The Corrosion Behavior of N80 Steel in Multiple Thermal Fluid Environment Containing O2 and CO2

Abstract

The corrosion behavior of N80 steel in Multiple thermal fluid environment containing O2 and CO2 was analyzed by Scanning Electron Microscopy (SEM), Energy-dispersive Spectrometry (EDS) and X-ray Diffraction (XRD) techniques. The results showed that, the corrosion products formed on N80 steel showed double layer structure. The outer layer are loose and porous, providing little protection. The inner layer are mainly FeCO3 crystals, and a small amount of Fe2O3 and FeOOH composition. The formation of Fe oxide on the inner layer of the film destroyed the integrity of the inner layer, resulting in localized corrosion. During the development of pitting, Cl− is enriched only at the tip of the pitting hole, which is the main cause of pitting corrosion and eventually leads to the formation of dendritic localized corrosion. The difference between internal and external potentials, the O2 concentration and the decrease of pH in the pitting holes combined to increase the corrosion process.