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:

Nitric Acid: The traditional industrial standard. Highly effective at removing free iron, but requires strict hazardous chemical handling, ventilation, and specialized disposal protocols.
Citric Acid: An increasingly popular, environmentally friendly alternative first popularized in the 1990s. It is organic, safer for shop operators, and biodegradable while delivering equal passivation performance.

The 4-Step Passivation Process

Achieving a true passive finish requires a tightly controlled sequence:

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.
Acid Bath Immersion: The vessel is submerged in a controlled nitric or citric acid bath to dissolve free iron and surface contaminants.
High-Purity Rinsing: The part is thoroughly rinsed with clean water to flush away acid residue and prevent chemical staining.
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.

How To: WesselsVessels.com E-Shop Tutorial

Requesting quotes, checking prices, placing orders, viewing product literature, and downloading 3D models have never been easier thanks to the new WesselsVessels.com E-shop.

Don’t have an account? That’s ok! Anyone can use the site to build an order and request a quotation from our customer service or network of sales representatives. Navigating the website is simple. Either click the left side menu or scroll down the frontpage to navigate by product category or, if you know the product you’re looking for, type it in the top search bar.

If you search by category, you’ll be brought to a page with product tables. From here, you can get a quick glance at product information or filter by sub-categories like “ASME” or “High Velocity”. You can click an individual model name to get more information about that product or click “Add to Quote” to add it to your quote request. If you are logged in, you will be able to see your pricing and an “Add to Cart” link instead.

If you click a model name, you will open that specific product’s page. If you are logged in, you will see your net price under the model name in blue. If you are the Wessels Vessels Rep admin login for your account, you will find both the list price and your special net price on this page.

Further down, you will find an “Add to Quote” or “Add to Cart” button depending on whether you are logged in. Under the data table, you will find downloadable links to relevant product literature and CAD models.

Click the cart icon on the top right of the website when you’re ready to submit your quote request or online order. Click proceed and enter your contact information. If you’re logged in and placing an order, you can select a Ship To address. You can also enter optional order notes and a required Purchase Order (PO) number. Click “submit” for quotation or “place order” to send a copy of your order to yourself, Wessels Customer Service, your account admin, and your account purchasing agent. Someone from Wessels will reach out to you shortly with either an order acknowledgement or quotation. And that’s it!

The WesselsVessels.com E-Shop makes finding prices and placing orders with Wessels Company easier and faster than ever. To inquire about eligibility for a login pricing or admin account, please email [email protected]

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Stainless Steel Pricing Alert and Price Book Notice

Stainless Steel Pricing Notice

Due to changing costs associated with stainless steel manufacturing, Wessels Company list prices are the net prices for quoting stainless steel products until further notice, effective immediately. There are no discounts at this time. All stainless steel quotations must be renegotiated.

Our new Wessels Reference List Price Catalog PDF is now available for download upon request. If you’ve received special pricing, you already have the list price for affected stainless steel products, but if you would like to receive a new CSV, please contact your regional manager or customer service agent.

We apologize for any inconvenience as we continue to navigate the fluctuating pricing environment brought on by changing world events.

To request printed copies of the Wessels 2022 Price Book Reference Catalog, please send number of copies and address to [email protected]

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New 2022 Pricing Now Available on E-Shop

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Materials Surcharge and Affected Lead Times

New Materials Surcharge – Effective 1/4/2022

Due to continued supply chain delays and the inflation of steel, rubber, and plastics, the following surcharges will be added to all future orders. We are working towards issuing a new pricebook within the next few weeks to compensate for these changes. While we anticipate it is only a temporary change, a materials surcharge will be applied to all orders beginning Jan 4, 2022 and will continue until further notice. Please also be aware that lead times may be affected by material availability.

Impacted product percentage breakdown:

• 10% – Carbon Steel Tanks, GMP’s, Replacement Bladders, Glass-Lined Tanks, Misc.
• 15% – Stainless Steel Tanks or Components

Surcharge will be shown as a separate line item on your order acknowledgements.

Wessels Company greatly appreciates your continued business and support through these unprecedented times. Rest assured, our team is dedicated to delivering competitive pricing and quality products. If you have any further questions or concerns, please contact your Customer Service Representative.

