Stainless steel is widely accepted as corrosion-proof, which, in reality, is a mischaracterization. Stainless steel is actually just highly corrosion-resistant. This means that its passive layer – the stainless steel surface which protects the rest of the metal – requires regular maintenance and strengthening to ensure many years of reliable service.
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Although the importance of developing a data-based schedule of regular, preventative maintenance has been discussed in other articles from Astro Pak, selecting the correct passivation provider is equally important.
Choosing the wrong provider can lead to a greater expense than hiring a firm with an established track record in serving the specific type of equipment that needs passivation.
Here are some essential considerations that must be taken into account:
Documentation
The axiom “no job is complete without the proper documentation” holds for many industries and agencies that oversee them. The higher the standards needed for operation, the more critical it is to document that the procedure has been performed following those standards.
Many cosmetics, food and beverage, medical device manufacturers, and bio-pharma companies work closely with the USDA, FDA, and agencies overseeing animal health to develop procedures that ensure compliance with Current Good Manufacturing Practice (CGMP) regulations.
Each step must be recorded and signed off as it happens. If a facility is not able to show that each step has been taken, the likely outcome is that the process must be repeated.
ASTM Standards
Any process is meaningless without having some metric against which the work can be measured. There are two standards that direct how stainless steel shall be passivated to avoid corrosion and contamination. These are ASTM standards A967 and its A380 expansion to include the use of citric acid at specific temperatures.
Doing the Correct Process
The “one size fits all” model cannot be applied to passivating stainless steel. Many providers will take shortcuts - skipping the cleaning process, for example. If the surface is not clean or if rouge remains, the passivation will not be successful. Different steel grades and finishes also need different concentrations of acids and treatment lengths if the standards required by regulators are to be met.
Using Citric Acid Instead of Nitric Acid
Many providers still use nitric acid instead of taking advantage of the benefits of citric acid. Nitric acid is highly hazardous and non-selective; it will attack both the free ion and base metal. It is necessary to purge the nitric acid from the system fully; otherwise, the dissolved free iron will plate back onto the surface, creating the same initial problem.
After use, nitric acid must be disposed of as a hazardous chemical. Citric acid, on the other hand, is less toxic, much safer, targets the free iron, and will not etch the surface even if it is run at higher temperatures or longer intervals.
It can be disposed of using existing drainage systems without special handling or equipment. Unlike nitric acid, citric acid does not simply dissolve the free iron; it binds or chelates with it and renders it chemically non-reactive.
The result is that any free iron that does not get flushed out with the chemistry cannot begin the corrosive process anew in another part of the system.
Using the Right Equipment
Passivation is more than “plug and play” with off-the-shelf equipment. When dealing with new construction, for example, pumps with insufficient velocity will not be capable of flushing the debris before commissioning, creating the risk of rejected production batches almost from the start.
Astro Pak crews bring their own custom Clean in Place (CIP) skids that contain the variable speed suitable for the job and the necessary hoses and filters, which allow them to hook up to any system, thus ensuring that the chemistry is appropriately circulated.
Conclusion
While clients may be tempted to employ the cheapest service provider, the resulting cost can be much higher. Improper paperwork can result in a shutdown, insufficient passivation may lead to early failure, and taking shortcuts during cleaning can lead to the costly loss of ruined batches – all of which directly hit the bottom line. Gain in the short term gain can lead to pain in the long term.
Acknowledgments
Produced from materials originally authored by Jordan Schaecher, Regional Technical Sales Manager, Astro Pak.
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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