Crack detection and defect classification using the LLT-technique

A method in current use for defect detection in thick walled components is the tandem technique (1). With the aim to replace this cumbersome two-probe technique, a high sensitivity one-probe technique for the detection of perpendicularly oriented cracks and lack of fusion defects has been developed (2-4). The high sensitivity of this so-called LLT-technique results from the effective mode conversion at the defect from a longitudinal wave and the exploitation of the specular reflections. In comparison to the tandem technique the LLT-technique shows an improved defect localization, improved acessibility of the inspection regions, minor obliquity dependence and minor cladding effects in the inspection of cladded components from the outside. Further, mode conversion effects can be used for a defect classification.