Creep of Thick-Walled Cylinders Subjected to Internal Pressure and Radial Heat Flux at Elevated Temperatures

Abstract

The creep tests of thick-walled cylinders subjected to internal pressure and heat flux through the wall were conducted on a low carbon steel at elevated temperature, and the results were discussed from the standpoint of multiaxial creep theory, considering the transient creep.The conclusions obtained are as follows:(1) The feature of creep curves for tubular specimens with temperature gradient is similar to that for the case without temperature gradient.(2) The method of analysis employed by R.W. Bailey, L.F. Coffin, J.E. Traexler and others for the steady state creep of thick-walled tubes with radial temperature gradient was extended to the case of transient creep, by using a strain hardening type stress-strain rate equation. It was found that the analytical creep strain based on the Mises effective stress was smaller than the measured creep strain, while the Tresca effective stress gave larger deformation than the experimental one.(3) We can take a temperature level for the test temperature of a thick-walled cylinder under internal pressure yielding the same amount of creep strain with similar cylinder subjected to the same amount of internal pressure with radial temperature gradient. It is called the equivalent temperature and can be determined by analysis for a given test condition. It enables us to predict the creep rupture life of the tube under internal pressure with radial temperature gradient, and to provide, at this temperature, the creep rupture data by using the Tresca mean effective stress.(4) The analytical creep deformation of the cylinder under internal pressure with heat flux from inside to outside is larger than that of the cylinder with inverse heat transmission within the same temperature range.(5) The creep activation energy of the material tested is 7×104 cal·mol-1 which was obtained from the temperature-creep rate relations for uniaxial creep tests at the stress of 12kg/mm2 and the temperature 500°C. This agrees fairly well with the self diffusion energy of α-iron.