Nondestructive Assessment of Residual Stresses and Distortion in Austenitic Stainless Steel Weld Joints

An ultrasonics-based nondestructive technique was developed and applied for the measurement of surface/subsurface residual stress distribution across weld joints using longitudinal critically refracted waves. The ultrasonic technique is based on the acousto-elastic principle, which indicates that propagation velocity of elastic waves depends on the presence of stress in the materials. Tungsten inert gas (TIG) and activated flux tungsten inert gas (A-TIG) weld joints were prepared in 5 mm thick type 316LN steels. Accurate ultrasonic transit times were measured parallel to the weld direction and across each weld joint. Measured transit times were converted into quantitative values of residual stresses using the predetermined acousto-elastic constant for this steel. The presence of residual stresses also causes distortion in weld joints. Distortions were measured using an electronic height gage in each weld joint. A comparison of the residual stress present in the TIG and A-TIG weld joints indicated that there was a significant reduction in the peak tensile residual stresses by 25% in the A-TIG weld joint. It was observed that the angular distortion was reduced significantly by 60% in weld joints made by an A-TIG welding process as compared to that of weld joints made by a TIG welding process. Residual stresses and distortion in stainless steel weld joints were measured nondestructively employing an ultrasonic technique and a height gage, respectively.