This invention relates to material for and a method of insulating pipes or ducts especially for sub sea pipe¬ lines but also other types of piping and ducting where it is necessary or desirable to insulate or to prevent condensation. Effective insulation of a sub sea pipeline prevents the formation of waxes and hydrates forming in the line and also retains the correct viscosity of crude oi l. Various systems have been used previously, such the injection of polyurethane foam into an anulus between a pipeline and a carrier pipe. P.U. foam is not resiistant to hydrostatic pressure or the ingress of sea water; consequently the foam requi res the physical protection of carrier pipe. It was found that P.V.C. crosslinked foam had the abi lity to resist both hydrostatic pressure and water ingress. P.V.C. foam is classed as a rigid closed cell foam which restricts the method of application. The foam is manufactured by producing a moulded embroy block which is expanded in steam or hot water to provide blocks of a specified density approximately 1.5 mts. long -x 0.7 mts . wide x 30 mm thick.

Anti corrosion protection is also a requirement of an insulation system. The P.V.C. foam is therefore used in conjunction with an elastomer which provides both the anti corrosion protection and a flexible base for the P.V.C .

The first method of application used for a P.V.C. foam insulated line was to apply approx. 6 mm of elastomer to the pipe (anti corrosion) followed by thi rd-ci rcumference shells of foam approx. 1 m long and 25 mm thick. Once the pipe was coated with the P.V.C. foam a mould was applied over the pipe and polyurethane injected, providing a protective coating and totally encapsulating the foam. This method was very labour intensive as it was necessary to

build the sections of foam onto the pipe by hand. Another method presently in use, is to apply the elastomer onto a corrosion coat followed by an application of P.V.C. foam in strip form by machine in a hel cal manner, until the pipe is coated. Subsequent Layers are appl ed in the same manner until the required thickness is achieved with a 1 mm thick rubber between layers to provide a bond and to provide flexibility of the system. A further layer of elastomer is applied as an outer coating. The material is then cured in an autoclave forming one homogeneous mass. To be able to mac ine apply the P.V.C. foam in a spiral manner, it has to be prepared in a strip form approximately 100 mm wide and 5 to 10 mm thick dependent on density and pipe radi us - This second method, a Ithough automated, requires the build up of the system in relatively thin layers, the t ickness of the P.V.C. foam being determined by its density and the radius of the pipe. The cost of preparing strip P.V.C. foam is expensive. An object of this invention is to provide material for and a method of insulating a sub sea pipeline which obviate or mitigate the disadvantages of the aforementioned materials and methods.

According to one aspect of the present invention, there s provided'a flat block of insulation material having parallel longitudinal sides and comprising a plurality of bars of rigid P.V.C. foam disposed in parallel across the block and spaced apart, the bars being flexibly interconnected at their bases whereby the block can be rolled over on itself.

Preferably, the block is a single piece of rigid P.V.C. foam one major face of which is deeply grooved to form the bars and the flexible interconnect on.

Preferably also, the bars are disposed at an angle to the transverse axis of the block so that the block can be

rolled over on itself in a spi ral manner.

Preferably also, the other major face of the block has applied thereto a friction fabric, preferably, a synthetic fabric mesh in an uncured elastomer compound. Blocks may be placed end to end and oined together by an adhesive.

According to another aspect of the present invention there is provided an insulation material for use in insulating a pipe or duct, said material comprising a flat block having parallel longitudinal sides, a plurality of spaced parallel bars extending across the width of the block and disposed at an angle to the transverse axis of the block, the bars being flexibly interconnected at their bases to allow the block to be rolled onto a curved surface of a pipe or duct in a spiral manner.

According to another aspect of the present invention there is provided a method of insulating a pipe or duct comprising the steps of applying an anti corrosion coating to a pipe or duct, assembling a plurality of insulating material blocks as defined in the preceding paragraph into a continuous strip, winding the insulating material in one layer on to the coated pipe or duct in a spiral manner whereby the bars of each block engage the coated pipe or duct, applying an outer protective coating of elastomer and curing the completed coating.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig. 1 is a perspective view from the top and one end of an insulation material according to the invention;

Fig. 2 is a sectional side elevation on the line 11-11 of Fig. 1 showing a detai l; and

Fig. 3 is a perspective view showing an insulated pipeline in the process of assembly. Referring to the drawings, the insulation material

comprises a plurality of flat blocks 10 disposed end to end and joined toget 'er by an adhesive to form a continuous strip 11 CFig. 3) which is spirally wound round the pipe 12. Each block 10 in the preferred embodiment, is formed from a single piece of rigid P.V.C. foam of dimensions wh ch may vary between 350 to 700 mm width, 12 mm to 40 mm thickness and approximately 1.3 m in length.

One major face of the block is deeply grooved Cstriated) across its width to form a plurality of parallel spaced bars 13 which are interconnected at their bases by webs 14, the bars 13 being disposed at an angle to the transverse axis of the block. The angle at which the bars are disposed, the width, depth and shape of the bars are determined by the radius of the pipe 12 and the thickness of the block. When the block 10 is spirally wound onto the pipe, the bars 13 lie longitudinally of the pipe and the gaps (grooves 14) between the bars close.

Thus, the grooves are sufficiently deep to impart a flexibility to the thin web 15 of P.V.C. foam between bars 13 as best illustrated in F g. 2. The bars are conveniently of quadrilateral shape in side section with two opposed sides converging upwardly from the base, aLso illustrated in Fig. 2 .

Each block 10 has a backing 16 applied to the other major face, and said backing is conveniently a synthetic fibre mesh embedded in a 1 mm th ck layer of uncured elastomer compound.

In use, a plurality of, e.g. five blocks 10 are placed end to end on a table (not sho n) adjacent to the pipe 12 to be insulated, and joined together ⁵ as at 17 using a quick dr ing adhesive to form the continuous strip 11.

The pipe 12 is first coated with an anti corrosion elastomeric material 18 after which the strip 11 of insulating material is spirally wound onto the pipe 11

and continually added to by adhesively joining further blocks to the end of the strip 11. As the strip winds around the pipeline the bars 13 locate longitudinally of the pipe and the gaps between the bars close. Thus, a single layer of insulation material of the desired thickness is provided.

An outer coating of elastomer (not shown) is applied as a protective coating and the completed insulating coating is then cured in a steam autoclave. In view of the fact that the insulation can be spirally wound onto the pipe in a single layer which may have a width and thickness in excess of known insulating strips, the saving, in time and materials, using the method and blocks of the invention are considerable. Maximum uti lization of the P.V.C. foam block s realised with a minimum waste.

Each block is a parallelogram having two longitud¬ inal parallel sides and two ends which are at right angles or otherwise to the longitudinal sides. The ends however, may be curved or otherwise formed such that the ends of adjacent blocks can be joined together to form the strip

1 -

In a modified arrangement, the bars of P.V.C. foam are formed separately and mounted in thei r parallel dispositions and a flexible base.

For blocks to be wound in circular manner round a pipe, the bars are disposed transversely of the block. Such blocks are wound round the pipe individually and their ends joined. Whi le the insulation and method of applying the insulation is particularly suitable for sub sea pipelines, they may also be applied to other types of piping or ducting where it is necessary or desirable to insulate or to prevent condensation.