Depth Sizing of Surface Breaking Flaw on Its Open Side by Short Path of Diffraction Technique

Central Research Institute of Power Industry has developed a highly accurate and low cost flaw depth sizing technique which is easy-to-use in comparison to standard techniques such as crack tip diffraction and TOFD techniques. This technique is called the short path of diffraction (SPOD) technique. In this technique, an angle beam transducer and a 0-degree transducer are used to excite and receive waves. So far the applicability of SPOD to depth sizing on flaw open side has not been discussed. This paper deals with the effectiveness of SPOD in this application. Finite element modeling for wave propagation revealed that two echoes were obtained which were obviously related to the tip and opening of a surface breaking flaw in SPOD configuration. Based on this result, an equation was derived to calculate the flaw depth from the difference of the relative beam paths. To demonstrate the applicability of SPOD to surface breaking flaws, depths of fatigue cracks introduced in stainless steel blocks were measured. Because the depths measured were in excellent agreement with actual ones, SPOD could be applied to flaw depth sizing on its open side.