Method and apparatus for preventing foam disbondment

1. An insulated piping system for conveying high temperature fluids, comprising:

a first and second length of insulated and jacketed pipe, each having a joining end to be joined to an end of the other length, each pipe length comprising an inner carrier pipe having an interior surface and an exterior surface, an envelope of foamed insulation surrounding the inner pipe exterior surface, and an outer protective jacket surrounding the envelope of insulation, the joining ends of adjacent pipe lengths being welded together to form fixed joints, whereby the adjacent pipe lengths provide a continuous length of fluid conduit for conveying high temperature fluids;

a discrete length of an external slip wrap located at a selected location along the length of the piping system at which location the piping encounters an angular shaped change in direction, the slip wrap comprising a loosely received outer sleeve for the piping which surrounds the outer protective jacket without being bonded thereto, whereby the insulated and jacketed pipe can move axially relative to the slip wrap for a selected distance once the pipe is buried in the ground, the location of the external slip wrap along the length of piping being selected in order to prevent disbondment of the foam insulation from the inner carrier pipe.

2. The insulated piping system of claim 1 , wherein the external slip wrap is a sleeve formed of a flexible polyolefin material having characteristic coefficient of friction which allows the jacketed pipe to slide within the sleeve.

3. The insulated piping system of claim 2 , wherein the external slip wrap is formed of polyethylene.

4. The insulated piping system of claim 3 , wherein the inner carrier pipes are metal pipes and wherein the location of the slip wrap along the length of piping is selected to prevent disbondment of the foam insulation from the inner carrier pipe would otherwise occur by preventing separation of the envelope of foamed insulation from the exterior surface of the inner metal pipes as the temperature of the inner metal pipes increase.

5. The insulated piping system of claim 4 , wherein the foam insulation is selected from the group consisting of polyurethane foams and polyisocyanurate foam.

6. The insulated piping system of claim 4 , wherein the outer protective jackets of the insulated and jacketed pipe are formed from a synthetic polyolefin.

7. The insulated piping system of claim 4 , wherein the slip wrap is installed at a location which precedes a U-shaped expansion loop in the piping system.

8. The insulated piping system of claim 4 , wherein the lengths of insulated piping being joined are part of a pipeline conveying steam, hot water or other hot fluids at a temperature in the range of above about 200° F.

9. A method of coupling lengths of insulated piping used to form a high temperature fluid conveyance system, the method comprising the steps of:

providing a first and second length of insulated and jacketed pipe, each having a joining end to be joined to an end of the other length, each of the first and second lengths of pipe comprising an inner pipe, an envelope of foamed insulation surrounding the inner pipe and an outer protective jacket surrounding the envelope of insulation;

the joining ends of adjacent pipe lengths being welded together to form fixed joints, whereby the adjacent pipe lengths provide a continuous length of fluid conduit for conveying high temperature fluids;

wrapping selected locations along the piping system with a discrete length of an external slip wrap, the location which is selected being a point in the piping at which the piping encounters an elbow shaped change in direction, the slip wrap comprising a loosely received outer sleeve for the piping which surrounds the outer protective jacket without being bonded thereto, whereby the insulated and jacketed pipe can move axially relative to the slip wrap for a selected distance once the pipe is buried in the ground, the location of the external slip wrap along the length of piping being selected in order to prevent disbondment of the foam insulation from the inner carrier pipe.

10. The method of claim 9 , wherein the foam insulation which is used to surround the inner pipes is selected from the group consisting of polyurethane foam and polyisocyanurate foam.

11. The method of claim 9 , wherein the protective jackets are formed of HDPE.

12. The method of claim 9 , wherein the slip wrap is installed at a location which precedes a U-shaped expansion loop in the piping system.

13. The method of claim 9 , wherein the lengths of insulated piping being joined are part of a pipeline conveying steam at a temperature of 400 degrees F. or greater.