Ultrasonic reflection properties of planar defects within austenitic welds

Reflection of ultrasonic beams from the faces of planar weld defects is affected by the anisotropic nature of the weld material. The simple laws of geometrical reflection no longer hold and energy may be strongly reflected into unexpected directions. This has important consequences for ultrasonic inspection techniques relying on specular signals for defect detection. In this Paper a ray tracing approach is used to study, theoretically, the expected patterns of defect reflection behaviour for several weld types and several defect locations and orientations. In general we find that when the ultrasonic beam is generated in the austenitic weld material without first passing through the base metal then the strongly reflected specular signal travels in very unexpected directions. If, however, the ultrasonic beam travels into the weld metal via the base metal then reflected signals usually occur close to the expected directions, except for vertically polarized shear waves. Furthermore, for a given weld type it is obviously useful to minimize ultrasonic ray paths within the weld material, to minimize both attenuation and curvature of ray paths.