WO1993014970A1

WO1993014970A1 - Improvements in or relating to anti-fouling coatings

Info

Publication number: WO1993014970A1
Application number: PCT/GB1993/000205
Authority: WO
Inventors: Thomas Christopher Arnott
Original assignee: Thomas Christopher Arnott
Priority date: 1992-02-01
Filing date: 1993-01-29
Publication date: 1993-08-05
Also published as: NO942852L; GB9202185D0; AU3456693A; NO942852D0; GB2279100A; GB9415382D0; GB2279100B

Abstract

An anti-fouling coating for a tubular structure (11) having an electrically insulating anti-corrosion coating (12) is provided by a plurality of panel sections (15) of anti-fouling material bonded to the surface of the anti-corrosion coating (12) in a helical series extending along and about the tubular structure (11), adjacent edges of serially adjacent panels (15) extending substantially parallel to the long axis of the tubular structure, and said adjacent edges being spaced apart by a predetermined distance (14) to accommodate differential thermal expansion and contraction of the anti-corrosion coating (12) and the anti-fouling material. The panel sections (15) may be pre-cut and assembled into a segmented strip with predetermined gaps between the adjacent panels prior to winding. The panels (15) are connected by strips (16) of material having tensile strength at least equal to that of the anti-fouling material, the connector strips (16) extending substantially the whole length of the gaps (14) with overlaps bonded to the edges of the adjacent panels (15). Alternatively, a continuous strip of anti-fouling material may be wound onto the tubular structure and subsequently slit along the length of the tubular structure at a plurality of equispaced circumferential locations so as to divide the wound strip into panels and to form said predetermined gaps between serially adjacent panels.

Description

"Improvements in or Relating to Anti-Foulinσ Coatings"

This invention relates generally to coatings or coverings for protecting tubular subsea structures, risers, conductors and caissons from fouling by marine organisms and to processes for applying the coating or covering.

Marine fouling of offshore structures and their appurtenances by marine organisms, especially mussels, is extremely troublesome and incurs high costs. The major growth of mussels occurs from L.A.T. down to minus 100 ft. Growth rates vary dependent upon water temperature, tides and prevailing weather conditions. In ideal conditions mussel build up can be as high as 200 mm in a growing season.

Offshore operators require to increase the amount of steel required to construct an offshore structure to compensate for the additional weight (many tons) of accumulated marine organisms, but more importantly to compensate for additional wave loadings due to the increased dimensions of affected members.

It has been a known fact for many years that copper, or copper nickel with a high percentage of copper, emits copper ions when in a submerged condition, which in turn prevents adherence of marine life to the copper surface.

Copper or copper nickel sheet must not be allowed to come into contact with the steel it is protecting, otherwise a galvanic action occurs accelerating corrosion and also making the copper ineffective as an anti-fouling material (a switching off effect).

Many of the appurtenances of offshore structures as well as some of the main structures are normally protected from corrosion by elastomer coatings vulcanised and bonded to the steel surfaces. The elastomer coatings are normally factory applied to steel members before the platform is constructed. The elastomer coating provides an ideal electrical insulation between the steel and the anti-fouling material.

Many attempts in the past have been made to provide a technically acceptable and cost effective method of applying copper or copper nickel to tubular steel. Systems which have been used in the past are:-

a) Forming two half shells of copper nickel which are prepared and applied to the uncured elastomer coat and bonded in position.

b) Supporting copper nickel wire mesh or copper nickel granules in a matrix of elastomer or epoxy which is then applied in sheet form to the anti-corrosion coat on the tubular member.

c) Producing the copper nickel sheet in strip form approximately 150 mm wide in which a corrugation effect or a regular depression has been formed, which is then prepared and helically wrapped around the elastomer coat.

The coated pipe is placed into a steam autoclave where the temperature crosslinks the elastomer and forms a bond between the elastomer and steel and between the elastomer and copper nickel.

System a) is very labour intensive as only short lengths of half shells can be applied at one time and require precise positioning to leave the longitudinal gaps between the half shells necessary to accommodate differential thermal expansion between the shells and the elastomers.

System b) is not cost effective as major manufacturing costs are involved in producing the wire mesh or granules in a rubber or epoxy matrix. A further disadvantage is that only approximately 35% of the surface area has an exposure of copper nickel.

System c) provides an effective anti-fouling coating but requires a substantial elastomer beneath the corrugation or concave deformation of the copper nickel to prevent the copper nickel contacting the steel. Any variance from a smooth cylindrical form increases the CD. (drag coefficient) , lift and vortex shedding of the tubular member, and increases the forces generated by water velocity.

