A combined computational and experimental study on vibration stress relief for large welded DH36 steel tube

Vibration stress relief (VSR) is an effective and economic method for reducing residual stress in various welding components. Compared with other methods, it costs much less time and energy. In this study, finite element method (FEM) was used to assist VSR treatment of large DH36 steel welded tube by determining the 1st order vibration mode of the tube and the natural frequency of the tube in a hypothetic zero-stress state. According to the computational results, proper vibration exciting assembling and excitation strategy was selected. An effectiveness index, eta, for fast and quantitative estimation of the residual stress decrease rate was proposed. eta is determined by 1st order natural frequencies of the tube in three states, i.e. as-welded, VSR treated and a hypothetic zero-stress state. eta in this study was 49.8 %, meeting well with the experimentally measured residual stress decrease rate, similar to 50 %. Thus, the validity of the effectiveness index was verified. This study provides a novel method for analysis of VSR effectiveness. In comparison, maximum residual stress was reduced by 20-57 % when traditional local post weld heat treatment (PWHT) was used. This indicates that VSR is a good stress relief method for DH36 welded structures.