An experimental and finite element analysis of temperature and stress fields in girth welded 304L stainless steel pipes

This research sought to understand the residual stress development during 304L stainless steel pipe girth welding process with an emphasis on thermomechanical history measurements, residual stress measurements, and computational modeling of welding and stress mitigation precesses.; Thermomechanical histories were measured for three 406-mm-diameter, schedule 40 pipe girths welds. Two welds were standard V groove prepared and completed in six and nine passes with multiple start-stop positions, while the third one had a narrow groove configuration and was finished with four passes and one start-stop position. Thermomechanical history measurements were taken on pipe inner surfaces to monitor weld shrinkage, surface temperatures, surface temperatures, surface strains, and radial deformations. The results show that: (1) the temperatures profiles in V groove weldments are axisymmetric, while in the narrow gap groove weldment they are axisymmetric except in locations near welding start-stop position; (2) the strain/deformation value is decided by the last one or two welding passes; (3) the strain/deformation profile in the weldment is not axisymmetric suggesting that the residual stress is not axisymmetrically distributed; (4) the four-pass narrow gap weldment has the lowest level of radial deformation among the three pipe weldments indicating that the narrow gap weldment would have the lowest overall residual stress level among the three pipe weldment.; Residual stress measurements were performed on outer surfaces of the four- and six-pass weldments by the air-abrasive hole-drilling method and on the inner surface of four-pass weldment by the neuron diffraction method. The results show that the residual stress distribution is not axisymmetric. This comparison between the residual stress measurements demonstrates that the four-pass weldment has the lowest residual stress level among the three pipe weldments.; A 3D finite element model was established to simulate the narrow gap pipe girth welding process. The calculated temperature histories and their distributions are in good agreement with the experimental data. The calculated residual stress distribution is axisymmetric except in locations near the welding start-stop position. This is not in agreement with the experimental observation. The overall comparison between the calculated and experimental stress results demonstrated reasonable agreement between them.; An axisymmetric 2D finite element model was conducted for four-pass welding and welding plus cooling stress improvement (CSI). The results indicate that the weld induced stresses on the pipe inner surface are tensile in weld region and remain so for a certain distance from the weld centerline. CSI treatment after welding can convert the tensile stresses to compressive values.