Accuracy of crack size measurement in welded joint by advanced aut system for non destructive evaluation of fracture strength

For non destructive estimation of brittle fracture strength at welded joint, fracture mechanics require to monitor fracture toughness of weld metal and two dimensional flaw sizes of length and height. Up to now, many methods have been proposed to measure both flaw length and height in laboratory. However, industrial inspection methods estimate only flaw length and other advanced methods proposed have several barriers for applying industrial problems. As the results, NDE measurement data have been used only for flaw detection, and strength has never been estimated non destructively for industral structures. In this paper, the authors applied the advanced automatic ultrasonic inspection system to measure not only flaw length but also flaw height for industrial welded structures. Using this system, 22 specimens with artificial inner and surface cracks in welded joint varying crack length and height were measured non destructively. After non destructive measurement, welded joint specimens were broken by tensile test in liquid nitrogen, and the crack size were measured by fractography. Comparing the crack size by fractography to the one by ultrasonics method, errors in non destructive sizing by the ultrasonic system were estimated accurately. Using the fracture mechanics procedures, effect of the error in non destructive flaw sizing on strength estimation was investigated.