Erosion Corrosion and Synergistic Effects under High Velocity Multiphase Conditions

The present study has been conducted to investigate the interaction between erosion and corrosion processes under high velocity multiphase conditions. Tests were performed on martensitic stainless steel samples of grade UNS S42000. Pure erosion and pure corrosion as well as erosion corrosion impingement tests were carried out at three different impact velocities up to 60 m/s. CO₂ at a pressure of 1,500 kPa was used as the gas phase. The sand content, with grain size below 150 µm, was 2.7 g/L brine. Artificial brine with a NaCl content of 2.7 % was used as liquid phase. The experiments were designed to understand whether erosion enhances corrosion or vice versa and whether, and if to which extent, synergistic effects between erosion and corrosion do occur. Damaged surfaces of specimens exposed to the high velocity multiphase flow were investigated by stereo microscopy, scanning electron microscopy (SEM) and an optical device for 3D surface measurements. Moreover electrochemical investigations according to ASTM G 61 were performed to determine electrochemical behavior of tested materials including critical pitting potentials E_pit and repassivation potentials E_repass. Furthermore, surface near regions of tested samples were investigated by applying atomic force microscopy (AFM), magnetic force microscopy (MFM) and nanoindentation measurements. From the analysis, flow velocity and sand content show the greatest effect on the degradation rate. In this paper the erosion corrosion behavior and rates of grade UNS S42000 are presented and compared to the results of higher alloyed stainless steels.