Ultrasonic Response on Artificially Produced Fatigue Cracks in AISI 321 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. ;Fatigue cracks can nowadays be produced artificially as thermal fatigue or mechanical fatigue cracks. Mechanical fatigue crack production is well known and widely used method and can produce very realistic cracks. Thermal fatigue crack production is also very well controlled in matter of size and opening. Those kinds of cracks are also very realistic option compared to the real service-induced cracks. The aim of the study is to get a wider perspective to the differences in different sizes and orientations of mechanical and thermal fatigue cracks. ;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.