Correlation between the degree of corrosion and ultrasonic parameters in steel [abstract]

Abstract

In metallurgical engineering corrosion is considered as one of the main reasons for the failure of metallic components. Inaccurate estimations, inaccessibility of the areas of failure, limitations for the destructive tests can be identified as some of the main reasons for the wrong and misleading preliminary corrosion investigations, which tead to catastrophic failures. Conventionally, the degree of corrosion is determined using destructive testing methods which are practically difficult, and to certain extend, inaccurate. In contrast, Ultrasonic testing methods would be more effective and convenient to overcome above limitations and open a new area of estimating the degree of corrosion accurately. 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. In conclusion, since corrosion penetrates as pits beyond the general corrosion layer, conventional weight loss analysis cannot give a complete picture of the actual corrosion. Also ultrasonic attenuation coefficient linearly increases with the corrosion rate as well as with the degree of corrosion. Ultrasonic attenuation coefficient is affected both by the general corrosion and by the formation of the pits beyond the general corrosion. As such, ultrasonic attenuation coefficient measurements can be used to estimate the degree of corrosion in inaccessible regions. Ultrasonic shear wave velocities can also be used for this purpose. However, further studies are required on this area.