Simultaneous measurement of corrosion potential and hydrogen penetration using double-head scanning Kelvin probe

High-strength steels, such as high-strength bolts or steel plates are considerably sensitive to hydrogen embrittlement. Serious safety problems in steel structures are possible, because they are exposed to atmospheric condition containing chloride ions. Embrittlement is induced by hydrogen penetration during atmospheric corrosion. We developed Double-Head Scanning Kelvin Probe (DHSKP) equipment to clarify the relationship between the corrosion process and hydrogen permeation. Each probe can simultaneously measure the corrosion potential on the corroded side and surface potential on the hydrogen-detecting side at the same time. In this study, we investigated the correlation between the corrosion potential and hydrogen permeation under changing conditions from wet to dry processes on the surface of a steel sample. During the drying process, the corrosion potential at the rust layer that precipitated in the early wetting condition showed a less noble potential locally, whereas the surface potential of the Pd film on the hydrogen detection side showed a less noble potential locally. The hydrogen permeation sites were limited to small spots in the opposite area, where the corrosion potential showed a less noble local-potential during the drying process. Hydrogen penetration by corrosion likely occurs in acidic liquids under the rust layer during the drying process.