Research On Pitting Susceptibility Of Hastelloy C-276 In High Chlorine Medium

In the process of chemical production technology optimization,the operation cycle of equipment is increasing. Corrosion-resistant of equipment requirement is also constantly improved. The service life of chemical production equipment will directly affect the safety of chemical production. Selecting and processing corrosion-resistant materials properly has become an important way to control corrosion. Hastelloy is a kind of advanced nickel base alloy. This kind of material can show excellent corrosion resistance in many strong corrosion medium. Hastelloy as one of the preferred material in chemical equipment manufacture has gradually replaced some commonly used stainless steel. Using Hastelloy as gasifier materials is helpful for chemical enterprises to extend the equipment operation cycle, extend the service life of the equipment and reduce the cost of production. But in the process of chemical production, there exist different chemical composition in the production equipment system.The corrosion resistance of equipment which Immersed in these complex medium will be tested all the time.In the light of the special chemical component of medium in industrial dust sink of gasifier equipment system, we simulate the high chlorine medium in this paper. Using immersion experiment and electrochemical experiment we can study the pitting susceptibility property of Hastelloy in high chlorine medium of different pH, different Cl- concentration and different temperature. Using immersion test we analyzed the pitting corrosion morphology and density of Hastelloy in simulated high chlorine medium.Using electrochemical method (Including the polarization curve method, potentiostatic polarization test and electrochemical impedance spectroscopy), we analyzed the pitting corrosion behavior of Hastelloy in simulated high chlorine medium of different pH, different Cl- concentration and different temperature. Using metallographic microstructure test, scanning electron microscopy (SEM) test cooperate with electrochemical experiments, we can analyzed the difference of material corrosion morphology to support the conclusion of electrochemical experiments conclusion. The research content and conclusions including:With the increasing of pH, the pitting density, pitting corrosion size and depth of Hastelloy C-276 significantly reduce, which proved the rise of pH is helpful to reduce the pitting sensitivity of Hastelloy C-276. With the increase of pH in simulated high chlorine medium, pitting corrosion breakdown potential Eb has increased. With the increase of pH, Hastelloy C-276 corrosion current density Iss will reduce. Using electrochemical impedance spectroscopy analysis surface of Hastelloy C-276,electrochemical impedance spectroscopy has characteristic of capacitive reactance arc. With pH increasing, the charge-transfer resistance and the resistance of passivation film is continuously increasing, passivation membrane capacitance decrease, the stability of the passive film is increasing. Mott-Schttky curve manifests that with the increase of pH in high chloride medium, ND in passivation film reduce, the protection of passivation film become stronger, the pitting susceptibility of Hastelloy C-276 in simulated high chlorine medium reduce. This also suggests that pitting sensitivity of Hastelloy C-276 will increase if the pH in simulated high chlorine medium increase.With the increase of concentration of Cl-, the pitting density, pitting corrosion size and depth of Hastelloy C-276 significantly increased, which proved the rise of concentration of Cl- will increase the pitting sensitivity of Hastelloy C-276. With the increase of Cl- concentration in simulated high chlorine medium, pitting corrosion breakdown potential Eb reduced. This suggests that pitting sensitivity of Hastelloy C-276 will decline if the concentration of Cl- increase. With the increase of Cl- concentration, Iss of Hastelloy C-276 will increase. Using electrochemical impedance spectroscopy analysis surface of Hastelloy C-276, electrochemical impedance spectroscopy has characteristic of capacitive reactance arc. With the concentration of Cl- increases, the charge-transfer resistance and the resistance of passivation film is continuously decreasing, passivation membrane capacitance increasing, the stability of the passive film is decreasing. Mott-Schttky curve manifests that with the increase of concentration of Cl- in high chloride medium system, the ND in passivation film increase, the protection of passivation film decrease, the pitting susceptibility of Hastelloy C-276 in simulated high chlorine medium increase.With the increase of temperature, density, pitting corrosion size of pitting increases slightly, which also prove that the increase of temperature will improve the Hastelloy C-276 pitting sensitivity in simulated high chlorine medium.