Effects of flow velocity on corrosion and galvanic corrosion behavior in wet CO2 environments were investigated using flow loop tester for materials and material combinations from carbon steels to corrosion resistant alloys (CRAs) more than 13%Cr stainless steels. The flow velocity dependence of corrosion rate of carbon steels and low alloy steels obeys one- third-power law at the velocities up to the critical velocity for erosion-corrosion and 0.62th-power law above it. A corrosion rate of CRAs is constant irrespective of flow velocity in passive state or in the case of stable film. On the other hand, corrosion rate obeys 0.8th to
1.2th-power law over the critical velocity when the corrosion film of CRAs became unstable. The ratio of a corrosion rate of a material in coupled to that of uncoupled defined as galvanic effect index (GEI) was studied under flowing fluid condition. GE1 is almost constant irrespective of corrosion rate of the less noble material and is at most 2.0 with equal anode and cathode area. GE1 in the flow condition is less than that in the static condition . Keywords: CO2 corrosion, galvanic corrosion, oil country tubular goods, carbon steel, corrosion resistant alloys, flow velocity, loop tester, critical velocity, erosion- corrosion.