GB2027158A

GB2027158A - Protected and insulated pipeline

Info

Publication number: GB2027158A
Application number: GB7923811A
Authority: GB
Original assignee: Salter L A Evans P H
Current assignee: Salter L A Evans P H
Priority date: 1978-07-07
Filing date: 1979-07-09
Publication date: 1980-02-13
Also published as: GB2027158B

Abstract

A pipeline to which are applied a plurality of protective/thermally insulating/sealing layers, said layers including an anti-corrosive layer of a urethane elastomer, a thermally- insulating layer of for example polyurethane and a sealing layer of a urethane elastomer, the urethane elastomer(s) and the polyurethane being compatible to ensure adherence of adjacent layers with each other. A method of jointing two of said pipelines to all but the end extents of which have been applied the aforementioned layers involves securing together the abutting ends of the pipelines and applying around the joint an anti-corrosive layer of a urethane elastomer, a thermally- insulating layer of for example polyurethane and a sealing layer of a urethane elastomer, said layers around the joint overlapping the layers on the two pipelines to provide a continuous seal along the full length of the interconnected pipelines.

Description

SPECIFICATION Improvements in or relating to pipelines This invention relates to pipelines, particularly to metal pipelines for carrying fluids such as oil or gas.

Extended lengths of metal pipeline are commonly used to carry oil or gas over land, under ground or under the sea. The pipeline commonly consists of a plurality of interconnected individual lengths of pipe and, in order to protect the metal of the lengths of pipe from the effects of the environment, it is common practice to apply an anti-corrosive coating to said lengths of pipe.

Heretofore such coating has commonly comprised coal tar or bituminous enamel reinforced with a fibre glass wrap.

However, it is becoming increasingly necessary to provide pipelines capable of carrying fluids which may be well above ambient temperature (for example high wax content oils) and fluids which may be well below ambient temperature (for example liquid petroleum gas or ethylene).

An anti-corrosive coat of coal tar or bituminous enamel is not suitable for high-temperature applications.

When transporting such fluids it is advisable to insulate the pipeline. One known method of achieving this is to locate an open-ended polyethylene tube around the pipeline and to fill the annulus so formed between the tube and the pipeline with foamed polyurethane. The ends of the insulation are then capped, usually with a polyethylene heat-shrink bulkhead which is shrunk onto the pipeline and onto the poyethylene tube.

With such an arrangement, it has been found difficult to control the quality of the foamed polyurethane within the annulus in respect of density and the elimination of voids, as such faults cannot be detected through high density polyethylene tube as would commonly be used for sub-marine applications or where a land pipeline was likely to be subject to damage.

Further, it has proved difficult both to adhere the polyurethane foam to the anti-corrosive coating and to adhere the bulkheads to the ends of the insulating material because of incompatibility of the materials involved.

When using such pipelines under water, an outer negative buoyancy layer of, for example, concrete, which is preferably reinforced, is normally applied over the polyethylene tube.

Again the poor adhesion between concrete and polyethylene has caused problems.

In an alternative known method of insulating a pipeline, preformed sections of insulating material are fixed directly to the pipeline, said insulation then being wrapped with either waterproof tape or waterproof sheet material the ends of which are taken down over the ends of the insulating material and adhered to the pipeline so as to encapsulate said insulating material.

As with the first-mentioned known method, this alternative method has proved unsatisfactory insofar that it is difficult to ensure complete watertight integrity at the bulkheads at the ends of the insulating material and to ensure complete adhesion and water-tight integrity at the junction between the waterproof coating and the pipeline.

According to one aspect of the present invention there is provided a pipeline comprising a length of metal pipe to which is applied a first, anti-corrosive layer of a urethane elastomer, a second, thermally-insulating layer surrounding said first layer and consisting of a material which adheres to said first layer, preferably a cellular material such as polyurethane, and a further sealing layer totally encapsulating said second layer and of a urethane elastomer which adheres to said second layer.

The thermally-insulating layer may consist of preformed sections of material or, alternatively, may be applied by spraying.

An outer protective layer or negative buoyancy layer of a high-density material such as concrete, preferably reinforced concrete, may be applied over said sealing layer.

Such a pipeline can obviate the aforementioned disadvantages of existing pipelines, particularly in that the various layers applied to the length of pipe are of compatible materials which ensure the necessary adhesion and sealing, while the preformed nature of the thermal insulation or the use of controlled spray techniques to apply said insulation eliminates the possibility of the aforementioned faults developing therein during application thereof.

According to a further aspect of the present invention there is provided a method of jointing two of said lengths of pipe to all but the end extents of which have been applied said first, second and further layers, the method comprising the steps of securing together the abutting ends of the two lengths of pipe, for example by welding, applying an anti-corrosive layer of a urethane elastomer to the adjacent end extents of the two lengths of pipe, said layer sealingly overlapping an end extent of the further layer on each length of pipe, .

applying a layer of thermally-insulating material, preferably a cellular material such as polyurethane, over said anti-corrosive layer, said thermally-insulating material adhering to said anti corrosive material and said layer of thermally insulating material abutting the end regions of the further layer on each length of pipe to form a continuation of the second layers on said lengths, and applying a sealing layer of a urethane elastomer totally encapsulating said thermally insulating layer and overlapping the further layer on each length of pipe.

