Effect of chlorine ion on the pitting corrosion behavior of Cr13 stainless steel for RFT (repeat formation tester)

The corrosion weight loss and the electrochemical behavior of Crl3 stainless steel electrode are studied in the simulated downhole environments of different chlorine ion concentrations in a high-temperature and high-pressure unit. The experimental results shown that, the pitting damage on the surface of Crl3 stainless steel can not be avoided when the concentration of chlorine ion is higher in formation water or drilling fluid; the uniform corrosion speed of Crl3 stainless steel and the corrosion pits on the surface of test samples increase with the increase of the concentration of chlorine ion; the adsorption of local chlorine ion in the form of FeCl₂ and FeCl3 on the surface of test samples is the main cause resulting in passivating film damage. Therefore, the detention time of RFT in the environment with chlorine ion should be reduced or the grade of the stainless steel for RFT should be enhanced to decrease its corrosion.