Influence of the Hydrogen Sulfide Concentration on the Corrosion and Hydrogenation of Pipe Steels (A Survey).

We consider the process of corrosion of steels in hydrogen-sulfide media of different concentrations with regard for the specific features of the formation of sulfides of different chemical compositions and their influence on the course of redox reactions. We present different points of view on their role in corrosion processes. On the basis of generalization of the influence of iron sulfides on electrode reactions, release and absorption of hydrogen by Armco iron, U8 steel, and 45 steel of different structures, it is established that, despite the fact that iron sulfides mainly reduce the overvoltage of cathodic reactions and increase the amount of hydrogen released under cathodic polarization, they do not always promote the hydrogenation of these materials. Iron sulfides predominantly affect the reaction of hydrogen release, whereas its absorption depends on the structures of steels. By an example of 17G1S-U steel, we show that the corrosion rate is affected by the nature of sulfides formed on the surface. Indeed, for their concentrations varying within the range 25–100 mg/dm3, the corrosion rate decreases by almost an order of magnitude. Moreover, for hydrogen-sulfide concentration CH2S ≥ 500 mg/dm3, we observe the formation of porous sulfides, corrosion defects are localized, and the intensity of absorption of hydrogen by steel becomes almost twice higher than at lower concentrations, which promotes the development of cracking and corrosion cracking. It is shown that the critical concentration for the development of hydrogen- sulfide corrosion cracking of steels of this class is CH2S ≤ 100 mg/dm3. [ABSTRACT FROM AUTHOR]