Corrosion of Carbon Steel in Sour Water From the Oil Industry

Among the corrosion problems, one of the most important present in the refining oil industry, is specifically the related to the sour water generated in primary distillation plants. Despite the efforts made in the industrial field, and in fundamental studies; the different operating conditions as well as different concentrations of pollutants, makes their control very complicated. 

The studies that have been trying to simulate the operating conditions in sour waters have increased in the last ten years, in which the characteristics of the raw obtained, have changed resulting in corrosive environments much more aggressive than before. The purpose of these studies was to try to find ways, in which various agents affect or minimize corrosion, with the purpose of determining the predominant mechanism of corrosion in such environments. 

On the other hand, carbon steel AISI 1018 is widely used as construction material in many industries due to its excellent mechanical properties and low cost . So, the evaluation of carbon steel corrosion in H2S environments is very important in the petroleum industry, as this phenomenon is responsible for costly social, economic and sometimes even human losses . The sour water is considered as waste water containing sulfides and chlorides, among other components; this kind of water is very harmful to metallic equipments that are in contact with it, producing high corrosion rates leading to failures and material drainage and spilling . An important factor involved in the process of corrosion, is the temperature, because the corrosion rate increases as the temperature increase in the corrosion medium on the reactions proceeding in pure acids.

However, this does not happen in all systems, for example, the steel AISI 304 SS; results indicated higher corrosion at high temperatures (more than 75 ºC), but at mid temperatures (between 50 and 75 ºC) corrosion rates were similar; and at low or moderate temperatures (between 25 and 50 ºC), the stainless steels are in true passive state below the transpasive region. From early studies in the same work on the corrosion behaviour of AISI 304 using anodic polarization method, it was observed, a smaller passive range at higher temperature and hence an unstable passive film. Finally, failures due to wet H2S cracking have been experienced extensively in production operations, in refining and in pipelines. Many commonly used steels and alloys are susceptible to cracking under the prevailing high temperatures, pressures and stresses.

Source:http://www.electrochemsci.org/papers/vol6/6105016.pdf