Study On Pitting Behavior Of P110 Steel In West Sichuan Gas Field

P110steel is the main material used in West Sichuan gas field, localized corrosion perforation is the main form of corrosion damage in PI10tubing and casing. It made normal production and sustainable development of Western Sichuan gas field severely affected. Therefore, the study of pitting behaviors on P110steel and the influences of temperature, Cl-concentration, HCO-3concentration and the concentration of SO42-on the process of P110steel pitting corrosion are necessary for prediction and preventing of pitting damage.The electrochemical behaviors of early stage of pitting on P110steel, the influences of some factors, such as temperature, the concentration of Cl-, HCO3and SO42-on the pitting process of P110steel and the pitting corrosion behavior of P110steel under the effect of corrosion inhibitor were studied. The current-time measurement, polarization curve measurement and EIS were employed. SEM was also used to observe the corrosion morphology of P110steel surface. The main conclusions are as follows:(1)Before the stable pitting occurred on P110steel, small current fluctuation were observed, and each peak current ripple represent a metastable pit nucleation, growth and re-passivation process. The metastable pitting corrosion potential Em followed Gaussian distribution.(2)Potential increases, the number of metastable pit nucleation N, growth velocity K, pesk current I and the life-time of metastable pits had a tendency to increase. During the metastable pitting period, the pits active sites on P110steel surface dissolved slowly, the metastable pit grew slowly but repassivated fast. When the corrosion products covering the metastable pit, occluded cell formed, and the metastable pits gradually transformed to stable pits.(3)The influences of some factors, such as temperature, the concentration of Cl-, HCO3and SO42-on the pitting process of P110steel were studied. Effect of temperature on pitting behaviors of P110steel was highly significant, Effect of Cl-concentration and SO42-concentration on pitting behaviors of P110steel were significant, Effect of HCO3-concentration on pitting behavior of P110steel was less significant, the order of these four factors is:temperature>Cl-concentration>SO42-concentration> HCO3-concentration.(4)After adding corrosion inhibitor H, the pitting corrosion potential of P110steel changed more positive, and the capacitive arc radius bacame bigger. Corrosion inhibitor can effectively inhibit the occurrence of pitting corrosion of P110steel, and when the concentration of corrosion inhibitor was100mg/L, the effect of corrosion inhibition achieved the best, inhibition rate was as high as91.23%, the inhibition effect can satisfy the requirements of the site.