GB2431974A

GB2431974A - Insulation coating for pipework

Info

Publication number: GB2431974A
Application number: GB0522240A
Authority: GB
Inventors: Dominique Marianne Luc Flahaut
Original assignee: Corus UK Ltd
Current assignee: Corus UK Ltd
Priority date: 2005-11-01
Filing date: 2005-11-01
Publication date: 2007-05-09
Anticipated expiration: 2025-11-01
Also published as: GB2431974B; GB0522240D0

Abstract

A pipe 10 comprises an external protective coating formed of multiple layers 18 of a polymeric composition, between which are sandwiched a particulate solid 20. This has proved to be an efficient manner of introducing the particulate solid into what is effectively the bulk of the polymeric material. By thermally fusing the layers (at least partially) in a preferred embodiment, the coating can be made essentially solid. This is particularly useful when using hollow ceramic particles such as microspheres and other silicates, and for foamed polymeric compositions. The multiple layers 18 can be wound helically around the pipe, preferably overlapping. This allows the multiple layers to be formed from a single polymeric sheet, wound in an overlapping helix. In this way, the production process (Figure 3) is simplified considerably. Preferably, the protective coating layers 18 are wound around a steel pipe 12, which is covered with a layer of fusion bonded epoxy resin 14 to provide corrosion resistance and a thin layer of adhesive 16. An outer layer 22 of solid polypropylene preferably covers the multiple layers 18.

Description

Insulation Coating for Pipework

FIELD OF THE INVENTION

The present invention relates to insulation coatings for pipework.

BACKGROUND ART

This invention seeks to provide an insulation coating suited to the needs of undersea pipelines in the oil and gas exploration industry. However, the coating that has been developed is of course suited to any context that has like requirements of high performance insulation in a physically demanding environment.

European Patent No. 259 373 Bi for insulation and weight coating subsea pipelines describes that it is possible to form a foam from a thermoplastic with addition of a bldwing agent. Other pipeline coating companies use the addition of microspheres to bulk polypropylene to provide thermal improvements without the addition of a blowing agent.

The increasing demands placed on the insulation coating by technical developments in the oil and gas exploration industry has led to the proposal of pipe coatings with ever increasing numbers and types of layers. This tends to complicate the process of manufacture, with inevitable cost and quality control implications.

SUMMARY OF THE INVENTION

The invention seeks to offer higher performance insulation systems for underwater pipelines. In deeper water applications, the need for mechanical strength as well as thermal performance increases due to the hydrostatic pressure on the foam. This causes the material to creep, loosing its thermal properties as its structure is compressed.

The present invention therefore provides a pipe comprising an external protective coating formed of multiple layers of a polymeric composition, between which are sandwiched a particulate solid. This has proved to be an efficient manner of introducing the particulate solid into what is effectively the bulk of the polymeric material. By thermally fusing the layers (at least partially), the coating can be made essentially solid.

Given the context in which the invention arose, we particularly expect that the protective coating will be for insulation purposes. However, as a means for entraining the particulate solid within the bulk of a polymeric coating, the invention is applicable in other contexts.

The advantages of the invention are particularly apparent when the particulate solid is ceramic. The physically gentle process by which the particles can be introduced mean that ceramics are unlikely to be harmed. This contrasts with aggressive mixing and moulding techniques such as are required if the particles are introduced to the polymer when the latter is in a fluid state.

In particular, the invention is useful in respect of hollow ceramic particles such as microspheres and other silicates.

The invention is also particularly useful where the polymeric composition is foamed, as it allows the foaming and the particulate mixing steps to be kept separate. If this is not done, the weight of the particles can adversely affect the foaming process.

The multiple layers can be wound helically around the pipe, preferably overlapping. This allows the multiple layers to be formed from a single polymeric sheet, wound in an overlapping helix. In this way, the production process is simplified considerably.

There is preferably an adhesive layer between the protective coating and the pipe, to assist in securing the coating in place. A resin layer can also be provided between the pipe and the adhesive layer to provide a secure transition.

A suitable resin is epoxy.

There is preferably also a further layer over the protective coating, to provide physical protection to the coating. This applies particularly where the coating is foamed. The further layer can be polymeric and is preferably solid as opposed to foamed. Polypropylene is suitable, and will form a good contact with a polypropylene-based coating.

The present invention also provides a method of forming a composite coating on a cylindrical member, comprising the steps of forming a polymeric sheet, dropping a particulate material onto the sheet, and winding the sheet around the cylindrical member in an overlapping helical manner.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described by way of example, with reference to the accompanying figures in which; Figure 1 is a transverse cross-section through a pipe according to the present invention; Figure 2 is a schematic illustration of an enlarged part of figure 1; Figure 3 is a perspective view illustrating the method by which the pipe according to the present invention is constructed; and Figure 4 is a longitudinal section through a pipe according to the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

An aim of the invention is to provide a coating for pipelines that is suitable for underwater use and which is based on a thermoplastic foam reinforced with microspheres to improve the long term insulation and mechanical performance.

