NUMERICAL ANALYSIS OF STRESS AND STRAIN STATE IN MEMBRANE WALLS WELD JOINTS PERFORMED BY SUBMERGED ARC WELDING

The article presents investigation on stress and strain state in weld joints of boiler membrane wall by performing numerical analysis (finite element method). The main purpose was to create 3D model which will correspond to real membrane wall geometry under consideration, which will allow to perform strength simulation of numerical models considering variable parameters depending on the temperature. The model was fragment of boiler membrane wall made of X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar welded with submerged arc method. The research included the assumption of boundary conditions such as temperature cycles, welding method, type of mounting and base materials or heat treatment cycle. Three simulations have been performed depended on base material and temperature cycle adopted. As a result of the simulations, the distribution of temperature, displacement and stress in analyzed cases were obtained. The numerical simulation in dissimilar welded joints X10CrMoVNb9-1 pipe and 10CrMo9-10 flat bar heat treated afterwards, showed that the differences in linear expansion coefficients favour the development of cracks in the welds caused by increased level of stress. In parallel materials used for boiler membrane walls are the reason for difficulties in determine the proper technology of welding, preheating temperature and post-weld heat treatment parameters. Simulations indicated that the state of stress in weld joint is dependent on type of parameters adopted, and in closest scenario to real conditions, simulation showed that post-weld heat treatment had no positive effect on the stress state caused by discrepancy in linear expansion coefficients of both base materials.