A structural corrosion-monitoring sensor based on a pair of prestrained fiber Bragg gratings

Corrosion deteriorates engineering structures, in particular large structures that are designed to have long lifetimes. This note describes a fiber optic Bragg gratings-based sensor head that enables monitoring of the corrosion of such structures. A corrosion-free fiber optic network can last longer than the lifetime of a given structure and has a remote sensing capability. Fiber Bragg gratings provide clear and reliable sensor responses and can be effectively implemented on a large structure due to their multiplexing capability. Many fiber optic corrosion sensors have been developed but most are environmental sensors. In order to monitor the corrosion of a target structure and not that of the sensor itself, the corrosion of a sacrificial plate made of a material identical to that of the target structure is monitored through Bragg wavelength release of a prestrained fiber Bragg grating installed on the sacrificial plate. The sensor head contains a corrosion-resistant casing for structural installation and a reference sensor for thermal effects compensation. The compensated Bragg wavelength shift determines the corrosion-induced loss in mass per unit of surface area of the target structure. (technical design note)