This foam will ideally be applied to the pipe via a continuous process, which offers economical and operational benefits over competing cast' systems.

Microspheres are small alumino-silicate particles, typically between 10 and 1,000 pm in diameter. They are obtained from certain flue gases as a waste product, and generally have a hollow centre filled with gas. This gives them a low density and a relatively good thermal conductivity. Meanwhile, their particulate nature allows them to flow and therefore allows them to be handled and formed easily. Microspheres have been used in this example as they are readily available, are inexpensive as a result of their nature as a waste product, and are well characterized. However, other particulate materials with similar properties could of course be substituted.

As noted above, a pipeline for underwater use in accordance with the invention has an insulating coating of many layers of thermoplastic foam and micro-spheres, where the micro-spheres are deposed as a layer on the top of the thermoplastic foam sheet. The thermoplastic foam has some intrinsic strength for use in shallow underwater applications, but the increasing demands for pipelines able to operate in deeper seas make it (alone) too weak to be able to be stable in a long term under this increasing subsea pressure. Accordingly, we apply on the top of the thermoplastic foam extruded sheet a layer of microspheres. These layers of microspheres will improve various properties of the composite layer.

Figures 1 and 2 show a section through a pipe structure 10 constructed in accordance with the present invention. A steel pipe 12 is covered with a layer of fusion bonded epoxy resin 14 to provide corrosion ressistance. On this epoxy layer 14, a thin layer of adhesive 16 is applied prior to winding a length of foamed polypropylene 18 around the pipe 12. As this is wound repeatedly around the pipe 12, it forms a spiral pattern (in section) around the pipe.

Prior to winding, the foamed polypropylene layer 18 is liberally dusted with microspheres 20 such that the surface of the polypropylene is largely covered. Thus, when the foamed polypropylene has been wound around the pipe 12, the microspheres 20 are trapped between layers 18. The foamed polypropylene is dusted and wound at an elevated temperature, ideally during cooling from the temperature imposed to cause the blowing agent to activate.

As a result, the polypropylene is still hot while wound and the layers merge to become one contiguous solid with the microspheres 20 trapped within its bulk.

Thus, a too liberal dusting of microspheres 20 will inhibit attachment of adjacent layers, whereas insufficient dusting will reduce the insulation properties of the coating. We have found that the optimum lies approximately as illustrated in figure 2, i.e. a dusting that leaves the surface of the foamed polypropylene layer 18 almost but not quite covered with a single layer of microspheres 20.

Finally, the structure 10 is completed with an outer layer of solid polypropylene 22. Thus can be wound or cast in place and provides a hard shell to the foamed layers 18 for mechanical protection.

Thus, the mechanical properties of the insulation layer are improved in that the micropheres are mechanically stronger than the foam because of their shape and the material used (typically alumino-silica based, sometimes glass).

As the microspheres are bonded to each layer of foam they provide mechanical reinforcement to each individual layer. The combined effect will give enhanced strength to the overall system.

In addition, the thermal properties are also improved since the micro-spheres include a gas with better insulation properties than the thermoplastic foam. This can give a combined thermal conductivity of less than 0.11 Wm'K'.

Further, the repeated transition between layers of foam and microspheres further improves the insulation performance of the system, due to the insulation barrier effect created by the numerous changes of material layers.

The process of manufacture of the composite insulation layer will now be described, by way of example. Raw materials which could be used include: Fusion Bonded Epoxy Jotum 2002 HW Adhesive Borealis PB127E PP base Borealis BA2O2E Blowing agent Crompron Celogen AZ-760A A particularly beneficial size of the microspheres is between 3Opm and 500pm, preferably between 100pm and 500pm.

To construct the insulated pipe, the exterior of the pipe is washed with potable water and the blast cleaned in order to clean the surface. Shortly after, a chromate solution is applied to improve the cleanness of the surface and increase the adherence between pipe and coating. After induction heating to bring the pipe surface to the temperature recommended by the material supplier, a layer of epoxy powder follow by adhesive is applied via electrostatic spraying.

The thermoplastic foam is formed from virgin thermoplastic base mix with a blowing agent. The blowing agent can be mixed into the thermoplastic base in one of two ways. A first option is to pre-mix the blowing agent powder with a partial part of the thermoplastic charge base pellets. In this way, the thermoplastic pellets are rounded by blowing agent powder. The alternative is to use premix pellets, which are pellets of thermoplastic supplied with a high content of blowing agent. These are made by introducing the blowing agent into the thermoplastic when viscous. Either option results in a mixture containing a high concentration of blowing agent.

