The TEST KIT FERROXYL is designed to determine whether austenitic stainless steel needs to be pickled or whether it has been pickled satisfactorily. When structure on the surface of austenitic stainless steel has not been evenly restored, an excess of metallic iron will be present (so-called embedded iron) which will adversely affect the properties of the stainless steel.
The presence of embedded iron in the stainless steel surface disturbs the chromium oxide film reducing the corrosion resistance locally. When embedded iron is not removed, serious (pit) corrosion may set in.
Example of pit corrosion caused by the presence of embedded iron
Principle of the measurement
The test is based on a reaction of potassium ferricyandide with iron in a strongly acid medium. The excess iron dissolves in this strongly acid medium as ferrous ion to form a blue complex, known as Prussian Blue.
When during this test this blue colouration manifests itself it means that the surface of the stainless steel does not yet have the correct structure and has been insufficiently pickled.
When the blue colouration does not appear this means that the structure has been restored and indicates that the surface has been satisfactorily pickled.
Contents of the kit
- 1 transparent dropping bottle 25 ml
- 1 brass measuring scoop
- 1 pack filter paper O / 11 (cm)
- 1 demineraliser bottle
- Ferroxyl Reagent I
- Ferroxyl Reagent II
Ferroxyl Reagent II contains strong acid. Avoid contact with skin and eyes.
- Place 5 measuring scoops Ferroxyl Reagent I in the dropping bottle. Augment this with 25 ml Ferroxyl Reagent II to the scale mark. Close the bottle and agitate until all Ferroxyl Reagent I is dissolved.
- Moisten a filter paper with this solution (ca. 5 drops) and place this filter paper on the surface to be tested.
- Wait approx. 1 minute.
- When a blue colouration appears the surface tested has been insufficiently pickled and iron is still present.
- When no colouration appears the surface has been satisfactorily pickled.
- Finally, after removing the filter paper, rinse the surface tested with demineralised water.
- Remark: The ferroxyl solution described above cannot be preserved for more than a few hours! This means that fresh solution must be prepared for every test.