Pulsed eddy currents for estimation of remaining ligament under steel corrosion scabs
V Demers-Carpentier, M Rochette, S Champagne, D Deschatelets, M M Sisto and A Potvin
Eddyfi Technologies, Québec G1P 0B, Canada
Tel: 1 418 780 1565; Web: www.eddyfi.com
Atmospheric corrosion of low-carbon steel structures may result in corrosion product build-up on the steel surface. This build-up, or corrosion scab, may be several millimeters thick and prevents the use of many non-destructive techniques for the estimation of the remaining steel wall thickness. Typically, surface preparation and scab removal are not recommended due to safety considerations and the risk of pipe leakage, forbidding conventional ultrasonic and visual inspections. Radiographic methods are commonly used on scabs but are limited to relatively small structures. Also, accurate wall loss estimation may be challenging on areas with severe and irregular corrosion. Pulsed eddy currents (PEC) technology is an established technique for the estimation of wall loss under scabs on low-carbon steel structures. PEC can be applied to large structures, such as vessels or large-diameter pipes and requires no surface preparation. However, PEC inspection on thick scabs is non-trivial because large build-ups of corrosion material may distort the PEC signal, affecting the accuracy of wall loss estimation. In this communication, the authors analyse the effect of corrosion material on the PEC signals and propose several mitigation techniques. Experimental evidence of the effectiveness of these techniques is reported, based on studies on ex-service and manufactured pipe samples.