The temperature profile during manufacture is controlled so as to form the foam just at the exit of the extruder. This provides a uniformly structured foam with small cells. This is then allowed to travel a distance of at least about 1 metre from the exit of the extruder to the pipe. This allows the foam to be fully formed and to expand before being applied to the pipe, and also permits a slight decrease of temperature which increases the strength of the foam. For example, a foam sheet layer of 4mm can expand to 7mm thick from a die opening of 1mm.

During this transit, the microspheres 20 are applied as a layer on the top surface of the foam sheet 18 as shown in figure 3. As a consequence of the temperature of the foam sheet and the chemical affinity between the thermoplastic foam and the microspheres, the microspheres stick or adhere to the surface of the thermoplastic foam sheet. The microspheres can be applied by an automatic sieve machine, or by an automatic gun spray, for example.

The rate of application should be controlled, to apply a quantity of microspheres which optimizes their additional properties but avoids a mismatch or lack of adherence of between the successive foam sheet layers applied on the pipe. Ideally, there should be a complete layer of microspheres, or nearly so, without the layer becoming significantly thicker than one or perhaps two micros ph e res.

The foam 18 thus formed can then be wound around the pipe 12 whilst still at an elevated temperature. Several layers can be applied from a single sheet by applying this in an overlapping helical formation 24. Thus, to provide a 35mm or 40mm foam thickness on the pipe, 14 or so wraps of foam sheets 18 can be applied thereby providing 14 layers of microspheres 20. Clearly, it is straightforward to adjust the width of the foam sheet 18 and/or the helix angle to obtain a greater or lesser thickness through more or fewer wraps.

As illustrated, the material is top wound, but it could equally be bottom The end result is as shown in figures 1 and 2 (described above) and figure 4 which is a longitudinal section through a wall of the complete pipe structure 10. The steel pipe 12 has an epoxy layer 14 and an adhesive layer 16 as before, and multiple layers 18 of foamed polypropylene can be seen. Each layer overlaps previous layers of the helix and, at the point where these end, moves slightly closer to the pipe 12. Over the foamed layers 18 there is (again) a layer of solid polypropylene 22 to provide mechanical protection.

One advantage of this alternative multilayer foam is that it avoids the production difficulties created by the production of 1 or 2 sub-layers of thermoplastic solid to increase the mechanical properties of the foam. Indeed, such a process involves the simultaneous use of 2 extruders or several passes of the pipe to the extruder in order to obtain the required coating combination. This can complicate the production process, incur additional costs, and give rise to more opportunities for defects to be created.

Where a thermoplastic foam with sub-layers of a thermoplastic solid is called for, the present invention can be applied by substituting the desired solid for the microspheres.

It will of course be understood that many variations may be made to the above-described embodiment without departing from the scope of the present invention.

Claims

CLAIMS

1. A pipe comprising an external protective coating formed of multiple layers of a polymeric composition, between which are sandwiched a particulate solid.

2. A pipe according to claim 1 in which the layers are at least partially thermally fused.

3. A pipe according to claim 1 or claim 2 in which the protective coating is for insulation purposes.

4. A pipe according to any one of the preceding claims in which the particulate solid is ceramic.

5. A pipe according to claim 4 in which the ceramic particles are hollow.

6. A pipe according to claim 4 or claim 5 in which the ceramic particles are a silicate composition.

7. A pipe according to any one of claims 1 to 3 in which the particulate solid is microspheres.

8. A pipe according to any one of the preceding claims in which the polymeric composition is foamed.

9. A pipe according to any one of the preceding claims in which the polymeric composition is polypropylene.

10. A pipe according to any one of the preceding claims in which the multiple layers are wound helically around the pipe.

11. A pipe according to claim 10 in which the helical windings overlap.

12. A pipe according to claim 11 in which the multiple layers are formed from a single polymeric sheet, wound in an overlapping helix so as to provide the multiple layers.

13. A pipe according to any one of the preceding claims in which there is an adhesive layer between the protective coating and the pipe.

14. A pipe according to claim 13 in which there is a resin layer between the pipe and the adhesive layer.

15. A pipe according to claim 14 in which the resin is epoxy.

16. A pipe according to any one of the preceding claims in which there is a further layer over the protective coating.

17. A pipe according to claim 16 in which the further layer is polymeric.

18. A pipe according to claim 16 or claim 17 in which the further layer is solid.

19. A pipe according to any one of claims 16 to 18 in which the further layer is polypropylene.

20. A method of forming a composite coating on a cylindrical member, comprising the steps of forming a polymeric sheet, dropping a particulate material onto the sheet, and winding the sheet around the cylindrical member in an overlapping helical manner.

21. An insulated pipework system substantially as herein disclosed with reference to and/or as illustrated in the accompanying figures.