In the past, the presence of ammonium bisulfide (NH4HS) or ammonium chloride (NH4Cl) in hydrotreater stripper overheads was relatively rare. However, designs of newer units and revamps to older units, are resulting in corrosive levels of NH4HS or NH4Cl in overhead systems. This is primarily due to the addition of a hot high pressure separator (HHPS) with the bottoms going directly (or through another separator) to the stripper. This paper presents data on one corrosion case history in detail, a summary of another case history reported in Refin-Cor 3.0 and the results of a brief survey targeted to units with HHPS designs. Some correlations of the process conditions to the severity of corrosion are made based on the survey results, and recommended materials selection and other corrosion control methods to minimize the risk of this
problem are given. Keywords: hydrotreaters, hydrodesulfurizers, ammonium bisulfide, ammonium chloride, corrosion, material selection