Visualising dynamic passivation and localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients

A new method of visualising dynamically changing electrode processes has been demonstrated by mapping localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients. Dynamically shifting external electrical interferences such as anodic transients are known to affect the efficiency of cathodic protection (CP) of underground pipelines; however unfortunately conventional techniques including electrochemical methods have difficulties in measuring such effects. In this paper we report that the wire beam electrode has necessary temporal and spatial resolutions required for measuring and visualising the dynamic effects of anodic transients on CP, passivation and localised corrosion processes occurring on buried steel surfaces. For the first time a critical anodic transient duration has been observed and explained as the incubation period for the breakdown of passivity and the initiation of localised corrosion.

Wear mechanisms and microstructure of pulsed plasma nitrided AISI H13 tool steel

AISI H13 tool steel discs were pulsed plasma nitrided during different times at a constant temperature of 400 °C. Wear tests were performed in order to study the acting wear mechanisms. The samples were characterized by X-ray diffraction, scanning electron microscopy and hardness measurements. The results showed that longer nitriding times reduce the wear volumes. The friction coefficient was 0.20 ± 0.05 for all tested conditions and depends strongly on the presence of debris. After wear tests, the wear tracks were characterized by optical and scanning electron microscopy and the wear mechanisms were observed to change from low cycle fatigue or plastic shakedown to long cycle fatigue. These mechanisms were correlated to the microstructure and hardness of the nitrided layer.

Carbon dioxide corrosion inhibition : an overview of recent research on new inhibitor development

Since the introduction of inhibitors to the oil and gas industry in the 1940’s, corrosion inhibition has played a key role in carbon dioxide (CO2) corrosion control. Major inhibitor discoveries occurred from the late 1940's to the late 1960's, followed by the refinement of formulations and the development of improved application methods. Over the past two to three decades, although some new derivatives of existing inhibitors such as amide, amine and imidazoline have been reported, there have been few if any discoveries of new CO2 corrosion inhibitors. In recent years, the development of environmentally friendly inhibitors and the inhibition of localised corrosion have become driving forces behind new advances in corrosion inhibitor technology. Recently a rare earth metal organic compound, lanthanum 4-hydroxy cinnamate has been found to be an efficient corrosion inhibitor for mild steel in CO2 containing aqueous media. A resorcinarene acid has been found to provide effective localised corrosion inhibition by promoting a random distribution of insignificant anodic currents. The advent of advanced scanning probe techniques and an electrochemical integrated multi-electrode array have facilitated the discovery of corrosion inhibitors. This paper provides a brief overview of recent progress in this field.

A corrosion inhibition study of steel grinding balls in an oxygen and alkaline environment

The corrosion of steel grinding balls is a major recurrent cost for mill operators concerned with the production gold. Subsequently, the use of corrosion inhibitors in production fluids, which is typically at pH >9, is an attractive and economical option. This study reports on the corrosion wear of steel grinding balls under alkaline/oxygen conditions and in presence of cyanide. A fundamental study on the influence of several inorganic-based inhibitors (i.e., nitrite, chromate, silicate, hexametaphosphate) on the corrosion rate of carbon steel was undertaken. Subsequently, the corrosion performances of various inhibitors were evaluated in stirred vessels. Corrosion rates were determined via mass loss and electrochemical methods (i.e., linear polarisation, Tafel). It was observed that inhibitors based upon chromate provide superior protection under the conditions investigated in this study. In lime treated, high chloride waters, chromate gave over 80% protection at levels of 10 100 ppm with no evidence of pitting.

Synergistic corrosion inhibition of mild steel in aqueous chloride solutions by an imidazolinium carboxylate salt

Mild steel infrastructure is constantly under corrosive attack in most environmental and industrial conditions. There is an ongoing search for environmentally friendly, highly effective inhibitor compounds that can provide a protective action in situations ranging from the marine environment to oil and gas pipelines. In this work an organic salt comprising a protic imidazolinium cation and a 4-hydroxycinnamate anion has been shown to produce a synergistic corrosion inhibition effect for mild steel in 0.01 M NaCl aqueous solutions under acidic, neutral, and basic conditions; an important and unusual phenomenon for one compound to support inhibition across a range of pH conditions. Significantly, the individual components of this compound do not inhibit as effectively at equivalent concentrations, particularly at pH 2. Immersion studies show the efficacy of these inhibitors in stifling corrosion as observed from optical, SEM, and profilometry experiments. The mechanism of inhibition appears to be dominated by anodic behavior where dissolution of the steel, and in particular the pitting process, is stifled. FTIR spectroscopy provides confirmation of a protective interfacial layer, with the observation of interactions between the steel surface and 4-hydroxycinnamate.

