Wear indicator system for offshore corrosion protection covering systems

Abstract

A corrosion protected metal pipe for installation in an offshore structure or for producing a pipeline laid in water is provided. The metal pipe has an at least two-layer covering on the pipe with a lower layer facing the pipe and an upper layer on a side of the lower layer not facing the pipe is provided. The layers are formed such that the lower layer is electrically conductive and the upper layer is electrically insulating, the lower layer is optically contrasting to the upper layer, or the lower layer is electrically conducting and optically contrasting to the upper layer and the upper layer is electrically insulating. Thus, in the event of damage to the layer or layers lying above, a visual or electrical signal can be detected. Damage to the corrosion protection covering can therefore be detected easily and, if appropriate, reported by remote monitoring.

Claims

1. A method of determining corrosion of an installed cover metal pipe, the method comprising: performing an inspection for corrosion of the installed covered metal pipe, which comprises a metal pipe with an outer at least two-layer covering and is at least partially submerged in water comprising salt, via the at least two-layer covering operable as a corrosion detector, wherein the at least two-layer covering includes a lower layer facing the metal pipe and an upper layer on a side of the lower layer not facing the pipe; and wherein the lower layer is electrically conductive and the upper layer is electrically insulating, the lower layer is optically contrasting to the upper layer, or the lower layer is electrically conducting and optically contrasting to the upper layer and the upper layer is electrically insulating.

2. The method according to claim 1, wherein the lower layer is electrically conductive and the upper layer is electrically insulating.

3. The method according to claim 2, wherein the lower layer comprises an electrically conductive material.

4. The method according to claim 3, wherein the electrically conductive material is selected from the group consisting of conductive carbon black, an axially extending conductive wire or tape and a wound conducting wire or tape.

5. The method according to claim 2, wherein said performing is carried out by applying an electric voltage to the electrically conductive lower layer with respect to the water and detecting an electrical signal.

6. The method according to claim 1, wherein the lower layer is optically contrasting to the upper layer.

7. The method according to claim 6, wherein the optical contrast corresponds at least to a grey scale of 4 according to DIN EN 20105-A02.

8. The method according to claim 6, wherein the lower layer is colored and the color of the lower layer is in optical contrast to a color of the upper layer.

9. The method according to claim 6, wherein said performing is carried out by measuring the optical contrast in accordance with DIN EN ISO 11664-4 using a spectrophotometer and detecting a visual signal.

10. The method according to claim 1, wherein the upper layer and the lower layer each, independently, comprise a polymer material.

11. The method according to claim 10, wherein the upper layer is a polyamide moulding compound applied by extrusion.

12. The method according to claim 1, wherein the at least two-layer covering further comprises at least one layer between the metal pipe and the lower layer.

13. The method according to claim 12, wherein the at least one layer is selected from the group consisting of a ceramic layer, a priming layer, an adhesion promoting layer and a textile reinforcement.

14. The method according to claim 13, wherein the at least one layer comprises a priming layer, which is an epoxy resin or a water-based mixture of an epoxy resin and a polyacrylate latex.

15. The method according to claim 13, wherein the at least one layer comprises an adhesion promoting layer, which is a polyamide hot-melt adhesive or a polyolefin having functional groups.

16. The method according to claim 13, wherein the at least one layer comprises a textile reinforcement, which is a woven fabric or mat.

17. The method according to claim 1, wherein the metal pipe is made of a metal material selected from the group consisting of steel, stainless steel, copper, aluminium, cast iron, zinc, a copper alloy, an aluminum alloy, a zinc alloy, brass, galvanized steel, cadmium-coated steel, aluminium-coated metal, and steel coated with a metal alloy.

18. The method according to claim 1, wherein the covered metal pipe is comprised within an offshore wind power plant, an offshore drilling rig, or a lighthouse.

19. The method according to claim 1, wherein the lower layer directly contacts the metal pipe.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) FIG. 1 shows a protected pipe structure according to one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(2) The object described above has been achieved by a metal pipe which has an at least two-layer corrosion protection covering with an upper and a lower layer, the lower layer being finished such that, in the event of damage to the layer or layers lying above, a visual or electrical signal can be detected. Thus the metal pipe is covered with an at least two-layer covering having a lower layer facing the pipe and an upper layer on a side of the lower layer not facing the pipe; wherein the lower layer is electrically conductive and the upper layer is electrically insulating, the lower layer is optically contrasting to the upper layer, or the lower layer is electrically conducting and optically contrasting to the upper layer and the upper layer is electrically insulating.

