This invention relates to lined pipes.

It is long established that pipes assembled into pipelines are used for the transport of fluids (liquids or gaseous). In a considerable number of instances, the fluids to be transported are under pressure, with a consequent need for a pipeline of considerable pressure bearing capability. It is therefore well known for pipes for assembly into pipelines to be formed from carbon steel.

It is equally well known that pipelines frequently need to be lined, to prevent corrosive materials flowing through a pipeline from damaging the pipeline.

As a means of positioning a liner within a pipe, it is known such as from British Patent

Application 2186340A, to employ a synthetic liner, that is heated and pulled through a die and then through the pipe to be lined, followed by pressurising the pipe to cause the liner to expand into contact with the inner wall of the pipe.

It is also known from such as European Patent 0341941 to pull a length of liner through a die and then through a pipe, and when the pulling load on the liner is removed, it reverts to its original diameter and into contact with the inner surface of the pipe.

Such linings of pipes can be most effective in providing protection for the inner surface of the pipe against damage/erosion caused by the fluid being transported, but can only provide limited insulation against heat loss from the fluid being transported when the pipeline is deployed in a cold and hostile environment, or unwanted heat gain by the fluid when the pipeline is, e.g. above ground in a hot environment.

The primary object of the present invention is to provide a lined pipe that improves on those lined pipes presently known. Other objectives of the invention will become clear later.

According to the present invention, a lined pipe comprises an outermost pipe and an innermost liner, there being between the innermost liner and the outer pipe at least one insulatory liner of a compressible and expandable insulatory material. Thus, the innermost liner can be reduced in diameter by any known method such as swaging or roll down techniques and inserted down the insulatory liner, and once the combined innermost liner and insulatory layer is within a pipe, an expansion of the innermost liner attempts to revert it to its original diameter, thereby exerting a pressure on the intermediary liner to force it into contact with the inner surface of the outer pipe, thereby generating a tight fitting insulatory liner between the outermost pipe and the innermost liner, able to accommodate an ovality or other deviation from truly circular, of the inside of the outermost pipe.

The insulatory liner may be, for example, a compressible polyurethane foam.

Insulated pipelines are frequently required to transport such materials as hydrocarbons, and there is the need to ensure that in the event of a drop in operating pressure inside the innermost pipeline bore, gas that may have permeated the insulatory liner can be evacuated back into the innermost pipeline bore to ensure the annular gas pressure outside the pipeline bore never exceeds that of the innermost pipeline bore. It is therefore a further object of the invention to provide for control over permeating gas.

According to a second aspect of the invention, a lined pipe comprises an outermost pipe and an innermost liner, there being pre-moulded half shells fitted around the innermost liner and surrounded by an insulatory liner, the inner surfaces of the half shells having a number of recesses to provide chambers for gas permeating through the innermost liner. Preferably, the half shells are connected together by a snap-fit arrangement that additionally serves as an expansion joint.

A preferred method of assembly is to swage, e.g. using the Swagelining (RTM) technique or otherwise reduce the diameter of the innermost liner and then to loose fit the half shells thereto using the snap fit connectors and then position the innermost liner and the half shells within the insulatory liner. The insulatory liner may be fastened to the half shell arrangement or the insulatory liner may be in moulded form of a predetermined size. The combined outside diameter of this arrangement will remain smaller than the inside diameter of the host pipeline. When the arrangement has been fully inserted into the host pipeline, the tension on the innermost liner is released causing it's diameter to expand and expand the half-shells that in turn expands the insulatory liner and create a tight fitting arrangement.

By causing a movement of the half shells, and creating gaps, a pathway for gas between the recesses is created, and by having at least one vent in the innermost liner, cooperating with a respective recess in a half shell, there is first an ability for permeated gas to migrate from one recess to another, and prevent the build-up of pressure at any particular point, and second an ability for the gas to be returned to the interior of the innermost liner through the vent, should there be a pressure drop in the fluid flowing through the pipe.

Preferably, the half shells are formed from an appropriate polyurethane or other suitable polymer.

Two embodiments of the invention will now be described by way of example only in the accompanying drawings, in which:-

Figures 1 to 4 are schematic longitudinal sectional views of the sequence of operations of a first embodiment of the invention;

Figure 5 is a transverse sectional view of a second embodiment of the invention; and

Figure 6 is a longitudinal section of the embodiment of Figure 2.

As is illustrated in Figures 1 to 4, a lined pipe arrangement has an outer pipe 1 of such as carbon steel and an innermost liner 2 of a corrosion resistant material, and between the outermost pipe and innermost liner is an insulatory liner 3 of a compressible and expandable material such as compressible polyurethane foam.

As is indicated in Figures 1 to 4, the innermost liner 2 may be passed through swaging dies 4, to bring about a reduction in its diameter and which is then inserted down the insulatory liner 3. The innermost liner 2 and insulatory liner 3 are then inserted down the outermost pipe following which there is an expansion of the insulatory liner 3 as the innermost pipe 2 attempts to revert to its original diameter, to force the insulatory liner 3 into contact with the inner wall of the outermost pipe, thereby ensuring a tight insulatory fit between the insulatory liner 3 and the outer pipe 1 , able to accommodate any ovality or other deviation from truly circular of the inside of the outer pipel .

In Figures 5 and 6 there is shown an arrangement of lined pipe suited to the transport of materials such as hydrocarbons.

Here, there is an outer pipe 1 of e.g. carbon steel and an innermost liner 2 of an appropriate polymer material, the diameter of which has been reduced by the known Swagelining (RTM) technique. The innermost liner 2 in its reduced diameter state, is fitted with pre-moulded half shells 5 that provide a number of recesses 6 providing gas chambers, and the half shells 5 are fitted with snap fit connections 7, and pins 8 that serve as expansion joints. The half shells are formed from a polyurethane or other suitable polymer.

The innermost liner 2 and half shells 5 are positioned within a moulded insulatory lining 3 having an outer diameter less than the inner diameter of the outer pipe 1 , to allow the assembly of insulatory lining 3 innermost pipe lining 2 and half shells 5, to be inserted down the outer pipe 1.

Along the length of the innermost lining is a series of vents 9 that communicate with the recesses 6.

Thus, with the assembly of innermost lining 2 insulatory lining 3 and intervening half shells 5 inserted down an outer (host) pipe 1, tension in the innermost lining 2 is released by techniques well known in the art, applying a pressure in the direction of arrows A to cause an expansion of the assembly of half shells 5, with a consequent expansion of the insulatory liner 3 within the outer pipe 1 , to create a tight fit between the insulator lining 3 and the inner wall of the outer pipe 1 and between the innermost lining 2, the half shells 5 and the insulatory lining 3, and as with the construction of Figure 1 , any ovality or other deviation from truly circular of the outer pipe 1 is accommodated.

During expansion of the assembly of innermost lining 2 half shells 5 and insulatory lining 3, there is caused a movement of the half shells to create gaps between adjacent half shells that create a pathway between the adjacent recesses 6. Thus, gas that permeates through the innermost lining 2 is gathered in the recesses 6 and by ensuring a pathway is provided between adjacent recesses, a build-up of pressure in any one recess is prevented. Also, by providing vents 9 associated with the recesses 6, gas gathered in the recesses is allowed to return to the interior of the innermost lining 2 in the event of a pressure drop in the fluid flowing through the innermost lining.