Design of Heated Cylindrical Pressure Vessels in Transient Creep

Long, thick cylinders with closed ends undergoing transient creep as a result of a step change in pressure and an axisymmetric temperature history are analyzed. It is assumed that the initial stress state is elastic and that the subsequent redistribution of the stress state is governed by a temperature-dependent, strain-hardening creep law. The results are applicable to a wide variety of both conventional and nuclear power generating equipment, and are illustrated for the temperature histories and geometries that are encountered in the headers of power boilers. A procedure for evaluating the results of such calculations is suggested and illustrated. Results obtained by these procedures indicate that current ASME Boiler and Pressure Vessel Code practices can lead to unconservative predictions of fatigue life if the equipment is to be operated at temperature levels in the creep range.