Experimental Study On The Corrosive Effect Of Typical Saturated Sodium Salt Sand On X80 Steel

In this paper,electrochemical impedance spectroscopy?EIS?,polarization curve?PC?and scanning electron microscopy?SEM?were used to study the electrochemical corrosion behavior and corrosion mechanism of X80 steel in saturated sodium salts?sodium chloride,sodium sulfate,sodium bicarbonate?sand and solution under 1 D and 1 h of on-DC current.The polarization curves and electrochemical impedance spectroscopy of X80steel before and after electrification in NaCl solution and sand were tested and analyzed.It was found that the corrosion rate of X80 steel increased with the increase of salt concentration,while the corrosion ability of solution decreased with the increase of salt concentration.The corrosion rate first increased and then decreased with the increase of concentration after 24 hours of electrification,and the corrosion ability first increased and then decreased with the increase of concentration.In NaCl sandy soil,the corrosion rate increases with the increase of salt concentration,while the corrosion capacity of sandy soil decreases first and then increases.After 24 hours,the corrosion rate increases first,then decreases and finally increases with the increase of salt concentration,while the corrosion capacity increases first and then decreases.The polarization curves and electrochemical impedance spectroscopy of X80 steel before and after electrification in Na₂SO₄ solution and sandy soil were tested and analyzed.It was found that the corrosion rate of X80 steel increased with the increase of concentration when electrification did not occur in Na₂SO₄solution,and its corrosion ability firstly decreased and then increased with the increase of concentration.In Na₂SO₄ sandy soil,the corrosion ability firstly decreased and then increased.The corrosion rate increases firstly and then decreases with the increase of the concentration,while the corrosion ability increases firstly,then decreases and finally increases with the increase of the concentration.After electrification,the corrosion rate increases with the increase of the concentration,while the corrosion ability decreases with the increase of the concentration.The polarization curves and electrochemical impedance spectroscopy of X80 steel before and after electrification in NaHCO₃ solution and sand were tested and analyzed.It was found that when electrification was not conducted in NaHCO₃ solution,the corrosion rate firstly increased,then decreased and finally increased with the increase of concentration,and the corrosion ability firstly decreased and then increased with the increase of salt concentration.After electrification,the corrosion rate and corrosion ability firstly increased,then decreased and finally increased with the increase of concentration.In NaHCO₃sandy soil,the corrosion rate increases with the increase of NaHCO₃concentration,but the corrosion ability increases firstly and then decreases.The instantaneous corrosion rate and corrosion ability firstly increase and then decrease with the increase of concentration after electrification.The Nyquist diagram of electrochemical impedance spectroscopy of X80steel in different sodium salt solutions and sands shows that the capacitive arc radius of X80 steel in sandy soil is larger than that in solution of the same concentration when no electricity is applied,and X80 steel is more likely to be corroded in solution;after DC,the arc radius of X80 steel in sandy soil is similar to that in solution of the same concentration in NaCl and Na₂SO₄ systems.However,in NaHCO₃ system,the radius of X80 steel in solution at medium and low concentration is larger than that in sand at the same concentration.Electricity will affect the corrosion of X80 steel in solution and sand,and has a greater impact on NaHCO₃ system.By comparing and analyzing the fitting results of polarization curves of X80 steel in different sodium salt solutions and sand,it is concluded that the corrosion rate of X80 steel in normal NaCl and Na₂SO₄ systems in solution is higher than that in sand at the same concentration.In NaHCO₃ system,except when the concentration is 0.3%,the corrosion rate in solution is higher than that in sandy soil,but in other concentration,the opposite law appears.The corrosion rate of X80 steel in sandy soil in NaCl and Na₂SO₄ system under electrified condition is higher than that in solution at the same concentration.Comparing the macro and micro morphologies of X80 steel in solution and sand,it is concluded that the corrosion type of X80 steel in NaCl and Na₂SO₄solution with higher concentration is pitting corrosion,while the corrosion type in sand soil is overall corrosion;compact corrosion products are formed in NaHCO₃ solution and sand soil with higher coverage.