From Steel Sheets to Space Shuttles an Inside Look at Pressure Vessels

Pressure vessels are described as a closed container that is fabricated to hold gases or liquids. The key feature of pressure vessels is that they are designed to hold its content at a pressure which is different from the ambient pressure. In theory they can be almost any shape. In most cases they are constructed using sections of spheres, cylinders and cones. More complex designs have been used but have come at a much higher cost and are more difficult to analyze when it comes to safety. One of the most common designs also incorporates end caps which are often called heads.

When it comes to strength spherical pressure vessels have at least twice the strength of a cylindrical pressure vessel with the same exact wall thickness. However, the downfall for using a spherical shaped design is that it is more expensive and more difficult to manufacture. With this being said most pressure vessels are cylindrical shaped using the end cap design. When it comes to smaller vessels they are usually assembled from a pipe, along with two covers.

Next we take a closer look at a pressurized water vessel. They deal with extremely high pressures so during construction safety is at a premium. They use a core container which is difficult to build but provides the most security in case of an accidental explosion. The cylinder walls are constructed from single sheets of high-strength steel that are rolled together and welded. The steel that is used can be up to 25 cm thick. The inside of these pressure vessels are also lined with stainless steel to resist corrosion. To build a pressure vessel it takes a specialized skill and specific equipment. Highly skilled welders must weld the material so it is as strong as the steel plates. This welding is vital so that the vessel remains structurally sound.

Regardless of what shape your vessel takes, the minimum mass of a vessel scales with the pressure and the overall volume. This is inversely proportional to the strength to weight ratio of the material used for construction. Simply said, minimum mass decreases as the strength increases. They are held together against the pressure from the forces inside the walls of the container. Normal stress within the walls of the container is always proportional to the radius of the vessel and inversely proportional to the overall diameter of the walls. After all of this you might be asking yourself, how and why is all of this important and how is it used? Pressure vessels are used in many different applications. Some examples include diving cylinders, distillation towers, oil refineries and even space shuttles.

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