METHOD OF COATING A SURFACE WITH SHEET MOULDING COMPOUND AND SURFACE

PROTECTION ARRANGEMENT

The invention relates to the field of corrosion repair and corrosion reduction by coating a corrodible surface with a sheet moulding compound (SMC) material.

SMC is a composite material generally comprising a polyester resin in styrene monomer, fillers, pigments, glass fibre reinforcement and a curing agent. The SMC is normally soft and malleable but will harden when stimulated by a curing initiator. Typically SMC is manufactured in rolls, and when unrolled a sheet is generally around 10m long, Im wide, and 1- 2.5mm thick.

SMC may be used as a corrosion resistant barrier for protecting surfaces that are prone to corrosion. A particular application is in the oil and gas industry for protecting pipes made of metal. For example, SMC may be wrapped around a steel pipe to prevent it from rusting. Generally the SMC that is used in this field is curable such that it is normally malleable but becomes rigid upon interaction with its curing initiator. A typical curing initiator is ultraviolet (UV) light, as this is present in natural sunlight. By cylindrically surrounding a pipe with UV curable SMC and then exposing the SMC to natural sunlight and allowing it to cure, corrosion to the external surface of the pipe may be substantially averted.

A particular advantage of using SMC to protect oil and gas pipes from corrosion is that SMC techniques do not require high temperatures or voltages that could be hazardous for volatile pipe products. Thus, pipes do not have to be shut down while they are being coated. This may be

desirable because the cost of shutting down oil and gas pipes may necessitate working on the pipes while they are live.

A problem in the prior art is that low-level corrosion continues to occur to some surfaces even after they have been coated with SMC material. It is an object of this invention to recognise the cause of this corrosion and to reduce its effect. It is also an object of this invention to improve the strength of interaction between a treated surface and its SMC coating.

According to an aspect of the present invention there is provided a method of fixing a coating to a surface, the method comprising the steps of: arranging the coating between vacuum application means and the surface; and drawing air from between the coating and the surface with the vacuum application means so as to fix the coating to the surface, wherein the vacuum application means comprises a flexible sheet through which a vacuum can be applied.

By applying suction, air may be drawn out of the gap between the coating and the surface. This may create a very tight join between the coating and the surface, even if there is no actual adhesion between the two.

By fixing a coating to a surface it may be possible to significantly reduce the corrosion to that surface. Also, by drawing air out of the gap between the surface and the coating, any low level corrosion that would have occurred due to small amounts of air may be reduced or eliminated. Such low level corrosion may occur when air itself is a corrosive reactant. For example, a ferrous surface would be prone to rust due to a chemical reaction involving iron and oxygen. By removing air, and therefore oxygen, rust on the surface may be avoided.

Air may be drawn from between the surface and the coating at the periphery of the coating, but preferably air is drawn through the coating itself; this means that the air may be arranged to bubble through the coating when a vacuum is applied by the vacuum application means.

The air that is drawn through the coating may comprise air that is initially present in an air pocket in the coating material. By reducing the air content of the coating material it may be possible to improve the homogeneity of the coating which may provide a better corrosion resistant barrier. It may also be desirable to remove air pockets from the coating because any air left in air pockets may itself be a cause of corrosion, if left for many months and years.

The air that is drawn through the material may comprise air that is initially present between the coating and the surface. In this way a low pressure may be created in the gap between the coating and the surface. The higher atmospheric pressure may then act to push the coating onto the surface, fixing the two together.

Preferably the coating is curable. Curable materials may be hardened when influenced by the relevant curing initiator. Preferably the coating is cured after it has been fixed to the surface, and once cured the coating may be an effective barrier against corrosion. Also, a cured coating may be capable of restoring structural strength to a damaged surface.

The method may comprise the step of curing the coating and, for example, the coating may be cured with ultraviolet (UV) radiation. UV radiation

may be a convenient initiator for curing a curable material because UV is present in natural sunlight.

In addition, the method may involve the step of shielding the coating from UV radiation, while drawing air from between the coating and the surface with the vacuum application means. This may be particularly desirable when a UV curable coating is used. By shielding the coating from UV radiation, the coating may be placed on the surface while it is flexible and a vacuum may be applied through the vacuum application means. Thus, air may be drawn through the coating while it is still in a flexible form.

Once the coating has been fixed to the surface the UV shield may be removed and the coating may be cured by the UV radiation. A typical shield may be a canopy for shielding the coating from the UV in natural sunlight.

In an alternative, the coating may be cured with heat. This may be preferable in certain situations when UV may not be such a convenient curing initiator. One example may be in deep sea applications where natural sunlight is not available. Another example may be where the coating is opaque to UV light; this may occur when certain strengthening agents are used together with the coating, hi such situations heat curable materials may be most convenient to use.

