Specialised Passivation of Stainless Steel for High-Purity Environments
As our name suggests, INOX Passivation is a specialist in passivation processes. Our process, which uses proprietary chemical blends and equipment designed specifically for the pharmaceutical industry, is suitable for high-purity environments and is intended to reduce the safety and environmental risks associated with chemical cleaning. Our products are often non-hazardous and pH neutral, and can be sent directly to the client's waste system. ASTM sets international standards for materials, products, systems, and services. Our procedure aligns with the standards outlined in ASTM A380 to ensure optimal surface cleanliness. Our passivation process will significantly increase the chrome-iron ratio of your stainless steel components and exceed the recommended requirements set by ASME BPE. By following ASTM A380 guidelines, we deliver consistent and high-quality passivation outputs. ASTM A380 also supports our commitment to maintaining the highest levels of safety and performance in stainless steel treatment.
Why Passivation Matters
Repair/Cleaning of surfaces
Stainless steel passivation enhances corrosion resistance by removing free iron from the metal surface. A comprehensive passivation process will remove all extraneous material from the stainless steel component, often introduced during fabrication and installation. This process will ensure that the surface is in the optimal condition to form a consistent and all-encompassing passive layer that gives stainless steel its corrosion-resistant qualities.
Improved corrosion resistance
Passivation removes free iron and leaves a chromium-enriched surface. ASME BPE recommends that the chrome-to-iron ratio be above 1.3. A correctly passivated surface (using our proprietary citric acid blend) should achieve a Cr/Fe ratio in excess of 1.8. The more chromium on the surface available for oxidation, the more effective the passive layer and the more corrosion-resistant the component. Regular stainless steel passivation ensures the longevity and performance of stainless steel components in harsh environments.
Adherence with ASTM & ASME
In stainless steel passivation, ASTM guidelines ensure proper surface preparation and treatment. Compliance with ASTM standards helps achieve consistent and reliable passivation results. Many industries rely on ASTM specifications to maintain quality and safety. The two widely recognised specifications—ASTM A967 and ASME BPE—are the main foundation for many clients' internal specifications. These specifications are typically referred to during installation, commissioning, and ongoing validation of a stainless steel system. Our passivation process conforms with both specifications and exceeds their minimum requirements. ASTM A380 is also frequently used to guide cleaning and preparation before passivation. By incorporating ASTM A380, we ensure a more consistent and reliable stainless steel passivation process.
Delayed formation of rouge
Rouge is a naturally occurring phenomena on stainless steel in (usually hot) purified aqueous media. Whilst there are various mechanisms that can cause the onset of rouge, class 1 rouge is usually considered to originate from iron particles within the system. These particles could have detached from components within the system that are of a lower grade material or are damaged (pump cavitation for example), but they are more likely to have been introduced during fabrication and installation. Thorough passivation will remove this debris, thereby removing the material that would otherwise cause rouge early on during the equipment’s life-cycle.
Frequently Asked Questions
Chemical passivation is the process which the stainless steel surface is exposed to a chemical in order to remove any contamination and increase the chromium to iron ratio. This leaves the surface inert and in optimal condition for forming a dense chrome-oxide layer. Oxidising chemicals can augment the formation of this passive film, ensuring that the stainless surface is not left unprotected.
Un-passivated stainless steel (particularly after fabrication), is vulnerable to corrosion through surface contamination.
Pickling is generally specified when the component needs scale, weld-heat-tint and metallic contamination removing. It etches the surface (and therefore is not suitable for polished finishes).
Passivation will not damage the surface finish. It will only remove lightly adhered ferrous contaminants (free-iron) and helps to restore the chrome-oxide layer (passive layer) that makes stainless steel corrosion resistant.
Derouging is a term used to describe the removal of “rouge” – an unusual form of corrosion peculiar to high-purity water and steam systems. Rouge is most commonly found in a pharmaceutical manufacturing environment.
After derouging, passivation is required to optimise/form the passive layer.
We can passivate the stainless steel – in all of its forms (martensitic, ferritic, austenitic, duplex, etc.) Other chrome-nickel alloys (such as Hastelloy, etc.) can and should also be passivated to improve the corrosion resistance.
The recognised tests can be loosely grouped together into four categories. Accelerated corrosion testing, positive-indication testing, electrochemical testing and surface chemical analysis.
When using carefully selected chemicals, passivation will not damage the surface finish. Your passivation provider should also consider other materials within the system that could be adversely affected by acids, etc. These include gaskets, seals, glass, and many other items.
Passivation will not remove weld-heat-tint or rouge. Pickling is required to remove weld-heat-tint. A dedicated derouging process is required to ensure the removal of rouge.
The chrome-oxide layer that gives stainless steel its protective properties is easily damaged during the various fabrication and handling processes that it goes through before it goes into service. A thorough passivation process will remove contaminants and restore the passive layer, ensuring that (in a suitable environment), the component is not going to corrode, and you will get the best possible performance from your equipment.
This is very subjective and can be affected by many things. In most cases, a fairly typical purified water loop (<1,000 litres volume) can be fully degreased and passivated within 1 to 2 days, dependent upon the complexity.
ASTM stainless steel passivation typically uses nitric acid or citric acid solutions to remove free iron contaminants from stainless steel surfaces. Nitric acid is often combined with sodium bicarbonate for enhanced performance, while citric acid is a safer and more environmentally friendly alternative. Both methods offer corrosion resistance. Stainless steel passivation is essential after fabrication or welding to restore the protective oxide layer and offer durability.
Find Out More
To find out more about our passivation and derouging services and how they can support your business, please get in touch with one of our experts today by clicking here.
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You can ask us for advice or help on any or all of the following:
- Passivation
- Derouging
- Oxygen Cleaning
- Biofilm Removal
- Riboflavin Testing
- Pre-Commissioning Flushing
- Carbon Steel Pickling
Simply confirm your details on the form provided and we'll be in touch ASAP. We look forward to hearing from you!
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