At a university Mechanical and Aerospace Engineering lab in North Carolina, researchers were building something rare: a hypersonic wind tunnel.
To support it, they needed serious vacuum infrastructure. And at the center of that infrastructure would be a 20,000-gallon stainless steel vacuum receiver.
There was just one problem.
There was nowhere to put it.
The vessel initially started life on paper as a horizontal tank, a conventional approach for a receiver of this size.
But a horizontal configuration would stretch roughly 34 feet across the ground, before accounting for the space needed around it.
The area beside the lab simply did not have that kind of room.
Moving the research facility was obviously not an option. Reducing the required capacity wasn't either.
So instead of trying to make the site accommodate the tank, Bendel made the tank accommodate the site.
The design went vertical.
The same 20,000 gallons that would have stretched across the property would instead rise 34 feet into the air. The required footprint shrank from roughly the length of a semi trailer to a 10-foot circle.
It solved the space problem.
But standing the tank up created a new engineering challenge.
Most pressure vessels are designed to contain pressure pushing outward from inside.
This vessel had to withstand the opposite.
Operating at full vacuum, atmospheric pressure pushes inward against the exterior of the shell. For a vessel 10 feet across and 34 feet tall, the primary concern becomes buckling rather than bursting.
Bendel's solution is also what gives the finished vessel its unmistakable appearance.
Six large stainless steel stiffening rings wrap around the shell, helping brace it against the pressure of the atmosphere. From a distance, they almost look like the hoops around a giant barrel. Up close, they tell the story of what this vessel was engineered to withstand.
Built from 304/304L stainless steel and designed to ASME Section VIII, Division 1 requirements, the finished vessel would weigh approximately 21,000 pounds.
Getting something that large from an idea on a drawing to a finished vessel required a lot of people.
About 16 Bendel team members touched the project along the way.
Sales. Estimating. Engineering. Project management. Material processing. Seaming. Fabrication. Cleaning. Testing. Quality. Shipping.
A third-party Authorized Inspector from Hartford Steam Boiler was involved as well.
By late February 2023, fabrication and inspection were complete.
Because the vessel would ultimately stand vertically at the university, Bendel hydrostatically tested it in that same vertical position at 20 psi.
It passed.
The vessel completed its ASME inspection, its welds were pickled and passivated, its surfaces were cleaned, and the U stamp was applied.
Eleven months after the order entered Bendel, a 21,000-pound stainless steel vessel stood finished and ready to leave the shop.
Except it couldn't leave yet.
In late March, the university let Bendel know that the concrete pad wasn't ready.
Installing a vessel this size required significant preparation at the university: a reinforced concrete foundation, anchor points, crane coordination, electrical work and other facility preparation.
Bendel had a choice.
Push the delivery, or hold the vessel until the site was actually ready for it.
Bendel held the vessel.
For several months, the completed tank remained at Bendel while the university finished its foundation and installation planning. The Bendel team stayed in coordination with the university throughout the delay rather than putting pressure on the customer to accept a 21,000-pound vessel before the site was prepared for it.
Then, on October 10, 2023, the tank finally rolled out of Bendel.
The next morning, a crane lifted it onto its foundation in North Carolina.
Today, the finished vessel stands beside the university's Mechanical and Aerospace Engineering lab.
It's hard to miss.
A gleaming stainless steel column rises beside the building, with six distinctive rings wrapped around its shell. It's connected to the vacuum pumps, exhaust and airflow system supporting the university's hypersonic wind tunnel research.
But perhaps the most interesting thing about the finished tank isn't its size.
It's why it looks the way it does.
Every major decision traces back to one deceptively simple constraint:
There wasn't enough room.
The capacity couldn't change, so the configuration did. Turning the vessel vertical solved the footprint challenge, but that decision created new engineering requirements that had to be addressed in the vessel design.
Then, when the vessel was finished before the site was ready, the project required flexibility of a different kind.
That's what custom vessel fabrication looks like when the equipment has to fit more than a process specification.
It has to fit the real world, too.
Why was the vacuum receiver built vertically?
The original concept was a horizontal vessel approximately 34 feet long, but the available area beside the lab couldn't accommodate that footprint. Bendel redesigned the 20,000-gallon receiver vertically, reducing the required ground space to approximately a 10-foot circle.
What makes a full-vacuum vessel different from a typical pressure vessel?
Instead of primarily resisting internal pressure pushing outward, a full-vacuum vessel must withstand atmospheric pressure pushing inward against its shell. For this vessel, buckling was the governing design concern.
Why are there six rings around the vessel?
The six external stainless steel stiffening rings help brace the shell against atmospheric pressure under full-vacuum conditions. They are both a functional part of the design and one of the vessel's most recognizable visual features.
How large is the finished vacuum receiver?
The receiver has a 20,000-gallon capacity, a 120-inch outside diameter and a 34-foot straight shell. The finished vessel weighs approximately 21,000 pounds.
Does Bendel design vessels around site constraints?
Yes. This project demonstrates how Bendel can engineer a custom ASME pressure vessel or vacuum receiver around both the process requirements and the physical limitations of the installation site.
Sometimes the biggest engineering challenge isn't what needs to happen inside a vessel.
It's where the vessel needs to go.
Bendel designs and fabricates custom ASME pressure vessels and vacuum receivers around your process requirements, operating conditions and available footprint.
For more information download our Case Study below:
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