Development of Methodologies for Continuous and Batch Inhibitor Film Persistency Investigation in the Laboratory

Organic corrosion inhibitors (CIs) are widely used in the oil and gas industry to mitigate corrosion in pipeline transmission systems. Upstream, there are two distinct internal pipeline corrosion mitigation methods using inhibitors: continuous injection and batch inhibition. Each treatment mode has its own challenges, requiring specific knowledge of inhibitor film persistency (i.e., interrupted continuous injection or irregularity in batch inhibitor application frequency). The performance of applied corrosion inhibitors is typically evaluated in laboratory conditions, prior to field application. This study is focused on development of methodologies to investigate inhibitor film persistency using inhibitor model compounds, possessing only one molecular type, in both continuous and batch inhibition. For persistency studies related to continuous treatment, experiments were divided into three main steps: pre-corrosion, inhibitor addition, and inhibitor dilution. For batch inhibition, an inhibitor testing procedure was developed that can maintain stable water chemistry and avoid O2 contamination, with the potential to be adapted for top-of-the-line corrosion (TLC) environments. Corrosion rates were monitored using linear polarization resistance (LPR) in all experiments (except in TLC conditions). The Langmuir isotherm model was used to calculate adsorption coefficient kA and desorption coefficient kD for benzyldimethylammonium (BDA) inhibitor model compounds, possessing tetradecyl and hexadecyl tails, at different temperatures.Application of corrosion inhibitors confer many advantages for combatting internal pipeline corrosion in the upstream oil and gas industry. It is known that the associated costs for using corrosion inhibitors are low compared to other mitigation techniques [1]. For continuous injection procedures, water-soluble inhibitors are not expected to form long-lasting films, so they must be continuously injected to maintain their effectiveness. Batch inhibitors are usually higher molecular weight species and oil soluble. They tend to be more tenacious, providing a protective barrier between the water and the metal over a long period of time. For corrosion inhibitors used in the field, the physicochemical characteristics of the inhibitor molecules is of vital importance. These characteristics determine whether the inhibitor is classified as water-soluble or oil-soluble; a major factor relating to effectiveness and the way the inhibitor is applied [2].