Study Of Inhomogeneity Of Galvanic Corrosion Of Brass/Stainless Steel Couple By Wire Beam Electrode

Galvanic corrosion occurs when two different metals are electrically connected, especially for couples with significant difference of electrochemical properties. Now corrosion potential and current density as evaluating indicators of evaluation standards of galvanic corrosion for GB/T 15748-2013 are average values of whole metal surface. It is hardly to characterize the corrosion difference between different areas. As we all know, inhomogeneity would influence later corrosion process. How to precisely characterize the inhomogeneity of galvanic corrosion plays an important role in the evaluation and prediction of galvanic corrosion of equipment components. And research on galvanic corrosion for couples with similar electrochemical property is rarely reported. Wire beam electrode technical can easily meet the request for heterogeneous corrosion measuring. Galvanic corrosion behavior between H62 brass and 316L stainless steel couple with similar electrochemical property was studied in 3.5%NaCl solution by this technical combined with traditional electrochemical technical and observation of corrosion product, and also the development with corrosion time. The main contents are as follows:(l)The behaviors of two single metal WBE made by brass and stainless steel respectively and couple WBE made by these metals in 3.5%NaCl solution were investigated. The distributions of electrochemical parameters reveal there is no apparent difference on brass WBE, and the corrosion current density is lower. Anode area and cathode area coexist on the surface, but location was not fixed. Corrosion rate decreased with immersion time. The potential of stainless steel WBE is more positive, and increases gradually during the exposure time. Small cathodic current density dispersed on the whole surface, without anodic current density. When these two metals are electrically coupled, the distributions of electrochemical parameters come to inhomogeneous. No matter which kind of current it was, current density was larger than those on single WBE. Galvanic corrosion effect is obvious, and had the characteristics of inhomogeneity. Corrosion degree decreases with corrosion time.(2)The effect of area ratio on inhomogeneity of galvanic corrosion was investigated. The results show that corrosion rate reach to a relatively steady state after 24h.With increasing of brass area, anode brass get cathodic current which is larger than that of stainless steel area, and galvanic corrosion become more heterogeneous. The corrosion rate increases at first and then decreases with increasing of brass area ratio, indicating that inhomogeneity accelerates corrosion rate in a certain degree. Polarization curve illustrates inhomogeneity of galvanic corrosion is observed because the difference between brass area internal is bigger than that of between brass area and stainless steel area.(3) The effect of temperature on inhomogeneity of galvanic corrosion was also investigated. The results indicate the potential on WBE surface decreases apparently and corrosion rate increases with the increase of temperature. Galvanic corrosion become more heterogeneous, the inhomogeneity of galvanic corrosion is largest at 50?. Analysis results confirm that the brass area internal corroded more severely with increasing temperature, resulting in reducing the galvanic corrosion effect of brass area internal.