The ABCs of passivation

Astro Pak has more than 60 years of experience perfecting passivation chemistries and processes. That expertise, along with highly trained personnel and state-of-the-art equipment, can be brought to facilities to perform pre-operational or maintenance cleaning and passivation on on-site systems and equipment.

Astro Pak's nationwide shop facilities are ideal for components, parts, and sub-systems that can be serviced out-of-place, giving affordable means to meet the customer's cleaning requirements.

Astro Pak has state-of-the-art facilities, accommodating parts of all sizes and volumes - such as overhead bridge cranes with 7.5-ton lifting capacity for oversized parts and dip tanks up to 40 ft.

In addition, pick-up and delivery services are available, along with cGMP-compliant documentation packages at the end of each job. Astro Pak's highly skilled technicians and controlled environments ensure consistent quality and compliance to industry and customer-specific standards.

During an audit tour from a regulatory agency, the lead Astro Pak technician had answers for things that I did not even know that I had to worry about."

Senior Utilities Engineer, BOEHRINGER-INGELHEIM

Our Passivation Standards

Astro Pak takes pride in its long legacy of meeting and surpassing the standards set forth by various organizations in numerous industries, such as ASME, ASTM, SEMI, and FDA, among others.

Trust the Experts in Passivation

Astro Pak's proprietary Ultra Pass® passivation process is held in high regard for its environmentally friendly blend of high-purity ingredients, including chelants that bind with metal ions, leaving them incapable of redepositing on surfaces. The result is that the material handling requirements and other on-site impacts are substantially reduced.

The Ultra Pass® passivation process also gives superior results, producing an optimal passive layer on the surface of stainless steels, giving rise to unmatched corrosion resistance.

Studies conducted by Astro Pak have revealed that the chrome to iron ratios achieved by Ultra Pass® passivation are significantly greater than ASME BPE recommended minimums and meet or exceed the requirements of many industries, including aerospace, semiconductor, biotechnology, and pharmaceutical.

Image credit: Shutterstock / Daniel Fung

What Materials Can Be Passivated?

Generally, stainless steels can be passivated, especially austenitic types. However, levels of improvement may vary between alloy type and the quality of surface chemistry present.

Does Passivation Remove Rust?

Passivation will remove iron and small amounts of very light rouge from the surface, enhancing corrosion resistance. More significant rouging requires derouging before the passivation treatment.

How Much Rouge Is Acceptable Upon Visual Inspection?

The amount of rouge that is acceptable will vary with respect to the quality level desired and the sensitivity of the production process to low levels of iron or iron oxides.

It also depends on which methods will be used for refining the final product, including evaporation/drying, filtration, or iron's effect on the biotech process. Slightly visible rouge or mildly discolored wipes are generally acceptable, whereas significant surface discoloration or distinctly colored wipes are not.

Filtration testing used to measure the amount and size of particles in the process fluids can be useful as a guide for evaluating the effect of rouge coming off the surface.

How Do You Test Passivation?

The quality of the passive film can be quantified by taking samples before and after the passivation and testing their chromium-to-iron ratio. The semiconductor and pharmaceutical industry has stringent measurable standards in place for systems or purity levels.

How Do You Know When All Free Irons Have Been Removed From the Surface?

Astro Pak conducts iron readings of the solution circulating in the system. In the initial stages of the passivation process, iron concentration levels begin high and gradually decrease and plateau when all the iron is removed.

In addition, 2% citric will hold 1% iron in solution (1% iron is equal to 10,000 ppm). Astro Pak typically sees iron concentration levels in the passivation process in the 1 to 50 ppm range. Astro Pak's proprietary blend uses significantly higher percentages of citric so that all iron is captured before the acid is exhausted.

Does Passivation Affect Surface Finish?

Passivation only affects the surface on a molecular level, enhancing the chemical makeup of the passive layer by increasing the ratio of very stable chromium atoms to the more reactive iron atoms in between three and five of the atomic layers of the metal's surface. Passivation does not affect surface finish.

Is Material Removed During Passivation?

Material is not removed in passivation. Passivation improves the corrosion resistance of the treated surface.

Why Is Pitting Corrosion Dangerous?

When pit develops, it starts shallow and deepens, but the debris inside it cannot be removed. The pitting process will eventually create a hole in the surface or pipe.

Can Passivation Be Reversed?

Passivation can generally not be reversed, however, corrosion will attack the passive film, which can be considered 'undoing' passivation. Reducing environments will undo passivation and leave the surface active or corroded. The passive layer is extremely thin (2 to 5 molecular layers) and may be eliminated by polishing or welding, corrosion, and reducing environments.

What Is the Difference Between Derouging and Passivation?

Derouging is the process of removing visible iron oxides and other metal oxides from the surface. Passivation removes iron or iron oxide from the surface in the passive film or top 3 to 4 molecular layers.

Derouging uses stronger acids to restore a surface to a visually clean condition by removing large visible accumulations of iron oxides. Passivation is designed to remove the small amount of free iron present despite the surface being visually clean.

Can the Passive Layer Be Removed?

The passive layer is extremely thin (2 to 5 molecular layers) and may be removed by polishing, welding, reducing environments, and corrosion.

How Long Does It Take To Passivate Stainless Steel?

Passivation typically takes between 8 and 10 hours in small systems and around 12 hours for larger systems. Depending on the condition of the surface, derouging alone can take 4 to 24 hours.

Why Is Passivation Necessary?

Passivation increases the ratio of very stable chromium atoms to the more reactive iron atoms in the upper three to five atomic layers of the metal's surface and therefore serves to enhance the chemistry of the passive layer.

Can Stainless Steel Become Pitted?

Stainless steel can become pitted; the surface appears to have spots (brown, white, or black), roughness, or hazing. The pits must be polished/sanded out and electropolished. If the pits are particularly deep, the surface must be ground, welded, polished, and electropolished.

Can Pitting Corrosion Be Prevented?

Routine preventive maintenance and reduction of corrosive conditions - reducing the use and concentration of chloride-containing solutions or choosing more resistant alloys where heat and chlorides are present, for example, can prevent pitting corrosion.

About Astro Pak Corporation

Astro Pak is the leader in providing Passivation, Precision Cleaning and High-Purity Chemical Cleaning services for a wide variety of “cleanliness sensitive” critical systems and components. Many of our customers have external agencies that drive their cleaning requirements, such as the FDA, NASA and others. We service such industries as Pharmaceutical, Biotechnology, Aerospace, Laser, Semiconductor, Water Treatment and more, including Industrial markets. Our services and products leverage decades of experience to deliver the most effective chemistries and techniques, resulting in increased equipment longevity, reduced corrosion-related downtime and regulatory compliance in client facilities.

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Last updated: Nov 15, 2022 at 10:28 AM


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