(3) The present invention also includes the use of the corrosion protected metal pipe for installation in an offshore structure, in particular in the foundation structure of an offshore structure, or for producing a pipeline laid in water.

(4) In a first embodiment, the lower layer, which is the layer facing the metal of the pipe, is designed to be electrically conductive, while the upper layer, facing the water, is designed to be electrically insulating. By application of an electric voltage with respect to the water, it may thus possible to detect damage to the coating by means of remote monitoring, as a result of the short circuit that then occurs. The water is preferably water which contains dissolved salts, for example seawater or brackish water. The electrically conductive layer may be insulated with respect to the metal. However, it may also be conductively connected to the metal, so that the metal construction is at the same potential.

(5) In a second embodiment of the present invention, the two layers lying one above the other are constituted in an optically contrasting manner. In general, they differ in colour. If, for example, the upper layer is set to be yellow and the lower layer red, then damage to the upper layer may be detected by means of the occurrence of red areas. The contrast preferably corresponds at least to the grey scale rating of 4 (according to DIN EN 20105-A02), particularly preferably at least to the grey scale rating of 3 and in particular preferably at least to the grey scale rating of 2/3. The measurement may be carried out in accordance with DIN EN ISO 11664-4, using a spectrophotometer (sphere).

(6) In a third possible embodiment of the present invention, the first and the second embodiments are combined with each other. Damage may then be detected by means of the occurrence of a short circuit and reported by remote monitoring; on-site, the damage may then be found and repaired quickly by the optical contrast. This principle is illustrated in FIG. 1.

(7) In FIG. 1, a steel pipe with concrete filling is illustrated, which has been covered with a layer made of an electrically conductive plastic and thereafter with a layer made of an electrically insulating plastic. The two plastic materials are coloured differently. The outer, electrically insulating covering layer has been damaged at a point, so that the electrically conductive layer comes into contact with seawater. As a result, a short circuit is detected via an electric resistance measurement. The damaged point may be found by locating the optical contrast on the pipe.

(8) The electrical conductivity of the lower layer may be obtained by any of conventionally known methods, for example, by using a moulding compound filled with conductive carbon black or by embedding axially extending or wound electric conductors, for example wires, stranded wires or tapes.

(9) The offshore structure may preferably be an offshore wind power plant, a drilling rig or a lighthouse.

(10) The foundation structure of an offshore wind power plant is the structure which carries the tower. It extends from the foundation elements, which are anchored in the sea floor, via the structure which is located underwater, as far as the point at which the tower begins and which may be located above the calm water level.

(11) The following types, for example, are used as the foundation structure:

(12) The monopile construction comprises a cylindrical hollow pile. The monopile is used close to the coast in many European offshore wind parks; it is suitable for foundations at water depths of up to currently about 20 meters. Monopiles can be installed simply and quickly; however, heavy pile driving equipment is needed for the erection. In recent times, trials of a gentle installation using a drill head have been carried out.

(13) The jacket is a latticework construction made of steel which resembles the construction of conventional power masts. At its four feet, the jacket is anchored in the sea floor with piles. The jacket construction has already proven worthwhile in the oil industry at relatively great water depths. As a result of the latticework construction, 40 to 50% steel can be saved as compared with the monopile. Thus, the project costs when this construction is used at relatively great water depths increase only relatively slightly. Since the individual structural elements are relatively small, they can be produced easily and can be transported and mounted simply.

(14) In the case of the tripod, the structure comprises a tripod formed from steel pipes, on which the central pipe is placed centrally. The legs of the tripod can each be seated on a pile or on a plurality thereof. In order to drive the pile, centring sleeves are arranged at the corner points of the equilateral triangle that results. The piles are connected to one another by horizontal struts and connected to the central pipe via diagonal bracing. The central pipe does not enter the sea floor. Since steel pipes having smaller diameters are used in this case, the tripod can be used for water depths of more than 20 meters.

(15) The quadropod is a modification of the tripod concept with four instead of three struts. In this case, increased foundation rigidity is achieved at great water depths.

(16) The tripile comprises three steel piles, which are anchored under water. Above water, a tripod construction is placed on these steel piles. According to manufacturer's information, tripile foundations are suitable for water depths of 25 to 50 meters.

