Stainless steel that is machined, formed, or fabricated can ultimately be susceptible to rust. This is due to the free iron introduced during manufacturing. This free iron adheres to the surface, leaving it vulnerable to corrosion. Gleco offers ASTM A967 and AMS 2700 nitric passivation to remove this surface and deliver longer-lasting corrosion protection to stainless steel parts and products.
Known as controlled corrosion, as the acid in the bath actually corrodes free surface iron, passivation is a widely used metal finishing process. It uses a nitric acid chemical treatment to create a protective oxide layer or passivation film. This passivation film then helps to prevent chemical reactions and protect against rust.
Although passivation normally occurs in a uniform, controlled manner, flash attacks caused by improper control leave the stainless steel with a dark, etched surface (the opposite of what this process is meant to achieve).
The Passivation Process
Nitric passivation is a simple three-step process:
- First, the stainless steel surface is cleaned.
- Then, it is dipped into a nitric acid bath at 120-150 degrees Fahrenheit for about 20-30 minutes to be chemically treated.
- Finally, the passivated stainless steel is tested using one of a number of methods, including:
- Copper sulfate testing: Placing the passivated piece into a copper sulfate path for a minimum of 6 minutes
- Salt spray testing: Placing the passivated piece into a salt-spray testing chamber for a minimum of 2 hours
- Water immersion testing: Placing the passivated piece into a tank of distilled water for a minimum of 24 hours
- High-humidity tested: Placing the passivated steel into a humidity chamber for a minimum of 24 hours
The Benefits of Nitric Passivation
Nitric passivation is used on stainless steel parts and products due to several unique benefits:
- Its chemical barrier provides an extra layer of rust protection.
- The process removes surface contaminants.
- It reduces maintenance costs and extends product life.