A study on the pre-cyclic-load-induced burst of creep deformation of a pipeline steel under subsequent static load

Room temperature creep of X-52 pipeline steel was studied under various loading conditions. Due to cyclic hardening, the steel exhibits cyclic creep retardation, which is less pronounced at lower stress-ratio and under cyclic load with periodical hold at peak stress. Pre-cyclic loading has significant effect on subsequent static creep. Up to 40 cycles, pre-cyclic load results in a smaller cumulative creep than that of pure static creep deformation. This is attributed to the high rate of cyclic hardening during the initial few cycles, which limits further creep deformation in the subsequent static loading. With increasing number of cycles, pre-cyclic loading causes a burst of creep deformation under subsequent static loading, which results in significantly larger cumulative creep strain than that of pure static creep. The burst in creep deformation requires an incubation period that increases with the number of prior load cycles. The burst strain is dependent on the number of cycles of prior cyclic loading in a more complicated manner. The possible dislocation mechanisms related to the pre-cyclic-load-induced burst of creep deformation are also discussed in the paper.