Corrosion resistance of rolled and rerolled super martensitic steel in media containing chlorides and hydrogen sulfide

Resumo

In the oil and gas industry, super matensitic steels have been used primarily in the manufacture of seamless steel pipe for use in drilling oil and gas. The objective of this work is to evaluate the corrosion resistance of rolled and rerolled super martensitic steels in electrolytes of aqueous solution of NaCl 35 g/L, and aqueous solution of NaCl 120 g/L, sodium acetate 0.4 g/L, with pH 4.5 (standard solution), saturated and unsaturated with H₂S, simulating the service conditions of petroleum industry in the pre-salt operation. For this evaluation, the electrochemical tests used are electrochemical impedance spectroscopy (EIS) and cyclic polarization test. The characterization techniques used are optical microscopy, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The effect of H₂S saturation of the solutions studied on the corrosion resistance of steels was detrimental. The super martensitic steel in the rerolled condition showed a higher corrosion resistance than the rolled steel in an aqueous solution of 35 g/L NaCl and in a standard solution saturated with H₂S. In the 35 g/L NaCl aqueous solution saturated with H₂S and in the standard solution, the rolled steel showed a higher corrosion resistance than the rerolled steel. In an aqueous solution of 35 g/L NaCl, the rolled and rerolled steels showed pitting diameter of 140μm and 100μm, respectively.

Keywords: polarization, rolled super martensitic steel, rerolled super martensitic steel.