Coupled Multielectrode Array Research Articles

Mapping the Galvanic Corrosion of Three Coupled Metal Alloys Using Coupled Multielectrode Array: Influence of Chloride Ion Concentration.

The galvanic corrosion behavior of three metal alloys commonly used in water desalination plants was investigated using coupled multielectrode arrays consisting of aluminum-brass (HAl77-2), titanium alloy (TA2), and 316L stainless steel (316L SS). The three electrode types were coupled galvanically and arranged in different geometric configurations. Their corrosion behavior was characterized as a function of the chloride concentration. The potential and current distributions of the three-electrode coupling systems display electrochemical inhomogeneity. Generally, the aluminum-brass wires are anodic versus the titanium alloy and stainless steel. The titanium alloy acts as a primary cathode, and the 316L SS acts as a secondary cathode. The corrosion rate of aluminum-brass depends on the concentration of chloride ion, with a maximum corrosion rate at a chloride concentration of 2.3 wt %. In terms of geometrical arrangements, when the anodic HAl77-2 wires are located on the edge and are connected to the 316L SS wires in the coupling system, the main anodic area enlarges, especially in the area adjacent to the 316L SS wires. When the HAl77-2 wires are located between (in the middle of) the two other types of wires, the corrosion rates are higher than the corrosion rates observed from the other two geometrical arrangements.

Coupled Multi-Electrode Array with a Sintered Ag/AgCl Counter/Reference Electrode to Investigate AA7050-T7451 and Type 316 Stainless Steel Galvanic Couple under Atmospheric Conditions

The corrosion electrochemistry of AA7050-T7451 and Type 316 stainless steel were investigated under thin electrolyte films and droplets utilizing a coupled multi-electrode array (CMEA). The CMEA was embedded in a 7050 panel in combination with a sintered Ag/AgCl electrode which functioned as both the reference and counter electrode. This coupled multi-electrode array enabled net cathodic and anodic reaction kinetics to be monitored as a function of position, time, and electrolyte shape. Cathodic kinetics increased under thin films and droplets of electrolyte relative to full immersion. Under droplet conditions, electrodes at the droplet edge experienced an increase in oxygen reduction compared to the center of the droplet. Lastly, a dissimilar metal galvanic couple CMEA enabled an understanding of galvanic corrosion rates under atmospheric conditions. For the first time, anodes switching to cathodes due to copper replating was observed in real time.

Study Pitting Corrosion of P110 Steel by Electrochemical Frequency Modulation Technique and Coupled Multielectrode Array Sensor

By using the electrochemical frequency modulation (EFM) technique, coupled multielectrode array sensor (CMAS), and other corrosion research techniques, the pitting corrosion behavior of P110 steel in oilfield formation water was studied. The results showed that serious pitting corrosion was observed on P110 steel at 90°C in oilfield formation water. The EFM and CMAS techniques could be used for monitoring or detecting pitting corrosion effectively. The average corrosion rates obtained by EFM and CMAS both decreased with time. At the first 12 h of the test the average corrosion rate was quite high and general corrosion occurred, and then the average corrosion rate decreased and the pitting corrosion was observed from the EFM results. The CMAS result showed that when the pitting corrosion happened, there were obvious localized anode and cathode pots on the metal surface that directly caused the pitting corrosion and might be related to the structure of the protective layer.

Monitoring copper corrosion in bentonite by means of a coupled multi-electrode array

ABSTRACTThis work focuses in monitoring the corrosion processes on copper in a slightly saline environment under oxic conditions, which simulated the first part of high-radioactive waste disposal in bentonite. Besides coupled multi-electrode arrays (CMEA), also electrochemical impedance spectroscopy measurements were implemented. It was expected that this combination of methods would define the general corrosion rate, as well as the spatio-temporal evolution of anodic and cathodic processes. Anodic currents measured by CMEA showed that the corrosion rates decreased with time. Since maximum anodic activity switched between the electrodes, this situation was not individually valid for all the electrodes. At the end of exposure, different spectroscopic techniques were applied in order to identify the modes of corrosion and types of corrosion products. Uneven general corrosion without evident pits was indicated.This paper is part of a supplement on the 6th International Workshop on Long-Term Prediction of Corrosion Damage in Nuclear Waste Systems.

Stifling of Crevice Corrosion and Repassivation: Cathode Area Versus Controlled Potential Decreases Assessed with a Coupled Multi-Electrode Array

The effects of limited remote cathode area on crevice corrosion propagation, repassivation, and anode site reorganization were investigated on AISI 316 stainless steel (UNS S31600) in 0.6 M NaCl at 50°C. Both multiple crevice assemblies and rescaled coupled multi-electrode arrays were utilized. Potentiostatically activated crevices were subjected to conditions that limited propagation by either: (i) stepping the potential downward below the repassivation potential, (ii) performing a downward scan of the potential from high potential, or (iii) decreasing the area of a galvanically coupled platinum cathode situated outside the crevice. In the first two cases, repassivation occurred when the potential reached the lower statistical limit of the repassivation potential measured on creviced specimens in a downward scan. During the galvanically coupled test, repassivation occurred when the galvanic cathodic current supplied became lower than the current required to maintain a couple potential equal to the repass...

