Ultrasonic monitoring of steel corrosion during accelerated corrosion testing and outdoor field exposures

As corrosion is a major issue for many industries, numerous inspection and monitoring techniques have been developed to assess corrosion level and integrity of metallic structures. Amongst them, ultrasonic measurements are widely used to monitor or control wall thickness and, in general, thickness loss by the corrosion of these structures. However, in most cases, the accuracy of these measurements is in the order of hundreds of micrometers for corroded materials. For laboratory corrosion tests such as accelerated corrosion tests developed by automotive manufacturers, a higher accuracy level is needed and classical evaluation methods such as weight loss measurements are normally used. However, these measurements are destructive and do not provide information on the kinetics of degradation.
Following recent works by Ström and co workers, the aim of the present work was to qualify the use of ultrasonic measurements for an accurate monitoring of steel corrosion during accelerated corrosion tests and, more generally, during outdoor field exposures.
So, in this work, wall thickness of cold rolled steel panels was continuously monitored during several accelerated corrosion tests. Results of ultrasonic measurements were compared to classical evaluation methods (e.g. mass loss or micrometer). Ultrasonic measurements have also been used on steel panels exposed in severe environments, e.g. on the deck of a ship. The results of these experiments clearly showed that non destructive ultrasonic measurements provided corrosion data as accurate as classical methods and, moreover, it allows direct and in-situ measurements of the corrosion rate of steel.
Keywords: corrosion monitoring, ultrasonic, accelerated corrosion test, steel