The Role of Residual Stresses in Circumferential Welding Repairs of Pipelines in SCC Susceptibility

The main objective of the present study is to measure the residual stresses in the circumferential welding joints of X52 pipeline steel with multiple welding repairs, and then relate these residual stresses to study the influence on the high pH stress corrosion cracking (SCC) susceptibility. Four conditions of shielded metal arc welding (SMAW) repairs of the girth weld were evaluated. The residual stresses were measured through X-ray diffraction (XRD) on the internal side of the pipe in longitudinal and circumferential direction. Residual stresses in the circumferential and longitudinal direction reach values of about 98 and 74% of the yielding strength (360 MPa) respectively. The effect of residuals stresses in the high pH-SCC susceptibility of X52 pipeline steel was evaluated through slow strain rate tests (SSRT) in a simulated soil solution. Relation between SCC index and residual stresses on the SCC susceptibility was analyzed. Results of SCC index taking account the ratios obtained from the mechanical properties of the welding joints evaluate (containing different levels of residual stresses) showed good SCC resistance. It was observed that increasing the magnitude of residual stresses, the SCC susceptibility increases. For all the SSRT specimens the failure occurs in the base metal and heat affected zone (HAZ) interface.