Abstract
Crude feed often contains contaminants such as sulfur and nitrogen compounds, which can react with hydrogen to form hydrogen sulfide (H2S) and ammonia (NH3) and can lead to formation of ammonium bisulfide salts (NH4HS) when cooled. Water washing ahead of NH4HS salt formation is a common practice to prevent wet salt corrosion. However, the dissolved ammonium bisulfide (in the aqueous phase) can still cause significant corrosion across equipment exposed to alkaline sour water. Such corrosion may be exacerbated by presence of cyanides, high levels of wall shear stress as well as high operating temperatures. A corrosion model developed by author’s organization, was utilized in this work to perform real time sour water corrosion predictions for a Fluid Catalytic Cracking (FCC) unit overhead piping and downstream equipment. The model stems from a comprehensive database generated from three phases of extensive Joint Industry Project (JIP) research on NH4HS corrosion. The corrosion model is integrated with a real time framework, which collected relevant operating parameters (temperature, pressure, flow rates etc.) from the Process Historian automatically and enabled real time predictions for corrosion rates along with other important parameters related to flow and water chemistry. Metal loss was calculated by continuous tracking the corrosion rates. The software was run for about three months and demonstrated good agreement between predicted metal loss and field inspection results.