(17) Constructions of this type are described, for example, in the following publications: Fundamente fr Offshore-Windenergieanlagen [Foundations for Offshore Wind Power Plants], Deutsche Energie-Agentur GmbH, as at 12/09; Florian Biehl, Kollisionssicherheit von Offshore-Windenergieanlagen [Collision Safety of Offshore Wind Power Plants], Stahlbau, Vol. 78 (6), pp. 402-409 (2009); K. Lesny, W. Richwien (Publishers), Grndung von Offshore-Windenergieanlagen-Werkzeuge fr Planung and Bemessung [Foundations of Offshore Wind Power PlantsTools for Planning and Dimensioning], VGE Verlag Glckauf 2008, ISBN: 978-3-86797-035-8; DE 103 10 708 A1.

(18) The upper and the lower layers of the corrosion protection covering according to the present invention may be of a polymer material, for example a polyamide moulding compound, a polyolefin moulding compound, a fluoropolymer moulding compound (for example based on PVDF), a moulding compound based on a thermoplastic polyurethane, a cross-linked polyurethane or a cross-linked epoxy resin.

(19) In a preferred embodiment, the upper layer is a polyamide moulding compound applied by extrusion. The lower layer may then either likewise be a polyamide moulding compound, a polyolefin moulding compound or another polymer material. The material of this lower layer may contain an adhesive resin, for example epoxy resin (for example Araldite); in this case, this layer can be applied directly to the metal surface.

(20) In general, however, between the metal surface and the lower layer there may be at least one further layer. For example, this at least one further layer may involve one or more of the following layers: a ceramic layer, for example, such as described in WO 03/093374; a priming layer, for example of epoxy resin (U.S. Pat. No. 5,580,659) or a water-based mixture of epoxy resin and polyacrylate latex (WO 00/04106); an adhesion promoter layer made of a polyamide hot-melt adhesive which, for example, can be applied as powder by spraying, etc. (EP 1 808 468 A2), or of a polyolefin which bears functional groups. Suitable functional groups are, for example, carboxyl groups or acid anhydride groups (WO 02/094922), epoxy groups or alkoxysilane groups (EP-A-0 346 101). The polyolefin layer may also be foamed. The polyolefin may preferably be polyethylene or polypropylene; a differently composed adhesion promoter, which is intended to ensure that the composite comprising polyamide layer and base material is not impaired under mechanical stress; a textile reinforcement in the form of woven fabrics or mats, for example made of glass fibres or aramid fibres (Kevlar).

(21) The optional ceramic layer, priming layer, adhesion promoter layer and/or textile reinforcement may be applied to the pipe in accordance with any conventionally known method.

(22) The materials of the upper and lower layer may be applied to the pipe in accordance with methods which are conventionally known, for example by means of tubular or wrapping extrusion. In one possible variant, both layers, possibly together with an adhesion promoter layer, may be produced and applied by means of co-extrusion of a multilayer composite.

(23) The tubular and the wrapping extrusion are covering methods that have proven worthwhile over a long time for pipes. These methods are described in more detail in the Stahlrohr-Handbuch [Steel Pipe Handbook], 12th edition, pp. 392-409, Vulkan-Verlag Essen, 1995.

(24) The applied layers must be at least so thick that they can be produced as a closed layer under the application conditions. The layer thickness may preferably be at least 0.5 mm, particularly preferably at least 1.0 mm and in particular preferably at least 1.2 mm.

(25) Usually, layer thicknesses up to about 8 mm, preferably up to about 7 mm, particularly preferably up to about 6 mm and in particular preferably up to about 5 mm have proven worthwhile. If required, however, the layer may be thicker, for example up to 30 mm or more.

(26) The metal pipe may be steel, stainless steel, copper, aluminium, cast iron, zinc, alloys with one of these metals as main component, brass, galvanized steel, cadmium-coated steel, aluminium-coated metal, steel coated with metal alloys, such as GALFAN, or of any other metal. The pipe may be produced by all conventional methods, including for example, as welded or seamless pipe.

(27) The outer diameter of the metal pipe may preferably be at least 20 mm and at most 8000 mm.

(28) The individual pipes are connected to one another constructionally by conventionally known methods, for example, by welding.

(29) A particular advantage of the invention is that the damage may be detected and repaired when the metal construction itself has not yet begun to corrode. In this case, the repair may be considerably less complicated overall.

(30) Numerous modifications and variations of the present invention are possible in light of the above description. It is therefore to be understood that within the scope of the appended claims, the invention can be practiced otherwise than as specifically described herein.