Pressure vessel

A pressure vessel is a closed container designed to hold gases or liquids at a pressure different from the ambient pressure. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The end caps fitted to the cylindrical body are called heads. The end caps on a cylindrically shaped Pressure vessel are commonly known as 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 does not contribute to the potential energy stored in the vessel. The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. ) In the United States, the rules for pressure vessels are contained in the American Society of Mechanical Engineers Boiler and Pressure Vessel Code.

1 Uses
2 Shape of a pressure vessel
3 Design Standards
4 Alternatives to pressure vessels
5 History of pressure vessels
6 See also
7 External links
8 Further reading
9 References
10 Notes

Uses

A pressure tank connected to a water well and domestic hot water system

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. Compressed air A diving cylinder, scuba tank or diving tank is used to store and transport high Pressure Breathing gas as a component of SCUBA (Self-Contained A recompression chamber is a Pressure vessel used to treat divers suffering from certain Diving disorders such as Decompression sickness. Fractional distillation is the separation of a mixture into its component parts or fractions such as in separating Chemical compounds by their Boiling point by heating An autoclave is a pressurized device designed to heat aqueous solutions above their Boiling point at normal atmospheric pressure to achieve sterilization Mining is the extraction of valuable Minerals or other geological materials from the earth usually (but not always from an Ore body An oil refinery is an industrial Process plant where Crude oil is processed and refined into more useful Petroleum products, such as Gasoline Petrochemicals are chemical products made from raw materials of Petroleum or other Hydrocarbon origin This article is a subarticle of Nuclear power. A nuclear reactor is a device in which Nuclear chain reactions are initiated controlled A spacecraft is a Vehicle or machine designed for Spaceflight. A submarine is a Watercraft that can operate independently below water as distinct from a Submersible that has only limited underwater capability Pneumatics, Pressurized gas to affect mechanical motion Pneumatic power is used in Industry, where it is common to have factory units plumbed for Compressed For the mechanical technology see Hydraulic machinery and Hydraulic cylinder Hydraulics is a topic of science and Engineering An air brake is a conveyance braking system applied by means of compressed air. Air brakes are used in Trucks Buses trailers, and Semi-trailers. Ammonia is a compound with the formula N[[hydrogen H3]] It is normally encountered as a Gas with a characteristic pungent Odor Chlorine (ˈklɔriːn from the Greek word 'χλωρóς' ( khlôros, meaning 'pale green' is the Chemical element with Atomic number 17 and Propane is a three- Carbon Alkane, normally a gas but compressible to a liquid that is transportable Butane, also called n -butane, is the unbranched Alkane with four Carbon Atoms CH3CH2CH2CH3 Liquefied petroleum gas (also called LPG, GPL, LP Gas, or Autogas) is a mixture of Hydrocarbon Gases used as a Fuel

Steel Pressure Vessel

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 is 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. The Pressure Equipment Directive 97/23/EC (PED of the EU sets out the standards for the Design and Manufacture of Pressure equipment The European Union ( EU) is a political and economic union of twenty-seven member states, located primarily in This article is about Japanese Industrial Standards in general see JIS encoding for the character encoding used in representing the Japanese language for computer software Established in 1919 the Canadian Standards Association (CSA is a not-for-profit association composed of representatives from government industry and Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page International standards are Standards developed by international Standards organisations International standards are available for consideration and use worldwide The Lloyd's Register Group is a maritime Classification society and independent risk management organisation providing risk assessment and mitigation services The Germanischer Lloyd AG is a Classification society based in the city of Hamburg Germany. Det Norske Veritas or DNV is a Norwegian company established in 1864

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 1,000 litres (35 cu ft), 250 bars (3,600 psi) pressure vessel might be a diameter of 914. The litre or liter (see spelling differences) is a unit of Volume. The cubic foot is an imperial and US customary (non- metric) unit of Volume, used in the United States Canada and the United Kingdom The bar (symbol bar) decibar (symbol dbar) and the millibar (symbol mbar, also mb are units of Pressure. The pound per square inch or more accurately pound-force per square inch (symbol psi or lbf/in² or lbf/in²) is a unit of 4 millimetres (36 in) and a length of 1,701. The Millimetre ( American spelling: millimeter, symbol mm) is a unit of Length in the Metric system, equal to Inches redirects here To see the Les Savy Fav album see Inches. 8 millimetres (67 in) including the 2:1 semi elliptical domed end caps.

Construction materials

Generally, almost any material with good tensile properties that is 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. A polymer is a large Molecule ( Macromolecule) composed of repeating Structural units typically connected by Covalent Chemical bonds Uses PET can be semi-rigid to rigid depending on its thickness and is very lightweight Copper (ˈkɒpɚ is a Chemical element with the symbol Cu (cuprum and Atomic number 29

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. The specific strength is a material strength divided by its Density.

