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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


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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Wessels Launches New E-Commerce Site

Wessels Launches New E-Commerce Site

March 2021

Contact: Rebecca Bennett- Marketing Coordinator
[email protected]
317-888-9800

For Immediate Release

Wessels Company Introduces New Website

Greenwood, IN – Wessels Company has unveiled a brand-new e-commerce website called WesselsVessels.com. At the time of launch, users can browse through an interactive version of the Wessels product catalog, as well as download brochures, submittals, manuals and 3D models like SAT’s, STEP’s, and Revits.

In the coming weeks, rolling updates to WesselsVessels.com will include new products, add-to-cart quote requests, and special pricing for select customers. Eventually, new customers will also have the option to create accounts to unlock purchasing directly through the website.

Wessels Company’s corporate website, westank.com, will continue to be operational as the central place to get the latest news, information, press releases, and more. Wessels looks forward to promoting the new e-commerce site to make ordering a more streamlined, user-friendly experience.

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New! WVA-MAX Air & Dirt Separator

New! WVA-MAX Air & Dirt Separator

Maximum Performance, Maximum Value

Wessels has launched the new WVA-MAX Air & Dirt Separator with patented coalescing media. Air & dirt separators eliminate entrained air and separate debris associated with start-up and maintenance of any hydronic system. Extend the life of your HVAC system by improving heat transfer, saving energy, reducing pump cycles, and protecting components with the new WVA-MAX for maximum protection backed by 5 year warranty.
U.S. Patent No. 10,708,538

WVA-MAX Complete Package Includes:

  • Increased flow rate performance
  • Patented removable coalescing media
  • ASME certification
  • WesMag® Magnetic filtration
  • Extended 5 year warranty

Visit the WVA Product page to learn more about Wessels Air & Dirt Separators, high velocity, Air only and Dirt only separators, as well as the industry leading integration of WesMag® Magnetic Filtration for removal of ferrous particulate.
WVA Air & Dirt Separator Product Resources

Lead Times (est.)

  • 2 Weeks: WVA-2-MAX thru WVA-6-MAX
  • 3 Weeks: WVA-8-MAX thru WVA-12-MAX
  • 4 Weeks: WVA-14-MAX thru WVA-36-MAX (Consult Factory)
Download WVA-MAX Submittal
Mural Brings Fresh Life to Wessels Company headquarters

Mural Brings Fresh Life to Wessels Company headquarters

September 2020

Contact: Rebecca Bennett- Marketing Coordinator
[email protected]
317-888-9800

For Immediate Release

Mural Brings Fresh Life to Wessels Headquarters

GREENWOOD, IND. — Wessels Company has announced that the large-scale, outdoor mural at their headquarters in Greenwood, Indiana is complete. It took just over a week for the sketching and painting to be completed on the 100-foot by 20-foot wall.

The mural depicts the company’s logo as well as its products, like air and dirt separators and expansion tanks, which are manufactured at the factory. From concept to final design, some changes were made in collaboration between Wessels Company and local artist Macey Dickerson.

“When [Wessels] initially sent me reference photos to incorporate into the mural design, the expanded view of the heat exchanger really caught my eye,” Dickerson said. “It was such a cool diagram and I knew I wanted that the be a prominent feature. I really like how that part looks.”

She added, “Painting the Wessels logo was also really fun. I like how the curviness of the font contrasts nicely with the rest of the mural, which is more geometric.”

 

Dickerson was assisted in painting by her brother, Garrett Dickerson and her friend, Nick Service. “I enjoyed the process of working with my brother and friend who helped me bring the design to life,” Dickerson said. “I usually do projects solo, so it was fun working in a team and sharing the experience. I also enjoyed getting to meet the employees at Wessels. Everyone was so friendly and supportive! When it was break time, people were sure to stop by and say ‘hi’ and give encouragement. I felt so welcome.”

Jim Fuller, president of Wessels Company, says he is pleased with how the mural turned out.

“It adds color and art to the neighborhood,” Fuller said. “It also conveys our pride in our products, our employees, and being part of the Greenwood community.”

