The ratcheting behavior of carbon steel piping elbows under cyclic bending moment and temperature

In this paper, the effect of temperature and out-of-plane dynamic moments on ratcheting behavior of pressurized elbows have been investigated. The combined hardening model (Chaboche kinematic hardening model with isotropic hardening rule) is used for the plastic analysis of materials. Piping elbow specimens had temperatures of 50, 100, 150 and 200 degrees C. By using of many tension-compression-stabilized tests of specimens under symmetric strain-controlled, constant parameters for materials are obtained. The results obtained by the FE method of specimens show that the deformations occurred mainly because of creep at high temperature and ratcheting strain by out-of-plane moments. Also, ratcheting rate increases by increasing moment bending and temperatures. Initial, strain accumulation rate is low, and it increases with the increasing temperatures, which express softening phenomenon due to thermal creep. The strain accumulation is highest along the hoop direction at flanks, similar to results from experimental data without considering temperature effects. The results show that the increase in ratcheting due to high temperature may lead to incontrollable damages to pipework structures. Of course, the prediction of strain accumulation is improved in the presence of isotropic hardening rule.