Subsurface Corrosion Detection in Industrial Steel Structures

Corrosion is a central problem for the oil and gas and nuclear industries, affecting pipelines and nuclear waste storage tanks. Reliable methods for timely corrosion detection and integrity evaluation are needed for a range of industrial structures where corrosion under insulation manifests as wall loss. Commercially available detection systems cannot be used in harsh nuclear-storage environments. Moreover, these systems are not reliable for detecting the inner wall thickness of industrial structures made of multiple layers of material, including insulation layers. A novel nondestructive testing method based on low-frequency eddy-current induction was developed and tested on a multilayered steel structure, including an insulating gap. The method enables through-wall thickness measurements between 4 and 16 mm, with a measurement error of 1 mm. The technique is quantitative, nondestructive, and allows the sensor coil to be positioned on the outside of the composite steel structure, which is useful when the interior of an industrial container or pipeline is not accessible.