Co-extruded clad tubing that had experienced approximately 18 years of service in the heat exchanger sections of a coal-fired utility boiler was examined with respect to flue gas / coal ash corrosion on the O.D., steam corrosion on the I.D., and retention of mechanical strength on part of the alloy 800H core. The corrosion-resistant cladding (a 50Ni-50Cr alloy)
generally performed well, exhibiting pitting only at a very few locations where the most severe environment had prevailed. Corrosion of the alloy 800H cores on the steamside was negligible. Tensile and stress-rupture strength of the 800H cores actually increased during service, while tensile ductility dropped moderately remaining within acceptable levels.
Keywords : boiler, clad tubing, alloy 800H, flue gas, deposit, steam, corrosion, strength