This paper addresses hydrogen absorption of carbon steels caused by wet ammonium bi-sulfide (NH4HS) corrosion that occurs in effluent condensers of hydroprocessing units in refineries. Although it had been considered that hydrogen absorption of steels in wet H2S solution would be negligible in non-acidic conditions except for those containing cyanide (CN), our previous study confirmed that hydrogen absorption of steels was accelerated even in CN free non-acidic wet H2S environment at elevated temperature1). In this study, hydrogen absorption of steels in a wet NH4HS environment was investigated. Hydrogen absorption in low and high NH4HS solutions at elevated temperatures was observed which appeared to be associated with flow velocity and solution
temperature.