Magnetic Induction Sensing of Corrosion on Steel Pipes: Feasibility, Instrument Design and First Test Results

Underground steel pipes are an essential component of the water and energy supply chains, and assessing their damage with standard techniques implies a temporary interruption in their use, often at a high cost to the operators. Evaluating the damage outside of the pipe would minimize these interruptions. In this work, we propose a new approach to investigating corrosion by taking advantage of the reduction in the steel's magnetic permeability resulting from it. To enhance these variations, the pipe is excited by a static magnetic field produced by a rectangular loop, inducing magnetization in the pipe that will be weaker where corrosion is present. The secondary magnetic fields produced by this magnetization are measured using an array of triaxial magnetic sensors. A desktop study using finite-element modelling confirmed the feasibility of the approach and informed the design of a first prototype. Scans of test pipes over a custom measurement bench show that corroded zones, as well as welding joints, generate significant anomalies with a strong signal-to-noise ratio, easily identified using simple signal processing techniques. These results confirm the viability of this non-invasive magnetostatic methodology.