What is passivation?

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What is passivation? 
Passivation is the treatment of the stainless steel with an oxidizing chemical (typically nitric or citric acid) which promotes a thin oxidizing layer to form on the surface of the metal. This thin layer will help protect the metal from chemical attack.

Fabrication of the metal can reduce the overall corrosion performance of the stainless steel; therefore, making the passivation process an essential step. If iron particles become embedded in the surface of the metal during processing they must be removed. If they are not removed, these microscopic particles may promote discoloration, rusting or even pitting. By dissolving these particles in an oxidizing bath, it will enhance the corrosion resistance of the stainless steel thus fortifying the surface of the metal against such attacks.

The passivation process should be the last step in the fabrication process. It is generally performed by immersing the parts in either a nitric acid or citric acid bath and then rinsing in a clear de-ionized water and then dried. If due to the size of the part it is impractical to immerse the part in a bath, the acid solution may be applied to part using a swab and rinsed with water and dried. It is important that the surface of the steel is free from scale, oils or other lubricants prior to the chemical treatment in order for the passivation to be effective. There are several tests which can be performed on the metal to determine its passivity such as high humidity test, salt spray test, copper sulfate test or free iron test.
Stainless steel is not stain proof only stain less so by passivating stainless steel you have given the part the best chance of withstanding any corrosion in its life cycle.

Eagle Offers Surface Finishing Services
Stainless steel is often chosen for its aesthetic appearance, so make sure to specify the surface finish you need. The most common is the shiny, silvery finish manufacturers refer to as “bright”; alternatively, you can request a “pickled” or dull finish. Polishing and centerless grinding operations can be performed as secondary processes to produce desired RMS finishes as needed.

Sand Blasting
Produces a matte finish with various grit sizes. 60 / 100 / 180 / 220 / Glass Bead

Electro-Polishing
Produces a high bright finish

Belt Polishing
Produces a high luster finish using grits from 180 to 640

Black Oxide Finish
Minimizes light reflection

Centerless Ground Finish

Commercially Clean & Capped

Thermocouple Clean & Capped

Passivation (Chemical Cleaning)
Treatment of stainless steels after fabrication with oxidizing chemicals known as chemical cleaning or passivation. If iron particles or other substances have become embedded in the surface during fabrication or polishing operations, they must be removed. Otherwise, these minute particles may promote discoloration, rusting, or even pitting. Besides dissolving such particles, the oxidizing action of the bath also tends to enhance corrosion resistance of stainless steels by fortifying the natural passive surface film.

This processing should be the final operation on a stainless steel part. It is generally done by immersing in a nitric or citric acid solution and then rinsing in clear deionized water and drying. If immersion of the stainless steel piece is impractical due to size, the acid solution may be applied with a suitable swab and removed by rinsing with water.

Nitric acid is recommended because it will dissolve any iron particles and leave the stainless steel unaffected. It is necessary that the surface of the steel be free of scale, heavy grease and oil if the chemical cleaning treatment is to be effective.

Eagle has the knowledge, the expertise and the right equipment to give your finished parts the “look” you want.

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Download or request a hard copy of our updated design and manufacturing guidebook, offering valuable technical information to help you select the proper size and material composition for your unique needs. As a top stainless steel tube manufacturer we offer machining, welding, cutting, assemblies and bending while meeting or exceeding GMP and ASTM standards.

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Custom Tubing Designed for Your Needs
Making a difference in your design… from simple tubing to complex designs.
At Eagle, there’s nothing more important than producing a customized solution which exceeds our clients’ expectations and satisfies the unique specifications of their application. Our expertise with stainless steel custom tubing gives us the ability to help you design the product that will fit your project.

Complex designs need more than just stainless steel custom tubing. Secondary operations such as cutting to precision lengths, CNC and EDM machining, laser welding, bending, and precision grinding can transform a simple tube into just the part you need for your design.

We welcome the opportunity to share our expertise in developing product concepts and helping you solve your engineering problems. With decades of experience in the metals industry, you can count on Eagle as a resource for designing and fabricating your metal products.

Eagle Stainless Tube & Fabrication Inc.
Eagle Stainless Tube & Fabrication Inc.supplies stainless steel tubing to the medical, aerospace and high tech industries. Stainless steel, nickel alloys, aluminum, and titanium.

  • Cut to length
  • Precision machining
  • Laser cutting & welding bending
  • Electro-polishing and passivation.
  • Re-draw to specialty & millimeter sizes in both round, square and rectangular.
  • Grinding to precision tolerances
  • Assemblies