Residual stresses in weld thermal cycle simulated specimens of X70 pipeline steel

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Residual stresses in weld thermal cycle simulated specimens of X70 pipeline steel

Onsoien, M.I. / M'Hamdi, M. / Akselsen, O.M.

The present work concerns Satoh testing of X70 pipeline steel and was undertaken in order to assess residual stresses in steel weldments. Experiments using single, double, and triple temperature cycles were performed to study how different temperature histories affected the development of residual stresses in the tested specimens. In some of the single-cycle experiments, high tensile stresses or high compressive stresses were imposed on the sample at the start of the experiment to study the response of the sample to preloading. Residual stresses higher than 490 MPa have been measured. It was further found that samples with low austenite transformation temperature may build up higher residual stress than samples with higher austenite transformation temperature. A prerequisite for this behavior is that the transformation product in the first case has high yield strength and, the transformation product in the second case reaches its yield limit. It is also shown that the effect of preloading on the shape of the sigma-T curve is negligible for temperatures above the A(c1) temperature, i.e., the phase transformation relaxes the effect of differentinitial stresses and the final stress level is very similar for samples starting in high compression, high tension, or zero stress. It is further shown that the effect of multiple cycles on the shape of the a-T curve and on the final stress level is low, probably because of stress-strain relaxation during the phase transformations.