Passivation

Restore Corrosion Resistance.
Meet Your Specification.

Expert Electropolishing provides nitric acid, citric acid and electrochemical passivation options for stainless steel components.

Our controlled processes remove free iron and surface contaminants introduced during machining, welding, forming and handling. This allows the stainless steel surface to develop its natural protective oxide layer.

From high-volume small parts to large fabricated assemblies, we process each project according to the alloy, part condition, application and required specification.

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Select the Right Passivation Process

Nitric Acid Passivation

A proven chemical treatment commonly specified for stainless steel parts used in industrial, aerospace, medical, automotive and other controlled applications.

Nitric acid passivation removes free iron and other surface contaminants without applying a coating or materially changing the dimensions of the part.

Consider nitric passivation when:
  • Your print or customer specification calls for a nitric process
  • You need a widely established treatment method
  • Your alloy and application are compatible with the specified nitric solution
  • You must meet defined processing and verification requirements
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Citric Acid Passivation

Citric acid passivation provides an alternative method for removing free iron and helping stainless steel establish a clean, passive surface.

The process uses citric acid formulations instead of nitric acid. It can provide strong process results with fewer handling and disposal concerns when approved for the alloy and specification.

Consider citric passivation when:
  • Your specification permits a citric process
  • You want an alternative to nitric acid
  • Your components require removal of surface iron contamination
  • Environmental, safety or production requirements influence process selection
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Experience Matters

What Is
Stainless Steel
Passivation?

Stainless steel resists corrosion because chromium within the alloy reacts with oxygen and creates a thin protective oxide layer.

Machining, grinding, welding, stamping and contact with carbon-steel tools can leave free iron and other contaminants on the surface. These contaminants can interfere with the passive layer and create sites where rust or corrosion begins.

Passivation chemically removes this surface contamination. Once the surface is clean and exposed to oxygen, the protective passive layer can form naturally.

Passivation is a surface treatment—not a coating. It does not add material to the component or produce the smoothing, brightening and deburring effects associated with electropolishing. ASTM describes chemical passivation as the removal of contaminant iron and other foreign matter from stainless steel surfaces.

Benefits of Passivation

Proper passivation can help:
  • Remove free iron and ferrous contamination
  • Restore the stainless steel’s passive surface condition
  • Improve resistance to rust and corrosion

  •  Remove free iron contamination after machining, forming or fabrication

  • Treat components without adding a coating
  • Preserve part dimensions and surface texture
  • Support customer and industry specification requirements
  • Extend component service life in demanding environments

Passivation will not remove heavy weld scale, deep oxidation, burrs, scratches or major surface defects. Parts with these conditions may require descaling, pickling, mechanical preparation or electropolishing before final passivation.

Our Passivation Process

1. Review

We review your print, alloy, part dimensions, surface condition, volume and required specification.

2. Process Selection

Our team identifies the appropriate nitric, citric or electrochemical option based on the information provided.

3. Cleaning and Preparation

Parts are cleaned to remove oils, lubricants, shop residue and other contaminants that could interfere with treatment.

4. Passivation

Components receive the selected treatment under controlled process conditions.

5. Rinsing and Drying

 Parts are thoroughly rinsed to stop the chemical reaction, then dried to protect the treated surface.

6. Verification and Documentation

Verification requirements are established from the print, purchase order or customer specification. Copper sulfate testing may be provided upon request for suitable passivated stainless steel parts. Certificates of Conformance and supporting process documentation are also available.

Parts and Applications

Our passivation services support stainless steel components used in:

  • Food and beverage processing
  • Pharmaceutical equipment
  • Medical equipment
  • Aerospace and defense
  • Automotive and transportation
  • Marine applications
  • Industrial machinery
  • Packaging equipment
  • Pumps, valves and fluid-handling systems
  • Fabricated stainless steel assemblies
  •  

Passivation FAQs

1Does passivation remove metal?
Passivation targets free iron and surface contaminants. It does not intentionally remove a measurable layer of base metal like electropolishing.
2Does passivation change the appearance of stainless steel?
Passivation is not a polishing or brightening process. The visual appearance should remain close to the original prepared surface, though results can vary based on alloy and prior surface condition.
3Which is better: nitric or citric passivation?
Neither process is automatically better. The right choice depends on the alloy, required specification, customer approval and intended application. If the print specifies a method, that requirement should guide process selection.
4Can passivation remove weld scale?
Passivation alone is not intended to remove heavy weld scale or heat tint. Those conditions may require cleaning, descaling, pickling, mechanical preparation or another suitable treatment before passivation.
5When should stainless steel be passivated?
Passivation is commonly specified after machining, welding, forming, grinding or fabrication when these operations may introduce free iron or disrupt the clean stainless steel surface.
6Can you test passivated parts?
Copper sulfate testing may be available upon request for suitable stainless steel grades. Submit the required test method and acceptance criteria with your print or purchase order.
7Is passivation a coating?
No. Passivation does not deposit another material on the part. It cleans the stainless steel surface so its protective passive layer can develop.