Magnetic imaging of corrosion under insulation using quantum well Hall-effect sensors

Abstract

Corrosion Under Insulation (CUI) is one of the most pressing issues facing industries that make use of cladded steel pipes, costing companies trillions of dollars every year to maintain them. Currently while there are few devices capable of detecting corrosion under insulation, they remain expensive, bulky, and difficult to utilise over kilometres of cladded steel pipe [1]. This research presents a prototype device using novel Quantum Well Hall Effect (QWHE) sensors. These sensors are physically small (70-micron square), made on Gallium Arsenide substrates, capable of measuring magnetic fields in the tens of nanotesla, and have a linear response ideally suited to imaging applications [2], [3]. This prototype is capable of scanning insulated or cladded steel pipes. It can detect manufactured wall thickness loss of 1mm, 2mm, and 3mm, in a 10mm thick pipe, which represent 10%, 20%, and 30% loss respectively as far as 95mm from the surface with micron level resolution. The research presented here focuses on demonstrating the accuracy of the QWHE sensor-based prototype system by comparing the measured magnetic data to a scan of the same machined pipe acquired with a high precision laser. Together these two different scans demonstrate the possibility of using a QWHE sensor in future designs aimed at tackling the pressing issue of CUI.