The shift toward renewable fuels has introduced new operational realities for refiners. While biofuels offer clear sustainability benefits, their chemical composition and processing paths create corrosion mechanisms that differ in both severity and location from those seen in traditional petroleum refining. Understanding these differences is essential for maintaining plant integrity, minimizing unplanned downtime, and protecting long-term asset value.

The whitepaper, Corrosion Mechanisms in Biofuels, outlines these differences and how to manage them effectively.

Why it Matters

Biofuel processing plants often operate under tight economic and regulatory pressures. Unexpected corrosion can drive costly repairs, limit production rates, and shorten equipment life. Early detection and accurate understanding of corrosion behavior supports safer operation and more predictable performance as feedstocks and processes evolve.

Key Takeaways

• Renewable feedstocks introduce higher acid, water, nitrogen, and chloride loads, which alter corrosion behavior.
• Corrosion risks vary by process section and can shift rapidly with feedstock composition.
• Many biofuel corrosion mechanisms are localized and difficult to detect with infrequent inspections.
• Continuous wall-thickness monitoring enables faster, data-driven corrosion management.
• Effective corrosion control is essential for maintaining reliability as biofuel adoption expands.

Biofuel feedstocks vary widely. They include fresh vegetable oils, animal fats, and waste-derived materials such as used cooking oils and greases. These materials often contain higher levels of free fatty acids, organic chlorides, nitrogen compounds, water, and solid impurities. As feedstock quality and composition change over time, corrosion risks can shift rapidly across storage, pretreatment, reactor, and downstream systems.

Upstream of hydrogen addition, free fatty acids are among the most significant drivers of corrosion. These acids cause localized metal thinning that increases with temperature and flow velocity. Unlike some corrosion mechanisms in fossil fuel processing, fatty acid corrosion forms soluble metal salts that do not form protective layers. This makes damage harder to detect and can also contribute to catalyst fouling and pressure drop.

Water plays a central role throughout biofuel corrosion mechanisms. It enables acidic corrosion by dissolving organic acids, carbon dioxide, and chlorides. Water also supports microbiologically influenced corrosion in low-temperature sections such as tank bottoms, transfer piping, air coolers, and wastewater systems. Biofuel feedstocks often absorb moisture from the environment, further increasing risk.

Downstream of hydrotreating reactors, corrosion challenges become more complex. Oxygen in renewable feedstocks is converted to water and carbon dioxide, which together form carbonic acid. In areas where process temperatures fall below the water dew point, this can lead to corrosion, particularly in high-turbulence areas such as elbows, valves, and reducers. Organic acids formed during processing can further lower pH and increase metal loss.

Additional risks include corrosion driven by ammonium bisulfide, hydrochloric acid, and ammonium chloride salts. Variations in nitrogen, sulfur, and chloride content can lead to salt precipitation, fouling, and under-deposit corrosion. These mechanisms are often highly localized and can progress quickly, especially in areas with high velocity or uneven flow distribution.

Because many of these mechanisms are sensitive to feedstock changes and operating conditions, traditional inspection intervals may be insufficient. The whitepaper highlights the role of permanently installed wall-thickness monitoring in continuously tracking corrosion at critical locations. From Roxar intrusive probes to Rosemount non-intrusive thickness monitoring, Emerson corrosion monitoring solutions provide true insight into your plant’s health and performance.

Continuous monitoring enables operators to correlate corrosion rates with feedstock selection and process events, assess the effectiveness of mitigation measures, and make earlier, evidence-based integrity decisions. Read the whitepaper and visit the Corrosion & Erosion Monitoring section on Emerson.com to help you gain a complete understanding of your corrosion and erosion risks and the effect of those risks on your plant.