Abstract

The corrosion protection of stainless steels is based on the formation of a passive layer of corrosion products, mainly chromium oxides and hydroxides. The passive layer is thermodynamically stable, adheres firmly, is only a few atomic layers thick and is therefore not visible. When formed over the entire surface without any gaps, it protects the thermodynamically unstable material underneath from corrosion. Corrosion reactions can therefore still occur on the material at defective points in the passive layer. In these corrosion reactions, the alloying constituents of the material go into solution in accordance with the chemical composition, as a result of which the corrosion products consist predominantly of iron ions. This document specifies a method for determining the state of the passive layer by means of a color change using a KorroPad® , which is based on the detection of iron ions by means of indicator solution. The KorroPad® method is suitable for comparative testing of stainless steel surfaces with regard to their passive layer formation. It is possible to test surfaces where the passive layer has formed automatically under atmospheric conditions after the manufacturing or processing process, as well as surfaces where the passivation has been supported by specific post-treatment measures (e.g. pickling and passivation).

Begin

2023-10-26

Planned document number

DIN 50024

Project number

06236446

Responsible national committee

NA 062-01-77 AA - Corrosion testing