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Online Laboratory Magazine
09/26/2021

05/04/2017

Rapid test for the surface of stainless steel

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Whether it is a car, a skyscraper or a bridge: stainless steel is used almost everywhere in our daily life. Its corrosion resistance is important so that no safety risk arises. Stainless steels can be tested non-destructively in just 15 minutes using the rapid colour test developed by BAM before they are ever used. In the meantime, companies are already using the method called KorroPad and it is already on the curriculum in vocational schools and universities.

Tiny weak spots in the steel

Stainless steel is covered by a protective chromium oxide layer, also called a passive layer. The surface is protected from further corrosion by the passive layer. If the protective layer does not form across the whole surface, undesired corrosive reactions can occur. The reasons for an incomplete protective layer are many and diverse. Errors often occur as early as during processing. Since the passive layer is not visible to the naked eye, defective material may be further processed. As a result, safety risks can arise as stainless steels are used as starting materials for the production of a wide variety of components such as anchors, dowels and hazardous goods containers and are also used in complex chemical plants.

Detecting damage earlier and faster

KorroPad can be used to test stainless steel surfaces. The rapid colour test developed by BAM reveals damage to the passive layer significantly faster compared to traditional methods. KorroPad also offers another advantage: the component can be further processed or installed at the customer's premises after the test since it is virtually non-destructive.

Three pads, each about the size of a five-cent coin, are required for each test. The pads are pressed onto the degreased and alcohol-cleaned surface and peeled off with a spatula after 15 minutes. The KorroPad ingredients have a gel-like structure composed of water and an indicator for iron ions. If the passive layer is faulty, the indicator reacts with the iron ions in the material. This response changes the indicator's colour and blue dots appear on the pads. Each point indicates that the protective passive layer has not formed properly on the steel surface.

The process is so simple that even nonprofessionals can apply it.

Source: Bundesanstalt für Materialforschung und-prüfung (BAM)