Abstract: In order to replace a first underground pipe such as a metal pipe by a second pipe of mean diameter substantially equal to or greater than that of the first pipe, the first pipe is cut longitudinally by a localized projection of a flow of matter, particles or radiation thanks to a localized projection means which are displaced inside the first pipe in order to divide the first pipe longitudinally into at least two segments. Cutting by localized projection avoids in particular the creation of vibrations during fragmentation of the pipe to be replaced.

Abstract: The invention concerns a device for detecting variations in the physical state of the plastic material in a coupling piece used for welding pipes and incorporating a heating resistor, cavities which the softened material can enter and sensors for detecting the state of the material within the cavities. According to the invention, in order to obtain a weld of high quality, it is necessary for the distance between the bottom of the cavities and the part of the resistor nearest this bottom on the one hand, and for the linear dimension in the cross-section of these same cavities near their bottom on the other, to be less than or equal to the thickness of the material which is softened during the heating of the pieces. The invention applies to the control of the welding of sections of piping, particularly for the gas industry.

Abstract: The invention relates to the automatic welding of plastic parts possessing a built-in winding. In order to carry out an automatic welding operation without risking damaging the parts by subjecting them to an excessive welding temperature, there are regulating means for varying the electrical energy supplied to the winding, in order, during the welding phase, to maintain the temperature of the winding between a minimum temperature, below which welding cannot be carried out, and a maximum temperature, beyond which the parts will be damaged. The invention is used particularly for the production of systems for the distribution of gas under pressure by means of plastic pipelines.