In multiphase flow, bubbles are produced and collapse on the solid/liquid interface. Bubble collapse can enhance the CO2 corrosion of carbon steel pipe, as shown by coupon surface analysis, corrosion rate measurements and visualization of bubble movement in multiphase flow. Using the electrochemical limiting current density technique, experiments have been carried out to study the effect of bubbles on mass transfer in an electrochemical cell and in slug flow. The limiting current density signal as a function of time and frequency shows the direct influence of bubble movement on mass transfer. It also indicates the difference of mass transfer in fully developed turbulent flow, an electrochemical cell and slug flow. The enhancement of mass transfer coefficient by bubble collapse is considered an important factor that contributes to the increased corrosion rate in multiphase flow. © 2000 by NACE International.