The potential impact of Drag Reducing Agents (DRA) in internal corrosion management of liquid petroleum pipelines has not been fully evaluated, even though they are commonly used in combination with other chemicals like corrosion inhibitors (CI).

A bench-top apparatus was designed, based on a vertical Couette cell approach with a flush-mounted custom-designed Coupled Multielectrode Array Sensor (CMAS), to evaluate the effect of DRAs on the water accumulation height and localized corrosion near the oil/water interface.

It was found that the DRAs tend to accumulate at the oil/water interface forming “globs” when injected at relatively low liquid velocities, which may adhere onto the metallic surface. Localized corrosion occurred just above or below the water/oil interface, depending on whether the CI evaluated was water-soluble or oil-soluble, respectively. At most of the conditions evaluated, the injection of DRA to a system containing CI (without DRA deposits on the CMAS) did not significantly increase localized corrosion rate but modified where it happened.

Based on these results, the rag layer formed at the oil/water interface could be considered as a tertiary phase, where the presence of CI and DRA may induce unique corrosiveness compared to the water and oil phases.