Both nitric acid and citric acid are effective in passivating many grades of stainless steel, and both methods are described in the industry standards ASTM A967 and AMS 2700.
Citric acid passivation offers the following key differences. Compared to nitric acid passivation, citric acid passivation is:
- More environmentally friendly
In the past, some manufacturers avoided citric acid due to potential organic growth and molding issues. Today, modern formulations for biocides prevent organic growth in the solution. See our complete write up on the advancements of citric acid (specifically Citrisurf).
These advancements in citric acid have allowed smaller manufacturers that lacked experience with chemical handling and processing to bring their passivation in-house. For a more detailed comparison, please see our “Nitric vs. Citric Acid Passivation” page.