Study On Local Electrochemical Behavior Of Local Corrosion Of Metal Tubular Product

Combining with the current situation of metal corrosion research at home and abroad and the problems of metal corrosion detection are studied.The corrosion process of metal in corrosive medium was studied by using local electrochemical technique,and the corrosion resistance of different microstructure of metal was discussed by means of microstructure characterization,nano-indentation,Raman and electrochemical characterization.this paper's research contents can be summarized as follows:Firstly,the local corrosion behavior of the welded joint of X80 pipeline steel was studied by using scanning vibration electrode technique(SVET)and local electrochemical impedance technique(LEIS).The corrosion resistance rule of X80 welded joint is: weld metal > base metal > heat-affected zone;The microstructure of the base metal is composed of granular bainite(GB)and polygonal ferrite(PF).The microstructure of the heat-affected area contains more ferrite.The acicular ferrite in the weld metal is composed of ferrite and carbon-rich layer surrounded by nonmetallic inclusions,and the acicular ferrite carbon-rich layer is not easy to corrosion.LEIS test results show that the impedance of X80 welded joint increases first and then decreases.In the process of metal corrosion,corrosion product film is formed on the metal surface,and with the further extension of time,corrosion product film is broken due to the action of anions in the corrosive medium,leaving the matrix exposed to the corrosive medium again.The impedance and corrosion current density of the white spot in Inconel 718 alloy were studied by local electrochemical measurement.It found that the white spot area has low impedance and high corrosion current density,and the white spot area has high electrochemical activity.The microstructure of the white spot is large grain and less corrosion resistance.Finally,the corrosion resistance of nonmetallic inclusions in Inconel 718 alloy was studied.The conclusion is as follows: macroelectrochemistry and local electrochemistry test technology show that the non-metallic inclusions in Inconel 718 Alloy have better corrosion resistance;with the increase of the corrosion degree,the tendency of pitting corrosion of Inconel 718 Alloy increases;the corrosion of metal oxide dissolves and forms corrosion pit.