Most often, pressure vessels, also called air pressure tanks or boilers, are mostly used for applications pertaining to the food and beverage, chemical, pharmaceutical, plastics and oil and fuel industries. They can also be used for heating and cooling.
In 1495, Leonardo da Vinci came with the idea and designed air pressured containers for lifting purposes. However, the present-day application of pressure vessels was not devised until the advent of steam engines. In steam engines, pressure vessels were used as boilers, where steam was produced and contained for powering the cylinder.
At that time, in all external combustion engines, pressure vessels were major equipment. In the 16th century, they were even used for hauling up heavy weights underwater. However, pressure vessels were also the most unreliable part of external combustion engines, as the technology for manufacturing pressure vessels was in the formative stage. Moreover, the quality of materials used for making vessels was poor. The failure of pressure vessels was usually catastrophic, causing damage to the machines and killing operators. They were the source of explosions in an array of industries on a daily basis.
The first effort to modernize pressure vessels and improve their safety emerged in the United States. In 1911, American Society of Mechanical Engineers (ASME), which was established in 1880, came up with the idea of standardizing codes and inspection methods for making pressure vessels. From this, they came up with the Boiler and Pressure Vessel Code (BPVC). In 1914, they printed the first rules and code standards for boiler and pressure vessel construction.
In 1919, answering the call for pressure vessels that could withstand 10,000 psi, manufacturers put out a new pressure vessel design on the market. To help the tanks endure such high pressure, manufacturers spirally wound steel wires around the tank, and added steel rods for additional reinforcement. With this design, there was no rupture of the pressure vessels even under stressful conditions.
At the same time, welding replaced rivets, as industries, such as chemical plants and petroleum refineries, needed pressure steel vessels that could endure high temperature too. BPVC recognized how welding could make pressure vessels stronger and thus, safer, so welding was included in the fabrication code. It was the beginning of the modern manufacturing technique, as nearly all of them use welding for joining metal plates in vessels.
Over time, to make boilers and pressure vessels safer, engineers have designed different testing techniques and methods. For example, today, it is mandatory that all pressure vessels go through inspection after fabrication and before being sold. Traditional tests are mainly destructive; however, the modern tests are non-destructive. These new inspections include radiography and phased array ultrasonic. Moreover, to make sure pressure vessels safer and up to code, manufacturers have crafted new assessment and inspection methods. These have been a major player in promoting and achieving safety standards. Modern assessing and inspection methods, such as finite element analysis, can identify stress points. Manufacturers also use stronger materials, including better stainless steel and steel, than they did early on. If they so choose, they strengthen those steels and stainless steels.
The future of boiler and pressure vessel design is quite bright. As engineers continue to develop new ways to handle stress and pressure, the vessels will continue to become more stable. Likewise, it’s likely that they will continue to come up with stronger and more durable materials. With these improvements, engineers will be able to push for higher standards and more stringent codes, thus pushing us forward.
How It Works
Pressure vessels are designed to work by reaching the level of pressure required to make an application function, like holding air in a scuba tank. They can deliver pressure either directly through valves and release gauges, or indirectly via heat transfer. Potential pressure levels range from 15 psi up to around 150,000 psi, while temperatures are often above 750°F. A pressure tank can hold anywhere from 20 gallons to several hundred thousand gallons.
Process tanks are designed to simply hold and store liquids.
Autoclaves, such as grease kettles, use a combination of pressure and steam to create substance-producing chemical reactions. Their goal is to deliver both pressure and elevated temperatures to processes that need them. Examples include: medical sterilization, rubber vulcanization and curing and synthetic crystal growth.
High pressure vessels are the strongest type available, use the highest psi and offer the best corrosion, temperature and pressure resistance. They usually operate at pressure levels between 10,000 psi and 150,000 psi. Typically, high pressure vessels are made of stainless steel. Common high-pressure vessel roles include: high speed mixers, chemical reactors and supercritical extraction systems.
Expansion tanks are found in every residential closed water heater. There, they absorb excess water pressure so that the heated water has room to expand. By relieving pressure, expansion tanks also make pipe damage less likely.
Heat exchangers transfer heat for applications in: HVAC, chemical, power, petrochemicals and petroleum, sewage treatment and space heating. Usually, this heat transfer takes place between one solid object and one fluid, or between two or more individual liquids. A great example of a heat exchanger is the heat sink. This passive heat exchanger transfers heat from a mechanical or an electronic object, like a PC motherboard circuit, to a fluid medium, like liquid coolant or air. In the fluid medium, the heat dissipates and the circuit stays cool.
Storage vessels are designed to store contents under pressure in such a way that you can readily access them when they’re needed. Examples of storage vessels include: propane tanks, gas tanks, hot water tanks and air tanks.
