Understanding the effect of tensile stress on erosion-corrosion of X70 pipeline steel

Abstract

The pipelines in the oil and gas industry may simultaneously suffer damage from tensile stress and erosion at the internal surface, which could cause the pipeline failure easily. In this work, the combined effect of tensile stress and erosion on the corrosion of X70 pipeline steel was studied in a loop system coupled with a stress loading device. The general corrosion and localized corrosion under the combination of tensile stress and erosion was comprehensively investigated using finite element simulation analysis, potentiodynamic polarization curve, electrochemical impedance spectroscopy, scanning electron microscope as well as 3D ultra-depth microscope. The results show that both tensile stress and erosion can promote general corrosion independently. Furthermore, the combination of tensile stress and erosion can generate a synergistic effect on general corrosion of steels through reducing the compactness of corrosion products layer, accelerating the mass transfer process and improving the reaction activity of the steel, with a changed corrosion current density of 37.54 μA/cm2, even exceeding the influence of tensile stress (17.76 μA/cm2). For localized corrosion, erosion can enhance the inside-out diffusion of metal cations in the metastable pit and dilute the pit anolyte, while tensile stress may generate stress concentration on corrosion defects. Therefore, erosion shows a suppression on localized corrosion, but an enhancement effect from tensile stress.