[Haichuan Anti-Corrosion Knowledge] Amine Corrosion and Protection Mechanisms in the Refining and Petrochemical Industry | Influencing Factors | Protection Strategies

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Amine corrosion and protection mechanisms | Influencing factors | Protection strategies In the petroleum refining, natural gas processing, and chemical industries, amine units are primarily used to remove acidic gases such as H2S and CO2. However, the amine solution itself, as well as the \"amine-rich solution\" formed after it absorbs acidic gases, can cause severe corrosion to carbon steel and alloy materials. The following is an in-depth technical analysis of the mechanism of amine corrosion and its prevention strategies: 1. Main types and mechanisms of amine corrosion. Amine corrosion is not caused by pure amines alone, but rather results from the combined effect of amine solutions, acidic gases, degradation products, and process conditions. A. Amine stress corrosion cracking (Amine SCC) is the most dangerous form of failure, typically occurring in the welds and heat-affected zones of carbon steel equipment. Cause: The combined effect of residual tensile stress and the amine solution environment. Features: The cracks are usually branched and tend to propagate through or along the grain boundaries. This can occur in carbon steel that has not undergone post-weld heat treatment (PWHT), even at room temperature. B. Corrosion by acidic gases (wet H2S and CO2): Hydrogen damage: In an H2S environment, hydrogen atoms penetrate into the steel, leading to hydrogen embrittlement, sulfide stress cracking (SSC), or stress-oriented hydrogen-induced cracking (SOHIC). Uniform CO2 corrosion: CO2 dissolves in water to form carbonic acid, resulting in localized ulcerative corrosion or widespread thinning. C. Amine degradation products and heat stable salts: Amines degrade under high temperatures or in aerobic conditions, producing heat stable salts (such as formates, acetates, and oxalates) that are highly corrosive. HSS will destroy the passivation film on the metal surface. When the HSS content exceeds 1%–2%, the corrosion rate increases exponentially. D. Erosion-corrosion: In areas with high flow rates (such as the outlets of lean/rich liquid heat exchangers and behind control valves), the gas-liquid two-phase flow mechanically washes away the protective iron sulfide film on the surface, accelerating corrosion. 2. Key factors affecting corrosion: Type of amine: The corrosivity of diethanolamine (DEA) and methyldiethanolamine (MDEA) is generally lower than that of mon ethanolamine (MEA). Rich liquid load: The higher the acidic gas load, the greater the corrosivity. It is generally recommended to keep the following levels under control: oMEA: ≤ 0.35 – 0.40 mol/mol; MDEA: ≤ 0.45 – 0.50 mol/mol. Temperature: An increase in temperature accelerates the chemical reaction. The reboiler and the bottom of the regeneration tower are areas prone to corrosion (usually kept below 120°C). Solid impurities: Particulates such as iron sulfide powder can wear the sealing surfaces and impellers. 3. Protection and mitigation strategies: Material selection. Carbon steel + PWHT: For amine systems, the API 945 standard mandates post-weld heat treatment (PWHT) for all carbon steel equipment and pipelines in order to eliminate residual stresses and prevent Amine SCC. Applications of stainless steel: 304L or 316L stainless steel is used in high-temperature areas such as the top of regenerator towers, reboiler tubes, and lean/rich liquid heat exchangers. Duplex steel: For areas subject to severe erosion, 2205 duplex steel can be considered. Process control and monitoring: Control of HSS content: Keep the content of thermally stable salts at low levels using amine purification units (online ion exchange or vacuum distillation). Deoxygenation: Prevent oxygen from entering the system (e.g., by using nitrogen-filled storage tanks) to avoid the oxidative degradation of amines. High-efficiency filtration: Mechanical filters and activated carbon filters are used to remove solid particles and hydrocarbons. Corrosion inhibitor application: In some systems, film-forming corrosion inhibitors are added to form a protective film on the metal surface. Corrosion monitoring technology – Strip testing: Regularly check for thinning of the material. Online probe: Monitors changes in corrosion current in real time. Ion analysis: Regular sampling is carried out to analyze the iron ion content and HSS components in the amine solution. 4. In the design and operation of amine treatment systems, \"stress elimination\" and \"impurity control\" are fundamental. Post-weld heat treatment (PWHT) of carbon steel is the cornerstone for preventing cracking, while controlling operating temperature and the cleanliness of the amine solution are key to extending the lifespan of the equipment.