Abstract: The recognition and monitoring of localized corrosion at the early stage on the inner wall surface of pipes are extremely difficult and simultaneously the reliable approach for recognition and monitoring is missing. Here we report a spatially resolved method to recognize and monitor the localized corrosion in a non-destructive way based on the permeating hydrogen signal generated from localized corrosion itself. A simulative localized corrosion was created on one side surface of the carbon steel specimen where a dot of wet elemental sulfur was introduced to accelerate the corrosion on the local region. While, the potential on the other side surface (the reverse side of the corrosion site) of the specimen was measured using a scanning Kelvin probe. The results show that the permeating hydrogen generated from localized corrosion easily arrives on the reverse side surface of the corrosion site and then causes a huge change in surface potential. The location resolution of potential distribution can be revealed with micron level. Therefore, it is thought that the location of localized corrosion can be recognized by the permeating hydrogen signal distribution on the reverse side surface of the corrosion site since the region of potential decreasing is highly corresponding to the corrosion site. Moreover, the strength of the permeating hydrogen signal is highly related to the corrosion depth and transient corrosion rate of localized corrosion. This means that the localized corrosion development can also be monitored using the permeating hydrogen signal. Therefore, it can be expected that the localized corrosion occurring on the inner wall surface of pipes or equipment can be recognized and monitored successfully on the outer wall surface in a non-destructive way once the permeating hydrogen is present during the localized corrosion proceeding.

Key words: Permeating hydrogen, Localized corrosion, Potential, Corrosion monitoring, Scanning kelvin probe