Quantitative Evaluation of Corrosion in a Thin Small-Bore Piping System Using Bobbin-Type Magnetic Camera

Nondestructive testing (NDT) methods have been developed to ensure the integrity of heat exchanger pipes. NDT systems can be used to not only locate cracks on the pipes but also evaluate the size and position of the cracks. A bobbin-type magnetic camera (BMC), an electromagnetic NDT system, was developed to inspect both the inner and outer diameters (ID and OD, respectively) for stress corrosion cracking on a small-bore piping system with a high spatial resolution at high speeds. In this paper, an algorithm that discriminates the ID cracks from the OD cracks and estimates the crack volume is proposed. Artificial ID and OD hole-type cracks which have diameter of 1-4.5 mm and depth of 0.3-27 mm were used to imitate the corrosions on a 1.27 mm thickness and 16.56 mm inner diameter copper alloy pipe to verify the proposed algorithm. The inspection results of the BMC with respect to excited frequencies from 1-9 kHz are presented. 100 % of the ID and OD cracks were discriminated, and their volumes were estimated with a standard deviation of 1.132 mm(3) for volume from 1.00-9.01 mm(3).