastomeric coating to be accommodated during and after the vulcanisation process without undue stress on the bond between the coating (12) and the metallic covering (13, 13', 20).

6. A process according to claim 5, characterised in that the sheeting (13, 13', 20) is corrugated such that the corrugations (14) extend longitudinally or substantially longitudinally of the structure (10).

7. A process according to claims 5 or 6, characterised in that the sheeting is a strip (13, 13') which is corrugated transversely.

8. A process according to claim 7 characterised in that the strip (13) is wound spirally onto the coated structure (11).

9. A process according to any one of claims 4 to 7, characterised in that the corrugated sheeting (13, 13' 20) is cleaned chemically or mechanically and a bonding agent is applied to the contact surface thereof before the sheeting is applied to the coated structure (11).

10. A tubular sub sea structure (10) having an anti-fouling covering (13, 13', 20) applied to a surface (11) to be protected, said surface (11) being pre-coated with an anti-corrosion material (12) and said anti-fouling covering (13, 13', 20) comprising sheeting of an anti-fouling metallic material, characterised in that said sheeting is corrugated (14).

11. A structure according to claim 10, characterised in that the corrugations (14) extend Longitudinally or substantially longitudinally of the structure (10).

12. A structure according to claim 10 or 11, characterised in that the sheeting (13) is in the form of a strip which is corrugated transversely and is spirally wound onto the coated structure.

13. A structure according to claim 10 or 11, characterised in that the sheeting is in the form of a plurality of strips (13') each of which is corrugated transversely and is wound transversely onto the coated structure.

14. A structure according to claim 10 or 11, characterised in that the sheeting is in the form of two or more shell po rt i ons (20) which locate on the coated structure and which have longitudinal corrugations (14).

15. A covering to protect tubular sub sea structures substantially as hereinbefore described with reference to the accompanying drawings.