Fiber optic-based magnetostrictive sensor for monitoring pipe wall thickness

This article presents a novel sensor concept for continuous long-term monitoring of pipe or tank wall thickness that is based on strain measurements in a magnetostrictive material. The proposed sensor detects wall thinning in pipes or tanks by monitoring magnetic flux leakage (MFL) generated during corrosion or erosion. Leakage flux induces strain in a magnetostrictive element, which is measured with a fiber optic strain sensor. Apparent thermal strains are compensated by incorporating a nonmagnetic reference material with similar thermoelastic properties. Numerical simulations were carried out to evaluate the influence of key geometric parameters on sensitivity and to guide component sizing for a prototype design. The prototype was fabricated and tested on steel coupons of varying thickness. Experimental results indicate a sensitivity of approximately 1.16 μϵ per mil of wall loss, comparable to the performance of conventional MFL sensors employing pick-up coils or Hall effect devices. The proposed sensor concept offers important advantages for applications in the energy industry: it is noninvasive, requires no power supply, is safe in volatile environments, allows real-time continuous data collection, and can be deployed in remote locations over very large distances.