The Importance of Determining the Right Size of Pressure Vessels

September 26, 2019

As observed in past articles, pressure vessels are made in different shapes. Dependent on a containment unit's role, it could assume a spheroidal outline, a cylindrical shape, or some kind of composite outline, midway between a sphere and a cylinder. Indeed, these capsule shapes are popular across countless industrial applications. What about the size of a vessel, though? After the shape is decided, how big will it need to be?

Pressure Vessel Sizes: The Goldilocks Question

Neither too big nor too small, a pressure containment unit should contain the fluid volume it's designed to store. That might sound like an easy enough instruction to follow, but think about how things are changing inside the metal tank. For starters, the fluid is pressurized. That means it's going to occupy less physical space. Moreover, ASME guidelines don't advocate complete fills. There's typically a fluid to unoccupied tank ratio invoked, so the stored medium can expand or discharge a vapour-released fraction. And, according to the laws of fluid dynamics, different liquids compress and condense in different ways. With all of the above thoughts firmly in mind, design engineers size pressure vessels according to a broad number of ASME specified design guidelines. Criteria-wise, there's the fluid compressibility factor to weigh, plus the volume and storage unit flow rate, plus the amount of overhead provided by the chosen application.

Reviewing Transportation and Installation Matters

Application requirements set the size and shape of a client's pressure vessel, but that's not the end of the matter. Transportation practicalities rank high on the design agenda as well. If the final product, fabricated with all of its fittings installed, is too large, the odds of some kind of transportation-caused damage will obviously climb dangerously high. Some other kind of conveyance strategy will need to be worked out. And that's a thorny issue, especially since pressure vessels tend to end up in remote areas. One solution is to make the unit smaller, then to fabricate an array of these units, with all of them hooked together in a line.

The fluid dynamics question can be solved in a lab or office by a designer. For the vessel design, the size and shape and wall thickness are decided by using ASME guidelines and scientific reasoning. When shipping a monolithically huge pressure vessel on a large haulage truck, though, other disciplines take precedence. This is now a logistics based operation. Having no problem, the chosen haulage company must be equipped to convey such an unwieldy construct. Alternatively, back at the office drawing board, a smaller containment unit size is selected, and then it's multiplied. Conveyed in tandem, these dimensionally reduced constructs group together to handle large volumetric fluid loads.

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