A thin, flexible tubular membrane provides a heat containment tube for inserting into and inflation within an underground conduit to be repaired. Folded rigid thermoplastic pipe is inserted into the tube while not and flexible. The tubular membrane is pressurized to exclude unwanted fluids from within the existing conduit. Hot steam is injected into the tube to heat the pipe full-length externally and internally until flexible. The pipe is then rounded and expanded against the walls of the conduit with the tube therebetween. The rounding and expanding of the pipe is carried out progressively by moving a plug through the pipe and by injecting hot steam under pressure behind the plug.
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