Corrosion and Protection of High-Temperature H2 in Petrochemical Industries
Thread Content
I. Corrosion mechanisms: High-temperature H₂ corrosion in the petrochemical industry occurs primarily in hydrogen-rich environments at temperatures of 300–480°C within hydrogenation units. The core mechanism is high-temperature hydrogen attack (HTHA): hydrogen atoms diffuse into the steel, react with unstable carbides to form methane, resulting in surface decarburization or intergranular cracks, which leads to irreversible deterioration of the material’s mechanical properties. In hydrogen-rich conditions containing H₂S, hydrogen also destroys the integrity of the sulfide protective film, allowing H₂S to penetrate continuously and accelerating corrosion; this is more harmful than sulfur corrosion alone at high temperatures. II. Core protective measures: Material selection – Hydrogen-resistant steel should be chosen based on the Nelson curve; chromium-molybdenum steel containing Cr and Mo elements is preferred to enhance the stability of carbides ； When the corrosion rate exceeds 0.2 mm/a, a stainless steel composite plate or a surfacing weld structure should be used, with low-carbon stainless steel available as the coating material. Process control: Maintain the operating temperature and hydrogen partial pressure within the limits permitted by the material, to prevent operation under conditions of excessive temperature or pressure, and at the same time reduce the concentration of corrosive components such as H₂S in the medium. Manufacturing optimization: Strict post-weld heat treatment is applied to chromium-molybdenum steel equipment to prevent residual stresses from reducing the material’s resistance to hydrogen corrosion.
The original poster has summarized it very well; high-temperature hydrogen corrosion (HTHA) is indeed one of the most troublesome problems in hydrogenation units. The use of Nelson curve-based material selection and cladding/composite plate protection, as you mentioned, are already established practices in the industry. However, there are two points to add regarding actual implementation: details of welding and heat treatment – even if the appropriate chromium-molybdenum steel is selected, poor control of the parameters during post-weld heat treatment (PWHT) can still result in localized softening or residual stress areas near the welds, thereby creating a risk of hydrogen-induced cracking. It is recommended to determine the heating rate and holding time based on the on-site welding procedure qualification. Online monitoring and inspection: For equipment in operation, it is necessary to conduct regular ultrasonic testing (especially focusing on the decarburized areas and welds) as well as rechecks of hardness, since early hydrogen-induced damage may not be visible to the naked eye. Additionally, hydrogen escape detection (such as hydrogen probes) can also assist in determining the hydrogen content of materials. If you are designing a new device or troubleshooting an existing issue, it is recommended to provide detailed operating conditions (such as the H2S content in the medium and the range of operating pressure fluctuations), as this will enable a more accurate assessment of the risks. The above is merely a sharing of general experience; specific recommendations should be determined by referring to relevant standards (such as API 941) and the opinions of material experts.