Research on the corrosion characteristics of X70 steel with coating damage under mixed Alternating Current(AC)and Direct Current(DC)interference
Given the insufficient research on the corrosion behavior of coating damaged pipelines under mixed Alternating Current(AC)and Direct Current(DC)interference,the corrosion characterization of X70 steel with tiny coating damage under mixed AC and DC interference was carried out using weightlessness and electrochemical experiments,combined with optical microscopy,laser spectroscopic confocal microscopy,XRD,and other inspection methods.The results show that:(1)the corrosion morphology of the damaged coating specimens under mixed AC and DC interference is mainly pitting corrosion,and the maximum depth of the corrosion pits increases with the increase of AC and DC density.The larger the diameter of the coating damage is,the deeper the maximum depth of the corrosion pit is.(2)When i=180 A/m2,the larger the diameter of coating damage,the more serious the local corrosion of the coating damage area is.The corrosion depth of the damaged coating 5 mm specimen reaches 1883.18 μm and the diameter of the damaged coating extends from the original 5 mm to 7 mm in diameter.(3)The mixed AC and DC interference causes more severe corrosion on the oil and gas pipelines with coating damage,and the maximum corrosion pit depth of the uncoated specimens is much lower than that of the coating-damaged specimens at the same mixed AC and DC density.(4)Different mixed AC and DC densities may destroy the integrity of the corrosion product film.There is a critical current density of 120 A/m2.When i＜120 A/m2,with the increase in current density,the maximum depth of corrosion pits slowly increases;when i≥120 A/m2,with the increase in current density,the maximum depth of corrosion pits increases dramatically.the growth decreases with increasing the area of the coating damage.(5)AC and DC are not simple superposition effects;with the increase of mixed AC and DC density,the oscillating effect of AC is strengthened,which promotes the generation of pitting corrosion.Besides,The increase in DC density intensifies corrosion.
safety engineeringcorrosionmixed alternating current and direct current interferenceburied pipelinescoating damage
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