Tapered optical fiber sensor for monitoring corrosion processes of X70 pipeline steel in natural seawater

Abstract Corrosion monitoring is essential to assess the integrity of metal structures and prevent critical failures. Corrosion increased in coastal areas by the chemical reaction between moisture and sodium chloride. Because of this, different techniques have been developed for monitoring and contributing to the integrity in metal structures. However, more effort is needed to assess structural integrity in different industries. In this work, a tapered optical fiber sensor for monitoring corrosion processes in the X70 pipeline steel immersed in natural seawater is proposed and experimentally demonstrated. A DC electrochemical test was carried out to obtain potentiodynamic polarization curves, which are associated with different corrosion processes occurring in the metal samples at different electrode potentials. The fabrication process of the tapered optical fibers consisted mainly of heating the fiber with a flame and stretching it. The operating principle of the sensor was based on the interaction of the evanescent wave with corrosion products dissolved in seawater at 50 °C. The fiber optic sensor response was related to regions of the potentiodynamic polarization curve of X70-PS in seawater at 50 °C. Therefore, from 0.12 to 0.0285 μW correspond to the anodic and cathodic regions at potentials of the electrode between −2 and −0.5 V and −0.5 and 1 V, respectively. Moreover, this optical response could be correlated with some corrosion processes experienced by the metallic samples such as pre-passivation and passivation.