Corrosion monitoring beneath damaged coatings with localized pores on steel piles using distributed optical fiber sensors

Coated steel piles with high corrosion resistance are applied in the marine environment. However, coating damage is unavoidable during its application process, which can induce severe localized corrosion and corrosion perforation of coated steel piles, and even premature failure of the whole marine structures. Thus, in-situ monitoring of localized corrosion under coated steel pile surface is necessary to provide localized corrosion severity assessment. This study embedded a distributed optical fiber sensor inside the marine organic coating applied on the steel pile surface and monitored the localized steel corrosion under the damaged coating. The strain measured from the sensors were applied to analyze corrosion products induced coating deformation and the development and propagation of localized corrosion. The central depth models of localized corrosion pits were established based on the number of optical fibers and the relative position between the localized corrosion center and adjacent optical fibers. The parameters of the models such as expansion coefficient of corrosion area and volume expansion rate were quantified through calibration experiments. Thus, based on the corrected models and real-time monitoring data, time-dependent central depths of the localized corrosion pits were obtained, which was validated with corrosion pits of various positions and orientations on the tested steel pipes.