Experimental Study on the Effects of Harmonic Vibration on the Stress Relief of the Butt Welded AISI 1021 Pipes

The presence of residual stresses has severe effects in materials resistance to fatigue, corrosion and failure. The presence of local heat during welding leads to the formation of residual stresses. Vibration stress relief is a modern non-destructive method. This method can release the remained stresses without changing the metallurgical properties of the workpiece. In this study, stress relieving was carried out by harmonic vibrations in a welded joint from AISI 1021 steel, which was fabricated by the manual arc welding process in 2G position according to ASME standard. After the experimental evaluation of the resonance frequency of the welded pipe, the harmonic vibration was applied to the pipes. Hardness tests and measurements of residual stresses were done by hole drilling strain gauge method before and after the vibration stress relieving. For stress relaxation, the welded pipes were sinusoidally vibrated at frequency of 27.8 HZ for 40 minutes. The results show a 11.5% reduction in the hardness and 42% of the peripheral residual stress relieving in the central weld line after applying the vibration on the weld joint. The obtained results prove the efficacy of the vibratory stress relief technique in the release of residual stresses in a welded pipe.