Program Brief

Statement of Problem: Localized corrosion is one of the most common failure modes for engineering components. 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 for optimizing the performance of engineering components.

Approach and Accomplishments: Multiple miniature electrodes made of materials identical to the engineering component are used as sensing electrodes. The miniature electrodes are coupled together by connecting each of them to a common joint through independent small resistors, with each electrode simulating part of a corroding metal. In a localized corrosion environment, anodic current flows into the more corroding electrodes and cathodic current flows out of the less or noncorroding electrodes. The resulting electrical currents, as measured from the voltage drop across the small resistors, are indicators of localized corrosion.

Various prototypes have been fabricated with carbon steels, stainless steels, and nickel-based alloys. These prototypes were successfully used to measure localized corrosion occurring in simulated cooling water conditions and in concentrated chloride solutions, humid air, and under hygroscopic salt deposits. Chemical process plant tests also are being conducted.

A multichannel high resolution (10-9 V) voltage measuring electronic system and the associated software were developed also. The software has a graphical user interface for specifying the configuration of the measurement, including mapping the electrode locations. During measurement, the current values are stored in memory and displayed numerically and graphically on a computer monitor according to their location in the array.

Client Benefits: The coupled multielectrode sensor has been demonstrated to be a highly reliable localized corrosion sensor for a variety of materials in different environments such as aqueous solutions, humid air, and under salt deposits or biofilms. Furthermore, the coupled multielectrode sensor can be designed for wide ranges of temperatures (up to 900° C) and pressure (up to 1,600 psig).