KorroPad is a new rapid colour test developed at BAM Federal Institute for Materials Research and Testing. It enables stainless steel surfaces to be tested inexpensively and rapidly even by non-specialists.
The KorroPad test enables steel surfaces to be checked immediately after processing or in the delivery state. Three pads are needed for a test that provides a snapshot of the state of the passive layer. The pads are placed on the stainless steel surface. First, the surface is cleaned with acetone or alcohol and the pads are then lightly pressed onto the surface to be tested. They are removed with a spatula after 15 minutes and placed on a plastic support film where they can be scanned or photographed.
The period of 15 minutes is very fast compared to other methods, which often take several hours or even weeks. The gel-like pads are made of water and a ferric ion indicator. If the protective chromium oxide layer is missing on the steel surface, the indicator reacts with the iron ions in the material. The outcome is that the indicator changes its colour and blue dots appear on the slightly yellow pads. Each point indicates a spot on the steel surface where the protective passive layer was not able to develop.
