A device to measure corrosion of composite boiler tubes
Abstract
We evaluated the ability of an electromagnetic inductance (EMI) gauge to measure the cladding/overlay thickness of composite boiler tubes. The evaluation was based on cladding/overlay thickness measurements made on sections of composite tubes provided by suppliers, on a simulated corroded sample and on existing and replacement composite tubes in a recovery boiler. We conclude that the device is capable of providing accurate cladding/overlay thickness measurements when calibrated using a co-extruded standard, and, when multiple measurements are made on a specific location as a function of time. A significant finding was that Alloy 625 weld overlaid composite tubes are susceptible to considerable localized corrosion in less than 12 months of exposure. Consequently, Alloy 625 composite tubes may not be the universal solution to the corrosion-related problems affecting waterwall and floor tubes in recovery boilers.