Inspection of straight seam welded pipes by ultrasonic guided waves

Guided waves have a wide range of applications in nondestructive testing of pipes. The generation of pure symmetric guided wave modes in a pipe simplifies the interpretation of results. Higher sensitivity to pipe geometric variations and discontinuities can also be achieved by using pure symmetric modes. Most pipes used in low-pressure fluid transmission lines are manufactured by cold rolling of a plate followed by resistance welding of the two edges of the plate. Consequently, these pipes have a straight weld seam along their length. In this article, Finite Element Method is used for simulating the propagation of symmetric guided wave modes L(0,2), L(0,1) and T(0,1) in straight seam welded pipes. First, a comparison is made between the propagation of these wave modes in seamless and seam welded pipes. Results indicate that the angular amplitude profile of the L(0,2) wave mode does not change much in the presence of the seam weld. However, the weld has a slight effect on the propagation of the T(0,1) mode. The effect of the presence of the straight seam weld can be observed in the propagation of the L(0,1) mode which creates an asymmetric angular profile such that the amplitude of the L(0,1) mode in the weld line zone is largely reduced. This phenomenon may reduce the sensitivity of this wave mode in detecting defects in the proximity of the weld line. As a result, the other two guided wave modes L(0,2) and T(0,1) are recommended for the inspection of straight seam welded pipes .