Microstructural quantification, modelling and array ultrasonics to improve the inspection of austenitic welds

The fundamental obstacle to characterising accurately the defects in austenitic welds is the distortion of the sound field due to the anisotropic inhomogeneous material. This paper describes the development of the next generation of ultrasonic procedures which use phased array techniques and models to account for the distortion of the sound field, such that the detection, positioning and sizing of defects is improved in comparison to current capabilities. Each stage of the procedure development is described., along with the issues and obstacles which must be overcome. The electron back-scatter diffraction technique is used to evaluate the texture of the weld and then the microstructural information is input to a model capable of propagating ultrasonic waves through the anisotropic inhomogeneous medium. With knowledge of the distortion, a strategy of adapting the focal laws using time reversal concepts to improve sensitivity was developed.