Virtual Instrumentation Technology In Electrochemical Corrosion Measurement

Electrochemical methods are irreplaceable in corrosion monitoring and detecting. Virtual instrument technology is characterized with self-defined function and software implementation. The combination of both technologies makes the researchers able to build measurement systems according to their special project with shorter development cycle and higher cost performance, and shows broad development space in the field of on-line and real-time corrosion detecting and monitoring. In the work of this dissertation, electrochemical methods and virtual instrument technologies were applied to build measurement systems to make a study of some practical projects: electrochemical measurements for atmospheric and marine corrosion of the metal coupons at natural environmental corrosion test stations of China, initial detection for local corrosion of the nuclear structural materials with electrochemical noise technique, and electrochemical detection for corrosion of the grounding grids at power plants and transform substations.A measurement system based on electrochemical frequency modulation (EFM) technique was developed, which could implement EFM measurement. The EFM system and EFM technique were examined by laboratory experiments and proved to be available to determine the electrochemical kinetic parameters like corrosion rate in various of corroding systems. A corrosion electrochemical test system for in-field detection of the metal coupons in natural sea was also developed, and was used to detect the corrosion of Q235 steel in fully immersion zone at Zhoushan marine corrosion test site with linear polarization resistance (LPR) and EFM measurement. The results showed that although the Rp obtained with EFM tended to be lower than its real value, corrosion rate was offered directly. Thus, EFM technique was shown to be a possible candidate for corrosion detecting and monitoring at the national corrosion test sites.A measurement system and data analysis software were developed based on electrochemical noise technique, which were applied to detect the atmospheric corrosion of aluminum alloy and the stress corrosion crack of nuclear structural materials. The electrochemical potential and current noise were acquired by aluminum alloy atmospheric corrosion sensor in natural atmosphere as well as the noise resistance. Characteristic of the electrochemical noise signals were analyzed for 304 austenitic stainless steel and 800 Nickel-based alloy C-ring specimens in distilled water at room temperature. It was initially verified that EN technique was effective to detect atmospheric corrosion and local corrosion of nuclear structural materials, which provide a powerful tool for further research.A measurement system and data analysis software were developed for grounding grid corrosion detection. Polarization resistances of the grounding grid at measured positions were obtained with galvanostatic measurement as an evaluating parameter for corrosion. In-field experiments were performed at several power plants and transform substations, through which the effect of the apertural current limit sensor, the proper test apparatus and data analysis method were studied. The results showed that the current flowing between working electrode and auxiliary electrode were limited in a certain area by the apertural current limit sensor, and the noise disturbance and the IR drop caused by soil resistance were well eliminated by wavelet transform and Levenberg-Marquardt algorithm respectively. The grounding grid corrosion electrochemical test system could provide useful information for grounding grid corrosion diagnosis.