Corrosion mitigation of mild steel by new rare earth cinnamate compounds

Corrosion rate measurements based on weight loss (i.e., mild steel immersed for seven days in 0.01 M NaCl) and linear polarization resistance (LPR) techniques have shown that even low concentrations (200 ppm) of cerium and lanthanum cinnamates are able to significantly inhibit corrosion. Of all the compounds investigated in this work Ce(4-methoxycinnamate)3· 2 H2O and La(4-methoxycinnamate)3· 2 H2O compounds exhibited the greatest inhibition and, in comparison with the component inhibitors, a synergy was clearly observed. The mechanism of corrosion inhibition was investigated using cyclic potentiodynamic polarization (CPP) measurements. The results suggest that La(4-nitrocinnamate)3· 2 H2O and Ce(4-methoxycinnamate)3· 2 H2O behave as mixed inhibitors and improve the resistance of steel against localized attack.

ATR characterisation of synergistic corrosion inhibition of mild steel surfaces by cerium salicylate

The nature of deposits on mild steel surfaces formed by exposure to corrosive and inhibiting solutions has been examined by attenuated total reflectance spectroscopy. For cerium-based inhibitors, e.g. CeCl₃ the formation of cerium-containing coatings was detected whilst the cerium carboxylate Ce(sal)₃ (sal=salicylate), which combines the Ce³⁺ with the known organic inhibitor sal⁻, was shown to involve substantial deposition of both cerium and a salicylate species. These results, combined with corrosion inhibition data for the respective inhibitor compounds clearly indicate a synergistic corrosion mechanism for Ce(sal)₃ which underpins the improved performance of this corrosion inhibitor in comparison to the individual components (i.e. Na(sal) or CeCl₃).

Stability of oxide films formed on mild steel in turbulent flow conditions of alkaline solutions at elevated temperatures

In the industries involving alkaline solutions in different process streams, the nature and stability of oxide films formed on the metallic surfaces determine the rates of erosion–corrosion of the equipment. In the present study the characteristics of the oxide films formed on AISI 1020 steel in a 2.75 M sodium hydroxide solution at temperatures up to 175°C, have been investigated by employing electrochemical techniques of cyclic voltammetry and chronoamperometry. The experiments were carried out in an autoclave system based upon a ‘rotating cylinder electrode’ geometry to determine the effects of turbulence on the stability of the films. The results suggest that little protection is afforded in the active region (at about −0.8 V_SHE). In the passive region at low potentials (−0.6 V to −0.4 V_SHE), it appears the films are compact and more stable, and therefore provide good protection. At higher potentials (>−0.4 V_SHE) in the passive region, the results suggest that film formation and dissolution occur simultaneously and the increase in temperature and turbulence causes a breakdown of the passive film resulting in a situation similar to nonprotective magnetite growth.

Concentration monitoring and performance of a migratory corrosion inhibitor in steel-reinforced concrete

Inhibitor concentration depth profiles for concrete samples treated with a proprietary migratory corrosion inhibitor (of the Cortec MCI range) are presented. The treated concrete was cored and these cores were then sectioned and crushed before being immersed in distilled water to extract the available inhibitor. The amine concentrations were quantified using an ammonium-sensing electrode and were then related to the inhibitor concentration present. The inhibitor examined, reported to contain a combination of volatile amines and amino carboxylate compounds, was found to readily diffuse through concrete. The inhibitor was subjected to a 5-year trial and found to be effective in suppressing corrosion of steel reinforcement in the presence of high chloride concentrations. The concentration profiles indicate that only relatively low concentrations of inhibitor were required to achieve inhibition in this case.