Generally heat curable materials are cured at temperatures in the range of 150 ⁰ C to 200 ⁰ C. However, most preferably the heat curable materials are cured at temperatures in the region of 100 ⁰ C as this avoids the boiling of styrene at around 145 ⁰ C. Therefore, the optimum temperature for heating the coating to may be in the region of 80-145 ⁰ C.

It may be possible to provide a coating that is curable by any one of, or any combination of, heat, UV radiation and any other physical stimulus such as optical light.

As mentioned, the vacuum application means comprises a flexible sheet through which a vacuum can be applied. Preferably the flexible sheet is also a porous sheet through which and across which a vacuum can be applied. In this way, a vacuum can be applied through the porous sheet and the sheet can be bent in order to match the shape of the surface to which it is to be applied. Thus, the vacuum application means can be used to fix a coating to an unusually shaped surface.

The vacuum application means may comprise an inner chamber, and one side of the inner chamber may be the flexible, porous sheet. Thus, if a vacuum exists in the inner chamber a vacuum can be applied across the flexible, porous sheet.

The inner chamber may be defined between the flexible, porous sheet and an airtight sheet. Preferably the airtight sheet comprises a valve so that a pump can be connected to the valve for evacuating the inner chamber.

The airtight sheet is preferably flexible as well.

Preferably the vacuum application means comprises a flexible sheet having a valve. These flexible sheets are generally referred to in the art as vacuum bags. The vacuum application means may also comprise a pump which may be connected to the vacuum bag via the valve so that a vacuum may be applied through the sheet surface. In this way a vacuum bag may be used in a wide variety of different applications and for fixing coatings to a wide variety of different shapes of surfaces. For example, the vacuum

bag may be arranged in a cylindrical shape for fixing a coating onto a pipe or a strut with a circular cross-section. Of course, the vacuum bag could also be arranged in a suitable shape for fixing a coating onto a planar surface, a spherical surface, or any kind of bent or corrugated surface if required.

The vacuum application means may be hand-held and portable, and this may be a notable advantage of a vacuum bag. By using a vacuum bag a coating may be applied to a surface in any environment, provided that vacuum application means can be provided to draw air from between the coating and the surface. Thus, coatings may be fixed to surfaces away from factories, and in remote or underwater conditions where there may be no available mains power source.

The coating may be a sheet moulding compound (SMC). SMCs are commonly used as corrosion resistant coatings and may be convenient materials to work with in many embodiments.

The coating may comprise a strengthening agent. In this way, the coating may be used to restore strength to a damaged or corroded surface.

Possible strengthening agents may include synthetic fibres such as Kevlar (RTM). Typically the SMC would comprise glass fibre strands or glass fibre tissues.

The surface that is protected from corrosion may be metallic. Metallic surfaces are typically prone to corrosion, especially when oxygen and/or water are present. Typically one may look to protect metal surfaces such as steel from corrosion by fixing a coating to them. That said, many other

types of surface could also be protected; for example, concrete, stone, natural or synthetic surfaces.

The surface that is protected from corrosion may be the surface of a pipe. The protection of pipes from corrosion may be a particularly advantageous application of the present method. In many instances it may not be practical to stop the flow of a product through a pipe for maintenance. Therefore, to prolong the life of a pipe it is possible to fix a coating to it. The pipe may have any shape: for example the cross section of the pipe could be square, circular, oval or triangular. Also, the pipe need not have a closed cross-section, and an open cross-section could be semi-circular, for example.

As well as surfaces of pipes, many other surfaces may be protected from corrosion according to the present method. Other suitable surfaces include surfaces on: cables, structural struts, vehicles, underwater walls, and so on. Thus, it may be seen that the potential applications of the present method are wide and varied.

The method may involve the step of arranging a breathable film between the coating and the vacuum application means. Also, preferably the mass of the breathable film is low relative to the mass of the vacuum application means.

By providing a breathable film adjacent the vacuum application the breathable film may be drawn towards the vacuum application means rapidly when a vacuum is applied. However, the breathable nature of the film may mean that a vacuum can still be applied through the breathable

layer. It has been found that the provision of a breathable film reduces the entrapment of air in the coating material.

The breathable film may be of polythene and may comprise a plurality of holes.

According to another aspect of the present invention there may be provided a surface protection arrangement for fixing a coating to a surface, the arrangement comprising: a surface; a coating; and vacuum application means comprising a flexible sheet through which a vacuum can be applied, wherein the coating is arranged between the vacuum application means and the surface, and wherein the vacuum application means is arranged to draw air from between the coating and the surface so as to fix the coating to the surface.

Any of the method features may be provided with any of the apparatus features and vice-versa.

