This invention relates to a field joint insulation for insulated pipelines for use especially, but not exclusively, sub-sea. Pipes which are factory-coated with elastomer or insulation can only be coated to within approximately 200 mm of the pipe ends to allow pipes to be jointed together, normally by a welding process.

The pipes are normally welded together as an integral part of the pipe-laying process either by a lay barge method or by a reel ship in a continuous basis. The welding process takes approximately ten to fifteen minutes so, in theory, the pipeline can be laid at a rate of approximately 12 metres per ten to fifteen minutes. However, in order to maintain this rate of installat¬ ion, it is necessary to be able to complete the coating of a (previously) welded field joint ithin the ten to fifteen minutes in which another field ^' joint is being welded. In theory, the insulation at the field joint should meet a simi lar specification as that of the parent coating but using the process used for applying the parent coating to the body of the pipe would take in excess of two hours to apply to the field joint. The presently used solution to the problem of covering the field joint within ten to fifteen minutes is to apply a sheet metal mould to the bare metal of the jointed pipe, inject a quick setting anti- corrosion material, such as polyurethene or epoxy, allow it to set then remove the mould. The covering provided by th s process is primari ly an ant i -corrosion covering and does not effectively insulate the field joint. Con¬ sequently, the parent coating may have to have added insulation properties to compensate for the losses at the field joint.

In addition, and perhaps more importantly, the coated pi e passes over a roller as it heads out-board. If the

anti-corrosi on covering round a field joint has not completely set by then, the point loading on the roller can cause damage to the field joint covering resulting in further loss of insulation around the joint. An object of this invention is to provide an improved field joint insulation which can be completed within approximately fifteen minutes.

According to one aspect of the present invention there is prov ded a field oint insulation located around the bare joint of two joined insulated metal pipes, comprising a pre-fabri cated infil having insulation properties secured around the pipe oint to substantially enclose the length of pipe between adjacent insulation coatings of the two pipes, said infil forming an outer coating and containing an inner coating of anti-corrosion material between the infil and the pipe joint.

Preferably, the infil is a piece of flexible elastomer of a thickness slightly less than that of the insulation coatings on the pipes, and to the inner face of which is applied a layer of anti-corrosion material prior to location of the infil around the pipe joint.

Alternatively, the prefabricated infil is formed of an inner layer of insulation material and said outer layer of waterproof and abrasion resistant material and the anti-corrosion material is a quick setting fluent material injected into a space between the infil and the pipe oint.

According to another aspect of the invention there is provided a method of applying insulation to the field joint of two joined insulated metal pipes, said method compris ng applying a layer of anti-corrosion, adhesive paste material to the inner surface of an infil formed of a piece of flexible prefabricated insulation material of a length substantially the same as the length of bare metal of the field joint and

of a width substantially the same as the external ci rcumference of the bare pipe, applying said infil around the bare field joint so that longitudinal edges of the slab just touch or are slightly spaced to leave a narrow longitudinal gap, infi lling the circumferential joint between the infil and the adjacent insulations, and along the longitudinal gap, if required, and apply¬ ing a heat shrink sleeve over the infi l to cover the said gaps . According to another aspect of the present invention there is provided a field joint insulation located around the joint of two pipes, comprising a flexible prefabricated infi l, formed of an inner layer of insulation material and an outer layer of waterproof and abrasion resistant material, said infi l being secured around the bare metal of the joint to substantially enclose the length of pipe between the adjacent insulation coatings of the two pipes but with an opening for expelled air, and an internal fi lling of quick setting anti-corrosion material which has been injected through an injection port in the infi l to fi ll a space between the infi l, the pipe joint and the adjacent insulation coatings of the two pipes and said ai r outlet.

According to another aspect of the present invent- ion there is provided a method of applying a field joint insulation to insulated pipes, said method comprising the steps of locating a prefabri cated infi l around the area of the bare jointed pipes to enclose the pipe joint between the adjacent insulated coatings of the joined pipes, but with a longitudinal gap formed by the edges of the infi l not meeting, securing the ends of the infi l by clamp means and injecting a quick setting anti- corrosion material through an inlet opening provided in the infi l to fill the spaces between the infi l, the pipe and the adjacent coatings, allowing the injected material to set and removing the clamp means.

According to another aspect of the present invent¬ ion there is provided a method of forming the infil for a filled joint insulation as defined in the second pre¬ ceding paragraph, said method comprising the steps of cutting a piece of insulating material to size, forming a hole in the piece, locating the piece in a mould wherein a space is provided between a face of the piece and the wall of the mould, and injecting through said hole in the piece a"waterproof and abrasion resistant castable material which bonds to the insulation material.

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 longitudinal sectional elevation showing a pipe field joint insulation in accordance with one embodiment of the invention, in the process of being applied to the field joint;

Fig. 2 is a cross sectional elevation of Fig. 1 Fig. 3 is an end elevation of an infil of the insulation partially bent.

Fig. 4 is a longitud nal sectional elevation showing a pipe field joint insulation in accordance with a second embodiment of the invention; and

Fig. 5 s a perspective view of the insulation. Referring to the drawings, a pipeline field j.oint

10 is formed by welding two pipes 11, 12 together at 10A. Pipes 11, 12 are each coated at 13 to within a short d stance .from its ends, this parent coating 13 comprising an inner anti-corrosion layer 14 e.g. polyurethane or epoxy, a middle PVC foam insulation layer 15 and an external protective layer 16 which is waterproof and abrasion resistant and is e.g. polyurethane or epoxy resin or rubber. The outer protective layer tapers at each end to cover the nner and middle layers. The field joint 10 is therefore initially bare,

and a field joint insulation 20 is applied thereto.

