Improving the inspectability of stainless steel and dissimilar metal welded joints using inverse phase-matching of phased array time-domain signals

The ability to perform nondestructive testing of stainless steel piping and dissimilar metal joints in excess of 10.0mm (.4") wall thickness is very limited. In particular the use of ultrasound to detect closed (tight) cracking, which is not detected by X-ray techniques, is very difficult due to the acoustic anisotropic structure of the welded seam. Several Reactor Safety Program projects have presented extensive knowledge and better understanding of how to enhance the test procedures for this type of welded joint. Resulting standards and regulations for the qualification of applicable techniques and procedures provide evidence of the limitations of conventional X-ray and ultrasonic methods. Fundamental results were provided by simulating the sound propagation in model-described welded joints against the manufactured form. In principle, this permits the application of ultrasonic migration techniques, which allows for the consideration of phase influences during the summation process of the received time-domain signals. The fundamental capabilities of the Inverse Phase-Matching technique have been successfully demonstrated on heterogeneous and anisotropic design models and test samples supplied by the Reactor Safety Program. This paper discusses the principles and first application results of this technique.