Primary Creep in the Design of Internal-Pressure Vessels

Abstract

Abstract The paper evaluates the stresses and the permanent strains at a particular time, resulting from loading a thick-walled cylinder under constant internal pressure and elevated temperature when account is taken of the primary creep characteristics of a given material. The results are compared with permanent strains obtained by considering secondary creep as the general basis for pressure-vessel design. For a thick-walled cylinder of wall ratio of R1/R0 = 2 and of 12 per cent chromium steel, operating under 12,000 psi at 850 F, the permanent strain at the end of 25 hr by the primary-creep analysis was found to be equal to the strain at the end of 2000 hr, considering only secondary creep. The methods formulated are shown to be suitable for design of pressure vessels intended for short life.