A corrosion sensor utilizing fiber optics and the magnetic attraction force is proposed. The sensor aims to detect the internal corrosion of pipelines that are made of ferromagnetic materials. Its components include a beam made of a non-magnetic material, a strong permanent magnet, and a Fiber Bragg Grating (FBG) sensor that is very sensitive to strain changes. The sensor is based on the assumption that the magnetic attraction force generated between a magnet and a ferromagnetic material decreases if the thickness of the ferromagnetic material is decreased. To generate this force between the sensor and the pipe, the beam is positioned in a way that the magnet is only few millimeters away from the pipe. The internal corrosion causes a reduction in the thickness of the interior pipe wall, which according to the assumption should reduce the attraction force. As a result, the strain measured by the optical fiber will be affected as it is directly related to the variations in force. We present an initial numerical investigation of the feasibility of the proposed working principle utilizing a Finite Element Analysis (FEA) simulation tool. Simulation results show that the attraction force first increases then saturates with the increase in wall thickness. The change in force becomes significant once the thickness reduces to a threshold value. We also investigate the effect of changing the magnet size, magnetic permeability of pipe material, separation distance between pipe and magnet, and the magnetic flux density of the magnet.
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.
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