The method may further comprise the application of an outer protective layer or negative buoyancy layer of a high density material such as concrete, preferably reinforced concrete, over said sealing layer to form a continuation of the outer layers on the two lengths of pipe.

By way of example only, the invention will now be described in great detail with reference to the accompanying drawings of which: Fig. 1 is a longitudinal section through a length of pipe according to the invention and showing two alternative thermally-insulating layers; Fig. 2 is a transverse section through the length of pipe of Fig. 1, and Fig. 3 is a longitudinal section through a joint between two lengths of pipe according to the invention.

Referring to Figs. 1 and 2 of the drawings, a single length of steel carrier pipe is shown at 2, a plurality of such lengths being interconnected to form a pipeline as will be described hereinafter.

Such pipelines are commonly installed in corrosive environments and carry fluids which may be above or below ambient temperature.

Consequently, and prior to installation, such pipelines are provided with various coatings to combat corrosion and to minimise heat transfer between the fluid being carried and the surrounding environment.

The outer surface of the pipe 2 is prepared to receive the coating by, for example, shot-blasting and priming, a layer 4 of an anti-corrosive material then being adhered to the pipe. Said coating comprises a urethane elastomer, the precise nature of which will depend upon the application of the pipe and in particular upon the temperature of the fluid being carried pipe carrying hightemperature fluid, such as high wax-content oil, will be coated with a different urethane elastomer than a pipe carrying, for example, liquid petroleum gas.

A thermally-insulating layer 6 on the pipe comprises, in the illustrated arrangement, preformed sections of a cellular material such as polyurethane. The sections are of part-cylindrical shape and surround all but the end extents of the pipe. As shown in the bottom half of Figs. 1 and 2, the insulation may comprise a single layer of polyurethane or, as shown in the top half of Figs. 1 and 2, said insulation may comprise a plurality of superimposed sub-layers.

By preforming the sections of polyurethane, the mechanical strength and density of the material can be accurately controlled to suit particular requirements and to avoid flaws therein.

Conveniently the polyurethane is embedded into the anti-corrosive layer 4 whilst the urethane elastomer thereof is in a plastic state. When a plurality of sub-layers of insulating material are provided, a coating of a urethane elastomer can be applied between each sub-layer to act as an adhesive and as a sealing compound. It will be noted that, in the multi-layer arrangements in the top-half of Figs. 1 and 2, a single sub-layer comprises a plurality of individual sections, the longitudinal and circumferential joints between adjacent sections being staggered to provide a labyrinth pattern of joints.

All end faces and interfaces of the thermallyinsulating layer may be coated with a urethane elastomer to ensure adhesion, to fill all voids, to ensure complete sealing and to provide a homogeneous construction.

When a wide temperature difference between the fluid to be carried by a pipe and the environment is anticipated, pads 8 of resilient insulating material may be provided to absorb any differential expansion across the thickness of the coatings. Said pads may be positioned between the end faces of adjacent sections of polyurethane in a staggered fashion to maintain the labyrinth pattern, the pads being sealed with a urethane elastomer. With said wide temperature differences, it is preferable to provide a plurality of sub-layers of thermally-insulating material rather than a single thick coating so that the individual sections thereof are relatively free to move against each other to reduce stress in the layer that may otherwise occur with large temperature differences across the layer.

Binding bands or tapes 10 may be applied circumferentially around the thermally-insulating material to assist adhesion to the anti-corrosive layer 4 and to provide a ridged surface to the thermally-insulating layer for reasons to be detailed below.

Applied over the whole of the thermallyinsulating layer 6 to envelop said layer is a sealing layer 12 of a urethane elastomer. The sealing layer 12 is of the same material as, or a material compatible with, that of the anti-corrosive layer 4, and is also such as to adhere to the layer 6, said layer 12 extending down over the ends of the layer 6 to be firmly adhered and sealed to the layer 4.

Such an arrangement prevents the ingress of moisture or atmospheric vapours to the pipe 2 by providing a completely water-tight membrane around said pipe.

When bands or tapes 10 are present, the layer 12 continues over said bands or tapes to have a ridged outer surface thereto.

In certain applications of the pipe, such as submarine use or where substantial mechanical strength is required, it may be desirable to apply to the pipe an outer coating of reinforced concrete or other dense material. In such a case, a textured or roughened surface may be applied to the layer 12 whilst the material of said layer is in a plastic state. This may be achieved using coarse sharp sand or another material compatible with the outer coating to be applied.

Conveniently the outer coating, indicated at 14, comprises reinforced concrete applied using a rigid reinforced cage 16 held away from the sealing layer 12 by spacers (not shown), the concrete being impinged onto the layer 12 or cast in a mould.

In an alternative arrangement, the concrete is impinged onto the layer 12 and reinforced with a spirally wound meshed reinforcement.

It will be appreciated that the ridged outer surface to the layer 12 acts as a key to increase the axial shear resistance at the interface between the layer 12 and the coating 14.

