Iron contamination is a major problem for stainless steel pipes. Even a small degree of iron contamination when stainless steel is being welded can cause corrosion that can later ruin the pipe. Once the rust has bloomed, it will cause pitted corrosion if it is not treated. While alloyed iron is harmless and is also a major part of the creation of stainless steel, unalloyed iron needs to be prevented and removed if the stainless steel is exposed to it.
Detecting Contamination On Finished Pieces
If you already have a finished work piece that you believe has been contaminated with iron, expose the piece to water. If the piece begins to rust, it may have been exposed to iron.
Sources Of Iron Contamination
Any iron item that is in your workshop can be a potential source of contamination. This includes exposed metal parts of chairs, work benches, tools, shipping containers and shot and grit used to remove contaminants from surfaces. Objects you may not realize contain iron residue may be contaminated because of how the object was treated. This can be avoided by using methods of cleaning such as iron-free sand rather than cleaning with iron shot.
Removing Iron From Air And Water
One of the most challenging forms of iron contamination to eliminate is iron that is present in the air. Iron is most often present in the air in very industrial settings. To prevent contamination from this source, it is important to use air filtration to remove iron. Also, the surfaces should be cleaned with water to remove iron residue. The water must be filtered because some sources of water are contaminated with iron.
Contamination From Steel Brushes
Stainless steel brushes need to be used on stainless steel alloys during the process of pipe welding. If stainless steel is not used, this can lead to iron contamination. Both steel brushes and stainless steel brushes that have been used on plain steel can cause iron contamination.
Removing Iron Contaminants From Stainless Steel
If you are concerned that the stainless steel has become contaminated by carbon, you could bathe the piece in a nitric acid bath. This would clean and passivate the stainless steel. However, this process takes time and can slow down production. A faster approach is to use a nitric hydrofluoric acid mixture or electropolishing. Also, while acid will remove free iron, it will not remove iron oxide. However, when the other preventative measures are used, your stainless steel is much less likely to be contaminated. Contact a company like Tiger Metals, Inc. for more information.
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