The exploitation of fields with high H2S and/or CO2 content is nowadays of growing importance for oil companies. The presence of H2S and/or sulphur in production fluids can be responsible for both general and localized corrosion. However, the knowledge of materials behavior in plants handling those fluids is limited due to the difficulty in performing tests in such aggressive and dangerous environments. The so-called Nace Solution, used to assess Sulfide Stress Cracking susceptibility of steels, is a water-based solution simulating production fluids in equilibrium with one bar bubbling H2S gas. This solution does not simulate situations where High Pressure (HP) and Ultra High Pressure (UHP) of acid gas is present.
This paper describes tests performed in a laboratory with an autoclave designed to test up to a total pressure of 1000 bar of H2S and/or other gas mixtures, with and without the presence of water, to fully simulate the service environment.
Autoclave tests were performed on four point bend specimens of Carbon Steels, Stainless Steel and Corrosion Resistant Alloys at pressure up to 730 bar, with the aim at better understanding the effect of a small content of water in the corrosive properties of re-injected gas mixture. Results show that a small amount of water (1%) is enough to trigger damage – in the form of cracking - in Type 316 Stainless Steel. For Carbon and Low Alloy steel, there is competition between general and localized corrosion. The main finding however is that more work is needed to obtain a better understanding of the behaviour of high pressure H2S and CO2 mixtures; compliance of laboratory tests with field conditions is important towards materials selection.