Phased Array Ultrasonic Sizing Performance on Artificially Produced Fatigue Cracks in Austenitic Stainless Steel Weld

Qualification of non-destructive examination (NDE) procedures for in-service inspections (ISI) of nuclear power plant (NPP) components is performed using different types of artificial defects. The assessment of the reliability of a procedure requires representative defects compared to the real service-induced defects.
Artificial defects are typically used as a reference when the performance of an NDE procedure is demonstrated. Because of the lack of real defects, artificial defects are needed for certification and training of the inspectors. The NPP safety regulatory guides in Finland (YVL) emphasise that the description of defect indications exceeding the recording level shall be given in the inspection report. This information includes definition of defect size, character, location and orientation according to ASME Code, Section XI “Rules for in-service inspection of nuclear power plant components” and their comparison with the acceptance level. This code imposes some rules on the applicable defect types and it is thus important to verify the applicability of different available defects.
Ultrasonic indications are highly dependent on defect characteristics like roughness, crack opening, tilt and branching. This work studies the influence of different reflector properties on defect indications. Five inside surface breaking artificially produced fatigue cracks beside the weld root and one electric discharge machining (EDM) reference notch were made in a piping test specimen simulating PWR cooling line pipe (AISI 321). Defects were examined using phased array ultrasonic testing (PAUT).
This study was made as a part of Finnish national research program on NPP safety 2014-2018 (SAFIR2018), Non-destructive examination of NPP primary circuit components and concrete infrastructure, WANDA project.