It is accepted that it is not possible to successfully apply copper nickel sheet in strip form and in a helical wrap fashion due to the substantial variation in expansion and contraction between copper nickel and elastomer. During the vulcanisation process the elastomer goes into a flow condition before crosslinking. On cooling down after vulcanisation the elastomer coating contracts to approximately 80% of its original applied thickness. High forces are exerted between the elastomers and copper nickel resulting in either a break in the bond or a buckling effect of the copper nickel cladding.

System c) as previously described overcomes this problem due to the bellows effect of the deformations in the copper nickel allowing to some degree the copper nickel to contract mechanically from its original circumference, but with the stated disadvantages.

It is an object of the present invention to provide improved materials and methods for applying metallic anti-fouling coatings to tubular structures, which obviate or mitigate the abovementioned disadvantages of previous coating systems.

In accordance with a first aspect of the invention there is provided a metallic, anti-fouling, coating material adapted for helical winding about a tubular member having an electrically insulating coating applied thereto, said material comprising an elongate, segmented strip of anti-fouling material formed from a plurality of similar panel sections connected end to end by connector elements bonded thereto by an adhesive with a predetermined gap between adjacent sections, the adjacent edges of adjacent sections extending at a predetermined angle to the lateral edges of said segmented strip; said angle being determined by the pitch angle at which the strip is to be wound about said tubular member, and said gap being determined by the differential thermal expansion and contraction characteristics of said anti-fouling material and said electrically insulating coating; said connector elements each comprising a strip of material having tensile strength at least equal to that of the anti- bonding material, said strip extending along substantially the whole length of said gap and overlapping the edges of the adjacent panel sections on either side of said gap by a predetermined distance.

US-A-49877036 (W089/12144) shows a segmented strip of copper anti-fouling material, for application to a tubular structure by helical winding or in cigarette wrap fashion. The panels of the strip are connected by continuous narrow strips or a continuous mesh extending along the full longitudinal length of the segmented strip. The use of discrete, narrow connector strips spaced across the width of the panels, or of a mesh, results in non-uniform application of tensile forces during winding, causing buckling of the panels. Where the connector strips or mesh are of a material having greater yield than the panels, it is not possible for the panels to be bent by tensile force applied to conform to the curvature of the tubular during winding. Accordingly, the panels have to be pre-formed to the required curvature or else made sufficiently narrow (in the longitudinal direction of the segmented strip) that the flat panels do not deviate significantly from the curve of the tubular.

Preferably also, said anti-fouling material is copper or copper nickel.

Preferably also, said anti-fouling material is between 0.5 mm and 2 mm in thickness. Preferably also, said connector elements are of the same material as said panel sections, and are substantially equal to or greater than the thickness thereof.

Preferably also, said adhesive is a supercyanoacrylate adhesive. Alternatively, said adhesive is an acrylic tape adhesive.

Preferably also, the longitudinal length of each panel section is between 25 per cent and 50 per cent of the circumference of the tubular structure to which the material is to be applied.

Preferably also, said segmented strip is between 100 mm and 200 mm in width.

Preferably also, said predetermined gap between adjacent panel sections is between 2 mm and 6 mm.

Typically, the gap might be 3 mm and the connector strips 20 mm wide, overlapping the adjacent panel sections by about 8 mm each.

In accordance with a second aspect of the invention, there is provided a method of fabricating a segmented strip of anti-fouling material as defined above, comprising the steps of cutting a continuous strip of said anti-fouling material at said predetermined angle, at predetermined intervals, to- form a plurality of panel sections of predetermined length, establishing said predetermined gap between successive panel sections, and securing said connector elements across said gaps. In accordance with still a further aspect of the invention, a method of applying an anti-fouling coating to a tubular structure having an electrically insulating coating applied thereto comprises helically winding a segmented strip of anti-fouling material, in accordance with the first aspect of the invention, about and along said coated tubular member, and processing the resulting assembly to cure the electrically insulating coating and/or to bond the anti-fouling material thereto, wherein sufficient tensile force is applied to said segmented strip during winding so as to cause said panel sections to conform to the curvature of the tubular structure as they are wound thereon.

Preferably, the connector elements are removed after the final processing step.

Preferably also, the electrically insulating coating is of plastic or resin material.

Most preferably, the electrically insulating coating is of elastomer material.

Preferably, a suitable bonding compound or adhesive is applied to the inner surface of the panel sections of the segmented strip and/or to the surface of the electrically insulating coating prior to winding the strip about the coated tubular member.

