Measurement and Modelling of Through Thickness Ultrasonic Velocity in X70 Pipeline Steel

摘要

Ultrasonic testing (UT) is typically used for crack and/or flaw detection in the weld region of X70 pipeline steel. Alternatively, this paper uses ultrasonic velocity (longitudinal and shear) and attenuation measurements as a means of assessing microstructure through the thickness of a 15 mm thick X70 microalloyed steel skelp. The microstructure of the X70 steel was analysed using both metallography and quantitative X-ray diffraction (QXRD). QXRD provides a measure of the magnitude of texture in the skelp (texture index J) and an assessment of grain size via the predicted average domain size (L_(vol)) value. In addition, an ultrasonic wave velocity model, based on the Christoffel equation, is used to predict longitudinal and shear wave velocities for a non-textured steel system. The microstructure of the X70 was found to be relatively uniform through the thickness of the skelp. The measured ultrasonic velocities and attenuations were also found to be relatively uniform through the thickness, although a difference was observed between the shear velocities measured with the wave displacement parallel to the rolling direction versus the shear velocities measured with the wave displacement transverse to the rolling direction.