Instead of using preformed sections of thermally-insulating material for the layer 6, said material may be spray-applied over the layer 4.

This may be achieved either by rotating the pipe 2 relative to a fixed sprayhead and moving the pipe axially past said sprayhead at a controlled rate.

Alternatively the pipe may remain axially fixed and the sprayhead may be moved along the rotating pipe. The relative speeds of the pipe and sprayhead can be controlled to provide a layer of the desired thickness. For example a first thin layer of thermally-insulating material may be applied quickly to adhere closely on the layer 4 while the thickness of the layer 6 may then be built up gradually in one or more sub-layers.

Thus there is provided a pipe length the various layers on which are of compatible, relatively inexpensive materials whereby all layers are adhered strongly to one another.

As can be seen from Fig. 1, the end extents of the pipe length are not coated, this being to enable two lengths to be interconnected as will now be described with particular reference to Fig.

3.

Two lengths of pipe are connected by, for example, welding together the abutting ends thereof. An anti-corrosive layer 18 of a urethane elastomer is applied over the weld area after first preparing said area by cleaning, priming and applying an adhesive. This layer 18 overlaps the ends of the anti-corrosive layers 4 on the two pipe lengths as well as the ends of the sealing layers 12 on said lengths.

A thermally-insulating layer 20 is then provided around the layer 18. said layer 20 being of, for example, preformed sections of a cellular material such as polyurethane built up in one or more sublayers. The material of the layer 20 completely fills the joint area between the ends of the layers 4, 6 and 12 on the two lengths of pipe, all interfaces between the layer 20 and abutting layers being coated with a urethane elastomer to provide seals therebetween.

In a further arrangement the layer 20 may be provided by foaming polyurethane into a hinged mould surrounding the joint area. After curing, the mould would be removed. In a still further arrangement, the layer 20 may be spray applied by for example rotating a sprayhead around the joint.

In cases of anticipated high temperature differences across the width of the joint, pads of resilient insulating material, such as those shown at 8, may be incorporated in the joint at the end of each length of pipe prior to applying the thermallyinsulating layer. After application of said layer, the pads would be coated with a urethane elastomer to maintain the seal.

A sealing membrane 22 is then applied over the layer 20 to overlap the layers 12 on the two lengths of pipe. The membrane 22 comprises a urethane elastomer compatible with the material of the layers 12 and completely encapsulates the joint area to provide a continuous seal along the full length of the interconnected pipeline.

Again a textured or roughened surface may be applied to the membrane 22 to facilitate the adherence thereto of a negative buoyancy or mechanically protective outer layer 24 of concrete or other dense material which may or may not be reinforced and which forms a continuation of the outer coatings 14 on the two lengths of pipe. The concrete or other material may be applied either manually by trowelling or by injection of the material into an annulus formed by a hinged mould applied to the outer coatings of the two lengths of pipe and surrounding the joint area.

Claims

1. A pipeline comprising a length of metal pipe to which is applied a first anti-corrosive layer of a urethane elastomer, a second thermally-insulating layer surrounding said first layer and of a material which adheres to said first layer, and a further sealing layer totally encapsulating said second layer and of a urethane elastomer which adheres to said second layer.

2. A pipeline as claimed in claim 1 in which the thermally-insulating layer consists of preformed sections of material.

3. A pipeline as claimed in claim 1 in which the thermally-insulating material is applied by spraying.

4. A pipeline as claimed in any one of claims 1 to 3 in which the thermally-insulating material is of cellular construction.

5. A pipeline as claimed in claim 4 in which the thermally-insulating material is polyurethane.

6. A pipeline as claimed in any one of claims 1 to 5 and further comprising an outer protective layer of a high-density material applied to the metal pipe over said sealing layer.

7. A pipeline as claimed in claim 6 in which the outer protective layer is of reinforced concrete.

8. A method of jointing two lengths of pipe as claimed in any one of claims 1 to 7 and to all but the end extents of which pipes have been applied said first, second and further layers, the method comprising the steps of securing together the abutting ends of the two lengths of pipe, applying an anti-corrosive layer of a urethane elastomer to the adjacent end extents of the two lengths of pipe, said layer sealingly overlapping an end extent of the further layer on each length of pipe, applying a layer of thermally-insulating material over said anti-corrosive layer, said thermallyinsulating material adhering to said anti-corrosive material and said layer of thermally-insulating material abutting the end regions of the further layer on each length of pipe to form a continuation of the second layers on said lengths, and applying a sealing layer of a urethane elastomer totally encapsulating said thermally-insulating layer and overlapping the further layer on each length of pipe.

9. A method of jointing two lengths of pipe as clairned in claim 8 together with claim 6 or claim 7 and further comprising the step of applying an outer protective layer of a high density material over said sealing layer to form a continuation of the outer layers on the two lengths of pipe.

10. A pipeline substantially as described with reference to and as illustrated by the accompanying drawings.

1 1. A method of jointing two lengths of pipe to form a pipeline as claimed in claim 10, the method being substantially as described with reference to the accompanying drawings.