Thixotropic Silicone Mixture TECHNOLOGICAL FIELD

Examples of the disclosure relate to a curable silicone mixture, a coating being the reaction product of a curable silicone mixture, and a method of applying a curable silicone mixture to a substrate.

BACKGROUND

It is often required to provide substrates such as subsea oil and gas equipment, for example, wellheads, Xmas trees, spool pieces, manifolds, risers and pipe field joints, with thermal insulating coatings to maintain the temperature of the extracted fluids as they pass through portions of the equipment exposed to the cooling effects of sea water.

Hydrocarbon facilities are vulnerable to fires, such as jet fires. This situation can create particularly intense levels of localised heat which damages substrates such as pipework, valves and other process components. There is also a requirement therefore to provide such substrates with intumescent coatings to delay the effects of a fire, such as a jet fire, and slow the rate of temperature increase of the substrate.

Conventionally, thermal insulating coatings and intumescent coatings are formed from curable silicone mixtures, applied by injection moulding the coating around the substrate. In this instance, the curable silicone mixture is pumped into moulds fitted to a particular substrate on site to provide a coating with the required thickness and profile once the mixture has cured. Alternatively, pre-moulded coatings are provided for on-site assembly. Irrespective of which of the above methods is employed, a mould must first be manufactured for each particular substrate. This often presents a technical challenge and increases costs, and particularly for complex substrates for which it is difficult to manufacture an appropriate mould. Furthermore, expensive equipment is required for injection moulding, which may be bespoke for each particular application. A skilled operative is also required to operate the equipment.

There is a requirement therefore to provide curable silicone mixtures which can be applied to substrates using alternative method.

All proportions referred to in this specification are indicated as weight %.

BRIEF SUMMARY

According to various, but not necessarily all, examples of the disclosure there is provided a curable silicone mixture, wherein the curable silicone mixture comprises a thixotropic additive. The thixotropic additive may comprise one or more of: an organosilane, polyether, or silica based compound. The curable silicone mixture may comprise up to about 10 weight % thixotropic additive. The curable silicone mixture may comprise about 0.5 weight % to about 10 weight % thixotropic additive. The curable silicone mixture may comprise about 5 weight % to about 10 weight % thixotropic additive. The curable silicone mixture may comprise about 0.5 weight % to about 5 weight % thixotropic additive.

The curable silicone mixture may be a one part curable silicone mixture, or alternatively may be a two part curable silicone mixture.

The curable silicone mixture may be curable by exposure to moisture in the air, or may be curable by exposure to heat, or may be curable by exposure to ultraviolet light, or may be curable by an addition reaction in the presence of a metallic catalyst.

According to various, but not necessarily all, examples of the disclosure there is provided a method of applying a curable silicone mixture to a substrate, wherein the curable silicone mixture comprises a thixotropic additive, the method comprising applying the curable silicone mixture directly to the substrate. The curable silicone mixture may be applied to the substrate by brush-coating the substrate by hand, or may be applied by spraying the substrate, or may be applied by hosing the substrate, or may be applied by automated dispensing. The two part curable silicone mixture may be applied by way of a dynamic mixing head such that the two parts are separate until mixing in the dynamic mixing head.

The curable silicone mixture may be applied to the substrate as a layer with a thickness from about 5 mm to about 200 mm. A single application of the curable silicone mixture to the substrate may provide a layer with a thickness of up to about 80 mm. A single application of the curable silicone mixture to the substrate may provide a layer with a thickness of about 80 mm.

A second layer of the curable silicone mixture may be applied over a first layer of curable silicone mixture before the first layer has cured. Alternatively, a second layer of the curable silicone mixture may be applied over a first layer of curable silicone mixture once the first layer has cured.

The curable silicone mixture may be curable by exposure to moisture in the air, or may be curable by exposure to heat, or may be curable by exposure to ultraviolet light, or may be curable by an addition reaction in the presence of a metallic catalyst.

The method does not require the use of moulds. The method may comprise applying a curable silicone mixture to a substrate useable subsea, such as subsea oil and gas equipment, for example, wellheads, Xmas trees, spool pieces, manifolds, risers and pipe field joints.

