Evaluation of hoop residual stress variations in the thickness of dissimilar welded pipes by using the LCR ultrasonic waves

Stress measurement by using ultrasonic waves is based on acoustoelasticity law, i. e. the relation between stress and wave velocity in engineering materials. Longitudinal critically refracted (LCR) wave is a popular ultrasonic wave in the ultrasonic stress measurement application. The L_CR wave is a bulk longitudinal wave that travels within an effective depth underneath the surface. This paper evaluates hoop residual stress variation in the thickness of a pipe. The pipe is manufactured by welding two dissimilar pipes from AISI stainless steel 304 and carbon steel A106-B type. The residual stresses variations in the thickness of pipe are measured by using four different frequencies of transducers while the nominal frequencies are 1 MHz, 2 MHz, 4 MHz and 5 MHz. Using different frequencies enables the LCR waves to penetrate in different depths and measure the bulk stresses of pipe. It has been shown that the stress difference between inner and outer surfaces of pipes and also between the stainless steel and carbon steel side of dissimilar pipe can be evaluated by using the LCR waves.