GB2076499A

GB2076499A - Insulated pipes

Info

Publication number: GB2076499A
Application number: GB8017058A
Authority: GB
Original assignee: CHEMWELD ENGINEERING Ltd
Current assignee: CHEMWELD ENGINEERING Ltd
Priority date: 1980-05-23
Filing date: 1980-05-23
Publication date: 1981-12-02

Abstract

Pipes suitable for conveying high temperature fluids comprise an inner fluid conducting pipe (1), a first insulating layer (2) e.g. calcium silicate about said inner pipe (1), a layer of heat shrunk thermoplastics material (3) about said first insulating layer (2) and an outer casing of plastics material (5) e.g. polythene there being a second layer of insulating material (4) e.g. polyurethane between the outer casing (5) and the heat shrunk layer 3. The pipes which are made by applying successive layers about the inner pipe (1) overcome corrosion, condensation and insulation breakdown problems encountered with prior art pipes of the type used to carry superheated water or steam. <IMAGE>

Description

SPECIFICATION Pipes The present invention relates to pipes and more particularly relates to pipes suitable for conveying high temperature fluids and to a method of joining such pipes.

Previously known pipes for carrying high temperature fluids such as steam or superheated water consist of two inner fluid conducting pipes, one being for outward flow and the other for inward flow, housed within an outer carrier pipe which has an outer sleeve made of a steel with corrosive protection coating. Each inner fluid conducting pipe is surrounded by a shell of insulating material such as calcium silicate, and are spaced from each other and from the inside wall of the outer pipe by metal spacing members in such manner as to give an air space between the fluid conducting pipes and the inside wall of the outer carrier pipe.

The above type of pipes have the disadvantage that the air space can lead to condensation formation on the inside of the outer carrier pipe and hence to corrosion problems and possible insulation breakdown. In addition the aforementioned metal spacing members can cause the outer carrier pipe to become warm heat conduction thereto from the inner pipes via said spacing members.

It has now been found that a particular arrangement of insulating layers around a fluid conducting pipe with the substantially complete exclusion of air pockets therebetween overcomes the above disadvantages.

Accordingly, the present invention provides in one aspect a pipe comprising an inner fluid conducting pipe, a first insulating layer about said inner pipe, a layer of heat shrink thermoplastics material about said first insulating layer and an outer casing of plastics material, there being a second layer of insulating material interposed between said outer casing and said heat shrunk thermoplastics material.

The inner fluid conducting pipes are preferably made from a metal such as steel and the first insulating layer is advantageously an inorganic insulating material such as calcium silicate.

The heat shrinkable thermoplastics material used to form the heat shrunk layer is preferably a thermoplastics polymer and the second insulating layer is advantageously a foam material such as polyurethane foam. Finally, the outer casing is preferably a plastics material and is conveniently a plastics material which can resist corrosion such as, for example, high density polythene. The outer casing may also be made from a heat shrinkable thermoplastics material The pipe of the present invention may be conveniently made in the following manner:~ (1 ) A sleeve of the first insulating material is placed around the inner fluid conducting pipe.

Conveniently, this is performed by using a sleeve which is split along its length into two halves, the two halves being placed around the conducting pipe and then held in position by means of, for example, metal bands. The first insulating material should be a tight fit around the conducting pipe to ensure emission of trapped air; (2) A sleeve of heat shrinkable thermoplastics material is then fed over the insulated pipe obtained by step (1). Heat is then applied to shrink the sleeve into position thereby excluding air and providing an air barrier; (3) An outer casing is then fed over the pipe obtained after step (2) so as to be concentric therewith and the gap formed therebetween is filled with the second insulating material.

If two pipes of the present invention are to be joined together after they have been made, steps (1) to (3) above are carried out in such manner that at least the ends of the pipes which are to be joined have the various layers thereof in stepped formation. That is so that a particular layer does not extend for the whole length of the layer immediately adjacent thereto in the inwards direction. The joining process involves firstly sealingly joining the respective inner fluid conducting pipes. If the inner pipes are metal, this may be conveniently performed by welding.A sleeve of the first insulating material of a length corresponding to the length of exposed inner conducting pipe is then placed therearound, advantageously by using a sleeve of the material which is split along its length into two halves, the two halves being placed around the conducting pipe and then held in position by, for example, metal bands. After this operation, a sleeve of heat shrinkable thermoplastics material having a length when shrunk which corresponds to the length of the exposed first insulating material, is positioned therearound and shrunk in place by the application of heat.Thereafter, a sleeve of the second insulating material of a length corresponding to the length of exposed heat shrunk thermoplastics is then placed therearound, preferably by using a sleeve of the material which is split along its length into two halves, the two halves being placed around the pipe formed this far and then held in position by, for example, a split bush.

