Abstract
The chemical degradation of alloy components in sulfur-containing environments is a major concern in oil and gas production. This paper discusses the effect of elemental sulfur and its simplest anion, sulfide, on the corrosion of Cr-Mo alloy steel at pH 2 and 5 during 10, 20 and 30 h immersion in two different solutions. 4130 Cr-Mo alloy steel is widely used as tubing and tubular components in sour services. According to the previous research in aqueous conditions, contact of solid sulfur with alloy steel can initiate catastrophic corrosion problems. The corrosion behavior was monitored by the potentiodynamic polarization technique during the experiments. Energy dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) have been applied to characterize the corrosion product layers after each experiment. The results show that under the same experimental conditions, the corrosion resistance of Cr-Mo alloy in the presence of elemental sulfur is significantly lower than its resistance in the presence of sulfide ions.
Highlights
For more than 40 years, elemental sulfur deposition in pipelines and facilities has become a major concern in the sour oil and gas industry [1]
It is known from prior research that the presence of dry elemental sulfur in contact with carbon steel is not considered as a corrosion threat to steel; by adding water to the system, the corrosion process may be dramatically accelerated [2]
MacDonald et al hypothesized that an electrochemical reaction between iron and polysulfide could be the driving force for a corrosion process where elemental sulfur is present [4]: (x − 1)Fe (s) + Sy−1 S2− + 2 H+ → (x − 1) FeS (s) + H2 S (g) + Sy−x (s)
Summary
For more than 40 years, elemental sulfur deposition in pipelines and facilities has become a major concern in the sour oil and gas industry [1]. MacDonald et al hypothesized that an electrochemical reaction between iron and polysulfide could be the driving force for a corrosion process where elemental sulfur is present [4]:. Fang et al investigated the corrosion behavior of carbon steel at different temperatures with molten sulfur on the steel surface [5,6]. These investigations comprehensively studied the sulfur hydrolysis and direct sulfur/iron reaction, with either an electrically insulating or conductive barrier placed between the sulfur droplet and the metal surface
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