| 摘要 |
A section of conduit is insulated by a thermoplastic outer pipe and an insulating layer of foamed or beaded insulating material disposed in the annular space between the outer pipe and the conduit. The annular layer is preformed to substantially the size of the annular space, then the outer pipe is heated to cause expansion of its diameter and facilitate insertion of the annular layer within the outer pipe. The inner pipe, or the conduit, may also be thermoplastic and may be cooled to cause contraction to facilitate insertion of the annular layer over it. After the outer pipe and inner pipe have returned to ambient temperature, the annular layer is retained within by a shrink fit, without chemical bonding between the annular layer and the pipes. Sections of the pipe are joined by simultaneously heating the ends of the inner pipe, annular layer, and outer pipe, placing the ends of one section against the ends of the other section, and allowing them to fuse while cooling.
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