According to various, but not necessarily all, examples of the disclosure there is provided a coating for a substrate, the coating being the reaction product of a curable silicone mixture, wherein the curable silicone mixture comprises a thixotropic additive.

The curable silicone mixture may be curable by exposure to moisture in the air, or may be curable by exposure to heat, or may be curable by exposure to ultraviolet light, or may be curable by an addition reaction in the presence of a metallic catalyst.

The coating may be a thermal insulating coating. The coating may be an intumescent coating. The coating may be syntactic, and may comprise glass microspheres or macrospheres.

According to various, but not necessarily all, examples of the disclosure there may be provided examples as claimed in the appended claims.

BRIEF DESCRIPTION

For a better understanding of various examples that are useful for understanding the detailed description, reference will now be made by way of example only.

DETAILED DESCRIPTION

Examples of the disclosure provide a curable silicone mixture comprising a thixotropic additive. Examples of the disclosure also provide a coating for a substrate which is the reaction product of a curable silicone mixture comprising a thixotropic additive. Examples of the disclosure also provide a method of applying a curable silicone mixture comprising a thixotropic additive to a substrate. The viscosity of a curable silicone mixture comprising a thixotropic additive according to examples of the disclosure is dependent on the stress being applied to the mixture. Accordingly, under conditions of low stress, i.e. a static condition, the curable silicone mixture would have a relatively high viscosity, whereas under conditions of high stress, such as when the curable silicone mixture is agitated or shaken, the curable silicone mixture would have a relatively low viscosity.

The curable silicone mixture can be agitated, for instance, by rapid mixing or shaking, to decrease viscosity. Subsequently, the curable silicone mixture with a decreased viscosity can be applied directly to a substrate, for instance, by brush- coating by hand, spraying, hosing, or by automated dispensing. The curable silicone mixture may be applied directly to the surface of the substrate, or alternatively may be applied to a coated surface of the substrate. The surface of the substrate may be coated, for example, with a tie coat layer and/or an anticorrosion layer. The curable silicone mixture with a decreased viscosity flows sufficiently to form a uniform layer. Once applied, the curable silicone mixture is in a static state, and thus the viscosity of the curable silicone mixture increases. The increase in viscosity causes the curable silicone mixture to substantially set, i.e. to resist further flow. It has been found in examples of the disclosure that the curable silicone mixture can be applied to even a vertical surface and will substantially set without running down the surface or sagging. Furthermore, the mixture can readily be applied to complex substrate. The curable silicone mixture applied to a substrate will subsequently cure to provide the required coating. Examples of the disclosure therefore provide a means to provide coatings, such as insulating coatings or intumescent coatings, without the requirement for injection moulding or bespoke moulds. Furthermore, a skilled operative is not required to apply the curable silicone mixture to the substrate as specialist equipment is not required such as is the case with injection moulding.

The curable silicone mixture may comprise up to about 10 weight % thixotropic additive. In some examples, the thixotropic additive comprises one or more of: an organosilane, polyether or silica based compound. In other examples, the curable silicone mixture comprises a plurality of different thixotropic additives. The viscosity of the curable silicone mixture increases the greater the quantity of thixotropic additive. It is possible therefore to control the viscosity of the mixture by adjusting the quantity of thixotropic additive and/or selecting different combinations of thixotropic additives. The viscosity of the mixture can therefore be tailored to a particular application.

In some examples, the curable silicone mixture is applied as a layer with a uniform thickness, and may be applied using any of the techniques detailed above. In other examples, the thickness of the layer may be varied to create more complex structures. The curable silicone mixture may be applied as a layer with a thickness from about 5 mm to about 200 mm. A single application of the curable silicone mixture to the substrate may provide a layer with a thickness of up to about 80 mm, depending on the application technique used. In some examples, a single application of the curable silicone mixture to the substrate provides a layer with a thickness of about 80 mm without the mixture running down a surface of the substrate or sagging. In some examples, a second layer of the curable silicone mixture is applied over a first layer of curable silicone mixture before the first layer has cured. In other examples, a second layer of the curable silicone mixture is applied over a first layer of curable silicone mixture only once the first layer has cured. The additional layers may be applied with a uniform thickness, or alternatively the thickness of the additional layers could be varied to create more complex coatings.

