Pitting in the water/hydrocarbon boundary region of pipelines - Effect of corrosion inhibitors

Abstract

The boundary conditions leading to pitting in pipelines in the water/hydrocarbon (HC) interface region of the bottom-of-the-line (BOL) liquid were studied using electrochemical noise (ECN) with specially developed evaluation software. It was proved that intermittent surface wetting with HC and brine can increase the likelihood of pitting in the HC/brine boundary region of the pipeline steel. The frequency of the phase boundary movement affects the pitting intensity. Corrosive effects were strongly dependent on the presence of inhibitors, its concentration and phase behaviour influenced by isopropanol. Increasing the inhibitor concentration mitigates pit formation in all surface regions. ECN measurements in combination with the in-house developed evaluation software proved to be a sensitive tool to quantify parameter effects in short exposure times. © 2013 by NACE International.