Abstract
Surface corrosion product formation is one of the important factors affecting the corrosion rate and hydrogen uptake in a H2S environment. However, it is still unclear how the base material composition will affect the corrosion products that are generated, and consequently their impact on the corrosion rate. In this paper, corrosion product formation and the impact of the Mo content of the base material on the composition of the corrosion products and hydrogen absorption in a sour environment was investigated. The corrosion layer was composed of a double layered mackinawite (FeS1−x) structure, which was enriched with molybdenum and chromium. The layers were formed via two different mechanisms, i.e., the inner layer was created via a general oxide film formation corrosion mechanism, whereas the upper layer was formed by a precipitation mechanism. The presence of this double corrosion layer had a large influence on the amount of diffusible hydrogen in the materials. This amount decreased as a function of contact time with the H2S saturated solution, while the corrosion rate of the materials shows no significant reduction. Therefore, the corrosion products are assumed to act as a physical barrier against hydrogen uptake. Mo addition caused a decrease in the maximal amount of diffusible hydrogen.
Highlights
IntroductionThe interaction between steel and the H2 S containing surrounding environment results in the formation of a Fex Sy corrosion product
In the oil and gas industry, the presence of H2 S gas might induce sulfide stress cracking (SSC).The interaction between steel and the H2 S containing surrounding environment results in the formation of a Fex Sy corrosion product
The evolution of the corrosion products formed on the surface of the materials was investigated with scanning electron microscopy (SEM)
Summary
The interaction between steel and the H2 S containing surrounding environment results in the formation of a Fex Sy corrosion product. Hydrogen is generated during this corrosion process and can be absorbed into the material. The characteristics of this Fex Sy surface layer will significantly affect the hydrogen introduction in the material [3,4]. Different Fex Sy phases can be formed when steel is in contact with an aqueous H2 S containing environment. Shoesmith et al [5] were amongst the first researchers in this field. They showed that the most prominent phase appeared to be mackinawite (tetragonal FeS1−x ), which readily cracked and spalled from the metal surface. Smith and Pacheco [7] determined the minimum amount of H2 S
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