Breakage of floating head bolts in the acidic water cooler of the sulfur unit in a petrochemical refinery
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This post was last edited by Wang Wei2 on 2024-5-25 at 17:19. The floating head bolts of the acidic water cooler in the sulfur unit of a petrochemical refinery broke. Shortly after the sulfur unit began operation, the small floating head bolts of the acidic water cooler in the distillation section broke twice; as a result, large amounts of acidic water flowed into the circulating water system, severely contaminating it and causing corrosion in the coolers of other units. The original design material was 2CR13, with a hardness exceeding HB300; stress corrosion cracking occurred under acidic water conditions. The hardness of the bolts after the first replacement was around HB250, and fracturing occurred again. The hardness was specified to be less than HB200 for the second time; the bolt materials used were Q235 and 2CR13, and no issues were encountered after they were put into use. The reason is that the design does not specify the hardness of the bolts, and it is safer to use a U-tube cooler. Corrosion environment at the top of the distillation tower: H2O+HCL+H2S (H2O+NH4Cl+H2S), H2O+HCL+H2S+NH3+CO2+SOX+(organic acids with C1-C5 structure), NH4Cl+NH4HS. Corrosion mechanism: uniform corrosion caused by hydrochloric acid + corrosion under ammonia salt scales. Consequences: equipment corrosion, with chlorine, ammonia salts, and water present in the side stream oil
The small floating head bolts of the acidic water cooler in the sulfur plant fractured due to stress corrosion cracking, as no hardness standard for these bolts was specified during the design phase. Later, the problem was solved by reducing the bolt hardness and using two materials: Q235 and 2CR13. Corrosion environments are complex, containing various corrosive agents that cause equipment corrosion and pose safety risks. .
Hardness isn’t the main influencing factor; it’s probably the material itself. The corrosion caused by pickling water has a significant impact on carbon steel
It is mainly a matter of material selection for the design; regular 35CrMo bolts are used.