Pressure vessel Totally Explained

Everything about Pressure Vessel totally explained

A pressure vessel is a closed container designed to hold gases or liquids at a pressure different from the ambient pressure. The end caps fitted to the cylindrical body are called heads. The legal definition of pressure vessel varies from country to country, but often involves the maximum safe pressure (may need to be above half a bar) that the vessel is designed for and the pressure-volume product, particularly of the gaseous part (in some cases an incompressible liquid portion can be excluded as it doesn't contribute to the potential energy stored in the vessel.) In the United States, the rules for pressure vessels are contained in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code.

Uses

Pressure vessels are used in a variety of applications. These include the industry and the private sector. They appear in these sectors respectively as industrial compressed air receivers and domestic hot water storage tanks, other examples of pressure vessels are: diving cylinder, recompression chamber, distillation towers, autoclaves and many other vessels in mining or oil refineries and petrochemical plants, nuclear reactor vessel, habitat of a space ship, habitat of a submarine, pneumatic reservoir, hydraulic reservoir under pressure, rail vehicle airbrake reservoir, road vehicle airbrake reservoir and storage vessels for liquified gases such as ammonia, chlorine, propane, butane and LPG.
In the industrial sector, pressure vessels are designed to operate safely at a specific pressure and temperature, technically referred to as the "Design Pressure" and "Design Temperature". A vessel that's inadequately designed to handle a high pressure constitutes a very significant safety hazard. Because of that, the design and certification of pressure vessels is governed by design codes such as the ASME Boiler and Pressure Vessel Code in North America, the Pressure Equipment Directive of the EU (PED), Japanese Industrial Standard (JIS), CSA B51 in Canada, AS1210 in Australia and other international standards like Lloyd's, Germanischer Lloyd, Det Norske Veritas, Stoomwezen etc.

Shape of a pressure vessel

Pressure vessels can theoretically be almost any shape, but shapes made of sections of spheres, cylinders and cones are usually employed. More complicated shapes have historically been much harder to analyse for safe operation and are usually far harder to construct.
Theoretically a sphere would be the optimal shape of a pressure vessel. Unfortunately the sphere shape is difficult to manufacture, therefore more expensive, so most of the pressure vessels are cylindrical shape with 2:1 semi elliptical heads or end caps on each end. Smaller pressure vessels are arranged from a pipe and two covers. Disadvantage of these vessels is the fact that larger diameters make them relatively more expensive, so that for example the most economic shape of a 1000 litres, 250 bar (25,000 kPa) pressure vessel might be a diameter of 914.4 mm and a length of 1701.8 mm including the 2:1 semi elliptical domed end caps.

Construction materials

Generally, almost any material with good tensile properties that's chemically stable in the chosen application can be employed.
   Many pressure vessels are made of steel. To manufacture a spherical pressure vessel, forged parts would have to be welded together. Some mechanical properties of steel are increased by forging, but welding can sometimes reduce these desirable properties. In case of welding, in order to make the pressure vessel meet international safety standards, carefully selected steel with a high impact resistance & corrosion resistant material should also be used.
   Some pressure vessels are made of wound carbon fibre held in place with a polymer. Due to the very high tensile strength of carbon fibre these vessels can be very light, but are much trickier to manufacture.
   Other very common materials include polymers such as PET in fizzy drinks containers and copper in plumbing.

Scaling

No matter what shape it takes, the minimum mass of a pressure vessel scales with the pressure and volume it contains and is proportional to the strength to weight ratio of the construction material.

Spherical vessel

For a sphere, the mass of a pressure vessel is ť

M =

is the stress in the longitudinal direction, p is the internal gage pressure, r is the radius of the cylinder, and t is the wall thickness.

Winding angle of carbon fibre vessels

Wound infinite cylindrical shapes optimally take a winding angle of 54.7 degrees, as this gives the necessary twice the strength in the circumferential direction to the longitudinal.

Design Standards

BS 4994

ASME Code Section VIII Division 1

ASME Code Section VIII Division 2 Alternative Rule

ASME Code Section VIII Division 3 Alternative Rule for Construction of High Pressure Vessel

ASME PVHO (Safety Standard for Pressure Vessels for Human Occupancy)

BS 5500

Stoomwezen

AD Merkblätter

CODAP

AS 1210

ISO 11439

Alternatives to pressure vessels

Depending on the application and local circumstances, alternatives have come about which can replace pressure tanks. An example to this is in the private sector (for use in domestic water collection systems). Non-pressure vessel systems are increasingly seen with:

no storage tank or pump at all (gravity controlled systems) Gravity-controlled systems are usually created by placing the water harvester on an elevation (for example rooftops). This will produce about 0.5 PSI per foot of water head (height difference). However, municipal water or pumped water is typically around 90 PSI.

or with either inline pump controllers or pressure-sensitive pumps :

History of pressure vessels

Large pressure vessels were invented during the industrial revolution, particularly in England, for making steam engines.
Design and testing standards came about after some large explosions lead to loss off life and a system of certification and testing mutations.

Further Information

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