GB2231905A - Insulating system for protecting a structure against fire - Google Patents

Abstract

An insulating system for protecting a structure against fire comprises a fire protective coating 1 made of a material that has or generates good fire protective action on exposure to a fire, and an oversheath 2 made of an impermeable material which rapidly disintegrates on exposure to fire, thereby leaving the outer surface of the fire protective coating exposed to the fire. <IMAGE>

Description

INSULATING SYSTEM FOR PROTECTING A STRUCTURE AGAINST FIRE The invention relates to an insulating system for protecting a structure against fire.

Passive fire protective coatings are widely used on certain structural members on offshore platforms and other structures. It has not been general practice to provide such protection to the legs and support structure (known as the jacket) from the platform lower deck down to sea level. Recent events have highlighted the desirability of providing such protection. However, currently available fire protective materials are unsuitable for use in this region since they are not specifically designed to resist prolonged exposure to sea spray and wave action.

Fire protective coatings used offshore are frequently based on either a cementitious material or an organic polymer with an intumescent capability.

Cementitious materials have a relatively high heat capacity and may also absorb heat by liberating water. The ability to lose this water as vapour is therefore a key feature. Intumescent materials form a char on heating, which can be several times as thick as the original coating and this expansion imparts a low thermal conductivity. The ability to expand freely is therefore critical.

It is known from US patent 3,934,066 to cover a fire retardant intumescent coating with a flexible protective layer which yields or deforms, with or without rupture, under conditions of fire. The deformation of the protective layer allows the underlying intumescent coating to expand in the event of fire. A drawback of the known fire protection system is that the continuing encapsulation of at least part of the surface of the fire protective coating inside the flexible top layer prevents direct exposure of the coating to the environment so that this layer can not immediately swell in response to the fire or liberate water or other heat absorbing or fire extinguishing materials to absorb heat. This delay in activation of the fire protective material is particularly dangerous in the event of a hydrocarbon jet fire where an intense heat may be developed within fractions of seconds.

Accordingly the present invention provides a fire protective system with a top layer which separates the fire protective coating from the environment in a fluid tight manner but which enables a rapid exposure of the coating to the flames in the event of fire so that it is suitable to protect parts of an offshore structure in the splash zone.

The present invention thus relates to an insulating system for protecting a structure against fire, the system comprising: - a fire protective coating which covers at least part of the surface of the structure, said coating being made of a material that has or generates good fire protective properties on exposure to fire, and - an oversheath which covers an outer surface of fire protective coating, said oversheath being made of an impermeable material which rapidly disintegrates on exposure to fire thereby exposing the outer surface of the fire protective coating to the fire.

A rapid disintegration of the oversheath in the event of fire may be obtained by using rubber or rubber-like materials which rapidly burn away or partially burn and then fall away when they are exposed to fire.

It is furthermore preferred that the oversheath is bonded to the fire protective coating by a waterproof adhesive which loses its bonding properties under fire conditions. A suitable adhesive of this kind is a polyurethane adhesive.

In a preferred embodiment of the invention the oversheath consists of a thin layer of AQUATECT. The composition of AQUATECT is described in European patent No. 0171110 and it contains a top layer of a vulcanized silicone rubber based antifouling material and a water-impermeable base layer that may be made of a polyvinyl chloride or an epoxy resin. The two layers are joined together through a bonding film of a silicone ester of a (meth)acrylic acid.

It is furthermore preferred that the underlying fire protective coating comprises a vulcanized silicone foam or an intumescent or cementitious material. A suitable vulcanized silicone foam is described in British patent No. 2,107,810. A suitable intumescent material is AVCO CHARTEK 59, type III. A suitable cementitious material is MARINE MANDOLITE 550.

If the fire protective insulation system according to the invention is applied on structural members that are exposed to wave impact and a wet environment, such as framing members of an offshore platform a synergetic effect is created if the fire protective coating comprises an intumescent material and the oversheath is made of AQUATECT. In a normal use the AQUATECT oversheath protects the fire protective coating and underlying platform legs against marine growth and contact with water whereas if a fire occurs the oversheath rapidly burns or slides away so that the intumescent material is exposed to the fire and is allowed to expand to a very thick insulating layer with an excellent fire protective performance.

The invention may be carried into practice in various ways but one particular embodiment will now be described in more detail with reference to the accompanying drawing which shows a fire protective system according to the invention surrounding framing members of an offshore structure.

The fire protective system shown in the drawing consists of a fire protective coating 1 and an oversheath 2 of a formable and impermeable material. The coating 1 covers the steel framing members 3 of an offshore structure from the level of the platform under-deck 4 to below the sea level 5. The coating 1 may be optionally extended below sea level 5. The oversheath 2 forms a protective cover which protects the coating 1 against wave action and minor impact.

In the embodiment shown the oversheath 2 is made of AQUATECT.

The composition of this material is described in detail in European patent No. 0171110. This material has antifouling properties provided by a high-build layer which is made of a vulcanized silicone rubber and an exuding liquid, and sealing properties provided by a water-impermeable base layer. The two layers are joined together through a bonding film which contains a silicone ester of acrylic acid or methacrylic acid. Preferably the bonding film moreover contains at least 60% by volume of the materials of the high-build layer.

