The goal of this study was to computationally estimate the effect of geometry and boundary conditions on structural rigidity, stresses, strains and further on the possible risk for hot cracking in the case of narrow gap welding. Two different mock-ups were examined, the first was a plate mock-up and the second a nozzle mock-up. The computation was performed utilising specifically tailored finite element analyses. The material nonlinear characteristics were taken into account, and temperatures, deformations, stresses and strains were computed during and after welding. Plate thickness was 50 mm and length 400 mm. The nozzle mock-up was a tubular specimen having inner diameter of 750 mm and wall thickness of 110 mm. The materials of the plate mock-up were ferritic pressure vessel steel SA 508 with AISI 308L and 309L cladding and austenitic AISI 304 steel plate. The weld metal was Alloy 52. The materials, weld geometry and welding parameters of the nozzle mock-up were similar to the plate mock-up. In the case of plate mock-up cracking of the weld occurred in the first 7 weld passes. In the case of nozzle mock-up no cracking was observed. The computed equivalent plastic strain at the middle of the weld in selected locations was compared to the critical strain for ductility dip cracking obtained from literature. The comparison shows that there is a higher risk for hot cracking in the case of the plate mock-up due to higher computed equivalent plastic strain. The risk of hot cracking decreases as the welding proceeds. The reason for the computed higher risk for hot cracking of the plate mock-up is most probably due to different structural rigidity and weld geometry/configuration of the plate mock-up in comparison to the nozzle model.
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