Research On Pitting Corrosion Resistance Of P550 Austenitic Stainless Steel

P550 stainless steel is a high-nitrogen austenitic stainless steel with excellent corrosion resistance and comprehensive mechanical properties,which is widely used in the field of petroleum drilling.Corrosion failure is the main on failure mode of oil drill collar equipment,so it is necessary to investigate the pitting corrosion resistance of P550 stainless steel.Polarization curves and electrochemical impedance spectroscopy tests in NaCl solutions of different concentrations at two temperatures showed that when Cl^-concentration increases,the pitting resistance of P550 stainless steel has a downward trend,and the temperature rise further improves the its pitting eclipse tendency.Compared with the test results of 316L stainless steel under the same test conditions,the electrochemical parameters of P550 stainless steel are better than 316L,and the pitting corrosion resistance is excellent.The electrochemical test results of immension in 0.6mol/L NaCl solution for different times show that as the immension time increases,the pitting corrosion resistance of P550 stainless steel increases first,and then slowly decreases.Electrochemical tests in NaCl solutions at different pH values show that as the pH value increases,the pitting resistance of P550 stainless steel is better,but the change of pH value has less influence on the electrochemical impedance spectroscopy curve.The electrochemical test in FeCl₃solution shows that FeCl₃has a great influence on the pitting corrosion resistance of P550 stainless steel,and its pitting tendency increases significantly.The corrosion rate of P550 stainless steel was tested by the FeCl₃solution immersion test at two different temperatures.The corrosion rate of P550 stainless steel was compared with that of ordinary 316L stainless steel under the same immersion condition.The results showed that the corrosion rate of P550 stainless steel was lower,and the pitting resistance was better.The increase in pitting will increase the degree of pitting.Subsequently,the pitting corrosion growth model of P550 stainless steel was theoretically deduced and verified,and the results showed that the pitting corrosion growth law of P550 stainless steel basically conformed to the theoretical derivation of the pit ellipsoid model.