Study On Crevice Corrosion Of Oilifeld Materials In C02-saturated Solution

CO2corrosion was one of common corrosion in the industry of petroleum production, which can accelerate the corrosion rate of pipelines and equipment. It was easy to cause crevice corrosion at the cracks created by the equipment connections, which would lead to a great loss to our economy. The crevice corrosion behaviors of2Crl3stainless steel,316L stainless steel and N80carbon steel were studied in order to provide reference points for steel selection and application.The influence of temperature, chloride concentration and HAc concentration on crevice corrosion behaviors of2Cr13steel,316L steel and N80steel immersed in CO2-saturated NaCl solution were investigated by electrochemical measurements combined with SEM and EDS modern physical examination methods.The results showed that, the open circuit potentials of2Cr13steel were decreased with the increase of temperature, the Eb value of pitting corrosion and crevice corrosion reduced gradually, and the difference between Eb value increased with the increase of temperature, the maximum difference of Eb value was123mV at80℃. The open circuit potentials of316L steel were also decreased with the increase of temperature, the maximum difference of Eb value between pitting corrosion and crevice corrosion was40mV at80℃.2Cr13steel and316L steel were subjected to crevice corrosion easily in CO2-saturated NaCl solution at the same condition. Firstly, the corrosion rate of N80steel increased, then decreased and increased again with the increase of temperature, the corrosion rate reached the maximum at60℃. There was no significant difference between the crevice corrosion and pitting corrosion of N80steel.With the increase of chloride concentration, the pitting corrosion resistant capacity and crevice corrosion resistant capacity of2Cr13steel reduced gradually, the same as the316L steel. At the same concentrations of Cl", it was easier to cause crevice corrosion than pitting corrosion. For2Crl3steel, the difference of Eb value tended to be stable when the concentration of Cl" up to50g/L. For316L steel, the difference of Eb value increased with the increase of Cl-concentration, the maximum difference value of Eb value was82m V when the concentration of Cl*up to100g/L. With the increase of Cl-, corrosion rate of N80steel increased slightly, the corrosion rate got maximum at100g/L Cl-solution, and there was on significant different between pitting corrosion and crevice corrosion with the increase of Cl". With the increase of the concentration of HAc, the corrosion rate of2Cr13steel increased significantly, the crevice sample lost repassivation ability after the concentration reached1000pm. The corrosion rate of316L steel increased slightly with the increase of HAc, it could still keep good corrosion resistance, the difference of Eb value between pitting corrosion and crevice corrosion increased, the difference of Eb value tended to be stable after HAc reached1000ppm. N80steel was vulnerable to general corrosion in the solution containing HAc. Firstly the corrosion rate of N80steel increased, then decreased and increased again with the increase of HAc, the corrosion rate reached the maximum at1000ppm, the differences between the crevice corrosion and pitting corrosion was not significant.The electrochemical noise characteristics of2Cr13steel,316L steel and N80steel in CO2-saturated NaCl solution were obviously different. The crevice corrosion of2Crl3steel could be divided into three stages, an induction stage, a growth stage and a stable development stage. The corrosion rate increased400times once the crevice corrosion occurred. There were no obvious crevice corrosion stages in the monitoring time for316L steel. The corrosion rate of316L steel was low. N80steel suffered general corrosion in CO2-saturated NaCl solution. The corrosion rate of N80steel had little difference whether the crevice existed or not.