Spherical vessel

For a sphere, the mass of a pressure vessel is

$M = {3 \over 2} P V {\rho \over \sigma}$

Where:

M

is mass

P

is the pressure difference from ambient, i. "Globose" redirects here See also Globose nucleus. A sphere (from Greek σφαίρα - sphaira, "globe e. the gauge pressure

V

is volume

ρ

is the density of the pressure vessel material

σ

is the maximum working stress that material can tolerate. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface Stress is a measure of the average amount of Force exerted per unit Area.

Other shapes besides a sphere have constants larger than 3/2 (infinite cylinders take 2), although some tanks, such as non-spherical wound composite tanks can approach this.

Cylindrical vessel with hemispherical ends

For a cylinder with hemispherical ends:

$M = 2 \pi R^2 (R + L) P {\rho \over \sigma}$

where:

R is the radius
L is the middle cylinder length only, and the overall length is L + 2R

2:1 Cylindrical vessel with hemispherical ends

In a vessel with a 2:1 aspect ratio:

$M = 6 \pi R^3 P {\rho \over \sigma}$

Gas storage

In looking at the first equation, the factor PV, in SI units, is in units of (pressurization) energy. The aspect ratio of a Shape is the ratio of its longer Dimension to its shorter dimension For a stored gas, PV is proportional to the mass of gas at a given temperature, thus:

$M = {3 \over 2} nRT {\rho \over \sigma}$ (see gas law)

The other factors are constant for a given vessel shape and material. This articles outlines the historical development of the laws describing ideal gases So we can see that there is no theoretical "efficiency of scale", in terms of the ratio of pressure vessel mass to pressurization energy, or of pressure vessel mass to stored gas mass. For storing gases, "tankage efficiency" is independent of pressure, at least for the same temperature.

So, for example, a typical design for a minimum mass tank to hold helium (as a pressurant gas) on a rocket would use a spherical chamber for a minimum shape constant, carbon fiber for best possible $ρ / σ$ , and very cold helium for best possible $M / p V$ . Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical

Stress in thin-walled pressure vessels

The stress in a thin-walled pressure vessel in the shape of a sphere is:
$\sigma_\theta = \frac{pr}{2t}$
Where $σ θ$ is the hoop stress, or stress in the circumferential direction, p is the internal gage pressure, r is the radius of the sphere, and t is the thickness. A vessel can be considered "thin-walled" if the radius is at least 20 times larger than the wall thickness. ^[1]

The stress in a thin-walled pressure vessel in the shape of a cylinder is:
$\sigma_\theta = \frac{pr}{t}$
$\sigma_{\rm long} = \frac{pr}{2t}$
Where $σ θ$ is the hoop stress, or stress in the circumferential direction, $σ l o n g$ 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. Hoop stress is mechanical stress defined for rotationally-symmetric objects being the result of forces acting circumferentially (perpendicular both to the axis and to the radius

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. ^[2]

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 Merkblätterasa
CODAP
AS 1210
ISO 11439 ^[3]

Alternatives to pressure vessels

Depending on the application and local circumstances, alternatives have come about which can replace pressure tanks. BS4994 (formally British Standard 49941987) is the "specification for the design and construction of vessels and Storage tanks in Reinforced Compressed Natural Gas (CNG is a Fossil fuel substitute for Gasoline (petrol Diesel, or Propane Fuel. 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) ^[4] Gravity-controlled systems are usually created by placing the water harvester on an elevation (e. A storage tank is a container usually for holding liquids sometimes for compressed gases (gas tank For information on Wikipedia project-related discussions see WikipediaVillage pump. Water tanks are liquid storage containers these tanks are usually storing water for human consumption g. 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 ^[5]:

History of pressure vessels

Large pressure vessels were invented during the industrial revolution, particularly in England, for making steam engines. The Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture manufacturing and transportation had a profound effect on the A steam engine is a Heat engine that performs Mechanical work using Steam as its Working fluid.

Design and testing standards came about after some large explosions lead to loss off life and a system of certification and testing mutations.

External links

References

A. C. Ugural, S. K. Fenster, Advanced Strength and Applied Elasticity, 4th ed.
E. P. Popov, Engineering Mechanics of Solids, 1st ed.

Pressure Vessel Handbook, 14th Edition Eugene F. Megyesy PV Publishing, Inc. Oklahoma City, OK

Notes

^ Richard Budynas, J. Nisbett, Shigley's Mechanical Engineering Design, 8th ed. , New York:McGraw-Hill, ISBN 978-0-07-312193-2, pg 108
^ MIT pressure vessel lecture
^ Gas cylinders -- High pressure cylinders for the on-board storage of natural gas as a fuel for automotive vehicles
^ Domestic water collection systems also sometimes able to function on gravity
^ Alternatives to pressure vessels in domestic water systems

Dictionary

-noun

A container designed to maintain a volume at a significantly different pressure to that of ambient.

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