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January Employee Spotlight

Wessels Company is pleased to introduce John Paul as Director of Sales. John brings over 11 years of professional sales experience. As a manufacturer’s representative, he’s overseen product launches, training, recruiting and sales team development. John is an avid golfer and a diehard Michigan Wolverines fan and, like Wessels originally, hails from the Detroit metro area. He enjoys spending time with friends and family and being outdoors, especially to walk his dogs. Please join us in welcoming John to the Wessels Company family.

John Paul Fast Facts:

Favorite color: Blue
Favorite food: Mexican
Likes: Spending time with family, watching sports
and walking his dogs

Interesting fact: he is highly competitive

John Paul
Director of Sales
e-mail: [email protected]
phone: 317-888-9800 Ext. 1064

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Going Green with Plate Heat Exchangers

Download the Full White Paper “Going Green with Wessels Plate Heat Exchangers”

Purpose:

Illustrate how to design liquid to liquid plate heat exchangers to save money by reducing energy costs and carbon footprint at the same time. Also present a means for determining the operating costs of a plate heat exchanger. This is a road map for designing heat exchangers to do their part in reducing harmful emissions.

History:

And A Changing Future

Plate heat exchangers are used for the transfer of heat or cold into or out of a commercial building. They have a very efficient design transferring 100% of the energy from one fluid to the other. They are a vital component for providing economical chilled water for air conditioning to residential and office buildings, hospitals, and especially data centers where they help to speed up and reduce the cost of millions of high-speed data transactions. Plate heat exchangers are also utilized for ground and air source heat pumps and large city or college district heating/cooling systems that save energy and reduce cost along with their carbon footprint.

For too many years, most HVAC projects have been driven by “lowest installed cost” instead of future savings.

For too many years, most HVAC projects have been driven by “lowest installed cost” instead of future savings. That is especially true in heat exchanger design. The size and cost of a plate heat exchanger is driven by its heat transfer coefficient, which is the rate of the transfer of heat from one liquid to another. The heat transfer coefficient is increased significantly by making the corrugations on the plates more resistant to flow causing a more turbulent flow pattern. This reduces the size and cost of the heat exchanger, but the energy cost increases due to the greater pump horsepower required to overcome this increased resistance.

In heat exchanger design, if not specified, the heat transfer engineer will use a maximum pressure drop of 10 psi to yield the highest heat transfer coefficient and lowest Installed cost heat exchanger possible. This direction is short sighted! To go green, we must think about future long-term benefits.

Details:

Crunching the Numbers

To first determine the operating cost of an HVAC plate heat exchanger based on the water flow and pressure drop through the heat exchanger:

1) Calculate the Horsepower (HP) required to move the fluid through the heat exchanger:

HP = GPM X FT X SG / 3960

Where: GPM = water flow in Gallons Per Minute through the heat exchanger

FT = head loss in Feet through the heat exchanger

SG = Specific Gravity of the fluid (1.0 for water)

3960 = 33,000 ft-lb/min over 8.33 lb/gallon

2) Calculate the Motor Horsepower (MHP) required:

MHP = HP / (e1 X e2) = Motor Horsepower

Where: HP = horsepower

E1 = motor efficiency. Assume 0.95

E2 = pump efficiency. Assume 0.80

3) Calculate the Kilowatt usage of the heat exchanger based on flow and pressure drop:

Where: KW = 0.745 X MHP = KiloWatts = Energy consumption

KW = (GPM X FT X SG) / 3960 / ((e1 X e2) X 0.745

KW = GPM X FT /3881

Note: This is the power required to move water through the heat exchanger only.

It does not include other system effects.

4) Calculate the annual operating cost of the heat exchanger:

Where: AOC = Annual Operating Costs = $ / year

If utility cost = $0.10 / kwh and there are 6000 hours per year of operation the
Annual Operating Cost of the heat exchanger becomes:

AOC = GPM X FT / (3881 X $0.10 kwh X 6000 hours/year)

AOC = GPM X FT X $0.15 = $ / year

Visit westank.com/heat-exchangers to learn more about product lines and sizing.

Calculate:

Leading by Example

A typical application is to cool 2000 gpm of water from 55 ⁰F to 45 ⁰F using 2000 gpm of water at 43 ⁰F on the other side. This requires a total heat transfer of 10,000,000 btu/hr.

