Month: October 2021

Manufacturing stainless steel parts begins with fabrication or machining. All parts must be made to particular specifications and follow the guidelines of design and application. Once fabrication or machining is complete, parts are likely to have with free iron and other foreign material embedded in the surface.

Why it matters: As the final step, passivation is crucial because it ensures the corrosion resistance of stainless steel parts. The successful establishment of corrosion resistance on a critical part ensures long, efficient service of the part or vessel in whatever process it’s used in. Whereas failure to do this correctly leads to corrosion, reduced efficiency and ultimately, reduced lifespan of the part. Altogether, these factors can increase costs significantly.

What is Passivation?

Passivation is a combination process – part cleaning and part protective – that creates a passive layer on a stainless steel surface. This layer protects the metal from selective oxidation or corrosion.

Specifically, passivation is a chemical process involving a mild oxidant, such as a nitric acid solution, that removes “exogenous iron or iron compounds from the surface of stainless steel by means of a chemical dissolution…that will remove the surface contamination, but will not significantly affect the stainless steel itself…for the purpose of enhancing the spontaneous formation of the protective passive film,” according to ASTM A380.

The passivation process removes what’s known as “free iron” contamination. While this contamination is a normal in the machining and fabricating process for any stainless steel part, such contamination areas are also potential corrosion sites. If left in place, they will result in premature corrosion and deterioration of the part.

This is where the passivation process as a finishing step – or a routine maintenance step – becomes critical to the life and usefulness of every stainless steel part.

Why is Passivation Necessary?

Our customers will often ask if passivation is necessary. If the interest is in achieving the longest life and the best operation of a component in a manufacturing process, the answer is “yes.”

Even though the definition of passivation focuses on removing the “free iron” contamination, stainless steel components typically also acquire areas of grease, oil, and other substances on their surfaces during manufacturing.  Moreover, microscopic particles of shop dirt or iron from cutting tools can become embedded in the surface of the stainless steel parts during machining. These foreign particles impair the integrity of the original protective layer. Passivation cleans away these contaminants and creates the necessary passive layer, providing the best possible corrosion resistance.

How is Stainless Steel Passivation Done?

The first step of the passivation process involves cleaning the parts to prepare them for the solution. This step removes grease, dirt, dust and other surface contaminants.

Then comes the oxidizer or “acid dip” stage. Each job is different. So success at this stage requires deep knowledge of the chemistry of the acid mixture and other aspects of the process. These include which acid recipe works best for each situation, the ideal temperature, optimum duration of the bath, and how to adjust each of these factors based on the materials treated. When all of these factors are aligned into an ideal process, all free iron is removed from the surface, allowing the formation of an evenly-distributed oxide layer.

A thorough rinse in clean water is the final step.

How is Passivation Validated?

Ensuring a successful stainless steel passivation process is achieved through testing and validation.

This final step assures the effectiveness of the passivation process and most importantly, certifies compliance with ASTM, Mil-Spec, and other industry standards.

When additional assurance is required for specific processes, parts are further tested using methods such as high humidity, salt spray, water immersion, and ferroxyl testing. Such measures are particularly important for complex, highly-regulated industries and applications like aerospace, medical, military, and other areas where high reliability or safety are critical.

Is Passivation a One-Time Only Process?

No. Parts need to be re-passivated as a part of routine maintenance, depending on the service of the part. Factors include the demands of its processing conditions and how aggressive the chemicals are for processing and cleaning. Remember: experts who specialize in passivation are your best guide in helping you assess the best process for the specific needs of your parts – and your process.

Allegheny Surface Technology is an industry leader in passivation services, delivering high quality services to our customers. Request a quote or call us to speak to a specialist about stainless steel passivation today.

Pickling and passivation are different types of chemical metal finishing that provide corrosion protection on metal surfaces. Both processes remove excess (or exogenous) iron or oxidation from the surface of whatever metal undergoes the process. Pickling (removing an oxide layer) and passivation (applying an oxide layer) are different finishing processes.

Why it matters: In order to achieve the desired results, it’s important to understand that pickling is a preparatory process, while passivation is a finishing process.

What is Pickling?

Pickling, also known as chemical descaling, is the chemical cleaning of metallic surfaces to remove impurities, stains or weld scale. This is done with an acidic solution. Allegheny Surface Technology uses pickling solutions containing nitric and hydrofluoric acids to remove weld scale and underlying chromium-depleted layers of a metallic surface, in order to restore the corrosion resistance of stainless steel.

