Comparison of the Rotating Cylinder and Pipe Flow Tests for Flow-Sensitive Carbon Dioxide Corrosion

Corrosion can be affected by flow differently depending on the mechanism governing the corrosion process. Two major cases can be distinguished: the effect of flow on corrosion when no surface films are present and the effect of flow on corrosion in the presence of surface films (precipitates, inhibitors, etc.). In the absence of films, the primary effect of flow on corrosion is through mass transfer of the species involved in the corrosion reaction at the metal surface. For mass transfer in turbulent liquid flow, due to very large Schmidt numbers, all the concentration changes occur in a very narrow layer adjacent to the metal surface, deep within the viscous sublayer in the so-called mass-transfer boundary layer. The thickness of this layer is a function of the flow rate (Reynolds number) and flow geometry. Mass transfer usually is associated with limiting currents (i.e., with situations where the electrochemical processes at the metal surface proceed so fast that it is difficult to transport enough reactants from the bulk). Conversely, sufficiently rapid removal of corrosion products from the surface also can become limiting, which can lead to accumulation, (super)saturation and precipitation of surface films. However, if the ABSTRACT