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