Nondestructive Evaluation of Thick Austenitic Stainless Steel Weldments by Shear Horizontal Acoustic Waves

Abstract

Recent papers^1,2 reviewed the difficulties involved in ultrasonic testing of stainless steel weldments and the advantages of using horizontally polarized shear waves. The basic problem lies in the large grain size and anisotropic elastic properties of these welds. The grains grow epitaxially from pass to pass with the [100] direction parallel to the thermal gradient. This results in a highly textured, columnar structure (dendritic) that causes considerable mode conversion of the usual longitudinal waves, making ray tracing very difficult. Shear horizontal (SH) waves are polarized in the plane of the weldment, in the direction of the weld pass and normal to the growth direction of the columnar grains. Along certain directions they can propagate through the weld as pure shear waves and suffer little reflection or conversion by polarization coupling to the longitudinal (L) or shear vertical (SV) modes.² SH waves can be efficiently generated and detected with noncontacting electromagnetic acoustic transducers (EMATs).³