Metallic coating enabled optical fiber sensor for distributed corrosion monitoring

Abstract

It is important to monitor and locate internal corrosion along natural gas pipelines to prevent methane leaks and catastrophic failures. Corrosion proxy materials enable optical fiber sensors to provide insight into corrosive environments where the pipeline materials tend to corrode. A distributed optical fiber corrosion sensor was demonstrated using a metallic film-coated, single-mode optical fiber interrogated with an optical backscatter reflectometer (OBR), based on strain changes during metallic film dissolution. Electroless plating leads to inherent internal stress in the metallic coating and therefore induces strains on optical fibers. As the metallic film gets dissolved or corroded, the internal stress will be released and cause opposite changes in strain, which can be used for corrosion monitoring. The microstrains induced solely by electroless plating or metal dissolution were measured in situ and in real time using the OBR, and interferences from temperature changes and water-induced swelling were compensated through comparison between the treated section (sensitized and activated) and an untreated control section. High-pH Ni plating had a faster deposition rate with branching on the film and induced negative microstrains, whereas low-pH Ni plating had a slower deposition rate with smooth coating and induced negligible (near-zero) strains. Eletroless Fe plating with high pH didn’t cause significant microstrains. When exposed to corrosive HCl solutions, dissolution of high-pH Ni plated films induced positive microstrains, opposite to the Ni plating. The OBR allows for distributed monitoring of strain changes due to Ni dissolution, demonstrating the capability of identifying corrosion locations along the optical fiber.