Water pressure tanks are found in wells. They are designed to help deliver water from the well through and out the faucet. When a resident turns on the faucet, the air pressure stored in the water tank gets the message to force the water through. The air pushes the water until its pressure drops to a predetermined point, usually around 40 to 60 psi. Once it hits this point, the water pump gets the message to turn on, and it pulls water into the house. When the resident turns the faucet off, the pressure builds back up to its default level.
Vacuum tanks provide important, mostly short term, support to sewage applications.
ASME pressure vessels, also known as ASME boilers, are any pressure vessel with an ASME stamp. The ASME stamp indicates the vessel has undergone inspection and meets stringent ASME VIII code standards. In addition, the ASME stamps offers end-users information about the ASME boiler and its manufacturer.
Thin-walled pressure vessels are pressure vessels designed with a wall thickness, or shell thickness, no more than 10% (by ratio) the diameter thickness. Thin wall pressure vessels are available as spherical pressure vessels and cylindrical pressure vessels. Mainly, they are used to store and transport liquids and gases. They may also serve as components of rockets and hypersonic drag balloon skins.
Boilers are closed pressure vessels used to heat fluids, mostly water. These heated fluids are used for cooking, power generation, central heating, water heating and sanitation. In the US, “boiler” is synonymous with “furnace.”
Pressure vessels generally consist of: the main container, safety valve fittings and pressure vessel closures. The main container may be any shape. However, it’s usually a cylinder, sphere or cone. These simple shapes work better and are easier to analyze than more complex ones.
Possible additional components include: agitation systems or propellers for mixing, detachable lids, removable lids, heating and cooling systems, ladders, observation sight glass and stairs.
Design and Customization
Metal used in any pressure vessel manufacturing process is usually first cold rolled, rather than hot rolled. Also, to increase tensile strength and temperature resistance, metalworkers frequently temper, quench or galvanize them.
Once the metals are ready, pressure vessels are usually manufactured using one of three processes: forging, brazing and welding. All three processes utilize heat to join metal pieces together, but they all use it differently.
Forging forms metal parts through the application of heat and pressure.
Brazing refers to the process of joining two metals by filling the space between them with a non-ferrous metal.
Welding is a process in which two similar pieces of metal are heated until their edges melt together and they fuse.
Manufacturers design tanks from a variety of durable metals or high-strength plastics that can maintain their shape and properties under pressure. Examples include: stainless steel, zirconium, carbon steel, titanium, niobium, nickel alloy(s) and fiberglass.
Considerations and Customization
During design and before fabrication, engineers must determine sensitive design components like: pressure level, temperature, material components, size and shape. They can make custom pressure vessels with any one of these components personalized. In addition to regular safety info, manufacturer info and certification stamps, they can also inscribe special information on your tank, such as ownership details.
Safety and Compliance Standards
To be considered a finished and functional tank, many pressure heaters must adhere to regulations by and be registered with the American Society of Mechanical Engineers (ASME). The ASME Boiler and Pressure Vessel Code (ASME Section VIII code) and standards and inspection codes set out by others, like the American Petroleum Institute (API) help ensure worker and building safety; because tanks are under extreme pressure, even the tiniest leak could cause a large explosion with shrapnel damage.
Engineers may also take upon themselves to conduct mathematical and scientific studies to make sure that the design and construction of their pressure vessels meet requirements for appropriate size, shape, temperature, material and pressure levels.
Things to Consider
If you’re considering a pressure vessel purchase, the best thing you can do is consult with a knowledgeable pressure vessel manufacturer who can answer all of your questions and guide you in the right direction. Pressure vessel performance is extremely important because the malfunction of fluids of under pressure can be extremely dangerous. Even if it weren’t, you don’t want your system malfunctioning!
To relieve the stress that comes with wading through the countless pressure vessel manufacturers out there who may or may not be reliable or trustworthy, we’ve put together a list of several experienced manufacturers. You can have the profiles of those companies distributed throughout this page. To learn more about each of them, scroll up and check out those profiles. Before you do that, though, we recommend you put together a list of your own—a list of your specifications, requirements, questions and concerns. Don’t forget to include your spending budget, preferred timeline, delivery preferences and post-delivery support level preferences. With your list in hand, you’ll be able to more easily discern whether or not a company will work for you.
Now you’re ready to browse. Frequently consulting your list, choose three or four to whom you’d like to speak directly. Then, reach out to them. Discuss your specifications at length with each of them. Remember to ask if they offer other services, such as installation assistance, post-installation inspection, and post-installation repairs and/or parts replacement. Pressure vessel testing and regular inspection is an important part of tank construction and maintenance; any help your manufacturer can offer is extremely valuable. Once you’ve finished talking to each of them, compare and contrast all their answers, and pick the right one for you. Good luck!