ABSTRACTSeveral nickel base alloys are currently being considered for use in advanced ultra-supercritical (A-USC) boiler applications. At an operating temperature of 650°C to 750°C steam oxidation is the primary corrosion concern. However at much lower shut down temperatures steam will condense and settle into the bottom of the boiler tube bends. In this situation chloride or hydroxide contaminates could possibly lead to chloride or caustic induced stress corrosion cracking (SCC). This concern has prompted a test program to evaluate the SCC resistance of several candidate A-USC boiler tube alloys in accelerated laboratory environments. Candidate alloys UNS N07740 N06617 N07263 and N06230 were tested along with reference alloys N07718 N07750 and S34700. Specimens stressed above the yield strength were exposed to boiling magnesium chloride and boiling 50% sodium hydroxide. All candidate alloys were found to be relatively resistant to chloride SCC and significantly more resistant than reference alloys N07718 and S34700. All candidate alloys are reasonably resistant to caustic SCC though N07740 and N07750 show superior performance.