PTQ Q4 2025 Issue

Corrosion in amine units using MEA solvents for deep CO 2 removal: Part 3

Conversion of MEA solvent to the less corrosive MDEA solvent was performed to avoid corrosion

David B Engel, Scott Williams, and Cody Ridge Nexo Solutions

P art 3 completes the series on corrosion in amine units when using monoethanolamine (MEA) solvents for deep CO₂ removal, published in PTQ Q1 2025 (Part 1) and PTQ GAS 2025 (Part 2) . This article focuses on the solvent conversion from MEA to a less corrosive solvent. Corrosion of carbon steel in amine units has been well reported elsewhere. However, corrosion of stainless steel in amine units has not been given much attention. There are several reasons for experiencing stainless steel corrosion in amine units. One of the most common causes of corrosion is the presence of chlorides. The amine unit discussed in the article uses MEA as the solvent and has suffered from consistent stainless steel corrosion caused by high chloride (Cl - ) content in the solvent, as well as corro - sion in the lean amine side caused by poor regeneration. Hot lean amine solvents exiting the regenerator with higher loading than specified can cause considerable corrosion. Additional details on this amine unit and its associ- ated corrosion challenges were discussed in Parts 1 and 2. Usually, the maximum chloride content in amine units ranges between 250 and 500 ppmw. As Figure 1 shows, the chloride levels in the amine unit solvent are consist- ently within or above the maximum range. Chlorides cause chloride stress corrosion cracking (CSCC) of stainless steel, often aggressively. This process is sometimes described as ‘harsh pitting’. Contrary to this, carbon steel is often too soft to crack in the presence of chlorides. Suspended solids Another reason for stainless steel corrosion is the presence of large amounts of suspended solids, generating fouling over surfaces and causing a loss of local oxygen, with subse - quent loss of the protective oxide layer. Solids in amine units are often associated with corrosion products in the unit itself or poor filtration. Lately, several different contaminants have been observed to be causing suspended solids in the amine solvent, entering with the feed gas. Stainless steel tempera - ture probes had recently been installed in the amine unit, but they corroded rapidly and apparently did not have significant solids covering them when extracted (see Figure 2 ). The probe likely suffered from CO₂ pitting and CO₂ cav - itation from CO₂ release. It is also possible that the probe was sitting in stagnant liquid, where the chlorides content in

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Figure 1 Chloride ions in the MEA amine solvent solution

the solvent was enough to disrupt the protective oxide film, resulting in steel pitting. The probe showed distinct rounded pits often associated with CO₂ attack. Possibly, the high lean amine loading contributed to the attack along with chlorides. It is also possible that the probes were made with a grade of stainless steel with poor chloride resistance (for exam- ple, 410SS or 304SS). 316L should be the stainless steel of choice in facilities operating with elevated chloride levels. Operational changes The amine unit was operating with a high lean and rich amine loading. High rich amine loadings corrode carbon steel rapidly. Normally, to lower the rich amine loading

Figure 2 Corroded stainless steel temperature probe

PTQ Q4 2025