Effect of Chromium on the Pitting Resistance of Oil Tube Steel in a Carbon Dioxide Corrosion System

Pitting corrosion and structure characteristics of carbon dioxide (CO2) corrosion products on N80, 1Cr, and 4Cr steel were studied. The results indicated that Cr-containing steels can suppress pitting corrosion effectively. While the Cr content in the matrix reached 4%, no pitting corrosion appeared on 4Cr steel. Cr existed mainly as amorphous compound Cr(OH)3 in corrosion products. With the improvement of Cr content in the steel matrix, the content of Cr(OH)3 in corrosion products increased remarkably, which could not only reduce the electrical conductivity of corrosion products but could also improve the cation selectivity of corrosion products. These two factors could improve the pitting resistance of Cr-containing steels.