Abstract: In a subterranean heat insulated pipe system as laid with angellike bendings between straight pipe lengths, i.e. a district heating pipe underneath a street angle, the conventional bending elements are substituted by pipe elements joined so as to form a bending run of a relatively large bending radius, which, depending of the pipe size, has a minimum value, by which the pipe bending by itself and by interaction with the earth is able to take up the expansion and contraction forces, which are created in the pipe in response to temperature changes therein. The said minimum value has been found to be so low that in many instances it is hereby possible to avoid the sharp bending elements with their associated heavy problems due to expansion effects.

Abstract: A method of joining plastic pipes by welding, whereby juxtaposed ends of the plastic pipes welded together along a peripheral annular welding zone presenting a discontinuous meeting area between continuous or uniform welding zone portions as extending to both sides of said meeting area.

Abstract: For mounting a protective sleeve of plastic over a joint between prefabricated heat insulated pipes, typically subterranean district heating pipes, an axially split plastic sleeve is inserted laterally over the joint so as to bridge the opposed ends of outer protective plastic tubes of the joined pipes. A plastic welding strip provided with a number of embedded parallel heating wires, is placed along and over the relevant annular joint with its opposed ends located spaced from each other adjacent the axial split of the sleeve. The ends of the strip are provided with terminals for parallel connection of the embedded wires, and the wires are electrically heated to weld together the welding strip and the two plastic tube ends. The axial split is then scaled by a similar welding strip.