Behaviour of Alloy 617 OCC Under Hot Corrosion Conditions Encountered in Boilers in A-USC Power Plants

Abstract

Superheater and reheater tubing constitute very critical parts of the boilers operating in advanced ultra-supercritical (A-USC) power plants. They are subjected to severe hot corrosion conditions during operation. The operating temperature and pressure in these power plants are very arduous, and materials with high resistance to hot corrosion and creep are required to produce the said tubing. Increased use of superalloys comes into picture in A-USC power plants, because of the demanding operating conditions prevailing there. Inconel 617 has been a superalloy developed for use in the form of superheater and reheater tubing seen in the power plants operating in A-USC environments. There have been researches aiming at improving its creep resistance, and versions with optimum chemical composition have been developed. Alloy 617 OCC, an optimized version of the superalloy 617, has been produced as a candidate material for superheater and reheater tube manufacturing in the context of development of A-USC power plant technology in India. However, hot corrosion issues are equally important for such applications. In light of the foregoing, studies have been carried out to analyse the performance of Alloy 617 OCC in hot corrosion conditions in simulated A-USC power plant environments. Oxidation tests for the alloy were conducted in the laboratory air environment under identical temperature/time conditions for the sake of comparison. Hot corrosion process was examined using thermo-gravimetry, and the corrosion products were characterized using a variety of material characterization techniques. The study reported the comparative corrosion performance of the superalloy in the two environments.