Inspection of Pitting Corrosions on Weld Overlay Cladding Using Uniform and Rotating Eddy Current Testing

This study investigated the applicability of detecting pitting corrosions on stainless steel weld overlay cladding using uniform eddy current testing, which is insensitive to surface undulation, and rotating eddy current testing (RECT), which can be considered a superposition of uniform eddy current testing in orthogonal directions. The performance of the two techniques in detecting artificial pitting corrosions on and next to weld beads was compared. The signal distributions revealed that only RECT was capable of describing the surface profiles of pitting corrosions. The results of uniform eddy current testing could not distinguish between pitting corrosions and cracks. The probability of detection curves drawn to quantitatively indicate the detection capabilities of the two techniques revealed that uniform eddy current testing with induced eddy currents parallel and perpendicular to weld beads was better than RECT in detecting pitting corrosions on and next to weld beads, respectively. Scanning twice by uniform eddy current testing at orthogonal orientations may be a better process for detecting pitting corrosion on weld overlay cladding compared with using RECT. The measured signals of the two techniques in normal direction were located around the edges of the pitting corrosions, which only indicated the depth around edges. The results suggested that uniform eddy current testing and RECT with normal direction magnetic field signals may be inadequate for evaluating the maximum depth of pitting corrosions or large corrosions.