Abstract: The invention relates to a process for insulating pipes by applying a rigid polyurethane foam as an insulating layer and optionally an external top coating by the rotational casting process. The rigid polyurethane foam is obtained by a) an aromatic polyisocyanate, b) an organic polyhydroxyl compound, c) an aliphatic, cycloaliphatic or aromatic polyamine and/or polyimine having a molecular weight of from 32 to 1,000 as the cross linking agent in the presence d) a blowing agent, and optionally in the presence of e) known auxiliary substances and additives and in the presence of f) one or more compounds having a molecular weight of from about 166 to about 1,000 and being of the general formula ##STR1## wherein n represents an integer between 2 and 9, preferably 2 and 3,R.sup.1 signifies hydrogen, a C.sub.1 -C.sub.9 alkyl radical or a ##STR2## R.sup.2 signifies hydrogen, and R.sup.3 and R.sup.4 signify hydrogen or methyl.

Abstract: A process for insulating pipes comprises applying at least one layer of a polyisocyanurate plastic and then at least one layer of rigid polyurethane foam to a steel pipe. The foam is covered with an outer layer.