The focus in this paper is on the effects of multiphase flow on CO2 corrosion of mild steel pipelines. The significance of mass transfer in turbulent flow is discussed first: (i) when an increased rate of mass transfer of corrosive species, such as H+ ions, to the steel surface leads to an acceleration of the cathodic reactions and a higher corrosion rate and (ii) when an increased mass-transfer rate of the corrosion product, ferrous ions (Fe2+), away from the steel surface makes it harder to form protective ferrous carbonate layers. The mechanical interaction of the flow with the pipe walls is discussed next, where the wall shear stress is often blamed for removal of protective surface layers, such as iron carbonate or inhibitor films. Using macroscopic as well as atomic scale measurements [atomic force microscopy (AFM)], it was found that it is very unlikely that truly protective surface layers can be removed by mechanical forces alone. The other multiphase flow effects on corrosion, such as the effect of condensation on the top of the line corrosion (TLC) in wet gas pipelines, the effect of water settling and wetting in oil-carrying lines, and the effects of sand on erosion-corrosion and underdeposit corrosion in production pipelines, are outlined at the end.