Download the Press Release

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Mural Announcement Press Release

Mural Announcement Press Release

August 2020

Contact: Rebecca Bennett- Marketing Coordinator
[email protected]
317-888-9800

For Immediate Release

New Mural Brings Outdoor Art to South Indiana

GREENWOOD, IND. — Wessels Company is announcing their partnership with local artist Macey Dickerson to create a brand-new large-scale mural at their headquarters in Greenwood, Indiana.

Dickerson was born and raised in Indianapolis and is a lifelong Hoosier. She is an alumni of Franklin College in Franklin, Indiana, where she studied painting. She has been painting and creating art since she was very young.

“I kind of don’t remember a time when I wasn’t painting,” Dickerson says. She works in a wide variety of mediums –clay, photography, digital art –but says she loves painting the most.
“I think the transformational effect of it is my favorite part. Especially with a mural,” she adds. “It just uplifts people and changes their attitude to be around art in a big way.”

Macey’s art has been all over Central Indiana, including the restaurant Chef Oya’s The Trap, as well as work for an interior design company and other temporary installments. “It creates this whole other world and atmosphere which I really, really love,” she said.

Dickerson has been commissioned to paint a large outdoor mural on the 108 by 20 foot exterior wall of Wessels Company’s main office and manufacturing facility. The art will face North Meridian street and will feature abstract shapes and water motifs suggestive of products manufactured by the company.

Wessels is currently collaborating with Macey to design the perfect mural to show the community what the company is all about.

“As a leading manufacturer of industrial water equipment, it’s sometimes hard to appreciate the beauty of such a practical line of business,” Wessels Marketing Manager Jay Fuller-Ng said. “I’m glad this project will give us an opportunity to add art to the community that celebrates what we do.”

Work on the mural will begin in mid-August and the finished art is expected to be unveiled in September of 2020.

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TTA-Rx Antimicrobial Press Release

TTA-Rx Antimicrobial Press Release

June, 2020

Contact: Jay Fuller- Marketing Director
[email protected]
317-696-8916

For Immediate Release

TTA-Rx: Looking Forward to a Healthier Future

GREENWOOD, IND.- Wessels Company, headquartered near Indianapolis, is introducing a new Full Flow fixed-diaphragm domestic hot water expansion tank with a special flow-through internal coated in antimicrobial silver. The tank is called TTA-Rx and is available to specify now.

Expansion tanks have been established as a place where pathogens like Legionella can flourish. The new TTA-Rx Full Flow tank features a perforated internal that disrupts stagnant water with a flow-through design. In addition, silver plating or other antimicrobial coatings are applied to the internal to create a surface that can destroy harmful microbes through contact. Unlike normal rubber, the heavy-duty butyl bladder also does not support the build-up of nutrients key to forming biofilms.

The TTA-Rx is compatible with Wessels Smart Bracket system, which includes the WessView® bladder monitor and pressure gauge and comes standard on the vessel.

Wessels Company’s new smart bracket system can be easily retrofitted to include WessGuard® bladder monitors capable of being connected to an Energy Management System (EMS). To learn more about Wessels Company’s new Full-Flow Antimicrobial fixed-bladder expansion tanks, and the WessView® or WessGuard® bladder monitors, visit www.westank.com or contact a Wessels sales representative.

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January Employee Spotlight

January Employee Spotlight

Julie Storey is a Wessels Company Office Assistant who worked as a temporary employee for over a year and then was hired on as a full-time employee about 9 months ago. She enjoys reading, researching and looking into her family ancestry and genealogy. Julie enjoys playing tennis and rooting for Notre Dame during football season. She attended both Indiana State University and graduated from Ball State University with a degree in Social Work.

 

Julie fast facts:

Favorite color:  blue

Favorite food: anything Italian

Likes: genealogy, reading and playing tennis, loves jazz music

Hidden talent: she plays the recorder

December Employee Spotlight

December Employee Spotlight

Aidan Baird is a new member of the Wessels Company team. He has been a Product Design Engineer in our Engineering Department for nearly five months.  Aidan likes to play video games, board games and spend time with friends.  He loves dogs and adopted a 2-year-old Blue Heeler named Fitz, a few months ago.  Aidan grew up in Northern Virginia but attended Purdue University in West Lafayette, Indiana.

 

Aidan fast facts:                                                                                          

Favorite color:  blue

Favorite food: pizza

Likes: dogs, playing board and video games

Interesting fact: enjoys doing Martial Arts