When the electrically insulating coating is of elastomer, a temporary fabric wrap is preferably wound about the assembly after winding of the segmented strip, the processing of the fabric-wrapped assembly comprising heating the assembly to vulcanise the elastomer and bond the anti-fouling material thereto.

In accordance with a final aspect of the invention, there is provided an alternative method of applying an anti-fouling material to a tubular structure having an electrically insulating coating applied thereto, comprising the steps of helically winding a continuous strip of anti-fouling material about and along said coated tubular member, slitting said anti-fouling material along the length of said tubular member and substantially parallel to the long axis thereof, at a plurality of equispaced locations around the circumference of the tubular member, so as to divide said continuous, helically wound strip into a helically arranged series of panel sections and to form predetermined gaps between serially adjacent edges of the adjacent panel sections thereof, and processing the resulting assembly to cure the electrically insulating coating and/or to bond the anti-fouling material thereto.

Bonding compounds or adhesive may be applied, and in the case of an elastomer electrically insulating coating, fabric wraps may be employed, as for the method defined above.

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

Fig. 1 is a schematic perspective view of apparatus in use in fabricating anti-fouling material in accordance with the present invention; Fig. 2 is a schematic side view of the apparatus of Fig . 1 ; Fig. 2(a) is a side view of two adjacent panels of anti-fouling material connected by a connector element in accordance with the invention; Fig. 3 is a perspective view of an elastomer-coated subsea tubular having applied thereon an anti-fouling covering in accordance with the present invention; Fig. 4 is a perspective view of a part of a subsea tubular having applied thereon an anti-fouling covering in accordance with an alternative embodiment of the invention; and Fig. 5 is a side view of the tubular of Fig. 4 illustrating a method of preparation of said alternative embodiment.

Referring now to the drawings, Figs. 1 and 2 illustrate the preparation of a strip of anti-fouling material for application to tubular structures by helical winding.

A continuous strip of metallic anti-fouling material 1, preferably copper or a copper nickel alloy, is fed from a reel through adjustable pyramid rollers 2 to produce a consistently flat and regular strip. The material 1 is fed onto a preparation table 3 provided with lateral guide rails 4 for maintaining the alignment of the strip of material 1. The strip is cut into panel sections 15 at a cutting station 5 by any suitable cutting means (not shown), such as a guillotine. The sections 15 are cut at an angle to the long axis of the strip, the angle being determined by the pitch of the helical wrap as shall be discussed in greater detail below. The length of the sections 15 in the longitudinal direction of the strip is selected to suit the circumference of the tubular to which the material is to be applied, as shall also be discussed below.

Following the cutting of the strip, a predetermined gap 14 is established between adjacent sections 15 by means of temporary spacer elements (not shown) . The gap 14 will normally be in the range of 2 mm to 6 mm in width, the actual gap required in a particular case being determined by factors which shall be discussed in detail below.

The spaced apart sections 15 are fastened together to form a segmented strip which may be wound onto a storage reel 7 prior to application to the tubular. In accordance with the first aspect of the invention, the sections are connected together by means of connector strips 16, preferably also of copper or copper nickel, extending along substantially the whole length of the gaps 14.

The connector strips 16 overlap the adjacent panel edges by a predetermined distance, suitably about 8 mm or more.

The connector strips 16 are attached by degreasing and lightly abrading the surfaces of the strips 16 and panel sections 15, and securing the strips 16 with a suitable adhesive. Supercyanoacrylate adhesive or acrylic tape adhesive has been found to be suitable for this purpose.

The strip material 1 is preferably 100 mm to 200 mm wide, and 0.5 mm to 2 mm in thickness (most commonly, 0.7 mm to 1.75 mm). The connector strips 16 connecting the sections.15 are suitably of similar material and at least equal in thickness to the strip material 1, so as to have tensile strength not less than the strip material itself. The segmented strip is formed in a continuous length long enough to cover the tubular to be coated.

The segmented strip could alternatively be assembled from panel sections cut and prepared at an earlier time and/or remote location.

Fig. 3 illustrates the application of the segmented strip 13 of Figs. 1 and 2 to a subsea tubular, comprising a pipe 11 with an electrically insulating anti-corrosion coating 12. The use of the strip 13 is equally applicable for the protection of other tubular structures such as legs. The tubular 10 is shown partially cut away for clarity. The segmented strip 13 is chemically or mechanically cleaned and a bonding agent is applied to the inner surface thereof prior to winding the strip 13 onto the tubular 10, under tension, in a helical fashion. The strip 13 may be wound either by hand or by rotating the tubular 10.

