Numerical simulation of sleeve repair welding of in-service gas pipelines

The purpose of this study is to develop an appropriate numerical model for full encirclement, sleeve repair welding of in-service gas pipelines and to investigate the effects of in-service welding conditions. An axisymmetric finite element model was used to calculate the temperature distribution, maximum HAZ hardness, and the distribution of residual stress and plastic strain during multipass sleeve fillet welding of in-service API 5L X65 pipelines of 14.3 mm thickness. Experiments were also conducted for sleeve repair welding on pipe with internal pressure. The calculated geometry of the fusion zone and HAZ was in good agreement with the macrostructures of sleeve repair fillet welds. The calculated maximum HAZ hardness was in good agreement with the measured value. The effect of gas flow rate on the maximum HAZ hardness and the effects of internal pressure on residual stress and plastic strain distribution were investigated. Risk of melt-through and susceptibility to cold cracking were also estimated using a simplified analysis.