Study On Pitting Behavior Of Stainless Steel By Electrochemical Noise

Electrochemical Noise (EN) is measuring the spontaneous corrosion potentialnoise fluctuation (current noise fluctuation) at open circuit potential or fixed current.The waves of potential noise and current noise in the electrochemical corrosionnoise technology is generated by the reaction of corrosion process itself, not withthe interference of external disturbance. So lots of information can be obtainedconcerning internal corrosion process or electrode corrosion. Electrochemical noisetechnique is a nondestructive and in-situ corrosion monitoring technology, so it canbe used for the measurement of localized corrosion effectively.In order to understand the electrochemical noise technique and apply to the fieldof corrosion monitoring, we will study304and316L stainless steel corrosion inparticular corrosive medium by electrochemical noise technique, and SEMobservation.Through the spectrum analysis of the electrochemical noise data, subsection ofthe corrosion process can be studied according to the peak number andcharacteristics of transient peak of electrochemical noise. Four stages aresummarized: passive stage, meta-stable pitting stage, stable pitting stage, post stablepitting stage. The peak number and characteristics of transient peaks in the noisespectrum are important indexes for determining the pitting development process.The time domain analysis was conducted for both system. Accordingto the standard deviation of current noise, noise resistance changes in thewhole process of corrosion, it is known that when304stainless steel soaking in the3.5%NaCl about120hours, the pitting phenomenon occur. While when316Lstainless steel soaking in the10%FeCl3about48hours, the pitting occur.The frequency domain analysis was conducted for both system as well. Theslope K of PSD curves for304and316L stainless steels are-2.53893and-3.04089respectively, indicating that the corrosion process is a pitting process.Finally, the electrochemical noise data of both steels in different system arecompared. SEM morphology observation corresponds to what electrochemical noisehas achieved.