“…Li and Cho (2015) and Sheen and Cho (2012) have corrected the shape factor of the PDI methods united with ultrasonic guided wave to effectively discern the single corrosion and penetration hole defect in the plate-like structure. In addition, the shape factor b is of great significance for the establishment of damage recognition image in the PDI method confirmed by many studies (Li and Cho, 2015;Liu et al, 2016;Wang et al, 2009Wang et al, , 2010aWang et al, , 2010bWu et al, 2014;Zhou et al, 2011). However, the shape factor of conventional PDI approach is empirically chosen and maintains unchanged at all transducer paths (Liu et al, 2016;Wu et al, 2014;Zhou et al, 2011;Zhu et al, 2021), it does not accurately estimate the defect zone.…”