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Real Time Sour Water Corrosion Prediction for Fluid Catalytic Cracking Overhead System

Picture for Real Time Sour Water Corrosion Prediction for Fluid Catalytic Cracking Overhead System
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Crude feed often contains contaminants / heavy amounts of sulfur compounds that may degrade equipment or even the finished product. These sulfur and nitrogen compounds react with hydrogen to form hydrogen sulfide (H2S) and ammonia (NH3) within certain units and can lead to formation of ammonium bisulfide salts (NH4HS) when cooled. NH4HS salts may lead to plugging, and if wet, rapid under deposit corrosion can occur. Hence, water washing ahead of NH4HS salt formation is essential to prevent wet salt corrosion and ensure safe unit operations.

Product Number: 51323-18785-SG
Author: H. Li, P. Constantineau, C. Zhuang, Y. H. Hou
Publication Date: 2023
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$20.00
$20.00

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.

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.

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As a result of a Carbonate Stress Corrosion Cracking (CSCC) event at one refinery an investigation was made into the cause and mitigation of CSCC. This paper outlines the information obtained and the development of tools that could be utilized by other refinery fluidized catalytic cracker units (FCCU's) to better assess risk of CSCC.
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This paper provides an introduction on carbonate cracking and Los Angeles refinery’s recent experience with this corrosion mechanism. Also included in this paper is the methodology used for developing a risk assessment for equipment and piping susceptible to carbonate stress corrosion cracking in a fluid catalytic cracking unit (FCCU) gas plant.
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Product Number: 51300-10360-SG
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Case study: A leak occurred in a Fluid Catalytic Cracking unit main fractionator overhead line elbow in June 2006. Following this leak, investigations showed acidic corrosion-erosion in the overhead circuit. This type of corrosion was unexpected in this circuit.
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