Finally, a length of an outer casing material (which in this case is heat shrinkable) having a length when shrunk which corresponds to the length of exposed second insulating material, is positioned therearound and shrunk into position. The joint is then complete.

The present invention will be further illustrated with reference to the accompanying drawings in which:~ Figure 1 is a longitudinal cross-section of a preferred pipe of the present invention; Figure 2 is a transverse cross-section of the same preferred pipe shown in Figure 1; Figures 3 to 5 illustrate various stages of the completed pipe shown in Figures 1 and 2; Figure 6 is a cross-section along the line A-A of Figure 5 looking in the direction of the arrows; and Figures 7 to 9 show various stages in the joining of two preferred pipes of the present invention and each of which is shown in Figures 1 and 2.

Referring to Figures 1 and 2 an inner fluid conducting pipe 1 which is made of steel has a first layer of insulating material 2 thereabout, the layer 2 being composed of calcium silicate.

Around the calcium silicate layer 2, is a layer of heat shrunk thermoplastics 3. Interposed between the layer of thermoplastics 3 and the outer casing 5 of high density polythene is a second insulating material 4 which, in this embodiment, is polyurethane foam.

Referring now to Figure 3, two half shells 2a, 2b of calcium silicate are placed around the inner pipe 1, and are hold in place by means of metal banding straps 6. The next stage of manufacture is shown in Figure 4 where the sleeve of heat shrinkable thermoplastics 3 has been heat shrunk into position about the calcium silicate sleeve 2.

Figure 5 shows the next stage of manufacture in which an outer high density polythene casing 5 has been placed concentrically around the pipe, leaving a void between the inside thereof and the outside of the heat shrunk layer 3. This void 7 may be seen from Figure 6. The void 7 is then filled with the second insulating material which, as aforementioned, is polyurethane foam in this embodiment.

Reference is now made to Figures 7 to 9 in which like reference numerals have been used for parts already referred to in the preceding drawings. Referring to Figure 7, the two inner fluid conductors 1 are welded together by means of a weld 8 and the weld is painted and tested. With reference to Figure 8, two calcium silicate half shells 2a, 2b are placed over the welded conductors and are banded into position. A heat shrink sleeve 3' is then shrunk into position over the half shells 2a 2b. Turning now to Figure 9, two half shells of polyurethane foam 4a, 4b are placed over the sleeve 3' and are held in place by a split bush (not shown). The joints are sealed with cold applied bitumen tape 9 and subsequently an outer casing is heat shrunk over the polyurethane foam.

Claims

1. A pipe comprising an inner fluid conducting pipe, a first insulating layer about said inner pipe, a layer of heat shrunk thermoplastics material about said first insulating layer and an outer casing of plastics material, there being a second layer of insulating material interposed between said outer casing and said heat shrunk thermoplastics material.

2. A pipe as claimed in claim 1 wherein the inner fluid conducting pipe is made of metal.

3. A pipe as claimed in claim 1 or claim 2 wherein the first insulating layer consists of an inorganic insulating material.

4. A pipe as claimed in any of claims 1 to 3 wherein the second insulating layer consists of a foam material.

5. A pipe as claimed in any of claims 1 to 4 wherein the outer casing is a plastics material.

6. A pipe as claimed in claim 5 wherein the plastics material is a heat shrinkable thermoplastics material.

7. A method of making a pipe as claimed in claim 1 which comprises the steps of: (i) placing a sleeve of a first insulating material around an inner fluid conducting pipe; (ii) feeding a sleeve of heat shrinkable thermoplastics material over the insulated pipe obtained after step (i); (iii) applying heat to the sleeve of heat shrinkable thermoplastics material to shrink said sleeve about the layer of first insulating material; (iv) feeding an outer casing over the pipe obtained after step (iii) so as to be concentric therewith, said outer casing having an internal diameter greater than the external diameter of the pipe obtained after step (iv); and (v) filling the gap formed in step (iv) with a second insulating material.

8. A pipe as claimed in claim 1 substantially as herein described with reference to and as shown in the accompanying drawings.

9. A method of making a pipe substantially as herein described with reference to and as shown in the accompanying drawings.

10. A method of joining two pipes as claimed in claim 1 together substantially as herein described with reference to and as shown in the accompanying drawings.