Remote Estimation of Degree of Corrosion Using Ultrasonic Pulse Echo Methods

Even though the engineering structures are designed to achieve the potential to be very durable and capable of withstanding the degradation caused by adverse environmental conditions, failures in the structures do still happen; predominantly due to corrosion. Even though there are many conventional methods to evaluate the degree of corrosion, most of them are destructive. Though there are significant efforts made to estimate the degree of corrosion nondestructively, reliable methods are yet to be established especially, for hidden or inaccessible corrosion. Moreover, the available methods, whether destructive or nondestructive, focus only on the surface corrosion (except in the cases of intergranular corrosion [IGC] of stainless steel) completely ignoring the corrosion pits that form beyond the limits of surface corrosion. Hence, this study includes these corrosion pits in estimating the degree of corrosion. In this study, selected steel samples were subjected to accelerated corrosion conditions and then tested ultrasonically. Ultrasonic longitudinal wave velocity to shear wave velocity ratio and the attenuation coefficient were measured using Ultrasonic Flaw Detector. These measurements were done even after removing the corrosion products from the surface. SEM analysis and the conventional weight loss measurements were also carried out. The correlations obtained between the degree of corrosion and ultrasonic parameters are presented.