Multipoint fiber-optic-based corrosion sensor

Abstract

We present an optical fiber sensor for the corrosion process in metal (Aluminum) using the optical time domain reflectometry (OTDR) technique. Our proposed sensor system consists of several sensor heads connected to a commercial OTDR by a single-mode optical fiber and fiber couplers. Each sensor head consists of an optical fiber having the cleaved end coated with an aluminum film. For laboratory measurements the corrosion action was simulated by controlled etching of the Al film on the sensor head. The OTDR detects the light reflected by each sensor head. As the aluminum is etched the reflection decreases and the etch rate can be obtained from the OTDR traces. We present experimental results for the measurement of the corrosion rate of aluminum films in controlled laboratory conditions and also for the evaluation of the maximum number of sensor heads the system supports. Our proposed sensor system is multipoint, self-referenced, has no moving parts and can detect the corrosion rate for each head several kilometers away from the OTDR. This system may have applications in harsh environments such as in deepwater oil wells, for the evaluation of the corrosion process in the inner wall of the casing pipes.