EFFECTS OF HYDROTEST AND QUENCHING PROCESSES ON RESIDUAL STRESSES DUE TO SAW OF API 5L-X70 PIPES USING FEM

: This paper explores the effects of three of the most important post-welding processes on the residual stresses of large-diameter oil and gas pipes. The analysis is one of uncoupled thermo-mechanical applied for both 2D and 3D models of the pipe. The pipe body is assumed to be prestressed due to prior submerged arc welding of its seam. To analyze the processes, parametric programming in the ANSYS commercial software is utilized. The processes are hydrotest, quenching by Houcsh method, and quenching by the last pass heat sink welding, which is the most cost-effective technique. The processes are, respectively, performed by applying very high internal pressure to the pipe, induction heating plus spray cooling of the pipe, and cooling the weld zone simultaneously with the last past welding. The novel aspects of the study include investigation of the above processes for API 5L-X70 pipes and application of FE analysis to simulate the quenching of pipes for both the Houcsh method and the last past heat sink method. The effects of the processes on the residual stresses are compared. The simulations are verified qualitatively using experimental results reported in the literature.