The length of the individual panel sections 15 of the strip 13 is selected such that each section extends around between 25% and 50% of the circumference of the tubular. The width of the strip 13 and the circumference of the tubular 10 determines the pitch angle of the helical wrap, and the angle at which the panel sections 15 are cut is selected accordingly such that the gaps 14 extend substantially parallel to the long axis of the tubular 10 when the strip 13 is wound thereon.

The use of connector strips 16 having a tensile strength not less than that of the strip material means that sufficient tensile force can be applied to the panel sections 15 during winding to cause them to conform to the curvature of the tubular structure as they are wound thereon. This is not possible when the panels are connected together using material which is substantially more elastic than the panels themselves, in which case the panels have to either be pre-curved in an additional processing step or must be made sufficiently narrow (in the longitudinal direction of the segmented strip) that the flat panels do not deviate significantly from the curve of the tubular. Further, the fact that the connector strips extend substantially the full length of the gap between panel sections ensures that the tensile force is applied uniformly across the width of the panels. This avoids buckling or raised corners when the panels are wound around the tubular. The distance by which the connector strips overlap the panel edges must be great enough to allow a sufficiently strong bond to be formed.

The anti-corrosion coat 12 is applied to the pipe 11 prior to application of the strip 13. The coating 12 may be an epoxy resin or plastic, but is preferably an elastomeric material. Once the strip 13 has been wound onto an elastomer-coated pipe, a temporary fabric covering (not shown) is wrapped over the wound strip 13. This may be a nylon or cotton tape applied under tension of, for example, 50 to 100 kilos to provide a restricting force over the full length of the tubular to which the strip 13 has been applied. Thereafter, the elastomer coating is vulcanised by the application of heat, typically in a steam autoclave at a temperature of 110°C to 180°C for a specified time. Following vulcanisation the fabric wraps are removed. Where supercyanoacrylate adhesive is used, the high temperature steam atmosphere of the autoclave deteriorates the adhesive bond between the connecting tabs 16 and the panel sections 15, so that the tabs 16 can easily be removed following vulcanisation. Where acrylic tape adhesive is used, the tape becomes sufficiently flexible when heated that the connector tabs or strips may remain in place throughout processing and in subsequent use.

During the vulcanisation process the elastomer flows to fill any voids under the strip 13 and- forms a chemical bond thereto. Upon subsequent contraction of the elastomer as it cools to ambient, the gaps 14 between the panels 15 prevent any stress between the elastomer and the panel sections 15, and subsequently accommodate any differential thermal contraction or expansion of the elastomer and the panel sections. The required width of the gaps 14 is thus determined by the length of the sections 15 relative to the circumference of the tubular 10, and by the thermal expansion and contraction characteristics of the material of the strip 13 and the anti-corrosion material 12.

Fig. 4 illustrates an alternative embodiment of the invention in which a continuous strip 21 of anti-fouling material, to which a bonding agent and an elastomer cement have been applied, is helically wound under tension onto a tubular 22 similar to that of Fig. 3 (the cement could alternatively be applied to the surface of the elastomeric anti-corrosion coating of the tubular) . The elastomer cement may consist of the elastomer compound of the anti-corrosion coating reduced to a thixotopic solution in toluene solvent and tackifier. Once the strip 21 has been wound onto the tubular 22, the ends are secured by banding 17 and the strip 21 is slit along the full length of the tubular at a plurality of equispaced locations 18 around the tubular circumference. Preferably, 2 to 6 such slits are formed. The slitting of the strip 21 removes narrow strips of the anti-fouling material corresponding in width to the gaps 14 of the segmented strip 13 of Fig. 3, and serves the same purpose.

After the slitting of the anti-fouling material, the tubular is wrapped in fabric and the elastomer is vulcanised as in the previous embodiment. The elastomer cement acts as an adhesive retaining the anti-fouling material in position after the slitting, prior to the application of the fabric wrap. During vulcanisation the elastomer cement disperses within the elastomeric coating and forms an elastomer bond to the metal covering.

Fig. 5 illustrates the slitting of the anti-fouling material of Fig. 4 using a rotary cutting tool 19 fitted with a cutting depth control plate 20 to ensure that the tool 19 cuts to a depth no greater than, for example, 1 mm more than the thickness of the applied strip material.

The initial winding of a continuous strip of anti- bonding material also allows the strip to be pulled to conform to the curvature of the tubular during winding, without buckling.

