Research On Electrochemical Detection For Stress Corrosion Cracking Of Nuclear Plant Stainless Steel

Nuclear Power Plant has played an important role in our national energy resource developmental strategies. Many Large Nuclear Power Stations will have been built in the past ten years. However, corrosion is still great problem of the nuclear industry affecting components especially Stress Corrosion Cracking (SCC). The corrosion of Stainless Steel (SS) which is especially used as structural materials will influence the Nuclear power plant active time and security directly. It is significant to study the corrosion behavior, timely detection and proper action would reduce the costs of damage, and in some cases even prevent the occurrence of disastrous events. Electrochemical corrosion occurred under force is the essential of SCC. In this paper, Stress Corrosion Cracking of stainless steel electrochemical technologies is studied.In this paper, on line detective methods based on EN technology about SCC under the SSRT and constant load were presented in lab. The testing mode, data analysis and the system used in the field were discussed.Electrochemical voltage and current noise were measured by ZRA simultaneously during stress corrosion cracking (SCC) process of 304NG and sensitized 304SS in SSRT test. In order to characterize the SCC processes of austenitic stainless steel, Visual records and time analysis of the current and potential data along with the spectral estimation using FFT method and Wavelet analysis gave useful information on these corrosion processes. It obtained the curve of Rn. Moreover, EN potential and current spectrum characteristics were preliminary mastered and obtained the judgment to distinguish SCC generation from development.Acoustic emission (AE) technique and EN were used simultaneously to study the process of SCC on sensitized 304SS. There are at lease four stage of SCC which were the films formed, film rupture and SCC Initiation and propagation process. The analysis of the AE signals in conjunction with EN showed the two testing techniques had good consistency to detection of SCC.The corrosion behaviors of fatigue pre-cracking 304SS with and without stress were detected by means of EN measurements in different solution. The EN characteristics of cracking propagation were obtained. Moreover, the characteristics of surface morphology image and Volta potential distribution over the surface has been studied before and after experiment with Kelvin probe. The results showed that Kelvin and EN could get the same judgment that its cracking propagated.Use of electrochemical potential noise to detect corrosion behavior of the weld zone of 304SS in the heat concentrate lye, and analyzed its parameter. The high frequency roll-of slop K in the PSD plot could detect whether the localized corrosion occurred or not. When localized corrosion cracking initiation, amplitude was large and termination appeared, a high frequency plateau appeared in the power spectrum by use of the Fast Fourier Transform (FFT). Moreover, the different state of specimens had been distinguished by fn the frequency of events.Autoclave test system had been used to study the applicability of EN at high temperature and pressure with dynamic water system. Using the same electrodes measured by ZRA obtain the current and potential electrochemical noise in time domain. The results showed EN could be used to detect local corrosion sensitivity evaluation at high temperature and pressure with dynamic water system.