Austenitic Stainless Steel Grade 316L, Duplex Stainless Steel (22% Cr DSS) and Super Duplex Stainless Steel (25% Cr SDSS) corrosion resistant alloys (CRA) are used extensively in the water injection service for various applications such as process piping, pumps and valves. Currently the application of these materials is limited by many international standards to 10 Parts per Billion (ppb) of dissolved oxygen environments. However in actual plant operation of water systems, this limit could be exceeded due to various unavoidable upset scenarios also practically it is very difficult to control dissolved oxygen to less than 10 ppb. Higher grade materials (Nickel based alloys such as alloy 825 or Alloy 625) are selected for oxygen corrosion resistance properties which results in increased cost, compared to stainless steel materials. The objective of this study was to do a systematic study to evaluate the performance of stainless steels in various oxygenated environments. Pitting and crevice testing was conducted to assess welded 316L, 22% Cr duplex stainless steel (DSS) and 25% Cr super duplex stainless steel (SDSS) in environments containing various dissolved oxygen levels (20, 50, 100 ppb) at temperatures of 50 and 60 deg C with different salt concentrations (16, 100, 167 and 250 g/L NaCI). This paper will present the testing results and the effect of oxygen on CRA materials. The results show that SDSS material has better corrosion performance compared to other materials (316L, DSS) at various testing conditions.
There are many other factors affecting the corrosion of steel in high chloride environment (e.g sea water). These factors are chloride ion concentration, oxygen, velocity, temperature and stability of the formed film1.
Oxygen dissolved in water is one of the primary causes of corrosion in the oil field industry. Oxygen is considered as a strong oxidant and reacts quickly with metal. When oxygen is present in the fluid, the most common types of corrosion include pitting and crevice corrosion.2