Case of sulfide stress corrosion cracking in LPG storage tanks of refining equipment
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The following are typical accident cases of sulfide stress corrosion cracking (SSCC) in liquefied petroleum gas storage tanks of refining equipment: the \"11·6\" explosion and fire accident at Songyuan Petrochemical Co., Ltd. in Jilin Province (2011). The accident resulted in 4 deaths and 7 injuries. The involved gas fractionation unit’s deethanizer top reflux tank suffered from sulfide stress corrosion in a wet hydrogen sulfide environment; microcracks formed first in the heat-affected zone of the tank shell head welds and gradually expanded, eventually leading to overall fracture and a physical explosion. A large amount of liquid hydrocarbons in the tank leaked out, and upon contact with an open flame, this resulted in a flash explosion and fire. Post-event metallographic testing confirmed that the tank body exhibited extensive delamination, which is a major cause of hydrogen sulfide stress corrosion cracking. Such damage occurs without any obvious precursors and represents a typical case of delayed failure. Case studies of common stress corrosion cracking hazards in liquefied petroleum gas spherical tanks at refineries: In multiple domestic refineries, due to excessive hydrogen sulfide levels in the medium, and under the combined effects of a humid hydrogen sulfide environment, residual welding stresses, and high-strength steel materials, stress corrosion surface cracks were detected in the welds and heat-affected zones of numerous operational spherical tanks. Such cracks occur primarily in the vicinity of the welds, in line with the principle that \"the higher the surface hardness of the weld, the lower the critical stress value for SSCC and the faster the cracking rate.\" This represents a significant risk factor for liquefied petroleum gas storage tanks in the oil refining industry.
Thank you for sharing; this case is very typical. Stress corrosion cracking in a humid hydrogen sulfide environment is indeed a long-standing problem in the petrochemical industry. I would like to add two points: Such accidents often occur in the heat-affected zone of welds and at the layers in the base material, which indicates that welding process control and the quality of the base material (such as layering defects) are key areas that need to be carefully monitored and controlled. If possible, it is recommended to conduct regular ultrasonic and hardness tests on operational storage tanks, paying special attention to the areas that have been cold-formed or shaped. From a design perspective, it is recommended to use steel resistant to SSCC (such as quenched and tempered low-alloy steel), and to strictly control the operating temperature