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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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November Employee Spotlight

November Employee Spotlight

Aaron Johannigman has been part of the Wessels Company’s family for over 12 years. Aaron is the Director of Engineering at our headquarters office in Greenwood.  He enjoys spending time with his family and playing games in his spare time.  He graduated from Purdue University and roots for their sports teams.  But he also cheers on the Indianapolis Colts during football season and the Cincinnati Red during baseball season.

 

Aaron fast facts:                               

Favorite color:  blue

Favorite food: pizza

Likes: spending time with family, playing games

Interesting fact: 2nd degree black belt in Taekwondo

How To: Size Expansion Tanks Using Wessels Free Tank Calculator

How To: Size Expansion Tanks Using Wessels Free Tank Calculator

Wessels Company is proud to offer a free web and phone app (iOS and android) for sizing and converting a selection of our tank products online or on your phone.

In our easy-to-use app guide, you will find a quick reference page explaining the icons. Here are the icons most commonly found on the app:

    

The calculator allows you to select the type of tank you wish to size: HVAC expansion, domestic hot water, well & pressure booster, and buffer. You can also use the app to convert a compression style expansion tank to a removable bladder or fixed-diaphragm design. To learn more about each category of product, simply click or tap the (?) help buttons next to each product.

On each tank page, you will see a series of entry fields and drop down menus that will need to be filled out to determine the tank size you need for the job.

 

For HVAC expansion tanks, the first field you will need to answer is System Volume in gallons. If you don’t know your system’s volume, you can click the System Volume Estimator to get an idea.

You will also need to know the fluid type used within the system and the operating temperature range.  Finally, you will need the initial and final pressure, which both have estimators that can help determine an approximate value.

When you are ready to size your tank, click “Calculate” and you will be taken to the calculated critical sizing page.  Here you will be given a “Required Tank Volume” and product suggestions based on that calculation.

 

Once you’ve selected a product, the final page of the app will display the product submittal, installation & operation manual, and brochure.  If you decide to request a quote to purchase the product, you can click “Request Quote” and the app will auto-generate an email with your calculations that you can then send to the Wessels quotation department.

Wessels makes it easy to determine which product is best suited for your job, which volume is needed, and the details of the product.  Remember, if you are unsure about your selection, Wessels Company’s friendly customer service is available to help ensure you make the right selection. Send us an email at [email protected], give us a call at 317-888-9800 or live chat with us right on our website by clicking the floating “Start Chat” window.

You can find the Wessels tank sizing app online at https://www.westank.com/calculator/ or you can download it to your iOS or Android phone by searching your app store for “Wessels Company”.

October Employee Spotlight

October Employee Spotlight

Jay Fuller has been a consistently smiling face in the Wessels Company’s Marketing Department for the last 6 years. He has been the marketing manager for the last three years and his favorite part of his job is using new technologies to teach customers about Wessels products.  Jay graduated from Boston University.  In his free time, he can be found writing for an award-winning graphic novel series called The Cardboard Kingdom. He also enjoys writing, reading and gaming as well as virtual reality and graphic novels.

Jay fast facts:

Favorite color: Blue

Likes: virtual reality, video games and graphic novels

Favorite food: Impossible Burgers

Dislikes: bigotry and xenophobia

Hobbies: writing graphic novels

Nickname: Jay (full name is James)

Hidden talents: plays the piano and ukulele

September Employee Spotlight

September Employee Spotlight

Megan McDaniel is one of the smiling faces in Wessels Company’s filtration department.  Megan has been with Wessels for about 9 years and has been our filtration purchasing manager for 4 years. She attended University of Southern Indiana and she has two children, both of whom have red hair and blue eyes.  When she’s not in the office, she enjoys watching movies, listening to music and competing at trivia night.  An interesting fact about Megan is that she writes, eats, and brushes her teeth left handed, but plays all sports with her right hand.  During football season, she roots for the Indianapolis Colts and the Chicago Bears.

Megan’s fast facts:

Favorite Color: Purple
Favorite Food: Mexican
Hobbies: Playing outside with her kids and trivia night
Nickname: Megmo Jackson

Megan McDaniel
Filtration Purchasing Manager
e-mail: [email protected]
phone: 317-888-9800 ext. 1031
cell: 317-443-4154

How To: Acceptance Volume vs. Tank Volume

How To: Acceptance Volume vs. Tank Volume

Tank Volume: The overall volume of the tank, including air and water.

Acceptance Volume: The amount of water inside the tank.

Maximum Acceptance Volume: The maximum amount of fluid inside the tank before stretching the bladder/diaphragm.

Acceptance Factor: The percentage of of tank volume storing fluid, expressed as a decimal.

Drawdown Volume: The amount of water that is drawn out from a starting tank pressure down to the minimum pressure.

A tank’s drawdown volume is the amount of water that is stored between a high and low pressure, which is usually determined by a pump switch.  In real-world plumbing systems, the tank should not start at the maximum pressure and the air cushion pressure should not fall to zero.

The volume of water in a tank, called the acceptance volume, is sometimes expressed as a decimal or percentage against overall tank volume, called an acceptance factor. However, the tank should be charged on the tank’s air side to the minimum pressure needed within the system and filled to the maximum pressure in water required to adjust the tank’s pressure correctly. (pressure in the tank should be set accordingly: 10% below pump cut-in pressure (hydropneumatics); equal to pressure reducing valve pressure (hydronic), equal to line pressure (thermal – domestic water heater protection). As a standard, Wessels Company offers tanks pre-charged to 40 PSI, which can easily be adjusted and reduced in the field to fit the pressure needed within the system.

