Passivation of stainless steels is an often misunderstood process. In layman terms, passivation of stainless steel is designed to remove any iron contamination that may be on the surface of the stainless steel. It also assists in the formation of a passive oxide film.
This surface contamination can come about in many different ways but it is mostly a result of various metalworking operations. If it is not removed, stainless steel will start to corrode (rust) just like steel. This defeats the original purpose of choosing stainless steel.
Passivation is not designed to remove heat or weld scale. Pickling of stainless steel removes heat or weld scale and must be performed prior to passivation.
At Surface Coatings, we perform three different types of passivating: 1) nitric acid, 2) nitric acid with sodium dichromate and 3) citric acid. There is a wide range of immersion times and temperatures that can be used, depending on the specification that needs to be met. Nitric acid with sodium dichromate is used, primarily on 303 stainless steel and any 400 series stainless steel. Citric acid passivation is used almost exclusively in the medical industry.
INDUSTRIES SERVED
- Screw, Nut and Bolt Manufacturing
- Valve Industry
- Medical Equipment Industry
- Electronic Equipment
- Machine Shops
- Foundries
