Monitoring saltwater corrosion of steel using ultrasonic coda wave interferometry with temperature control

• Published in: Ultrasonics 2022-08, Vol.124, p.106753-106753, Article 106753
• Main Authors: Farin, Maxime, Moulin, Emmanuel, Chehami, Lynda, Benmeddour, Farouk, Nicard, Cyril, Campistron, Pierre, Bréhault, Olivier, Dupont, Lucie
• Format: Article
• Language: English
• Subjects: Coda wave interferometry; Corrosion; Engineering Sciences; Non destructive testing
• ISSN: 0041-624X; 1874-9968
• DOI: 10.1016/j.ultras.2022.106753

Assessing corrosion is crucial in the petrochemical and marine industries. Usual ultrasonic methods based on pulse-echo and guided waves to detect corrosion lack of precision and struggle in structures with a complex shape. In this paper, a complementary and sensitive ultrasonic method based on coda wave interferometry is presented to detect and quantify thickness loss caused by saltwater corrosion of a steel sample. The method consists in exciting the sample and measuring periodically the scattered coda signal. Correlation of the coda signal with a reference taken for the sample initial state permits the monitoring of corrosion spread with a high accuracy. A laboratory experiment is conducted with two steel samples immersed in saltwater with coda and temperature measured simultaneously. One of the samples is protected from corrosion and is used as a control sample to determine the influence of temperature on the coda signals. It is shown that the coda signals on the corroded sample can be temperature-corrected using the temperature measurement only. A control sample is not needed. A good correlation is found between a parameter quantifying the stretching of the coda over time and the corrosion surface, which is monitored with a camera. Finally, a simple theoretical model of coda signal is proposed to quantify the real-time average corrosion rate during the experiment with a sub-micrometric precision. The estimated final average corrosion depth is validated by independent depth profile measurements. The uncertainties and sensitivity of the presented method are investigated. •An ultrasonic method is presented to monitor saltwater corrosion on steel.•The method, based on coda wave interferometry, is more sensitive than standard ultrasonic methods.•The coda dependence to temperature is corrected using a reference sample or temperature.•A laboratory experiment is conducted in saltwater with temperature and coda measurements.•The temperature-compensated coda stretching factor correlates with the early corrosion surface.•The instantaneous corrosion depth is quantified with a simple coda model and validated.