During the manufacturing of heat-insulated pipes (1) with an inner duct (3) and an outer duct (2) and a foamed insulation (14) arranged in between, the inner duct is placed on a tension member (10). The latter is tensioned between tensioning means by means of a tensile force, such that it runs straight and that the inner duct is held straight. The latter is held on centering elements (16, 17) which are spaced from one another in a defined way by means of spacers (18). In this straight position the inner duct may be surrounded with foam inside of the outer duct, without needing spacers between the ducts.