Development of a Multi-Electrode
Array Sensor for Monitoring
Inclusive Dates: 08/01/00 - 12/12/02
Background - Localized corrosion is one of the most common failure modes for engineered structures. This form of attack often results in high rates of metal penetration at specific sites and leads to premature component failure, even though the majority of the metal surface may not be affected. An in-situ monitor that gives real-time indications of localized corrosion penetration rate is a highly desirable tool in optimizing the performance of engineered components in a localized corrosion environment.
Approach - The project was directed to develop a robust sensor for real-time monitoring of localized corrosion of engineered components, particularly the nuclear waste container components under alternating wet and dry conditions. Multiple miniature electrodes made of materials identical to the engineered component are used as the sensing electrodes of the sensor. The miniature electrodes are coupled together by connecting each to a common joint through independent resistors, with each electrode simulating part of a corroding metal. In a localized corrosion environment, anodic currents flow into the more corroding electrode and cathodic currents flow out of the less or noncorroding electrodes and such currents, as measured from the voltages across the resistors, are used as the signals for localized corrosion.
Accomplishments - A multichannel high-resolution (10-9 V) voltage-measuring system and the associated software were developed. The software has a graphical user interface for specifying the configuration of the measurement, including a map of the electrode locations, and data acquisition. The prototype sensor was fabricated with Type 304 stainless steel as the sensing electrodes. Experiments showed that the sensor responded well to changes in the chemical environment. Analyses showed that the degree of variation of the currents measured from the different electrodes can be used to indicate localized corrosion and estimate the penetration rate (see illustration below). Subsequent testing was conducted with sensors made from different alloys, including 1010 carbon steel; Types 302, 304 and 316 stainless steels; and Alloys 22, 276, and 600. The experimental results from these sensors showed that they can be used to effectively monitor localized corrosion in cooling water systems and concentrated chloride solutions, in humid air, and under hygroscopic salt deposits. If a proper insulation material such as ceramic is used, the sensor may be deployed under high-temperature, moderate-radiation field and episodic wet-dry conditions.