The invention thus provides improved materials and methods whereby improved anti-fouling coatings may be applied to tubular structures, and an improved, coated structure formed thereby. Modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

1 CLAIMS 2

3 l. A metallic, anti-fouling, coating material adapted

4 for helical winding about a tubular member having an

5 electrically insulating coating applied thereto, said

6 material comprising an elongate, segmented strip of

7 anti-fouling material formed from a plurality of

8 similar panel sections connected end to end by

9 connector elements bonded thereto by an adhesive with a

10 predetermined gap between adjacent sections, the

11 adjacent edges of adjacent sections extending at a

12 predetermined angle to the lateral edges of said

13 segmented strip; said angle being determined by the

14 pitch angle at which the strip is to be wound about

15 said tubular member, and said gap being determined by

16 the differential thermal expansion and contraction

17 characteristics of said anti-fouling material and said

18 electrically insulating coating; said connector

19. elements each comprising a strip of material having

20 tensile strength at least equal to that of the anti-

21 bonding material, said strip extending along

22 substantially the whole length of said gap and

23 overlapping the edges of the adjacent panel sections on

24 either side of said gap by a predetermined distance. 25

26 2. The coating material of Claim 1, wherein said

27 anti-fouling material is copper or copper nickel. 28

29 3. The coating material of Claim 1 or Claim 2, wherein

30 said anti-fouling material is between 0.5 mm and 2 mm

31 in thickness. 32

33 4. The coating material of any one of Claims 1 to 3,

34 wherein said connector elements are of the same

35 material as said panel sections, and are substantially equal to or greater than the thickness thereof.

5. The coating material of any preceding Claim, wherein said adhesive is a supercyanoacrylate adhesive.

6. The coating material of any one of Claims 1 to 4, wherein said adhesive is an acrylic tape adhesive.

7. The coating material of any preceding Claim, wherein the longitudinal length of each panel section is between 25 per cent and 50 per cent of the circumference of the tubular structure to which the material is to be applied.

8. The coating material of any preceding Claim, wherein said segmented strip is between 100 mm and 200 mm in width.

9. The coating material of any preceding Claim, wherein said predetermined gap between adjacent panel sections is between 2 mm and 6 mm.

10. A method of fabricating a segmented strip of anti-fouling material as claimed in any one of Claims 1 to 9, comprising the steps of cutting a continuous strip of said anti-fouling material at said predetermined angle, at predetermined intervals, to form a plurality of panel sections of predetermined length, establishing said predetermined gap between successive panel sections, and securing said connector elements across said gaps.

11. A method of applying an anti-fouling coating to a tubular structure having an electrically insulating coating applied thereto, comprising helically winding a segmented strip of anti-fouling material, as claimed in any one of Clamis 1 to 9, about and along said coated tubular member, and processing the resulting assembly to cure the electrically insulating coating and/or to bond the anti-fouling material thereto, wherein sufficient tensile force is applied to said segmented strip during winding so as to cause said panel sections to conform to the curvature of the tubular structure as they are wound thereon.

12. The method of Claim 11, wherein the connector elements are removed after the final processing step.

13. The method of Claim 11 or Claim 12, wherein the electrically insulating coating is of plastic or resin material.

14. The method of Claim 11 or Claim 12, wherein the electrically insulating coating is of elastomer material.

15. The method of Claim 14, wherein a temporary fabric wrap is wound about the assembly after winding of the segmented strip, the processing of the fabric-wrapped assembly comprising heating the assembly to vulcanise the elastomer and bond the anti-fouling material thereto.

16. The method of any one of Claims 11 to 15 , wherein a suitable bonding compound or adhesive is applied to the inner surface of the panel sections of the segmented strip and/or to the surface of the electrically insulating coating prior to winding the strip about the coated tubular member.

17. A method of applying an anti-fouling material to a tubular structure having an electrically insulating coating applied thereto, comprising the steps of helically winding a continuous strip of anti-fouling material about and along said coated tubular member, slitting said anti-fouling material along the length of said tubular member and substantially parallel to the long axis thereof, at a plurality of equispaced locations around the circumference of the tubular member, so as to divide said continuous, helically wound strip into a helically arranged series of panel sections and to form predetermined gaps between serially adjacent edges of the adjacent panel sections thereof, and processing the resulting assembly to cure the electrically insulating coating and/or to bond the anti-fouling material thereto.

18. The method of Claim 17, wherein a suitable bonding compound is applied to the inner surface of the anti- fouling material and/or to the surface of the electrically insulating coating prior to winding the anti-fouling material about the tubular structure.

19. The method of Claim 17 or Claim 18, wherein the electrically insulating material is of elastomer and wherein a temporary fabric wrap is wound about the assembly after winding of the anti-fouling material, the processing of the fabric-wrapped assembly comprising heating the assembly to vulcanise the elastomer and bond the anti-fouling material thereto.