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How To: Passivation for Stainless Steel Vessels

How To: Passivation for Stainless Steel Vessels
How To: Passivation for Stainless Steel Vessels How To: Passivation for Stainless Steel Vessels How To: Passivation for Stainless Steel Vessels How To: Passivation for Stainless Steel Vessels


Rapid data center expansion and modern HVAC demands have led more engineers and specifiers to choose stainless steel vessels for their systems. But what exactly is passivation, and what makes a passivated stainless steel vessel desirable over traditional carbon steel?

What is Passivation?

Passivation is a multi-step chemical finishing process performed after components are manufactured, welded, and assembled. Its primary goal is to maximize the steel’s natural corrosion resistance.

There is a common misconception that passivation physically fills surface flaws or mechanically alters the strength of the metal. In reality, it works chemically: during fabrication processes like cutting, machining, and welding, microscopic traces of free iron (tramp metal) from tooling get embedded into the steel’s surface. If left untreated, these iron particles react with air and moisture, triggering localized rust, pitting, and long-term surface deterioration.

Passivation removes these iron contaminants, allowing the stainless steel to protect itself as intended.

How Passivation Works: Building the Oxide Layer

Stainless steel owes its corrosion resistance to chromium ( of the alloy). When an acid bath selectively dissolves surface iron, it exposes an enriched concentration of chromium underneath.

Once rinsed and exposed to ambient air, this chromium rapidly reacts with oxygen to form an imperceptibly thin, continuous, and self-healing chromium oxide passive layer. This layer acts as a permanent barrier between the raw steel and the surrounding environment, keeping moisture and corrosive agents out.

Choosing the Acid Chemistry: Nitric vs. Citric

Passivation typically relies on one of two acid types:

The 4-Step Passivation Process

Achieving a true passive finish requires a tightly controlled sequence:

  1. Pre-Cleaning & Degreasing: Oils, machining coolants, and shop dirt are washed away. Acid cannot dissolve free iron if organic residues block direct contact with the metal.
  2. Acid Bath Immersion: The vessel is submerged in a controlled nitric or citric acid bath to dissolve free iron and surface contaminants.
  3. High-Purity Rinsing: The part is thoroughly rinsed with clean water to flush away acid residue and prevent chemical staining.
  4. Air Drying & Passive Layer Formation: As the vessel air-dries, exposed surface chromium reacts with ambient oxygen to form the protective chromium oxide film.

Why Passivation Is Exclusive to Stainless Steel

Passivation can only be performed on stainless steel and compatible high-chromium alloys. Carbon steel lacks the chromium required to build a protective oxide layer. If you submerge carbon steel into a passivating acid bath, the acid will aggressively etch and eat through the raw iron, weakening the vessel rather than protecting it. Carbon steel must instead rely on internal coatings, linings, or chemical system inhibitors for corrosion protection.

Stainless Steel Solutions from Wessels Company

By removing surface contaminants and enabling full passive oxide film growth, passivation ensures stainless steel vessels stand up to the most strenuous and harsh operating conditions.

Wessels Company offers passivation options across our stainless-steel product lines, including expansion tanks, thermal energy storage vessels, and air-dirt separators. In addition, some sourcing partners offer ferrous-free facilities to prevent cross-contamination. For more information on custom stainless steel vessel options or to request a quote, visit westank.com or call our headquarters at 317-888-9800.

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New! Live Order Tracking on Wesselsvessels.com

New! Live Order Tracking on Wesselsvessels.com

 

We’ve gone live with a brand new update to our online ordering platform wesselsvessels.com. For all new orders going forward, you can now click “Orders” or “Recent Orders” from your account page and then “View” on a particular order to get the latest status information.

 

 

 

New orders will display as “Firmed,” and once they’ve been approved for production, they will show as “Released”. Finally, when an order has shipped, it will display as “Closed” and the shipping date and tracking will appear. To get orders out quickly, sometimes portions of an order will ship separately, so be sure to note which line items have shipped.

We’ve also launched a live, direct to ERP link between wesselsvessels.com and production to get your orders into queue even faster. We hope these quality of life improvements will speed up the ordering, shipping, and tracking of all new orders placed online. And don’t forget, all online orders receive a 4% discount!

Have feedback? Let us know how we can keep improving.

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Stainless-Steel Manufacturing for Hyperscale Cooling

Stainless-Steel Manufacturing for Hyperscale Cooling

The rapid growth of data centers and other hyper-scale facilities is increasing demand for stainless-steel hydronic equipment capable of continuous operation, high flow rates, and pristine water conditions. As cooling systems become larger and more critical to facility operation, engineers and operators are specifying stainless-steel pressure vessels and components to improve corrosion resistance, maintain system water quality, and provide long-term equipment reliability.