Preferred features of the present invention will now be described, purely by way of example with reference to the accompanying drawings, in which:

Figure 1 is a perspective view of a pipe being coated with a UV curable material in an embodiment of the present invention;

Figure 2 is a cross sectional view of the pipe of Figure 1;

Figure 3 is a detailed view of the layers of material covering the surface of the pipe of Figure 1 ;

Figure 4 is a view of a strut having a heat curable material coating applied to it in another embodiment of the present invention; and

Figure 5 is a cross sectional view of the strut of Figure 4.

First Embodiment

Referring to Figures 1 and 2, a steel pipe 2 with a circular cross-section is provided for delivering a product 4 such as oil or gas. During normal use of the pipe 2 both the internal and external surfaces are prone to corrosion.

Since it may be impractical to stop the supply of product, it is presently intended to protect only the external surface of the pipe 2 from corrosion.

A UV curable Sheet Moulding Compound (SMC) material 6 is arranged to cylindrically wrap around the pipe 2. The SMC material 6 is normally flexible and may easily be wrapped around the pipe 2. Of course, the UV curable SMC 6 should be shielded from UV radiation until such time as it has been wrapped around the pipe, and to this end a canopy 8 is provided to shelter the working area from natural sunlight.

A vacuum bag 10 is arranged to wrap cylindrically around the UV curable SMC 6. The vacuum bag 10 is a flexible sheet having a valve 12 which is connectable to a pump 13. A vacuum may be applied through the valve 12 by the pump 13 so that a suction can be generated through the flexible surface of the vacuum bag 10. The vacuum bag 10 is fastened in place around the UV curable SMC 6 and sealant is provided at the axial peripheries of the vacuum bag 10.

The vacuum bag 10 comprises an inner chamber which is in fluid communication with the valve 12. Thus, when a pump is connected to the vacuum bag 10, a low pressure can be achieved throughout the entire inner chamber of the vacuum bag 10.

The vacuum bag has two planar surfaces connected at their peripheries. One of the surfaces is porous and a vacuum can be applied across the porous surface, where the inner chamber is at a low pressure. The other planar surface of the vacuum bag 10 is air tight and is arranged to face away from the surface to which a vacuum is applied. The valve 12 is situated in the air tight surface of the vacuum bag 10. In practice, the surface of the vacuum bag 10 that is directed away from the SMC 6 is air tight and the surface that is directed towards the SMC 6 is porous.

In order to protect the pipe 2 from external corrosion the external surface of the pipe 2 is first thoroughly cleaned. The UV curable SMC 6 is then wrapped around the pipe 2, and the vacuum bag 10 is wrapped around the UV curable SMC 6. A vacuum is then applied through the valve 12 in the vacuum bag 10 so that air is biased radially outwards from the external surface of the pipe 2 towards the inner cylindrical surface of the vacuum bag 10. The air that is biased towards the vacuum bag 10 may include: air that is initially between the vacuum bag 10 and the UV curable SMC 6, air initially present within the UV curable SMC 6, and air initially present between the UV curable SMC 6 and the pipe 2.

Prior to the curing of the SMC 6, the material is resin-like such that air may be drawn through the fabric of the material. Therefore, when a vacuum is applied through the vacuum bag 10, air may be sucked from between the SMC 6 and the pipe 2 so that it bubbles through the SMC 6

towards the vacuum bag 10. Any air that is initially present in air pockets in the SMC 6 may be drawn out of the SMC 6 by the vacuum. In another embodiment the vacuum bag 10 may be arranged to draw air from between the coating and the surface at the axial periphery of the coating on the pipe 2.

In this way, the SMC 6 may become firmly fixed to the external surface of the pipe 2. Even if there is no actual adhesion between the pipe 2 and the SMC 6, a vacuum is effectively created between the SMC 6 and the pipe 2 so that the SMC 6 is sucked onto the surface of the pipe 2. Following application of the vacuum, the canopy 8 may be removed, allowing natural sunlight on to the UV curable SMC 6, causing it to cure. The cured SMC 6 is impervious to air and the coating is firmly fixed onto the external surface of the pipe 2.

Although the above description only refers to a single coating layer, there could, of course, be several layers, depending on the needs of a specific application.

The strength of the connection between a coating and a surface is generally measured in units of pressure. "Pull-off' measurements measure the pressure that would be required to separate the coating from the surface. In the prior art a typical "pull-off" measurement would be in the region of 3-7MPa. However, by using vacuum application methods it is possible to achieve "pull-off measurements of up to 20MPa.

hi order to avoid any reduction in the "pull-off" measurement over time, the heat expansion coefficient of the SMC 6, once cured, is arranged to be very close to that of steel.

