Boundary layer effects in turbulent flow testing
- UMIST, Manchester (United Kingdom). Corrosion and Protection Centre
- CAPCIS Ltd., Manchester (United Kingdom)
Flow accelerated corrosion under turbulent flow is a complex process with enhanced mass transport, development of concentration gradients and film formation all influencing the corrosion rate. Published data from well established hydrodynamic correlations of mass transfer and flow, and shear stress and flow, are first compared to illustrate the relative magnitudes of the various parameters for different flow geometries. The results of these empirical studies are also compared with the universal velocity profile concept. The analysis shows that any lack of correspondence between corrosion data obtained with different, well characterize, flow apparatus, such as pipe loop, rotating cylinder electrode (RCE) or jet impingement rig, cannot be ascribed to any fundamental difference in correlations between mass transfer and shear stress. The corrosion system of carbon steel in CO{sub 2} containing brine is then used to demonstrate that the developing concentration profiles are a major factor in flow enhanced corrosion under turbulent conditions. Leading edge effects on electrodes have a significant influence not anticipated from fully developed flow data. The study indicates that the RCE provides baseline corrosion data comparable with that from an infinitely long pipeline. Test loop electrodes are usually of short length and experience conditions comparable to jet impingement. It is shown that local rates of mass transfer are significantly greater on short electrodes than on ``long`` electrodes and hence higher corrosion rates are expected. Also, the local ferrous ion concentrations will be lower (at a given corrosion rate) on short electrodes, thereby reducing the tendency to form protective films.
- OSTI ID:
- 106115
- Report Number(s):
- CONF-950304--
- Country of Publication:
- United States
- Language:
- English
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