The present invention relates to fire safety coatings for structures, particularly for steel line pipes for hydrocarbons in offshore activities, possibly for plastic material conduits for e.g. fire extinguishing installations in the oil industry, but also as a coating on e.g. flat or profiled structures of steel or other materials.

In catastrophic fires in oil/gas plants at sea it is important regarding crew safety that adequate time for evacuation is provided, from the moment when the fire is a fact. It is very important that the risers, which are fully loaded with hydrocarbons and have been shut on top as a result of automatic closing procedures, are not heated too rapidly by e.g. burning oil on the sea surface, because if these risers spring a leak due to high temperature, even more oil/gas will flow out and increase the extent of the fire to a substantial and maybe even fatal degree.

The risers mentioned are constructed of steel, and are often provided with a rubber cladding vulcanized thereon for corrosion protection and mechanical protection in the splash zone. However, in order to obtain also a high degree of delay of the temperature rise in the case of a typical surrounding temperature of 1000-1100°C, i.e. a hydrocarbon fire, it iε necessary to undertake a further refinement of the pipe cladding.

Fire protecting combination coatings, i.e. multilayer coatings, are per se previously known.

For instance from European patent application no. 90.635 there is known a three-layer material where the outer layer is heat reflecting, for example a metal sheath, the intermediate layer is a so-called endothermal material (i.e. it absorbs heat in connection with a phase transition) , e.g. aluminum hydrate, and the inner layer is a thermally intumescent and insulating material. These three layers come into effect successively, and will provide a substantial delay of the temperature rise inside the inner layer. But this type of

coating does not hold the mechanical strength necessary in a tough milieu like e.g. the splash zone beneath an oil plant.

Further, from European patent application no. 283.385 there is known a three-layer coating where the outer layer is a composite material with a mineral matrix surrounding structural reinforcement elements. Thus, the outer layer may be inorganic, since the mineral matrix can be a material similar to a ceramic, and the reinforcement elements are metal fibres or mineral fibres. The function of the outer layer is to provide structural solidity for the coating, and to provide resistance against flames and "thermal shocks". An intermediate layer consists of a felt of refractory fibres, and this layer is intended to constitute a fire-retarding shield for the material inside. The inner layer is a thermally insulating layer with a cell structure, preferably of an organic type, i.e. cork or resin of a heat curable or thermoplastic type. Not even such a cladding is suitable regarding mechanical strength and corrosion protection in rough surroundings. However, the function of the outer and inner layer in accordance with EP 283.385 corresponds to the particular fire safety functions for the inner and outer layers in accordance with the present invention in its general form, even though these functions are preferably obtained using other types of materials than in EP 283.385.

However, the intermediate layer of EP 283.385 suffers from the substantial drawback that oxygen may find its way therethrough, and hence lead to oxidation of the inner layer, thereafter leading to alteration of properties in an unfavourable direction, i.e. the thermal insulating property of the inner layer may in such a case be substantially impaired.

The present invention provides a coating where the drawbacks of the prior art regarding mechanical strength, corrosion retarding effect and oxygen barrier effect are remedied.

The 'above mentioned result is achieved by providing a fire safety coating of the type stated in the appended patent

claims. The invention will be described closer in the following by means of embodiment examples, and with reference to the appended drawings, where fig. 1 shows a section through a steel pipe with a fire safety coating in accordance with the essential aspect of the invention, and fig. 2 shows a corresponding drawing of an embodiment where additional layers have been included in order to provide a further improved fire protection.

In fig. 1 is shown the embodiment of the invention which comprises only the most important features: Steel pipe 1 which conducts hydrocarbons (not shown) in the center thereof, is to be protected. In the outermost position there is a layer 5 of natural rubber, synthetic rubber or plastic to constitute a mechanical protection layer. An inside layer 4 is provided to stop flame attacks, and is of an inorganic type. Preferably layer 4 consists of inorganic fibres, e.g. wound glass fibre ribbons.

