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Investigation of residual stresses in tank car shells in the vicinity of weld ends

A large number of cracks which develop in railroad tank car shells form near the ends of skip welds which are used to attach stiffeners to the tank. The development and growth of these cracks in fatigue are affected by the presence of residual stresses induced locally in the shell plate by welding. Leaking and the potential for tank failure pose significant safety concerns, especially in the case of tank cars containing hazardous materials. Determination of the distribution and magnitude of these residual stresses is important in assuring the structural integrity of tank shells. A three-dimensional thermo-elastic-plastic finite element model (FEM) of a skip weld has been developed to explore the residual stress distribution in the weld and the surrounding base material. The model geometry corresponds to that used in a series of experiments designed to measure residual stresses by means of X-ray and neutron diffraction. Model results are presented for characteristic skip welds on base plates of standard tank shell material and comparisons are made between the model predictions and the laboratory measurements. Validation of the model will permit its use in evaluating residual stresses in the vicinity of different weld geometries used for other tank shell attachments.