The inner surfaces and components of wet limestone flue gas desulfurization (FGD) system, are exposed to very aggressive corrosive environments. Temperatures at times approach boil ing, acids can concentrate to pH levels less than 1, and chloride concentrations especially in crevice conditions often exceed 100,000 ppm. To resist these ultra-corrosive conditions advanced corrosion resistance: nickel alloys are required. Some of the most recently developed alloys offer excellent resistance to environments which have caused excessive corrosion of some of the most corrosion-resistant alloy theretofore available. This paper looks at case histories of some recent applications and compares the performance of several nickel-chromium-molybdtmum corrosion-resistant alloys. In addition, the corrosion performance of weld merits are evaluated.