Corrosion performance of X70 and X80 line pipe steels in a simulated concrete pore solution contaminated with 3.5 wt% NaCl

Abstract

The present study uses electrochemical approaches, such as linear and cyclic polarization, to examine the effects of immersion time (7, 14, 21 and 28 days) on the corrosion behaviour of X70 and X80 line pipe steels in a simulated concrete pore solution (SCPS) contaminated with 3.5 wt% NaCl (pH ~ 12 to 13.8). The results show that the corrosion resistance of the X70 line pipe steel decreases from 7 to 21 days, and then increases significantly after 28 days. For the X80 line pipe steel, corrosion resistance improves from 7 to 14 days due to the preferential dissolution of the bainitic phase, which enables the building of a passive film. However, corrosion resistance declines after 21 days before improving again after 28 days. This occurrence can be ascribed to the formation of stable passive film on both the steels after extended immersion periods (beyond 28 days), driven by the elevated phase fraction of α/γ* in corrosion products, where α signifies the stable α-FeOOH phase and γ* encompasses the less stable phases, such as γ-FeOOH, β-FeOOH and Fe₃O₄.