The oversheath 2 is bonded to the fire protective coating 1 by a suitable adhesive that is chemically compatible with both, such as a polyurethane. Use of polyurethane adhesive has the advantage that this material rapidly loses its bonding properties at elevated temperatures so that the oversheath rapidly falls away or slides away from the coating 1 on exposure to fire. The oversheath 2 may be secured around the fire protective coating 1 as a continuous layer or as an overwrap of a helically wound strip with suitable interlayer bonding.

Use of AQUATECT for the oversheath 2 has the advantage that it can be formed into a cohesive, robust and impermeable layer which is able to protect the underlying fire resistant coating 1 from contact with the surrounding water and against damage caused by marine growth.

The thickness of the oversheath 2 is typically less than about 10 millimeters and preferably between 1 and 5 millimeters so that it rapidly burns away in case of fire thereby leaving the outer surface of the fire protective coating 1 exposed to the fire. In the embodiment shown the fire protective coating 1 comprises an intumescent material such as AVCO CHARTEK 59, type III.

This intumescent material chars when it is exposed to a fire and thereby swells up to a rigid foam having about 50 times the volume of the original layer. Because of this large volume increase the material becomes an excellent insulating material which protects the underlying framing members 3 against the heat of the fire over a long period of time. Calculations have shown that a tubular steel member 3 surrounded by a fire protective system according to the invention may survive forty times longer than an unprotected steel member 3. Instead of or in addition to application of the fire protective system according to the invention to tubular members of an offshore structure the system may also be applied to risers, conductor pipes, auxiliary structures and other components of an offshore or other structure.

It will be understood that the presence of the impermeable oversheath 2 allows the use of other intumescent materials than AVCO CHARTEK 59, type III for the fire protective coating 1. For the coating 1 fire protective materials of other types may be used as well, provided that the materials have or generate good fire protective action when exposed to a fire. A suitable alternative material is a cementitious material, such as MARINE MANDOLITE 550.

Another suitable alternative material is a vulcanized silicone foam described in British patent No. 2,107,810.

It will further be understood that instead of using AQUATECT for the oversheath 2 any other impermeable material which burns or falls away on exposure to fire may be used. Suitable alternative materials for the oversheath are materials selected from the group of natural rubbers, synthetic rubbers, such as butadiene rubbers, and other rubber-like materials. The oversheath may also be made of a series of preformed glass fibre reinforced sections, a shrink-wrapped polyolefin, or a sprayed in place chopped-glass reinforced polyester.

If an oversheath of the above materials is bonded to the fire protective coating by a waterproof adhesive which rapidly fails under fire conditions, such as a polyurethane adhesive, a rapid exposure of the entire outer surface of the fire protective coating to the fire is accomplished.

Claims (15)

1. An insulating system for protecting a structure against fire, the system comprising: - a fire protective coating which covers at least part of the surface of the structure, said coating being made of a material that has or generates good fire protective properties on exposure to fire, and - an oversheath which covers an outer surface of fire protective coating, said oversheath being made of an impermeable material which rapidly disintegrates on exposure to fire thereby exposing the outer surface of the fire protective coating to the fire.

2. The system of claim 1 wherein the oversheath is bonded to the fire protective coating by a waterproof adhesive which loses its bonding properties under fire conditions.

3. The system of claim 2 wherein the adhesive is a polyurethane adhesive.

4. The system of claim 2 or 3 wherein the oversheath consists of a series of preformed glass fibre reinforced sections.

5. The system of claim 2 or 3 wherein the oversheath consists of a sprayed-in-place chopped-glass reinforced polyester.

6. The system of claims 1, 2 or 3 wherein the oversheath consists of a shrink-wrapped polyolefin.

7. The system of claims 1, 2 or 3 wherein the oversheath is made of a material selected from the group of natural rubbers, synthetic rubbers, such as butadiene rubbers,and other rubber-like materials.

8. The system of claims 1, 2 or 3 wherein the oversheath comprises a water impermeable base layer and a high-build layer containing a vulcanized silicone rubber and an exuding liquid, which layers are joined together through a bonding film of a silicone ester of an acrylic or methacrylic acid.

9. The system of claim 8 wherein the water impermeable layer comprises polyvinyl chloride or an epoxy resin.

10. The system of claim 8 or 9 wherein the bonding film contains at least 60% by volume of the materials of the high-build layer.

11. The system of any preceding claim wherein the fire protective coating comprises material selected from the group of intumescent and cementitious materials and vulcanized silicone foams.

12. The system of any preceding claim wherein the fire protective coating and oversheath are co-axially arranged around tubular framing members of a steel structure which supports an offshore platform.

13. The system of claim 12 wherein the fire protective coating and oversheath surround said framing members from the level of the platform under-deck down to below the water-level.

14. The system of any preceding claim wherein the fire protective coating and oversheath are applied to risers, conductor pipes, auxiliary structures and other components of an offshore structure.

15. The system of claim 1 substantially as described with reference to the drawing.