The environment in waste incineration plants contains high concentrations of chloride, alkalis, sulfur, and low temperature melting species. This corrosive environment along with a need to fulfill the pressure vessel code requirement, calls for a dual purpose material in the waterfalls and superheaters of the boiler. Composite tubes consisting of a corrosion resistant cladding metallurgically bonded to the load-bearing core, make it possible to optimize both of the before mentioned requirements while meeting the demands for higher efficiency in waste-to-energy plants. During the last years several field tests of composite tubes have been performed. The experience of these tests will be the subject of this paper. Alloy 825 mod (UNS N08825 mod), Alloy 28 (UNS N08028), Alloy 65 (UNS N06625 mod) and AIloy 625 (UNS N06625) were evaluated as superheater tubes. Among these the Alloy 625 showed the best performance and it was estimated that the corrosion rate is about 10-20 times lower when compared to carbon steel. The superior corrosion resistance of Alloy 625 was due to its high Mo content in
combination with either a low Fe content or a high Nb content. All tested alloys suffered from corrosion neat sootblowers. However Alloy 625 corroded but at a considerably lower rate than the other materials. At a material temperature of about 54°C (1000°F) the wastage of Alloy 625 was ...
Keywords: high temperature corrosion, corrosion rate, waste incineration, field test, superheaters, evaporators, waterfalls, composite tubes