No abstract

No abstract

The influence of chloride ion concentration on the passivation film and corrosion product film of martensitic stainless steels (SS) (13% Cr, modified 13% Cr-1% Mo, modified 13% Cr-2% Mo, and 15% Cr SS) have been investigated using immersion tests and electrochemical measurements in sweet environments at temperatures of 150°C and 180°C in the presence of carbon dioxide (CO 2 ). The corrosion rate of conventional 13% Cr SS was found to increase with increasing chloride ion concentration at 150°C. However, the corrosion rates of modified 13% Cr SS and 15% Cr SS were independent of the chloride ion concentration at 150°C. The corrosion rates of modified 13% Cr SS increased with increasing chloride ion concentration above 1,000 ppm at 180°C. The corrosion rate of 15% Cr SS slightly increased at high chloride ion concentration at 180°C. Chromium-enriched corrosion product films were produced on all alloys considered, except for 15% Cr SS, at 180°C. A passivation film was maintained for 15% Cr SS at 180°C. In addition, the pitting corrosion behaviors were investigated by potentiodynamic polarization curves and open-circuit potential measurements. The behavior of the current density of anodic curves corresponded to the immersion test results. Pitting corrosion on modified 13% Cr-2% Mo SS is considered to repassivate because of low potential compared with pitting potential. KEY WORDS: CO 2 corrosion, high temperature, immersion test, martensitic stainless steel, modified martensitic stainless steel, pitting potential ISSN 0010-9312 (print), 1938-159X (online)

A new 13% Cr martensitic stainless steel (0.025% C-13% Cr-Ni-Mo) with excellent resistance to carbon dioxide (CO 2 ) corrosion and good resistance to sulfide stress cracking (SSC) was developed, and its application limits in oil and gas environments were clarified. The CO 2 corrosion rate of the 13% Cr steels with Ni and Mo was < 0.3 mm/y at 180°C (356°F) in 20% sodium chloride (NaCl). It was less than that of the conventional 13% Cr steel (0.2% C-13% Cr). The corrosion rate of the steel slightly decreased with the increase in Mo and Ni content. The SSC resistance improved with the increase in Mo content. The critical partial pressure of hydrogen sulfide (H 2 S) for the 2% Mo steel was > 0.005 MPa at pH 3.5. Effects of Ni and Cu on SSC were not distinctive for this kind of steel. These results depended upon hydrogen permeability. The critical H 2 S partial pressure for the 110grade steel was the same as that of the 95-grade steel at pH 4.5 and pH 3.0 and was slightly lower at pH values between 3.0 and 4.5. The new 13% Cr steel proved to have excellent properties in the sweet and slightly sour environments.

No abstract