Abstract: For use in heat-insulated pipe-lines produced from at least two heat-insulated pipe units joined end to end, each heat-insulated pipe unit consisting of a pipe surrounded over the greater part of its length by at least one layer of heat-insulating foam material which is in turn enclosed by an outer jacket of fluid-impervious protective material, the end parts of the pipe projecting beyond the corresponding ends of the layer or layers of heat-insulating material and the end parts of the jacket projecting likewise but for a shorter distance, so that annular recesses are formed in the ends of the pipe unit. The pipes of these two pipe units are interconnected end to end by a butt weld or mechanical jointing element between the projecting end parts thereof. Annular seals of rubber-like material are located in the annular recesses in the proximate ends of the two pipe units.