Review of critical issues in carbon dioxide corrosion testing and monitoring techniques

This paper presents a brief review of major techniques applied in carbon dioxide corrosion testing and monitoring. The focus is on the advantages and disadvantages of variously designed testing apparatus and monitoring devices for localized corrosion detection and assessment. Critical factors affecting the reliability and accuracy of major corrosion testing techniques are briefly discussed. It is concluded that major reasons that lead to reporting of inaccurate corrosion rates and patterns include: (i) limitations in conventional electrochemical and nonelectrochemical methods for localized corrosion measurements, and difficulties in data interpretation; (ii) challenges in simulating localized corrosion mechanisms and their changes with the extension of corrosion testing. Underdeposit corrosion testing is presented as a case to illustrate challenges in simulating localized corrosion processes and mechanisms. Experiment data have been presented to show potential difficulties of the artificial pit electrode method in evaluating underdeposit corrosion and its inhibitors. The wire beam electrode method has been used to study underdeposit corrosion with and without inhibitor present. Several interesting corrosion mechanisms have been revealed at different stages of underdeposit corrosion processes.

The corrosion inhibition mechanism of new rare earth cinnamate compounds — electrochemical studies

A combination of linear polarisation resistance (LPR) and cyclic potentiodynamic polarisation (CPP) measurements demonstrated that the lanthanum-4 hydroxy cinnamate compound could inhibit both the cathodic and anodic corrosion reactions on mild steel surfaces exposed to 0.01 M NaCl solutions. However, the dominating response was shown to vary with inhibitor concentration. At the concentrations for which the highest level of protection was achieved, both REM-4 hydroxy cinnamate (REM being lanthanum and mischmetal) displayed a strong anodic behaviour for mild steel and their inhibition performance, including their resistance against localised attack, improved with time.

Electrochemical impedance spectroscopy (EIS) measurements and modelling were carried out so as to propose a simple electrical model and correlate the extracted parameters to the inhibition mechanism put forward for REM-cinnamate based compounds. The results supported the high corrosion inhibition performance of the compounds as well as the build-up of a protective film with time. Based on a two-layer model the results suggested that the upper layer of the inhibitor film seemed to offer less resistance to the diffusion of electrochemically active species than the highly resistive inner layer at the film/metal interface.

Studying and evaluating anti-corrosion coatings and inhibitors using the wire beam electrode method in conjunction with electrochemical noise analysis

Purpose – To provide a summary of research work carried out mainly in the authors' group for evaluating various protective coatings including rustproofing oils, and also for studying corrosion inhibitors using the wire beam electrode (WBE) method.

Design/methodology/approach – A range of published papers published during the past 15 years was summarised and reviewed. Recent research work in the authors' group was also included, which involved the combined use of the WBE with electrochemical noise analysis and the scanning reference electrode technique.

Findings – The WBE method has been developed into a very useful tool of evaluating the performance of coatings and inhibitors. In particular, The WBE is uniquely applicable for determining the performance of coatings and inhibitors to control localised corrosion.

Research limitations/implications – Focusing mainly on recent research.

Practical implications – A useful source of information for researchers and graduate students working in the areas of organic coating and inhibitor research.

Originality/value – The first summary or review on this research topic.

A novel sensing technique for monitoring pitting corrosion of stainless steel type 316L

A novel electrochemically integrated multi-electrode array namely the wire beam electrode(WBE) in combination with noise signatures analysis has been designed to monitor pittingcorrosion of one of the best corrosion resistance ferrous alloys, stainless steel type 316L.From the direct correlation of electrochemical potential noise signatures and galvanic currentdistribution maps during pitting corrosion processes, two characteristic noise patterns wereobserved prior to stable pit formation: (i) the characteristic ‘peak’ of rapid potential transient,towards less negative direction, followed by recovery (termed noise signature I) was found tocorrelate with the disappearance of unstable anode; (ii) the characteristic noise pattern ofquick potential changes towards less negative direction followed by no recovery (termed noisesignature II) was found to correspond with the massive disappearance of minor anodes leadingto formation of highly localized major anodes in the galvanic current distribution maps.