Description

This test kist is specially designed to test of PICKLED staineless steel or to test of presence of embedded iron in the steel surface .
Use the “ferroxyl test.” Spray the surface with a solution of potassium ferricyanide. If free iron is present, a blue color will appear. This test is extremely sensitive and often gives false positive results, that is, it gives an indication of iron being present when it really is not. The ferroxyl solution must be made fresh each day.

Both the copper sulfate and the ferroxyl tests are described in ASTM A380.

It is a very highly sensitive & hazardous test and should be used only when traces of free iron or iron oxide is "objectionable". Personnel familiar with its limitations and hazards should only be permitted to use this test method.

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 coloration 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 coloration does not appear this means that the structure has been restored and indicates that the surface has been satisfactorily pickled.

After getting positive result Remove free iron and free iron oxides by using for example,  a phosphoric acid solution or  Citric acid.