Copper sulfate test for detecting free iron
The copper sulfate test is a visual method for determining the presence of free iron on stainless steel in particular. In many cases, the copper sulfate test is used as a test to confirm the passivation process, but it can also be used as a test to determine whether passivation is necessary. According to ASTM A380 or A967.
The presence of iron particles in the free state is usually the result of steel or stainless steel parts, but contaminated with iron. Machining, welding, bending/forming and other processes will change the crystalline structure of the steel and may cause inconsistent spread of chromium and attract free iron to the surface of the material or transfer free iron from the machine to the material.
The copper sulfate test for detecting free iron is very sensitive. It should be used if traces of either iron or iron oxides are observed on the surface of stainless steel and are undesirable. Iron contamination can cause subsequent corrosion or affect the chemistry of the medium in direct contact with the contaminated surface.
The solution for detecting free iron is prepared by properly mixing the reagents in the proportions prepared in the kit.
The result of the test is clearly visible, because free copper ions react with free iron particles and cause an oxidation reaction, which leads to copper-colored staining (shades of brown, red, orange) on the surface of stainless steel. If this reaction is present, the test has failed and the material contains an unacceptable amount of free iron. If this reaction is not present, the test was successful and either the passivation process proceeded as intended or the material does not require passivation.
The method is designed to work with stainless steel alloys with a chromium content of at least 16%.
The test is not recommended for use on equipment that will be used to process food, pharmaceuticals, or any products intended for human consumption unless you disinfect that equipment after testing.
