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Decreasing welding distortions in penetration nozzles by applying proper welding sequences

Welding distortions cause problems in assembly and performance of weldments, including nozzles in pressure vessels. In the present work, a three-dimensional thermo-mechanical finite element model was expanded to study the effect of the welding sequence on welding distortions in a pressurized nozzle. Among different types of distortions, shrinkage and angular distortions have been investigated. Since changes in the welding sequence increase the computational time and complicate the welding process, the effects of the welding sequence in different passes have also been studied. For the case studies, a five-pass shielded metal arc welding with V-joint geometry has been selected. The vessel has a diameter of 2000 mm and a thickness of 8 mm, and the nozzle has a diameter of 100 mm and a thickness of 8 mm. The pressure vessel and nozzles are made of 304 stainless steel material with the same chemical compositions. The finite element and experimental results have been compared, and turned out to be in good agreement. The results showed that welding in four sections with a proper sequence has significant influence on decreasing angular distortions, but the welding sequence is not an effective parameter to reduce the shrinkage type distortions. Moreover, sequencing can be used in some passes to simplify the welding process and also to decrease the process time.