CORROSION BEHAVIOR OF LOW-RESIDUAL CARBON-STEELS IN A SOUR ENVIRONMENT

Potentiodynamic testing was used to study the corrosion performance of low-residual carbon steels in a sour brine, as typically encountered in Kuwaiti oil fields Twenty-eight tests were Performed to determine t he effects of variations of carbon content from 0.1 to 0.49%; 1, 2, an d 3% additions of cobalt; and 1, 2, and 4% additions of chromium. Resu lts indicated carbon content decreased the corrosion rate in the absen ce of impurities and alloying elements because of the enhanced formati on of corrosion products in the sour brine. The corrosion rate was abo ut 254 mum/y (10 mpy). The addition of small amounts of Cr tended to i ncrease the corrosion rate, regardless of the C content. For the 4% Cr samples, the corrosion rate averaged 2032 mum/y (80 mpy). From the va lues of beta(c) for C steels and Cr-alloyed steels in the deaerated ba se brine, aerated base brine, and in the sour brine, the study conclud ed that Cr always depolarized the Cathodic reaction independent of the environment The Co-alloyed steels exhibited higher corrosion rates wh en compared to C steels, and the corrosion rate increased in the Co-al loyed steels with higher C content Hydrogen sulfide acted as a cathodi c depolarizer in Co-alloyed low-residual carbon steels. Co caused the corrosion reaction to change from a kinetic control reaction to a diff usion control reaction. Therefore, in the presence of Co, the corrosio n reaction depended highly on hydrodynamic conditions.