Sulfur Corrosion Due to Oxygen Ingress

Sulfur corrosion is usually associated with high H₂S systems but sulfur can also be deposited in systems containing small amounts of H₂S under conditions where oxygen is allowed to enter the gas stream. Oxygen ingress may be due to air drawn in by vapour recovery units on oil tanks or carried in with methanol injected for hydrate control. The solubility of oxygen in methanol is significantly higher than in water and sufficient amounts can be provided to react with H₂S and deposit elemental sulfur.  Case histories are presented where this has led to failures in pipelines and downhole equipment.