GALVANIC CORROSION BEHAVIORS OF CARBON STEEL UNDER CARBON DIOXIDE (CO_2) ENVIRONMENT

Galvanic corrosion is one of the most harmful corrosion during the exploration and transportation of oil and gas.The corrosion behaviors of the couples between the carbon steel and stainless steel as well as between the carbon steel and corrosion product scales of 1 percent NaCl water solution of the saturated CO2 were studied by means of the weightlessness method,galvanic current measurement,scan electron microscope and X diffraction.The results showed that under the same temper-ature condition,the bigger the Sc/a,of the carbon steel/stainless steel to the cathode and anode is.the higher the Vcorr couple to anode(N80 steel)will be.When the CO2 fractional pressure is relatively low(less than 0.1 MPa),the said VTO has a maximum value as the temperature keeps rising and the logarithm value of Vcorr has a linear relationship with the logarithm value of Sc/a.Under the condition of high CO2 fractional pressure(2.5 MPa).the said Vcorr has a maximum value and minimum value whenn the Sc/a.is less than or equate 4.The test result all showed that temperature has great influences on the CO.corrosion products' components of carbon steel.The corrosion product scales on the surface of the carbon steel under different temperatures can form corrosion galvanic couple with the bare metals.When the temperature is 90℃,the bimetallic corrosion of the corrosion product scales and carbon steel is most serious.These researches can provide significant references to the prevention of bimetallic corrosion.