Pressure Vessels

By Jenny Bengen
A pressure vessel is a type of storage tank. Essentially, a pressure vessel is a container that holds a liquid, vapor or gas at a pressure that is different from the atmospheric pressure surrounding the vessel. Usually, pressure vessels are designed to operate at 15 psi. This means that even high-carbonated soda bottles can be considered pressure vessels!

A Brief Introduction to Pressure and Force

Most of us have seen more than one pressure vessel in our lifetimes, though most of us have never stopped to consider the question – why are pressure vessels round? The answer has to do with pressure. Basically, when a container is pressurized, the pressure pushes against the walls of the container. Physics tells us that pressure is always perpendicular (at right angles) to the surface, no matter what the shape of the container is. The force that is exerted on the surface causes the surface to bow outward. This explains why pressure vessels are almost always round – and in fact, sphere pressure vessels are considered to be the most ideal shape.

Different Types of Pressure Vessels

There are many different types of pressure vessels:


Thinned wall pressure vessels are referred to as “thin” because their diameter is 10-times more than their thickness. Thinned wall pressure vessels are fairly common. However, thick walled pressure vessels are the least common. Thick walled pressure vessels have diameters that are 10 times thinner than the wall thickness. Storage tanks are considered thinned wall pressure vessels and they usually have pressure ratings less than 15 psi. Transportable containers are the most common form of pressure vessel. These are produced on large scales, and they must be tested every 10 years if they contain propane or gas.

Pressure Vessel Safety

Due to the fact that the contents in a pressure vessel are under pressure, there are a number of safety concerns which must be taken into consideration when handling these items. Some of the health and safety hazards that leaking vessels pose include: poisonings, suffocations, fires, and explosion hazards. If the pressure vessel becomes cracked or damaged in any way, the vessel's contents can leak out and become hazardous to those around it. Actual rupture failures can be much more serious and can cause terrible damage to people the environment.

There are a number of products which are intended to prevent over-pressurization and thus prevent explosions and fires. Some of these products include:


Rupture disks are considered the most versatile of these items. However, they can only be used once, and if a problem occurs, they have to be replaced. Rupture disks are also the only device which can be used along with other safety devices.

Relief valves are mainly used for pressurizing liquids, and safety valves are only intended to be used for pressurizing vapors and gasses.

Taking all of this into consideration, it becomes apparent that it is highly important that pressure vessels are correctly and safely installed by someone who really knows their craft. In order for pressure vessels to work well and to work safely, they must be correctly designed, installed, operated and maintained.