Research of CO2 corrosion behavior of 20# steel in gas well solution containing formic acid

AbstractThe influence of formic acid on the CO2 corrosion of the 20# steel in the formation water was studied, via corrosion immersion experiments using formation water as corrosion medium. The morphology of the corrosion products was observed with SEM, and the electrochemistry performance of the corrosion products was analyzed with EIS. The results indicated that the formic acid can accelerate corrosion of 20# steel. Corrosion rate increases with addition of formic acid in the solution. When the content of formic acid was 40ppm and 100ppm, uniform corrosion was observed. Simultaneously, shallow pits appeared on the surface. As the content of formic acid rose to 500ppm, pitting corrosion was much likely to occur. With the extension of corrosion time, the results of EIS tests showed that with addition of formic acid at 40ppm and 100ppm, the graph contains a high-frequency capacitive reactance and low-frequency inductive reactance trend, then convert to double capacitive reactance with increase of immersion time. And when the content of formic acid increased to 500ppm, double capacitive reactance was found in EIS pattern, and then convert to high-frequency capacitive reactance, mid-frequency inductive reactance and low-frequency inductive reactance with increase of immersion time