Erosion Corrosion and Synergistic Effects under High Velocity Multiphase Conditions

Abstract 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 between 10 and 60 m/s. CO2 at a total pressure of 15 bar 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 % at a gas liquid ratio of 20,000 (under standard conditions) was used as liquid phase. 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 Epit and repassivation potentials Erepass. Furthermore, near surface near regions of tested samples were investigated by applying nanoindentation in an atomic force microscope (AFM). Synergy effects as a function of impact velocity are quantified. At impact velocities of 10 m/s a pronounced synergistic effect of erosion plus corrosion was found, at high impact velocities this effect decreased due to domination of erosive damage.