Figure 3 shows a close up of the external surface of the pipe 2 of Figures 1 and 2, showing further layers that are preferably used together with the vacuum bag 10. Preferably the following layers are arranged in a sandwich between the vacuum bag 10 and the pipe 2, starting with the material closest to the pipe 2: a UV curable SMC material 6, a release film 14, and a breather layer 16. Both the breather layer 16 and the release film 14 may comprise nylon. The breather layer 16 is arranged to provide a buffer that prevents any damage to the vacuum bag 10, while at the same time maintaining an air path through which a vacuum may be applied. The release film 14 is a barrier between the UV curable SMC 6 and the breather layer 16. The release film 14 may comprise a number of holes through which the vacuum may be applied. Air 5 may be present between any of the layers mentioned and this air will generally be drawn out of the arrangement when the vacuum is applied through the vacuum bag 10. In addition, as mentioned previously, air pockets 18 may be initially present in the material 6 and these may also be drawn out by the vacuum.

Before a vacuum is applied through the valve in the vacuum bag 10, the layer of release film 14, and the breather layer 16 are arranged in loose contact around the SMC 6. When a vacuum is applied, the vacuum bag tightens around the lower layers to bring the layers into close engagement with one another. In the absence of the breather layer 16 and the release film 14 the vacuum bag would be drawn quickly and directly into contact with the SMC. The impact of a surface of the vacuum bag 10 on the SMC

6 could entrap small pockets of air in the SMC, which is undesirable. The provision of breather layer 16 alleviates this problem.

The breather layer 16 is preferably a light sheet of polythene comprising a plurality of holes. Thus, when a vacuum is applied by the vacuum bag 10, the first effect is that the breather layer 16 is drawn radially outwardly into contact with the vacuum bag 10. The second effect is that the vacuum bag 10 and breather layer 16 in combination are drawn radially inwardly into contact with the SMC 6. These steps happen in the described sequence due to the low mass of the breather layer 16 relative to the vacuum bag 10. It has been found that the provision of a breather layer 16 delays the vacuum bag 10 being drawn onto a surface of the SMC 6, and that this in turn reduces the entrapment of air in the SMC.

Once the SMC 6 has been fixed to the pipe 2 and cured, the breather layer 16 and the release film 14 may be easily peeled off.

During application of the vacuum, air is biased radially outwards, as indicated by arrows 11 in Figure 3.

It is important to recognise that while this embodiment relates to fixing a coating onto a pipe, it would be possible to fix a coating to a wide variety of different objects using the method described herein. Objects that could be coated in order to protect them from corrosion could include cables, vehicles, underwater walls, and surfaces on vehicles.

Second Embodiment Figure 4 shows a concrete strut 30 with a square cross-section surrounded by water 31. The strut may be used for bearing structural loads in an oil rig. A heat curable SMC material 32 is wrapped around the strut 30 to prevent corrosion occurring to the outer surface of the strut 30; the width of the SMC 32 in this example is around Im. In this embodiment it is

preferable to use a heat curable material rather than a UV curable material as there may be little natural sunlight even at low water depths.

In a variation from the first embodiment, the heat curable SMC 32 comprises a strengthening agent. By providing a strengthening agent, the cured SMC 32 may be able to restore some of the strength to the strut 30. It may not be desirable to use certain strengthening agents together with a UV curable SMC because many strengthening agents may be opaque to UV radiation. Many different strengthening agents may be used, although it may be convenient to use a synthetic fibre strengthening agent such as

Kevlar (RTM) in conjunction with a SMC coating.

Figure 5 shows a cross section of the strut 30 of Figure 4 showing the layers that are required to surround the strut. In this arrangement the heat curable SMC 32 wraps around the strut 30, the vacuum bag 40 wraps around the heat curable SMC 32, and a heat blanket 42 wraps around the vacuum bag 40. The vacuum bag 40 has a valve 41 which is connectable to a pump.

In order to fix the SMC 32 to the strut 30, a vacuum is applied through the vacuum bag 40 in order to draw air out of the arrangement. Air is drawn through the SMC 32 towards the vacuum bag 40 and, as previously explained, this causes the SMC 32 to become fixed to the external surface of the strut 30. Once the SMC 32 is fixed in place, the heat blanket 42 is switched on and the heat curable SMC 32 is cured.

The heat blanket 42 may be a silicone heat pad that is generally reusable. In use, the heat blanket 42 is arranged to heat the heat curable SMC 32 so that its temperature rises to between around 80 ⁰ C and 145 ⁰ C, and

preferably the SMC 32 cures at close to this temperature. In other embodiments the heat blanket 42 is arranged to heat the heat curable SMC 32 to around 150-200 ⁰ C. The curing time for the SMC 32 varies depending on its thickness and precise composition but 10 to 20 minutes is typical.