Effect of ultrasonic impact treatment on redistribution of residual stresses in dissimilar thickness girth welds

Effect of repeated ultrasonic impact treatment on redistribution of residual stresses in a dissimilar thickness girth butt weld of pipes with a diameter of 530 mm of low alloyed (0.9%C-2%Mn-1%Si) steel was studied. Residual stresses were measured by the X-ray method based on measurement of microdeformation of a crystal lattice of a material under its influence. The research results showed that tensile residual stresses in the girth weld were formed at the inner side of the pipe after welding. Ultrasonic impact treatment of the weld at the inner side caused complete transformation of residual stresses from tensile to compressive ones when speed was in the range from 0.06 to 0.12 m/min. However, reduce in speed of treatment down to 0.04 m/min gave a negative effect. The values of compressive residual stresses in heat affected zone on the side of the thinner pipe were decreased.