Study On The Electrochemical Noise Characteristics Of X70 Steels Corrosion In Soils And Their Analysis Methods

In this paper, electrochemical noise (EN) technique is applied to investigate thecorrosion behaviors of X70 steels in Daqing and Ku'erle soils in the initial and shortcorrosion period. Statistical and Cluster analysis methods are used to analyze the EN data.The corrosion status and EN during the initial corrosion period will be influenced bythe temperature (T) and moisture content of studied soils. In Daqing soil, as the T increased,the corrosion area and the rate of current noise drift increased and the amplitude offluctuation (noise peak) decreased. With the moisture content rising, the area and depth ofcorrosion and the rate of E, I drift increased, the amplitude of E fluctuations decreased andthe amplitude of I fluctuations increased.The moisture content will also influence the corrosion status and EN in the short termtest. The X70 steel corroded heavily as moisture contents increased in Daqing soil(0~45d)and Ku'erle soil (0~30d), which appeared that the corrosion area and depth developed asmoisture content increases. Along with time, the corrosion area increased and ENcharacteristic peaks decreased significantly.Through the statistical and cluster analysis to the EN data obtained from Daqing soil(30℃, 10% moisture content), two clusters were determined, in which the cluster 1 wasrelated to the corrosion state in the first 6 days and the cluster 2 was related to the continued6 days. This result is in good accordance with the EN characteristics in the differentcorrosion period. The values of E and I of the measured EN were larger in the first6days, and then decreased in the continued 6 days; the transient number and the transientamplitude of EN increased firstly and then decreased during 1-9d.The statistical and cluster analysis method was also successfully applied to analyze theEN data obtained from Daqing soil (30℃, 15% moisture content). The analysis showed thatthe three months experimental results can be classified into two corrosion states, includingquick development state and stable development state; the first 15 days for quickdevelopment state and the average corrosion rate is the maximum, and the corrosion rate isrelatively stable after 15 days. In addition, comparing the corrosion test results and statistical parameters of EN measured at different conditions, it implied the noise resistance(Rn) has a negative correlation with the corrosion rate.