Insulated pipe, esp. for transporting heating media underground - has inner steel pipe wrapped in glass or mineral fibre, and outer plastic jacket, with polyurethane foam in the space between

摘要

A heat-insulated pipe (I) for long-distance heating has an inner steel tube (A) for the heating medium and an outer plastic jacket (B) sepd. from (A) by spacers, with an insulating material (C) filling the space between (A) and (B). (C) consists of (C1) an annular layer of insulating material based on glass or mineral fibre (II) on the inner tube itself, and (C2) polyurethane (PU) foam which is expanded to fill the remaining space and keep layer (Cl) under compression. Layer (Cl) is bonded to the outside of tube (A). Specifically, (Cl) is bonded to (A) with an adhesive (III) which is stable to at least 250 deg C, pref. a phenolic resin adhesive. The thickness of (Cl) is such that, when the temp. in (A) is below 200 deg C, the temp. at the junction between (C1) and (C2) is below 130 (pref. below 120) deg. C.. The spacers are formed by annular layers of (II) sepd. from one another along the axis of the tube, which are compressed by straps encircling (C1) together with straps on the inside of tube (B). USE/ADVANTAGE - The method provides insulated piping for transporting a heating medium, e.g. at up to 200 deg C. The construction of (I) compensates better for the different thermal expansion of the inner tube and the outer jacket, so that the pipe can be laid at greater depths than prior-art pipes (as described, e.g. in DE-AS 2823051) with less likelihood of damage, esp. at expansion joints, due to cracking of the plastic followed by ingress of moisture.