Effect of Ca²⁺ on the Corrosion Behavior of 3Cr Steel in CO₂ Environment

Abstract

As the development of oil and gas enters a high water cut stage, the formation water environment with high Ca2+ and Cl- poses higher requirements for the safe service of pipe columns. In this work, the influence of Ca2+ concentration and exposure time on the corrosion behavior of 3Cr steel was analyzed by using high temperature autoclave to simulate the downhole flow environment and combining with the electrochemical research results. Research results showed that although the presence of Ca2+ could promote solution acidification, the corrosion rate of 3Cr steel in solutions containing Ca2+ depended more on the quality of the film on the sample surface. When the total Cl- concentration in the solution was 128 000 mg/L and the Ca2+ concentration ranged from 0 to 3 600 mg/L, the maximum average weight loss rate of 2.2 mm/a occurred at the Ca2+ concentration of 1 080 mg/L. Meanwhile, in an environment with a Ca2+ concentration of 180 mg/L, the weight loss rate curve of 3Cr steel showed an inverse “V” trend of weight loss rate over time, and the average weight loss rate of the sample reached the maximum value at the corrosion time of 240 h. When 3Cr steel was immersed in a solution containing Ca2+ with introducing CO2, the FexCa1-xCO3 compounds were formed on the surface of 3Cr steel. In addition, there was no strict ratio between Fe/Ca, and the product states depended on the Ca2+ concentration in the solution.

Keywords

• 3cr steel|corrosion behavior|environment containing ca²⁺|co₂ atmosphere|corrosion films