Wessels Company and its manufacturing partners offer a broad range of stainless-steel hydronic equipment for commercial and industrial applications, including equipment that supports direct-to-chip cooling systems and other high-performance computing (HPC) cooling applications. Manufacturing capabilities include ASME code pressure vessels fabricated from 304 or 316L stainless steel for applications requiring increased corrosion resistance. Product configurations include expansion tanks, air purgers, air and dirt separators, tangential air separators, filtration vessels, and other specialty pressure vessels.

Wessels stainless-steel manufacturing capabilities support a wide range of operating conditions and system sizes. Stainless-steel air elimination equipment is available for temperatures up to 450°F, while air and dirt separators are manufactured for operating pressures up to 150 PSI and are available in high-velocity configurations for higher-flow applications. Large stainless-steel tangential air separators can accommodate system flow rates ranging from 56 to 17,000 GPM.

For applications where system cleanliness and heat transfer performance are critical, Wessels also manufactures ASME-code stainless-steel bag and cartridge filtration vessels. Available in 304 or 316L stainless-steel, these vessels support flow rates exceeding 4,000 GPM, depending on configuration, and provide particulate removal for large hydronic cooling systems, including those serving HPC and AI data centers.

By combining stainless-steel fabrication, ASME pressure vessel manufacturing, high-flow equipment design, and a broad range of hydronic product configurations, Wessels Company can support engineered systems ranging from individual components to large, mission-critical cooling installations. These capabilities provide engineers and facility operators with durable equipment solutions designed to protect system performance, maintain water quality, and deliver reliable operation in demanding high-density cooling environments over the life of the system.

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Employee Spotlight – Landon Yan

Employee Spotlight – Landon Yan

Wessels Company welcomes Landon Yan to our engineering team! He has been a design engineer with us since April of this year and he says he enjoys the challenge that the position gives him. Landon is a Purdue University graduate, so he will fit right in with the long list of Purdue alumni at Wessels. When he’s not in the office, Landon is a budding YouTuber and Twitch streamer. He spends his spare time practicing martial arts, sketching and playing the guitar and accordion.  One of his dislikes is “being the new guy”, but we’re sure he will quickly fit in and become an integral part of the Wessels team.  Please join us in welcoming Landon!

 

Landon fast facts:

Favorite color: Black

Food: Pho, sushi and Hibachi

Likes: cars, gaming, woodworking and martial arts

Hidden talent: can speak conversational Chinese, and can write and speak some Japanese

 

Contact information:
Landon Yan
Design Engineer
[email protected]
317-888-9800 ext. 1077

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Employee Spotlight – Zach Pokrzywinski

Employee Spotlight – Zach Pokrzywinski

Please welcome a new member to our Engineering department: Zach Pokrzywinski. Zach joined the Wessels family in December of 2025 as a design engineer and says his favorite thing about the new job is being able to create tanks with great people. In his spare time, he enjoys playing video games, playing and watching sports, and working out. He also loves rooting for the Pittsburgh Steelers.

Zach fast facts:
Favorite color: Blue
Food: Steak
Likes: Video games & Sports
Interesting fact: Has an Australian Shepherd named Juju
Nickname: Pok

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Are You “Tanking” Advantage of the Data Center Gold Rush?

Are You “Tanking” Advantage of the Data Center Gold Rush?

Data centers are in a full-tilt gold rush and the winners are the ones “tanking” advantage of smarter HVAC design. With nonstop thermal loads and tight efficiency targets, system stability matters more than ever. Wessels TES thermal energy storage tanks allow operators to shift cooling to off-peak hours, smooth out fluctuations, and gain valuable capacity without oversizing chillers. When paired with Wessels buffer tanks and high-pressure bladder expansion tanks, chilled water loops maintain steady performance and protect uptime.

Reliability is equally critical in mission-critical environments. Wessels SS-AP stainless steel air purgers remove damaging entrained air that can disrupt pumps and reduce overall performance. Stainless construction options throughout the product line support glycol and strict water quality requirements in modern data center designs. From TES tanks that shave peaks to SS-AP air management that keeps systems clean and consistent, Wessels helps data centers turn HVAC infrastructure into a competitive advantage.

Thermal Energy Storage Tanks

Wessels TES Thermal Energy Storage Tanks are designed to store thermal energy for cooling data centers, renewable energy applications, loss of power, or delivery during off-peak hours. The tanks feature dual inner-screen WesPro Super Baffle Systems to stratify and reduce the thermal mixing zone (thermocline), increasing the delivery efficiency of hot or chilled water.

Low water volume systems require additional “buffer energy” capacity to eliminate problems such as excessive equipment cycling, poor temperature control, and erratic system operation. The TES Tank adds the necessary volume to “buffer” the system volume.

Download brochure

Air Purgers

In-line Air Purgers are used for commercial and industrial hydronic systems, to effectively control and eliminate entrained air.

The SS-AP Series air purgers:

  • Rated to 450°F and 150 PSI
  • Designed with an embossed flow indicator arrow for proper installation.

Download submittal

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