The field joint insulation 20 includes a flexible infi l member 21 which is pre-formed and wrapped around the bare steel pipe of the field joint 10 to substantially enclose the pipe between the ends of adjacent parent coat¬ ings .13. However, the infi l 21 is dimensioned so that its longitudinal edges do not meet thus forming a narrow longitudinal gap 22 to allow the escape of air. The infi l 21 is so positioned that the gap is at the top of the pipe. An injection port 23 dri lled in the centre of the infi l 21 is at the bottom of the infi l when positioned on the pipe. The process of insulating the field joint 10 comprises wrapping the infi l 21 around the bare pipe, and securing the ends of the infi l by two quick-release clamps 24. With the infi l 21 in position and acting as a mould, a qui ck s.e11 i ng castab le anti-corrosion material 14' is injected under the infi l 21 through the port 23 therein to fi ll the space between the infi l and the pipe as well as the space between the infil and the ends of the parent coatings and also the longitudinal gap 22 as i llustrated in Fig. 1.

Once the material 14" has set, the clamps 24 are removed leaving the infi l secured to the pipeline and the field joint insulation is ready to pass outboard over a roller (not shown) . The process takes about ten to fifteen minutes.

The infi l 21 is pre-formed at a factory by fi rstly cutting a piece of PVC foam 15' to the requi red size, namely of a thickness equal to that of the parent coating, a width equal to the circumference of the pipe less 1" and the length of the bare metal less 2". A hole 26 is made in PVC piece 15' which is then placed in a mould, indicated generally as 27 (not shown) and the protective coating material 16' is injected into the mould via hole 26 to bond to a face of the piece 15' .

In a preferred embodiment the mould is annular.

Thus the PVC foam piece 15' is firstly striated on one face, i.e. the piece 15' has a series of deep grooves 30 cut across its width to form a plurality of parallel spaced bars 31. The piece can thereafter be bent into a curve by making the striated face concave and causing the gaps 30 between the bars 31 to lessen and close.

To prepare the infil, the striated piece 15' is placed in the annular mould with the non-striated face innermost so that the protective coating 16' is bonded to that face. The resulting infil is flexible and when bent around the pipe, the grooves 30 in the striated surface close to form a solid inner surface, as illustrat¬ ed in Fig. 2. The protective coating 16" is preferably polyure¬ thane or epoxy resin.

The infil may be moulded flat for example when the outer protective coating is of rubber, in which case the PVC foam can be striated before or after the moulding process.

In a second embodiment, the field joint insulat¬ ion 40 includes a flexible infil member 41 which is preformed and wrapped around the bare steel pipe of the field joint 10 to substantially enclose the pipe between the ends of adjacent parent coatings 13. The infil is again dimensioned so that the longitudinal edges do not meet, or at least do not overlap, usually forming a narrow longitudinal gap 42 of 0 to about 8mm. The length of the infil is such that at each end there is usually a circumferential gap 43 of 5 to 10mm when the infil 41 is positioned around the field joint. These gaps are subsequently filled in.

The infil 41 in this embodiment is an elastomer. It is manufactured and prepared prior to use as a field joint insulation. The method of construction of the infil comprises applying elastomer coating of a thickness

5mm less than the parent coating 13, on a mandrel of approximately the same die as the pipe 11/12. The elastomer coating is then vulcanised. Once cured, the elastomer is cut longitudinally and then cut transversely into sections approximately 590mm in length. These sections form the infils 41 which, having been made on a mandrel, retain their cylindrical shape, longitudinally split.

The field joint insulation 40 is prepared by flattening the infi l and applying a bonding agent to its inner surface followed by a 5mm thick layer of an anti-corrosion adhesive material such as mastic rubber 45. The mastic rubber is a butyl-based non-curing material with a high adhesion on contact with prepared surfaces. A protective non-stick film is applied to the mastic rubber surface to provide protection and prevent contamination up to the point of application.

Before the insulation is applied to the field joint, the bare steel of the field joint is shot blasted to remove any contamination. A bonding agent, consisting of a catalyst in a solvent base is applied by brush to the prepared steel surface and also to marginal areas of the parent coatings 13.

The infi l 41 with its layer of mastic rubber 45 is wrapped around the field joint and squeezed into position, the mastic rubber being soft and yieldable. After the application of the elastomer infi l 41, any longitudinal gap 42 and the circumferential gaps 43 are fi lled in with mastic rubber 46. Finally, a heat shrink sleeve 47 is formed to complete the insulated field joint 40 covering the infi l 41 and overlapping the parent coatings 13 by approximately 100mm; this is done by wrapping a sheet of plastics material having an adhesive backing around the infi l 41 and the coatings 13 and heating it, using e.g. a gas torch to melt the

adhesive and shrink the plastics material. The sleeve is of a known abrasion resistant material, e.g. a polyethylene based material, and it serves to encapsulate the mastic rubber and prevent movement of the mastic rubber when subjected to external pressure.

In both the embodiments hereinbefore described, the field joint insulation can be applied in a period of 10 to 15 minutes. The field joint insulation as described in the second embodiment is advantageous over that described in the first embodiment in that it avoids the need to use quick setting polyurethene and also involves less equipment.