Case of hydrogen bubbling corrosion in refining equipment
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I. Hydrogen bubbling accident in the cooler for catalytic stabilization and absorption of off-gases at the Victory Refinery. The operating conditions of this cooler are as follows: gas inlet temperature of 45°C, outlet temperature of around 40°C, pressure of 1 MPa; the gas contains 6% H₂S, 0.1% CN⁻, and a small amount of water, and the material used for construction is 16Mn. Within less than 1 year of operation, the casing developed noticeable hydrogen bubbling, cracking due to those bubbles, and weld corrosion; this is a typical case of hydrogen bubbling failure in low-strength steel under a wet environment containing hydrogen sulfide and cyanide ions. The failure mechanism involves hydrogen atoms generated in the solution diffusing into the metal, where they combine to form hydrogen molecules within the pores of the steel. Since these hydrogen molecules cannot diffuse away, they accumulate and create high internal pressures, ultimately causing bulging or even cracking of the steel surface. II. Hydrogen blistering and cracking accident in LPG storage tanks: During a routine inspection, multiple irregular bulging defects were found in one LPG storage tank. Analysis confirmed that the existing delamination defects within the steel plates, combined with excessive hydrogen sulfide present in the stored medium, led to hydrogen blistering and cracking. This is a typical example of hydrogen blistering corrosion in the oil refining and storage processes. III. Hydrogen bubbling corrosion in catalytic stable absorption systems. The stable absorption systems in petroleum refining catalytic units operate in an environment subjected to corrosion by H₂O, H₂S, HCN, and NH₃; such conditions readily lead to hydrogen bubbling and hydrogen-induced cracking in the equipment. This represents a very typical scenario of hydrogen-induced damage during the direct processing of highly acidic oils, and similar cases of corrosion have been recorded in the relevant units of various petroleum refineries in China.
Thank the original poster for sharing this very typical case of hydrogen bubbling. Just by looking at the operating conditions and materials, it’s clear that this is a classic case of stress corrosion caused by wet hydrogen sulfide in low-strength steel. I would like to add a few of my own insights from dealing with such accidents for reference: 16Mn (now commonly the Q345 series) is indeed very sensitive in environments containing H₂S and CN⁻ along with water; in particular, cyanide ions in the medium facilitate hydrogen penetration. It is recommended to consider using HIC-resistant (hydrogen-induced cracking) steels when selecting materials in the future, for example in accordance with NACE MR0175/ISO 15156 requirements, while also controlling welding quality to prevent the formation of hardened microstructures. In practice, it is possible to evaluate the option of adding water for washing or corrosion inhibitors at the inlet in order to reduce local H₂S and CN⁻ concentrations. If the pH of the medium can be maintained at a slightly alkaline level, the risk of hydrogen bubbles is significantly reduced. If the equipment already shows bubbling but no perforation, it is recommended to conduct ultrasonic thickness testing and HIC testing as soon as possible to assess the remaining strength and prevent sudden leaks. In any case, this case is highly instructive; thanks for sharing! However, the specific engineering measures should still be determined by professional corrosion engineers in consideration of the on-site conditions; they must not be copied directly.