Recent Experience with Stainless Steels in FGD Air Pollution Control Service

Over the years, many materials have been used in the construction of components of wet limestone flue gas desulfurization (FGD) air pollution control systems ranging from duplex and austenitic stainless steels to highly alloyed grades of nickel-base corrosion-resistant alloys. Some recently constructed systems have experienced severe corrosion problems after short term operation, in some cases in less than one year. To better understand the corrosive attack and the conditions under which various materials may be used, operating systems were examined and both laboratory and field tests were conducted. Localized corrosion of materials in operating scrubbers was detected and examined. Conditions in various areas of the absorber vessels were investigated with conditions in some zones found to be considerably more aggressive than those in others. Samples of several different grades of stainless steels and alloys were exposed in an operating scrubber vessel to define which materials were suitable for the conditions experienced in the FGD system.