Feasibility of magnetic fiber-optic based corrosion sensor

Abstract

A fiber optic based corrosion sensor utilizing the magnetic interaction force is proposed. The sensor aims to detect corrosion in structures, which are made from ferromagnetic materials (e.g. pipelines made of carbon steel). It consists of a beam that is made from a non-corrosive material with embedded Fiber Bragg Grating (FBG) sensor and a permanent magnet. The beam is placed in a position such that the permanent magnet is within a few millimeters away from the ferromagnetic material to allow for the generation of the magnetostatic attraction force between the sensor and the pipe. The corrosion causes a reduction in material thickness, which increases the distance between the material and the magnet, thus the attraction force will decrease. This change in the force can be related directly to the change in the strain measured by the optical fiber as it causes a shift in the wavelength of the reflected light. We present initial analytical investigation of the feasibility of the proposed concept for practical application of monitoring the external corrosion process on the exposed pipelines. The estimated magnitude of strain change due to corrosion is within the measurement range of typical FBG strain sensors.