Threshold Chloride Levels for Localized Carbon Steel Corrosion in Simulated Concrete Pore Solutions Using Coupled Multielectrode Array Sensors

Threshold chloride levels for localized corrosion of carbon steel material have been studied in three types of simulated concrete pore solutions: sodium hydroxide-potassium hydroxide (NaOH-KOH) with pH 11.6, calcium hydroxide (Ca[OH]2) with pH 12.6, and sodium hydroxide-potassium hydroxide-calcium hydroxide (NaOH-KOH-Ca[OH]2) with pH 13.3. The nonuniform corrosion rates of carbon steel were measured with coupled multielectrode array sensors (CMAS) when the chloride concentration was changed from 0.0005 mol/L to 1 mol/L in each solution. Open-circuit potentials were also measured from the coupling joint of the CMAS probes and electrodes made of rebar specimens immersed in the simulated pore solutions to verify the results from the CMAS probes.

A Review of Recent Patents on Coupled Multielectrode Array Sensors for Localized Corrosion Monitoring

The coupled multielectrode array sensor (CMAS) is an emerging technology for monitoring localized corrosion, such as pitting, intergranular attack, crevice corrosion, or other forms of nonuniform corrosion. The technique has been used for online, real-time corrosion monitoring in laboratories and field systems. In this paper, the patents related to the development of CMAS technology for localized corrosion monitoring are reviewed. These patents include applications in mapping or monitoring localized corrosion; methods for localized corrosion rate measurements; method to minimize internal current; improvement in electronics and software; planar CMAS probe; and high-temperature electrochemical sensors. Current and future developments of this corrosion monitoring technology are discussed. Keywords: Coupled Multielectrode Array Sensors, Corrosion monitoring, Localized corrosion, electrochemical sensor, multielectrode array, high-temperature electrochemical sensor, pitting, anodic electrodes, Multielectrode systems, electrode arrays, wire-beam electrode, Multi-phase corrosion, multielectrode sensors, carbon-coated electrodes, stainless steel

A Review of Recent Patents on Coupled Multielectrode Array Sensors for Localized Corrosion Monitoring

A Review of Recent Patents on Coupled Multielectrode Array Sensors for Localized Corrosion Monitoring

Internal Current Effects on Localized Corrosion Rate Measurements Using Coupled Multielectrode Array Sensors

Abstract Coupled multielectrode array sensors (CMAS) have been used for real-time monitoring of corrosion, particularly localized corrosion. The internal anodic current on the most anodic electrode...

A Review of Coupled Multielectrode Array Sensors for Corrosion Monitoring and a Study on the Behaviors of the Anodic and Cathodic Electrodes

Abstract Localized corrosion is often the cause of many failures and unplanned shutdowns in industry. For example, statistics have shown that more than 80 % of the corrosion-induced failures in the chemical processing industry are due to localized corrosion, rather than general corrosion. Thanks to the advancement in coupled multielectrode array sensors (CMAS) technology, localized corrosion rates can now be quantitatively measured. If interfaced with controllers, CMAS probes can be used to automatically control the dosing of corrosion inhibitors and reduce the cost for corrosion control. This paper presents an overview for the CMAS technology and the experimental data that verifies the working principles of the CMAS for localized corrosion rate measurement.

Development of Crevice-Free Electrodes for Multielectrode Array Sensors for Applications at High Temperatures

Abstract Coupled multielectrode array sensors (CMAS) have been used as online and real-time monitors for localized corrosion in both laboratory and field systems. In a CMAS probe, multiple miniature electrodes made of materials identical to the engineering component are used as sensing electrodes. The application of CMAS at high temperatures, up to 150°C in corrosive environments, however, is limited by degradation of the insulating mounting material, such as epoxy. Degradation of the mounting material can lead to crevice corrosion and causes an increase in the exposed surface area of the electrodes. In this study, the effectiveness of a diamond-like carbon film to protect the Alloy 22 (UNS N06022) electrodes in an acidic sodium chloride-sodium nitrate-potassium nitrate (NaCl-NaNO3-KNO3) salt mixture was demonstrated at 150°C. The average localized corrosion rate measured from the probe with coated electrodes in the NaCl-NaNO3-KNO3 salt mixture at 150°C was approximately 0.43 μm/y. In contrast, the averag...

Development of diamond-like carbon-coated electrodes for corrosion sensor applications at high temperatures

Coupled multielectrode array sensors have been used as online and real-time monitors for localized corrosion in both laboratory and field systems. Multiple miniature electrodes made of materials identical to the engineering component of interest are used as sensing electrodes. However, these devices have an upper operating temperature limit of approximately 70 °C because crevice formation between the electrode and the mounting material impairs their performance. In this paper, a crevice-free electrochemical sensor for corrosion monitoring at temperatures above 100 °C is presented. A diamond-like carbon thin film was deposited on the sensing electrodes using plasma immersion ion processing and its properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and laser Raman spectroscopy. The effectiveness of the diamond-like carbon film in protecting the Alloy 22 (Ni-22Cr-13Mo-3Fe-3W) electrodes in a corrosive NaCl–NaNO 3–KNO 3 salt mixture at 150 °C was demonstrated. The effective corrosion monitoring capability of the new electrochemical sensor at high temperatures was attributed to the pinhole-free microstructure, high electrical impedance, and high corrosion-resistance properties of the diamond-like carbon film.

Evaluation of the coupled multielectrode array sensor as a real-time corrosion monitor

Coupled multielectrode array sensors made of carbon steel and stainless steels were evaluated and compared with electrochemical noise (EN) sensors. Good correlations between sensor signals and solution corrosivity were observed for all multielectrode array sensors. Some correlation between the average pit index and solution corrosivity was observed for the carbon steel EN sensors, but not for the stainless steel EN sensors. The time-average noise resistances from the stainless steel EN sensors correlate well with solution corrosivity. There were, however, large random fluctuations and drifting for all EN signals, which make the EN sensors unreliable as real-time monitors.