Sulfidation (w/o H2)

Processing crude slates with an escalating concentration of sulfur species amplifies sulfidation processes within the high-temperature sections of Atmospheric and Vacuum Distillation Units (CDU/VDU). This chapter aims to offer a comprehensive understanding of the sulfidation mechanism, coupled with the relationships between process variables and corrosion. Following this, we will delve into general guidelines for material selection in the context of sulfidation.

General Information

High temperature sulfidation, or simply sulfidation, results from reactions between various sulfur species and metallic materials, typically occurring at temperatures above 230°C (446°F). Sulfidation has been a presence in the refining industry since its inception; however, over the last 30 years, intensified processing of sour crudes has amplified the scale of the problem. Often exacerbated by naphthenic acid corrosion, sulfidation is considered a key and active damage mechanism that critically impacts refinery operations.

Primarily associated with distillation units (CDU/VDUs) and sulfur recovery units (SRUs), sulfidation is also present in other units such as fluid catalytic cracking (FCC) or delayed coking units (DCU). Refinery operators typically do not observe critical sulfidation impacts on units downstream of CDU/VDU when processing sweet crudes ((S_total <0.6wt%)). However, as the sulfur level in the processed crude oil increases, the risk of sulfidation rises, especially in units like FCC where e.g., furnace tubes, typically made of low alloy steels (typically 5% or less chromium). Therefore, if the total sulfur content in the feed (crude slate) increases, it is crucial to revisit the corrosion risk assessment, considering sulfidic corrosion not only in CDU/VDU but also in all units potentially affected by sulfidation. Table 1 provides a list of units and process areas likely impacted by sulfidation. ¹

Sulfidation is governed by a combination of several factors, including the type and concentration of sulfur compounds, temperature, and flow regime.

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Tools

Below is a user-friendly calculator to estimate sulfidation rate. Calculator is based on modified McConomy curves.

To calculate sulfidation corrosion rate please select the material and provide the inputs for Temperature and Total Sulfur. Corrosion rate is displayed in mm per year.

Calculator provides basic sulfidation corrosion rates only. It does not include impact of other important parameters like fluid dynamics or naphthenic acid interactions. Please remember that Total Sulfur may not reflect actual corrosivity due to distribution of specific sulfur species as highlighted earlier in the text.

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Calculator

Sulfidation Calculator

NOTICE: The provided tool is for advisory purposes only. Corrology Innovations Limited and its employees shall not be held liable for any damages, resulting from the use or inability to use the information provided.

References

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