Pickling is one of several possible pretreatment steps in other processing, such as passivation or electropolishing. Pickling is also useful as a superior cleaning operation on welded structures. The most commonly referred standard for pickling stainless steel is ASTM A 380, Standard Practice for Cleaning, Descaling, and Passivation of Stainless Steel Parts, Equipment and Systems.

What is Passivation?

Passivation is the chemical process (also involving an acid) that removes “free iron” from the surface of stainless steel, enhancing corrosion resistance of the metal. Passivation forms a chromium rich surface, as an invisible, inert (or “passive”) oxide layer when exposed to an oxygen-containing environment, such as air. The most widely used standards for passivating stainless steel are ASTM A967, AMS 2700, and ASTM A380.

What is the difference between Pickling and Passivation?

Pickling	Passivation
Pickling is a cleaning process.	A cleaning step is required before passivation.
Removes surface iron contamination, weld scale and heat tint from the surface.	Removes free iron contamination from the surface.
Uses acids that take off the surface of the metal to treat impurities on an atomic level.	Uses mineral or organic acids like either nitric acid or citric acid which are not as aggressive as the acids used in pickling.
Leaves a greater change to the metal. Leave a uniform matte finish.	Does not change the appearance or properties of the metal.

Passivation and pickling are often used as companion processes to remove contaminants and oxidation. Together, they improve corrosion resistance, thereby extending both the life and overall value of your stainless steel components.

Allegheny Surface Technology has metal finishing experts who will assist you in deciding which choice is the best for your stainless steel finishing needs.

The statement, “no job is complete without the proper documentation” holds true for many industries, as well as the organization overseeing them. The higher the operational standards, the more critical it is to document that procedures have been performed to meet or exceed those standards.

Most bio-pharma, food and beverage, cosmetics, and medical device manufacturers companies work closely with the FDA and USDA to develop procedures that ensure compliance with Current Good Manufacturing Practice (CGMP) regulations. When these procedures become a part of manufacturing practice, each step must be recorded and approved in real-time. If a facility is unable to “show its work” in a particular process, it’s very likely that the process will need to be performed again. This obviously costs time and money.

Consider this hypothetical example, where insufficient process documentation can lead to lost production time and reduced profits.

‘Henry receives a phone call from a customer who needs some parts electropolished. Unsure what electropolihing is, he looks online and finds a service provider that specializes in electropolishing. He receives a reasonable quote and sends out the parts to be processed. While waiting for the job to be completed, Henry researches electropolishing and develops certain expectations of what he can expect when his parts return. The parts are completed and returned on time. Henry inspects them and is pleased with results. He sends them on to his customer and, within a few days, receives an unexpected phone call in return. Unfortunately, his customer is not very happy and requests documentation detailing how these parts were processed. Henry is at a bit of a loss. He doesn’t have what his customer is asking for. He soon learns that without proper certification, the parts can’t be used and the process must be performed over again.’

Don’t be like Henry.

Quality documentation is too-often overlooked and missing, incomplete, inaccurate, or poorly-detailed certifications can lead to delays in product shipment or worse, products that must be reprocessed in order to fulfill a customer’s requirements.

The most reliable way to prevent such an unfortunate occurrence is to always request a sample of the certification provided for any requested process. A quality certification should be included with all processed parts with the following details:

Electropolishing

vendor’s company

owner/user’s name

description of component(s)

identification of the electropolishing procedure used

final surface finish report (Ra if required by the owner/user)

 

Passivation

owner/user’s name

description of system or component(s)

service provider’s company name

qualified passivation method used

documentation of passivation process, as follows: (1) written qualified procedure (2) documentation of process control of essential variables (3) instrument calibration records (4) certificates of analysis of all chemicals used (5) process testing and verification

postpassivation verification method(s) used

for material manufacturers/suppliers of components whose surfaces have been electropolished and/or passivated, a Certificate of Compliance for Passivation and/or Electropolishing stating that standard industry practices, such as ASTM A967 or ASTM B912, as applicable, have been used. If required to demonstrate the effectiveness of their procedure by a method mutually agreed upon.

When the metal finishing services you trust meet ASME BPE standards, you can be confident that they implement best practices to increase the safety and reliability of your parts.

By choosing an electropolisher that meets or exceeds these standards, you can increase your parts’ safety, reliability and service life. Allegheny Surface Technology has experience providing metal finishing services for a variety of bioprocessing industries, and always adheres to ASME BPE specifications.