A novel electrochemical method for monitoring corrosion under insulation

Purpose - The objective of this work was to develop practical experimental techniques for monitoring corrosion in "difficult-to-test" conditions such as corrosion under insulation (CUI).

Design/methodology/approach - An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) method has been used in combination with noise signature analysis for the first time to monitor the penetration of corrosive species under simulated corrosion-under-insulation conditions. Corrosion of aluminium exposed under insulation materials such as rock wool, glass wool, cotton wool and tissue paper has been successfully monitored.

Findings - A typical potential noise signature of a major potential jump from AA1100 WBE was observed which corresponded to the corrosive species reaching the WBE surface in WBE current distribution map. A good correlation between the galvanic current maps and the corroded surface was also observed.

Originality/value - The preliminary results suggest that the proposed novel electrochemical method is capable of monitoring CUI.

An electrochemical method for measuring localized corrosion under cathodic protection

 A new method has been developed to measure metal corrosion rates and their distribution under cathodic protection (CP). This method uses an electrochemically integrated multi-electrode array to take local measurements of cathodic current density while simulating a continuous metallic surface. The distribution of cathodic current densities obtained under CP was analyzed to estimate the anodic current component at each electrode of the array. Corrosion patterns determined by this new method have shown good correlation with visual inspection and surface profilometry of the multi-electrode array surface.

Electrochemical method for studying localized corrosion beneath disbonded coatings under cathodic protection

This paper presents a new method for measuring localized corrosion under disbonded coatings by means of an electrochemical sensor, denoted differential aeration sensor (DAS). It measures the distribution of electrochemical currents over an electrode array surface partially covered by a crevice that simulates a disbonded coating. The DAS has been evaluated using immersion tests at open circuit and under cathodic protection (CP) conditions. Under both conditions, anodic as well as cathodic current densities were detected within the crevice. A fundamental understanding for the detection of anodic currents under CP has been explained in terms of basic electrochemistry. Based on the current distribution data provided by the sensor, two different analysis methods have been used to estimate corrosion and its distribution. These methods consisted of a direct application of Faraday's Law to the anodic currents detected by the array, and on a sensor-specific method denoted corrected currents' method. It has been demonstrated that under diffusion controlled conditions this latter method produces a better corrosion estimation than the direct application of Faraday's Law. The corrected currents' method allowed the estimation of corrosion patterns outside the crevice under CP. Good correlation between electrochemical calculations and surface profilometry results has been obtained.

New crevice corrosion testing method and its use in the investigation of oil stain

A new electrochemical method was developed to investigate crevice corrosion and its inhibitors. A wire beam electrode was used to allow electrochemical parameters to be measured directly from the crevice area. As an example, oil stain was investigated using this method.

Characterising nonuniform electrodeposition and electrodissolution using the novel wire beam electrode method

An electrochemically integrated multi-electrode system namely the wire beam electrode (WBE) has been applied as a new method of characterising nonuniform electrodeposition and electrodissolution, by measuring and identifying characteristic patterns in electrodeposition and electrodissolution current distribution maps. Various patterns of electrodeposition current distribution have been obtained from Watts nickel plating and bright acid copper plating baths with the effects of several affecting factors such as bath concentration, temperature, agitation and electrolyte flow. Typical patterns of electrodissolution current distribution have also been detected over a WBE surface under anodic dissolution. This work suggests that the WBE method can be used as a new tool for monitoring, characterising and optimising electrodeposition and electrodissolution processes in the laboratory, and can also be applied as an experimental method to verify the accuracy and completeness of mathematical models for electrodeposition and electrodissolution.

Electrochemical methods applied in innovative corrosion inhibitor experiments : case studies

Electrochemical methods can be used more effectively if innovative experiments are designed and employed. This is especially true if a corrosion system to be tested involves inhibitors that could change the mechanism and pattern of corrosion in complex ways. This paper discusses corrosion inhibitor test design using several practical cases as examples. Particular attention is on difficult issues such as the simulation of localized corrosion phenomena and the influence of corrosion mechanism on inhibitor test results. ©2012 by NACE International.

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.

Characterising localised corrosion inhibition by means of parameters measured by an electrochemically integrated multielectrode array

Electrochemical parameters including maximum anodic current density, total anodic current density, the number of anodic sites and the localised corrosion intensity index have been extracted from galvanic current distribution maps that were acquired using an electrochemically integrated multielectrode array, namely, the wire beam electrode. Experiments have been carried out to demonstrate the application of these new electrochemical parameters for characterising localised corrosion inhibition of metals. A typical corrosion inhibitor, potassium dichromate, was found to affect localised corrosion processes in various ways, for instance in sodium chloride solutions, it was found to inhibit localised corrosion of aluminium alloy AA 2024-T3 by suppressing galvanic corrosion activities occurring over the alloy surface, whereas it was found to control localised corrosion of AA 1100 by creating a large number of minor anodes distributing randomly over the metal surface.

On-site determination of Pb2+ and Cd2+ in seawater by double stripping voltammetry with bismuth-modified working electrodes

To meet the urgent requirement of determining trace Pb2+ and Cd2+ in seawater on site, herein we developed a simple but novel electrochemical method, named as double stripping voltammetry, using only a portable heavy metal analyzer. The proposed method consisted of three steps: First, the targeted heavy metal ions in bulk solution were concentrated onto an ionic liquid-graphite-based paste working electrode (ILGPE), which exhibits a dramatic ability of accumulation, by electrodeposition in the presence of Bi3+. Second, the three-electrode arrangement, including the ILGPE loaded with the reduced products, was transferred into 1.0mL acetate buffer solution, followed by a stripping procedure. Third, the measurement was performed with the other stripping voltammetry procedure by using a glassy carbon electrode as working electrode. Under optimum conditions, the linear range values for Pb2+ and Cd2+ in seawater were 0.2-3.2 μg/L and 0.1-3.2 μg/L, respectively. The concentrations of Pb2+ and Cd2+ in five real samples collected from coastal sites of Qingdao City were determined on site, and the results were in good agreement with that obtained with the atomic absorption spectroscopy method. In addition, the analytical performance of working electrode modified with Bi film by in situ mode was investigated in comparison with that by ex situ mode. The results showed that the in situ mode was much better than the ex situ one.

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.