Inside layer 4 there is a layer 3 of a thermally highly insulating material, preferably of rubber or plastic, and with great mechanical ^'* strength. This layer 3 provides delay of the heat transport in toward steel pipe 1. Innermost toward steel pipe 1 there iε a corrosion inhibiting layer 2 of rubber or plastic, which possibly also may exhibit good heat insula-tion properties. Preferably a specially developed neoprene rubber material may constitute this layer 2 which has special corrosion inhibiting properties and is a mechanically strong layer 2 which is vulcanized directly on to steel pipe 1.

Thermally insulating layer 3 has special qualities in connection with a fire. In the first stage of a fire this material, which preferably is made of a special rubber compound or of a special type of plastic, works as a heat insulator. When this layer 3 is heated due to the fire, the layer develops reactive gases which draw outwards and react with the outside layers 4 and 5, converting these layers to a hard shell during the fire. The surplus thereafter remaining of the gases is combustible, and causes a counterfire on the

outer surface of layer 5, against the actual fire.

Due to the overpressure from the gases formed, or actually due to the outwards migration of the gases, oxygen wil not be able to penetrate from the outside to cause a combustion of intermediate layer 3 itself. However, intermediate layer 3 will all the time be subject to pyrolysis, i.e. degradation without any supply of oxygen. This pyrolysis process leads to the formation of a new material structure inside layer 3, but this new structure also exhibits very good heat insulating characteristics, and takes care of keeping away the fire heat from the underlying structure 1 to be protected.

As mentioned above, inorganic layer 4 works as a flame shield, consisting of a non-combustible material, which thus prevents the flames from reaching the underlying rubber or plastic. In addition to the mechanical protection constituted by layer 5, the material of layer 5 shall also be a rubber or plastic material which is impervious to water, and additio¬ nally it protects the rest of the materials from degradation due to influence from the sun or chemical substances like e.g. ozone.

In fig. 2 the same four layers 2, 3, 4 and 5 are shown surrounding a steel pipe 1, but further layers have been added. Innermost are the previously mentioned fire safety layers 2, 3, 4 and 5, and in order to further extend the time period until destruction of steel pipe 1 may occur, layers of the same type as layers 4 and 5 are repeated as layers 6 and 7, respectively 8 and 9. (Of course, even more layers than here shown may be used, but the increase of protection quality must here only be weighed against the increase in cost.) Thus, layer 9 is a mechanically protective layer, preferably of chloroprene rubber, layer 8 iε an inorganic flame inhibiting/flame stopping layer, preferably of inorganic fibres, layer 7 is a new mechanically protecting layer of chloroprene rubber and layer 6 an inorganic fibre layer.

Hence, the gas barrier which is formed, has the effect that no undesired oxidation occurs in the insulating

intermediate layer 3, which therefore maintains its favourable properties for a long time during a fire.

Generally it must be noted that all rubber layers 2, 3, 5, 7 and 9 present in the invention exhibit a great mechanical strength and are well suited for use in difficult surroundings. Also fibre layers 4, 6 and 8 are very strong. Thus, in total there is achieved, possibly only with the 4- layer protection which constitutes the essence of the invention, a fire safety coating with very good fire properties and which in addition is well suited as a coating against mechanical wear and corrosion under tough normal conditions.

It must be mentioned that fire tests which have been conducted, show that the coating _. in accordance with the invention is very effective. ^~ Steel pipes with a coating thickness of 3 mm for layer 2, 31 mm for layer 3 and in total 16 mm for layers 4-9, turn out to withstand a fire with temperature 1100°C with an inside temperature not exceeding 120°c during a time period of about 2 hours, which test result satisfies international safety requirements with good margin.

Finally it should be noted that the coating iε not in any manner intended to be used merely for protecting pipes, but also other constructions situated in a harsh climatic milieu, for instance construction parts, profileε and walls.