All replaceable bladder tanks Wessels offers are considered a full volume acceptance tanks, since the bladder inside can fully expand within the tank, allowing all the available space inside the tank to be used.  Fixed-diaphragm tanks are not full acceptance tanks because the diaphragm is confined to only a portion of the tank.

You can tell if a tank is a full acceptance tank by looking at its chart either online, on the submittal, or in the literature for each style of tank.  If the chart says tank volume, that means the usable volume inside the tank is the total volume of the tank.  For example, in a Wessels Company NLA series tank, the total volume of the tank is also the number of gallons the tank can hold, making the tank a full acceptance volume tank. A fixed-diaphragm tank like the NTA, however, lists both the tank volume and the maximum acceptance volume.

If you have more questions about tank volume and Wessels products, feel free to reach out by chatting with us in the chat window at the bottom right of our website, by emailing us at [email protected], or by calling our offices at 317-888-9800.

August Employee Spotlight!

August Employee Spotlight!

Guy Kirk has been part of the Wessels Company family for over 20 years!  He is the Vice President and East Coast Sales Manager.  He enjoys playing and watching all sports, particularly sailing and he loves eating seafood. In his spare time, he enjoys rooting for his favorite teams: New England Patriots, Boston Red Sox and the Indianapolis Pacers.

 

Guy fast facts:                                                                              
Favorite color:  Green

Favorite food: Steak and seafood

Likes: sports, sailing

Hobbies: rooting for and watching sports

How To: Understanding the Makeup of Glycol Makeup Packages

How To: Understanding the Makeup of Glycol Makeup Packages

How To: Understanding the Makeup of Glycol Makeup Packages

Wessels Company makes Glycol Makeup Packages in Glymatic, Single, Double, and Twin systems. The purpose of a GMP is to maintain system pressure.

In the sequence of operation in a system using a GMP, the glycol solution mixture is held in a solution container and then is pulled through a pump. The pump has an internal spring that utilizes a pressure relief valve, if the pressure in the system is too high. Fluid goes into the pump, the pressure is increased with a rotary vane, and then is discharged into the system at a higher pressure.

The package is protected by a low water cutoff probe in the solution container. Two probes are in the container and monitor the glycol mixture

level. If the level falls too low, the continuity between the offset probe is broken and the pump is shut off, which sounds an alarm.

The pump is controlled by a pressure switch, which is set to turn on at 60 psi and to cut off at 80 psi. The 80 psi of fluid is then stored in an expansion tank to hold the excess fluid. The expansion tank is a diaphragm tank that has a pre-charged pressurized air cushion, which helps maintain the pressure in the system to 80 psi.

The fluid then flows through a pressure reducing valve or PRV, which is set for the system’s required pressure. The valve’s range can go from 10 to 70 psi, which can be for whatever pressure your system needs.

Inside the PRV, a spring sets the tension that holds the valve open. The valve can be set to point downstream between 10 and 70 psi, the spring will hold the valve open until the downstream pressure equalizes the spring tension through the diaphragm, that will hold the diaphragm up and close the valve.

Wessels Company offers four different types of GMP systems: a glymatic, a single, duplex, and twin. A Glymatic system package is a free-standing solution reservoir that holds the glycol/water solution at atmospheric pressure. A pressure assembly is mounted on the solution reservoir’s cover keeping the pressurization unit off the floor. This GMP uses a pressure station to move fluid from a 6 or 15-gallon reservoir pressurized to between 1 and 25 psi, up to 130° F. The solution then remains stored until it is needed to replenish the system that has lost its glycol/water or water solution.

The single system GMP automatically services one closed-loop system. This GMP holds a reservoir of 50 or 100-gallons and 1/3 and 1/2 horse power pump pressurization control station with magnetic starter. The 1/3 HP is used for systems of 50 PSI pressure and the ½ HP station is used for systems up to 70 PSI.

The Duplex system or GMPD, services two separate closed-loop systems. This system is available with 50- or 100-gallon reservoir and 1/3 or ½ HP pump pressurization control also with magnetic starter.

The Twin system or GMPT also services one closed-loop system and is available with the 50 or 100-gallon reservoir with 1/3 or ½ HP pump.

However, a control panel with alternator and dual magnetic starter is used with this system to easily and automatically alternate between two pumps.

To see exactly how the GMP system works, you can watch our technical video, here.

You can also learn more about the GMPs, on our website, here.

Upgrades Coming to Fixed-Diaphragm Tanks

Upgrades Coming to Fixed-Diaphragm Tanks

Wessels Company is proud to announce the popular WessView Bladder Integrity Monitor and integrated pressure gauge are coming to the NTA, TTA, and FXT lines of fixed-diaphragm tanks.

By mid-September, Wessels will roll out these much-requested upgrades as standard features for our fixed-diaphragm HVAC expansion tanks, domestic hot water tanks, and well water and pressure booster tanks.

The WessView is an innovative bladder integrity monitor that alerts you to moisture outside the fixed-diaphragm inside the tank. In addition, a handy pressure gauge provides a quick and easy way to check the pressure of the air cushion surrounding the diaphragm.

These upgrades have been standard on Wessels Company’s on removable bladder tanks for over a year now and the reviews are in: our customers love it!

The new submittals are available on our website now: NTA, TTA, FXT

Updates to other literature are in development. Download the new NTA Brochure below.

 

NTA Brochure