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 MPa 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 number. This paper describes mass transfer measurements under multiphase 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 potassium ferro/ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6, and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The results show instantaneous peaks 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 mass transfer rates in some annular flows.