Abstract: A method of lining a pipe with a rigid plastic tube inserted in the pipe by enlarging the tube from inside with application of heat and pressure. The method includes enlarging the tube by an electrically heatable enlarging pig moved through the tube, retaining the enlarged portion of the plastic tube with compressed air supplied to the interior of the tube, and preheating the unenlarged portion of the plastic tube with a portion of the compressed air heated by being passed through air heating channels of the pig. The use of the pig eliminates the material limitations to be otherwise imposed on the tube, and therefore the softening point, of the plastic tube. The preheating of the unenlarged portion of the plastic tube renders the pig movable through the tube at an increased speed to achieve an improved work efficiency.

Abstract: A liquid sealant of the aqueous emulsion type to be delivered in foamed state into a pipeline requiring leakage repair and/or prevention. A large part of this sealant is drained from the pipeline, and the part of the sealant remaining on inner walls of the pipeline is allowed to cure. The sealant contains coagulations of weakly cohering fine particles of inorganic oxide at less than 5 percent, and the particles have diameters not exceeding 0.05.mu..

Abstract: A pipeline needing leakage repair and/or prevention is filled with a liquid sealant in foamed state of the aqueous emulsion type. Then an excess amount of the sealant in the center of the pipeline is drained from the pipeline, and the sealant remaining on the interior wall of the pipeline is allowed to cure wherein the sealant contains fine particles of inorganic oxide weakly adhering to one another into aggregations, said aggregations easily breaking into such fine particles that they can enter and plug fine cavities of the interior of said pipeline.

Abstract: A moving body comprises two members interconnected by a flexible linear member and each symmetrical with respect to a plane perpendicular to the direction of its movement through a pipe. The moving members are congruent with each other and are preferably made of an elastic material. Work is performed in the interior of pipes, for example, for lining with use of the moving body by applying a fluid pressure to the back side of the body. As a preferred example of lining work, the moving body is used for reforming an outworn underground pipe by lining the pipe with a resin layer having strength to withstand an external pressure of at least about 0.1 kg/cm.sup.2 G per meter of the depth at which the pipe is laid underground. The pipe is used as a frame for this operation.

Abstract: A method of lining a large pipe and small pipes branching therefrom with a seal composition, in which the pipes are lined as connected together, and the large pipe or the small pipes are lined first. The portion of the seal composition forced into the small pipes when the large pipe is lined with use of a running body is returned into the large pipe again and is subsequently applied, without being discharged from the system, to the lining layer of the large pipe as a top coat with use of a running body having a slightly smaller diameter than the running body. When one of the pipes has a greatly bent portion, a running body is used which comprises two members each shaped symmetrically, congruent with each other and interconnected by a flexible linear member.