Stainless Steel Passivation

Question:

In one of your previous replies, I was surprised to read that you are still promoting the use of hazardous nitric acid for passivation of stainless steels, especially for brush-on applications. Citric-based formulations have been in use for a number of years with excellent results and have been approved under ASTM A-967. They can be applied by immersion or spray and are very effective as a brush-on gel for cleaning weld areas.

Citric-based materials are non-hazardous for workers and environmentally friendly. As an added benefit, passivation results are much improved over nitric acid. Thanks. D.D.

Answer:

You are correct. Citric acid is a viable alternative for nitric acid in some passivation applications. It has the advantage of creating less hazardous waste and is safer to work with. Although nitric acid will not remove all heat tint and scale from a welding operation, it will work better than the citric acid. Additionally, the nitric acid is probably less expensive to charge with initially, although this difference is probably offset with the cost of disposal.