Using a 23 ft (Approximately 10 psi) of pressure drop, Wessels sizing software calculates the following:

AWP83 with 315 plates and 3892 square feet of surface area at a cost of $52,000

The Annual Operating Cost = (2,000 gpm)( 20 ft )($0.15) = $6,000/yr

Using a 12 ft (Approximately 5 psi) of pressure drop, Wessels sizing software calculates the following:

AWP83 with 341 plates and 4216 square feet of surface area at a cost of $57,000

The Annual Operating Cost = (2,000 gpm)( 10 ft )($0.15) = $3,000/yr

Final Thoughts:

Going Green Means Saving Green

In the previous example, the old idea of using a maximum pressure drop of 10 psi results in a slightly lower installed cost of $52,000 versus $57,000.

However, if your goal is to be more energy efficient and save money in the long term, then taking the 5 psi selection that operates at $3,000/yr versus the $6,000/yr of the
10 psi selection cuts the energy consumption and annual operating cost in half. Doing a very simple pay back calculation, the larger heat exchanger’s energy efficiency results in a 1.7-year return.

To be energy conscious with heat energy and an eye to the future, the conscientious engineer should always specify lower pressure drops through heat exchangers to save energy, reduce carbon emissions, and make a greener future for everyone.

All Wessels plate and frame heat exchangers are AHRI certified Standard 400 to guarantee efficient performance

Download the Full White Paper “Going Green with Wessels Plate Heat Exchangers”

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Downloading Drawings: BIM vs CAD

Wessels Company makes it easy to download a huge catalog of BIM and CAD files, which can be imported into software to generate product drawings and 3D models, but what’s the difference between Revit (.RFA), .STEP and .SAT files?

In the case of Revit, .RFA’s are Building Information Models (BIM) specifically compatible with Autodesk’s Revit software package. Revit is used by architects, engineers, and contractors to collaboratively design buildings using a shared resource pipeline from start to finish.

Computer Aided Design (CAD) files like .STEP and .SAT, on the other hand, are compatible with many more design programs. Wessels engineers primarily use Solidworks CAD software to design products. These .STEP and .SAT CAD files can be imported into other software packages such as AutoCAD, Inventor, Civil 3D and MicroStation, so they are commonly used to exchange 3D data across multiple software platforms.

Whether you use BIM or CAD files, it’s easy to import Wessels product files into your computer program of choice. From there, you can generate drawings, simulations, animations and more for use to build your system.

Wessels Company has expanded its offering of product BIM and CAD files on the new e-commerce website WesselsVessels.com. Simply navigate to a specific product and click the link of the desired file format at the bottom, to begin downloading.

Something missing? Contact [email protected] for help finding a file or to request downloading a family of files.

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What is NSF/ANSI Standard 61?

NSF the Organization

The National Sanitation Foundation was originally founded in 1944 as an organization dedicated to standardizing sanitation and food safety regarding soda fountains and luncheonette equipment. Today, NSF International has grown to become an accredited, independent third-party certification body that tests and certifies a wide range of products to verify they meet certain public health and safety standards. NSF is accredited by the American National Standards Institute (ANSI) to develop American National Standards and uses a ballot system similar to ANSI to revise and maintain those standards. Products that meet these requirements bear the NSF mark.

NSF Standards

NSF/ANSI Standard 61 pertains to products in contact with potable or drinking water in the United States. This is a performance-based standard that evaluates the amount of contaminants that leach from the products into drinking water, rather than setting prescriptive limits on content. These products include butyl bladders, pipes, gaskets, hoses, faucets, water fountains, filters, valves lubricants, coatings, adhesives and more.

The National Sanitation Foundation’s standards help keep potable water in safe, drinkable conditions for the public. The NSF/ANSI Standard 61 certification signals that a product is safe to be installed in a potable water system for public use or consumption and is verified by a 3rd party.

NSF Certification and Compliance

A product must undergo independent, 3rd party verification to be NSF certified. Regular on-site inspections and audits of materials, facilities, and product testing must be conducted to ensure rigorous adherence to NSF standards over time. Products that are NSF compliant adhere to the same strict standards but are not subject to the same independent testing. Wessels is proud to use parts that comply with NSF/ANSI Standard 61 in our relevant products.

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