Effects Of Protection Potential On Cathodic Process And Mechanical Properties Of Typical Steels In Marine Environment

With the rapid development and utilization of marine resources, cathodicprotection technology has been widely used on ocean engineering facilities.Reasonable and effective cathodic protection potential can restrain the uniformcorrosion of steel. However, over-protective potential would increase the tendencyof hydrogen evolution reaction, thus resulting in hydrogen embrittlement of thehigh-strength steel. Therefore, in the cathodic protection design, it is of vitalimportance to choose the reasonable cathodic protection potential.In this paper, electrochemical impedance spectroscopy, potentiostatic cathodicpolarization, potentiostatic polarization, Devanathan-Stachurski bipolar cell testing,tensile test, and microhardness testing methods are used to study the hydrogenembrittlement characteristics of steel for marine engineering with impressed currentcathodic protection (CP) in3.5wt.%NaCl solution, which is of great practicalsignificance for effective corrosion inhibition, providing a theoretical basis forpractical application in the future. The main research results are as follows:Electrochemical impedance spectroscopy as well as cathodic polarization curveis applied to analyze the electrochemical properties of ZG06Cr13Ni4Mo steel, Q235steel and304L stainless steel. The results show wider cathodic protective potentialranges of ZG06Cr13Ni4Mo steel and304L stainless steel than Q235steel in3.5%NaCl solution. The optimum protective potential for the three materials are-0.75V,-0.85V and-0.75V respectively. Hydrogen evolution potentials are-1.00V,-1.00V and-1.00V respectively. Hydrogen permeation results showed the hydrogen’sentry to the interior of the material matrix while the applied potential is not reachingthe hydrogen evolution potential, hydrogen concentration increase with the negativeshift of protection potentials.Static tensile test combined with fracture morphology analysis are used to studythe effect of optimum protective potential applied to ZG06Cr13Ni4Mo steel, Q235steel,304L stainless steel. Results showed that properties of the materials are notdramatically changed under optimum protective potential. ZG06Cr13Ni4Mo steelbrittle fracture has been observed without hydrogen evolution reaction happened. When reaching hydrogen evolution reaction potential, secondary crack appears andmaterial performance are totally destroyed.Microhardness test was used to characterize the mechanical properties of thematerial sueface. Results showed that in3.5%NaCl solution, the overall hardness ofQ235steel increased with negative shiftted cathodic protection, the hardness of thematerial under the same potential decreased from surface to center.