[2C3] Inspection for SCC in uncoated austenitic stainless steel
M Jones
ESR Technology Ltd, UK
Stress corrosion cracking (SCC) in austenitic stainless steel is difficult to detect and actual sizing of the crack extent is particularly challenging. A previous exercise by a HOIS member on the inspection of ex-service austenitic stainless steel samples with stress corrosion cracking showed that phased array ultrasonic testing (PAUT) could detect part of the larger cracks (with a depth of ~50% WT), but the finer, branched cracks were not detected, some of which had a depth of approximately 75% of the wall thickness of the component. The focus of this work was therefore on the detection and sizing of the finer, branched cracks that can sometimes progress deeper through the material than the larger stress corrosion cracks. The detection and sizing performance of full matrix capture-total focusing method (FMC-TFM), full matrix capture-phase coherence imaging (FMC-PCI) and time-of-flight diffraction (TOFD) were evaluated by means of a blind trial where an ex-service austenitic stainless steel sample containing stress corrosion cracking was inspected. These results were then compared with the benchmark values measured by sectioning of the plate sample and measuring the minimum remaining wall thickness at specific locations. The comparison between the trialist and benchmark results was very encouraging, as was the comparison of the scans and the corresponding macro sections.
