Corrosion Behavior Of X65Carbon Steel And316L Stainless Steel In Oilfield Produced Water

Corrosion is an important destruction factor for modern industry and life. Thecorrosion losses account for6%of gross national product in our country every year.With the development of oil and gas field with CO2, the accident of oil and gas fieldcorrosion becomes more and more, so the corrosion behavior of metal materials wasunderstood in oilfield environment, which has been a research hot spot in recent years.In this paper the behavior of X65carbon steel and316L stainless stain were studied,and it has practical value to explore the CO2corrosion mechanism.The effects of temperature, HAc concentration and CO2pressure on corrosionbehavior of X65carbon steel in oilfield product water were studied by using weightloss, polarization curve, electrochemical impedance spectroscopy, scanning electronmicroscope and X-ray diffraction. The results showed that corrosion rate in oilfieldproduct water increased with the increasing of temperature when the temperature is20-90℃, the max corrosion rate was2.75mm/a. There was limiting diffusive currentdensity in the cathodic curve in20℃, corrosion current density were improved in90℃. It is concluded that the corrosion is mainly dominated by cathode reaction inoilfield produced water because of bc>ba.That was a capacitive semicircle in EIScurve, the diameter of the capacitive loop reduced with the increasing of temperature.The surface of X65steel formed FeCO3in90℃, and the corrosion rate decreasedThe high temperature was better for the precipitation of FeCO3.The corrosion rateincreased with the increasing of HAc, when HAc concentration is0-2000ppm. Theaddition of HAc could speed hydrogen depolarization, and this reaction could be thereduction of the acetic acid. The higher temperature promoted the acetic acid to ionizemore H+, lowing solution pH, and hydrogen depolarization process would becomeeasy, so the corrosion rate is accelerated. The surface of X65steel couldn’t form FeCO3after immersing48h, it showed the more acetic acid could remove FeCO3layer. The corrosion rate of X65steel linearly increased with the partial pressure ofCO2,when the CO2partial pressure was0-0.2MPa in oilfield produced water. Withthe addition of saturated CO2at the same temperature, the anodic current density andthe cathodic current density increased, rapidly. The impedance spectra exhibited acapacitive semicircle an inductive loop in the low frequency range in CO2-saturatedsolution at20℃, the low frequency range disappeared in90℃. The surface of X65steel formed FeCO3in CO2-saturated solution at90℃, which inhibited the corrosionreaction. The addition of acetic acid has a synergetic effect on in CO2-saturatedsolution. There was the maximum corrosion rate at the mix conditions. The formationand dissolution of FeCO3is a dynamic process. Uniform corrosion is the mainbehavior to X65carbon steel in the simulated oilfield produced water.Corrosion behavior of316L steel in simulated oilfield water was studied byweight loss, the anode polarization curve, electrochemical impedance spectroscopyand scanning electron microscope methods. Effects of temperature, acetic acidconcentration and CO2partial pressure on the corrosion behavior were discussed. Theresults showed: the pitting corrosion is the main behavior to316L stainless steel in thesimulated oilfield produced water. Corrosion rate increased firstly, then decreasedwith the increasing of temperature. The maximum depth of pitting corrosion was0.145mm at60℃,and the pitting density is0.68/cm2. The break potential andprotection potential decreased, which the susceptibility to pitting initiation increasedat a certain temperature, however as the temperature was increased further to80℃,the corrosion product film with protective function is formed, and the pittingsensitivity decreased. The corrosion rate of316L steel increased firstly, thendecreased with the increasing of HAc concentration. The mix corrosion rate was theconcentration of1000ppm. The lower HAc concentration could damage passivationfilm easily, the break potential decreased firstly, then increase with the increasing ofHAc concentration. The corrosion rate of316L steel increased firstly, then decreased with the increasing of CO2partial pressure. When the CO2partial pressure was0.1MPa, the passivation film appear “glitches” phenomenon, and the passivation filmwas not stable, the corrosion rate had the mix now.