The curable silicone mixture may be curable by exposure to moisture in the air, or may be curable by exposure to heat, or may be curable by exposure to ultraviolet light. This is particularly the case for one part curable silicone mixtures. In examples in which a two part curable silicone mixture is used, the mixture is curable by an addition reaction in the presence of a metallic catalyst, such as a platinum catalyst.

Examples of the disclosure also provided a coating for a substrate, which coating may be a thermal insulating coating or an intumescent coating. The coatings are the reaction product of curable silicone mixtures comprising a thixotropic additive according to examples of the disclosure, applied using methods also according to examples of the disclosure.

Thermal insulating coatings according to examples of the disclosure may be applied to substrates such as subsea oil and gas equipment such as wellheads, Xmas trees, spool pieces, manifolds, risers and pipe field joints, to maintain the temperature of the extracted fluids as they pass through portions of the equipment exposed to the cooling effects of sea water. Intumescent coatings according to examples of the disclosure may be applied to substrates such as pipework, valves and other process components to delay the effects of a fire, such as a jet fire, and to slow the rate of temperature increase of the substrate. Table 1 below provides details of three curable silicone mixtures according to the disclosure. The amounts indicated are weight percent.

Table 1

In some examples, the ratio of the two part silicone is about 10 parts A to 1 part B (10:1). In other examples, the ratio of the two part silicone could be between about 20 parts A to 1 part B (20:1) and about 1 part A to 1 part B (1 :1).

In example 1 above, the curable silicone mixture is a one part curable silicone mixture. In examples 2 and 3 above, the curable silicone mixture is a two part curable silicone mixture.

In examples of the disclosure where the curable silicone mixture is a two part curable silicone mixture, the first part (part A) comprises a polydiorganosiloxane polymer, and the second part (part B) comprises an organohydrogensiloxane crosslinker mixable together so that the material will cure by an addition reaction in the presence of a metallic catalyst.

The polydiorganosiloxane polymer may comprise any of vinyldialkyl terminated polydialkylsiloxane, vinyldialkyl terminated polydialkylalkenylmethylsiloxane or mixtures thereof. The polydiorganosiloxane polymer may have at least two unsaturated groups per molecule. The organohydrogensiloxane crosslinker may have at least two Si-H bonds per molecule.

The organohydrogensiloxane crosslinker may be described by formula R ¹ 3Si(OSiR ² 2)x(OSiMeH)yOSiR ¹ 3,where each R ² is independently selected from saturated hydrocarbon radicals comprising from 1 to 10 carbon atoms or aromatic hydrocarbon radicals and each Ri is independently selected from hydrogen or R ² , x is zero or an integer and y is an integer.

There are thus described mixtures, methods and coatings with a number of advantages as detailed above.

Although embodiments of the present invention have been described in the preceding paragraphs with reference to various examples, it should be appreciated that modifications to the examples given can be made without departing from the scope of the invention as claimed.

Features described in the preceding description may be used in combinations other than the combinations explicitly described. Although functions have been described with reference to certain features, those functions may be performable by other features whether described or not.

Although features have been described with reference to certain embodiments, those features may also be present in other embodiments whether described or not.

The term "comprise" is used in this document with an inclusive not an exclusive meaning. That is any reference to X comprising Y indicates that X may comprise only one Y or may comprise more than one Y. If it is intended to use "comprise" with an exclusive meaning then it will be made clear in the context by referring to "comprising only one..." or by using "consisting".

In this brief description, reference has been made to various examples. The description of features or functions in relation to an example indicates that those features or functions are present in that example. The use of the term "example" or "for example" or "may" in the text denotes, whether explicitly stated or not, that such features or functions are present in at least the described example, whether described as an example or not, and that they can be, but are not necessarily, present in some of or all other examples. Thus "example", "for example" or "may" refers to a particular instance in a class of examples. A property of the instance can be a property of only that instance or a property of the class or a property of a subclass of the class that includes some but not all of the instances in the class. It is therefore implicitly disclosed that a feature described with reference to one example but not with reference to another example, can where possible be used in that other example but does not necessarily have to be used in that other example.

Whilst endeavoring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.