Time-of-flight diffraction (TOFD) technique for accurate sizing of cracks embedded in sub-cladding

This paper deals with an experimental study for evaluation of the TOFD technique for determination of size of cracks embedded in sub-cladding. It extends the results presented in the previous papers(1, 2). The study was confined to simulated cracks (machined slits) underneath the cladding. It was found that crack heights ranging from 1.68 mm to 19.04 mm underneath stainless steel, Inconel and ferritic cladding could be sized with an accuracy of 0.2 mm. Difficulty was experienced using TOFD to size cracks starting from the interface between Inconel/stainles steel cladding and the ferritic base ie (5 mm/6 mm below the scanning surface). However, these cracks could be detected and sized by scanning through the cladding from the opposite surface of the blocks. Even the small cracks of the order of 1.9 mm could be detected as long as they are not influenced by the lateral wave. Experimental errors are presented.