Burn-through prediction during in-service welding based on residual strength and high-temperature plastic failure criterion

Abstract The burn-through of in-service welding is affected by pipeline structure, welding procedure and the pressure of the internal medium, etc. It is a high-temperature failure process under the coupling action of structure field, temperature field, and stress field. Predicting the critical burn-through pressure of in-service welding is a challenging problem. In this paper, the existing burn-through criteria were comprehensively summarized and analyzed. Considering the multi-field coupling effect of in-service welding, two kinds of burn-through criteria based on the thermo-mechanical analysis model were proposed innovatively. One is the residual strength three-dimensional integral method. The residual strength in the high-temperature zone of in-service welding was calculated by this method, and the critical burn-through pressure was obtained by further calculation. The selection of effective integral temperature interval is the key to ensure the accuracy of three-dimensional integral calculation of residual strength. It is found that there is a linear relationship between welding heat input and the lower limit of the integral temperature interval. However, for different materials, the linear relation formula is different. The second criterion is the high-temperature plastic failure criterion. The most dangerous path is the one with the largest plastic failure depth along wall thickness. When the von Mises stress over 2/3 of the pipe wall along the most dangerous path is greater than the yield strength at the corresponding temperature, there is a high risk of burn-through. The accuracy of the two criteria in calculating the critical burn-through pressure was verified by in-service welding tests. The results show that the residual strength three-dimensional integration method and the high-temperature plastic failure criterion both have high accuracy and reliability in predicting the burn-through of in-service welding and will have important referential value in predicting the failure of defective pipe under complex temperature and stress conditions.