MULTIPHASE FLOW-ENHANCED CORROSION MECHANISMS IN HORIZONTAL PIPELINES

Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of gas bubbles (Gopal et al., 1997). Corrosion rate measurements have been made at pressures up to 0.79 MP a and temperatures up to 90 degrees C, and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude n umber. This paper describes mass transfer measurements under multiphas e slug and annular flows using the limiting current density technique. The experiments are carried out in a 10-cm-dia pipe using a 0.01-M po tassium ferro/ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6, an d 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The results show instantaneous peak s in the mass transfer-rates corresponding to the pulses of bubbles in slug flow. Instantaneous increases of 10-100 times the average values in multiphase flow are seen. Peaks are also seen in instantaneous mas s transfer rates in some annular flows.