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

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

Atomic force microscopy study of the adsorption of surfactant corrosion inhibitor films

The properties of an adsorbed corrosion inhibitor-tall oil fatty acid (TOFA) imidazolium chloride-on mica, gold, and X65 steel were studied using in situ atomic force microscopy (AFM). Topography images and thickness measurements show that the structure of inhibitor film changes from monolayer to bi-layer as inhibitor concentration exceeds its critical micelle concentration (CMC). Further kinetic study indicates that the developing of a full film took about 6 h. Quantitative force measurements were performed to evaluate the forces associated with adsorption of inhibitor films. Results show that the mechanical stress needed to physically remove adsorbed inhibitor molecules is of the order of MPa. © 2014, NACE International

Selection of electrode area for electrochemical noise measurements to monitor localized CO<inf>2</inf> corrosion

The simultaneous fluctuations of potential noise and current noise between two nominally identical X-65 mild steel electrodes were recorded using a ZRA (Zero Resistance Ammeter) to monitor localized CO 2 corrosion in CO 2 -saturated 1 wt% NaCl solution at 80°C. Electrochemical noise (EN) was obtained from both 11.6 cm 2 and 1 cm 2 specimens to understand how the surface area affects EN signals. Linear polarization resistance (LPR) measurements were conducted to investigate the general CO 2 corrosion behavior. Surface morphologies and pit depths were observed by scanning electron microscopy (SEM) and infinite focus microscopy (IFM) for 3D optical analysis. The results showed that the electrode area significantly influenced the EN signals of localized CO 2 corrosion. Transients related to metastable pitting were best observed with 1 cm 2 specimens but not clearly obtained for 11.6 cm 2 specimens. © 2012 The Electrochemical Society