Reveal Iron on the surface of stainless steel
Why do we need to test for Iron Contamination on stainless steel?
Iron contamination occurs when there is a deposit of iron surface of stainless steel. This typically is caused by abrasion or scratching of the stainless steel by iron or carbon steel during fabrication or handling. Iron residue might get transplanted onto a stainless steel when the equipment used to process one type of material may be used for the other without being properly cleaned between batches.
In most cases, the free iron on the surface of the stainless steel will be readily oxidized in environments where the stainless steel alloy should be relatively immune to any type of corrosive attack. The oxidation of iron on the surface of the stainless steel will result in the accumulation of rust stain that will then give the appearance that the stainless steel is being attacked.
These plain iron or steel particles can disrupt the protective oxide layer of a stainless steel work piece by ruining its corrosion resistance so that it starts to rust.
Common sources of iron contamination include:
- Stainless steel coming into contact with any other steel or iron materials
- Tools and parts previously used on steel or iron
- Environment and atmosphere – the area the stainless steel is kept in, including the air, water or other chemicals used to clean the surface
Free iron cannot be seen on the surfaces of contaminated parts. However, free iron particles left behind after welding can lead to the formation of iron ions in aqueous solution.
These particles are then able to cause local damage to the passive layer.
The ferroxyl test is able to show free iron on the stainless steel surface by converting into a visible form.
The ferroxyl test is able to show free iron on the stainless steel surface
Type of Iron contamination tests
1) Ferroxyl Test
Free iron cannot be seen on the surfaces of contaminated parts. However, free iron particles left behind after welding can lead to the formation of iron ions in aqueous solution. These particles are then able to cause local damage to the passive layer.
The ferroxyl test is able to show free iron on the stainless steel surface by converting into a visible form. The ferroxyl test is able to show free iron on the stainless steel surface
The aim and purpose of the test is to check the integrity of the passive layer on the stainless steel surface and guarantee that free iron and (to a limited extend) Iron oxide are entirely absent.
2) Copper Sulphate Test – Surface detection for passivation
The purpose of the copper sulfate test is to determine the presence of free iron which is usually induced onto the surface of a part during fabrication with steel components. It is a visual method of determining the existence of free iron in specifically stainless steel. In many cases, the copper sulfate test is used as a pass/fail examination of a passivation process on a part or stock material, but it can also be used as a test to determine if passivation is necessary in the first place.
Passivation is a treatment method to protect the metal from corroding through by making the material “passive” to the surrounding environment. However, it encourages corrosion to occur. A thin layer of a new non-reactive chemical will appear on the surface, which is less likely to chemically react with air and cause corrosion.
The purpose of the copper sulfate test is to determine the presence of free iron which is often transferred onto the surface of a part during fabrication with steel components. The principle of the test is based on an oxidation-reduction reaction which causes the dissolved copper ions to deposit or plate out onto the locations of free iron particles.
Application of Iron Contamination Test :
Hypersensitive test
Determines whether or not the surface needs to be pickled
To check f or embedded iron on austenitic stainless steel
Hypersensitive test
Determines w hether or not the surface needs to be pickled
To check f or embedded i ron o n austenitic s tainless steel
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The primary purpose of stainless steel is to avoid corrosion, however, residual surface iron will still corroded if present. Confirmation of the removal of the surface iron through passivation is essential to ensure that the parts or components will perform satisfactorily. Our expert testing team is able to confirm passivation using Copper sulphate test and detect free iron with Ferroxyl Test. For more information on our iron contamination test, call us or send us an enquiry today.
