Understanding Passivation

A material is considered passivated when it shows high resistance to corrosion in an environment where one would expect corrosion to occur. As an example, let’s consider NEE’s specialty, stainless steel. Stainless steel contains chromium. The chromium in stainless steel forms a thin, oxygen-enriched, passive layer on the steel’s surface. This layer makes the metal resistant to corrosion. Manufacturing processes such as cutting, machining, welding, and other production steps disrupt the passive layer and embed free iron and impurities in the metal. These impurities lead to corrosion. Passivation processes are specified to remove contaminants from the surface of the stainless steel and restore the chromium oxide layer that is normally present, thereby restoring the stainless steel’s corrosion resistance.

Advantages of Passivation through Electropolishing

Scientific studies have shown that passivation through electropolishing is the most effective means of passivation. Passivation through electropolishing provides greater corrosion resistance than processes such as nitric passivation and citric passivation (using nitric or citric acid immersion). At NEE we agree; parts passivated through an abbreviated electropolishing cycle meet or exceed the corrosion resistance performance of parts passivated using a chemical method. Passivation through electropolishing provides these key benefits:

• The passivation through electropolishing process is compliant with ASTM B 912-02 and ASTM A967-13, “Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts.”
• Passivation through electropolishing removes all free iron from the surface of the work-piece, immediately eliminating free iron corrosion potential.
• Electropolishing increases the chromium oxide layer to a greater degree than traditional passivation methods, thus enhancing the part’s corrosion resistance.
• A mild electropolishing cycle removes a small amount of surface material, including additional free iron and deeply embedded impurities below the surface of the part.
• Passivation through electropolishing increases the chromium oxide layer of stainless steel parts to a higher degree than chemical passivation methods, enhancing the part’s corrosion resistance.
• All grades of stainless steel can undergo passivation through electropolishing, including: 301, 302, 303, 304, 316, 316L, 321, 17-4, 410, 416, 420, 431, 430, 440, 455, and F18.

NEE recommends passivation through electropolishing as the optimum passivation process for stainless steel due to the increased corrosion resistance it affords. However, to thoroughly address your needs, NEE also offers nitric passivation and citric passivation services.

We are here to help

Tell us about your application requirements. Our knowledgeable staff is ready to meet your needs with the passivation processes best suited to your parts and application. Contact us today.