Risk analysis on formation and spontaneous combustion of FeS in gathering pipeline of Tahe Oilfield

The corrosion product FeS in the gathering pipeline of Tahe Oilfield is hypergolic. Once FeS spontaneously combusts, it will trigger fire and explosion accidents. The oil and gas in the pipeline has high contents of H₃S, CO₃ and chloride ion, and are likely to form corrosion products like FeS, etc. in the anaerobic environment with low flow velocity. X-ray diffraction test is adopted to analyze the components of corrosion products. It is found that under the coexisting condition of H₃S and CO₃, the corrosion products are mainly composed of FeCO₃, FeO(OH)and Fe₃O₄, while the sulfide of ferrum is mainly FeS with low content. Spontaneous combustion characteristics of seven corrosion products mixtures of different components are analyzed with solid spontaneous combustion point tester by heating. Results show that FeCO₃gives out heat, but it can not combust spontaneously. For the mixture of FeCO₃ and FeS, when the mass ratio of them is 15:10 and the mass fraction of elemental sulfur is 2.67%, the spontaneous ignition temperature of the mixture of FeCO₃ and FeS is 189.08 ℃ and the mixture is therefore prone to combusts spontaneously. It is suggested to take precautions to prevent FeS's spontaneous combustion in field pipeline's fire work.