Pressure vessel 1

Pressure vessel

Vertical pressure vessels installed in a structure

A pressure vessel is a closed container designed to hold gases orliquids at a pressure substantially different from the ambient pressure.

The pressure differential is dangerous and fatal accidents haveoccurred in the history of pressure vessel development and operation.Consequently, pressure vessel design, manufacture, and operation areregulated by engineering authorities backed by legislation. For thesereasons, the definition of a pressure vessel varies from country tocountry, but involves parameters such as maximum safe operatingpressure and temperature.

Uses

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

A few pressure tanks, here used to holdpropane

Pressure vessels are used in a variety of applications in both industry and theprivate sector. They appear in these sectors as industrial compressed airreceivers and domestic hot water storage tanks. Other examples of pressurevessels are diving cylinders, recompression chambers, distillation towers,pressure reactors, autoclaves, and many other vessels in mining operations,oil refineries and petrochemical plants, nuclear reactor vessels, submarine andspace ship habitats, pneumatic reservoirs, hydraulic reservoirs under pressure,rail vehicle airbrake reservoirs, road vehicle airbrake reservoirs, and storagevessels for liquified gases such as ammonia, chlorine, propane, butane, andLPG.

Pressure vessel features

Shape of a pressure vessel

Pressure vessels can theoretically be almost any shape, but shapes made ofsections of spheres, cylinders, and cones are usually employed. A commondesign is a cylinder with end caps called heads. Head shapes are frequentlyeither hemispherical or dished (torispherical). More complicated shapes havehistorically been much harder to analyze for safe operation and are usually farmore difficult to construct.

Theoretically, a spherical pressure vessel has approximately twice thestrength of a cylindrical pressure vessel with the same wall thickness.[1]

However, a spherical shape is difficult to manufacture, and therefore moreexpensive, so most pressure vessels are cylindrical with 2:1 semi-ellipticalheads or end caps on each end. Smaller pressure vessels are assembled from apipe and two covers. A disadvantage of these vessels is that greater breadthsare more expensive, so that for example the most economic shape of a 1,000litres (35 cu ft), 250 bars (3,600 psi) pressure vessel might be a breadth of914.4 millimetres (36 in) and a width of 1,701.8 millimetres (67 in) including the 2:1 semi-elliptical domed end caps.

Pressure vessel 2

Construction materials

Steel pressure vessel

Theoretically almost any material with good tensile properties that ischemically stable in the chosen application could be employed. However,pressure vessel design codes and application standards (ASME BPVC SectionII, EN 13445-2 etc.) contain long lists of approved materials with associatedlimitations in temperature range.

Many pressure vessels are made of steel. To manufacture a cylindrical orspherical pressure vessel, rolled and possibly forged parts would have to bewelded together. Some mechanical properties of steel, achieved by rolling orforging, could be adversely affected by welding, unless special precautionsare taken. In addition to adequate mechanical strength, current standardsdictate the use of steel with a high impact resistance, especially for vesselsused in low temperatures. In applications where carbon steel would suffercorrosion, special corrosion resistant material should also be used.Some pressure vessels are made of composite materials, such as filamentwound composite using carbon fibre held in place with a polymer. Due to the very high tensile strength of carbonfibre these vessels can be very light, but are much more difficult to manufacture. The composite material may bewound around a metal liner, forming a composite overwrapped pressure vessel.

Other very common materials include polymers such as PET in carbonated beverage containers and copper inplumbing.Pressure vessels may be lined with various metals, ceramics, or polymers to prevent leaking and protect the structureof the vessel from the contained medium. This liner may also carry a significant portion of the pressure load.[2][3]

Pressure Vessels may also be constructed from concrete (PCV) or other materials which are weak in tension.Cabling, wrapped around the vessel or within the wall or the vessel itself, provides the necessary tension to resist theinternal pressure. A "leakproof steel thin membrane" lines the internal wall of the vessel. Such vessels can beassembled from modular pieces and so have "no inherent size limitations".[4] There is also a high order ofredundancy thanks to the large number of individual cables resisting the internal pressure.

ScalingNo matter what shape it takes, the minimum mass of a pressure vessel scales with the pressure and volume itcontains and is inversely proportional to the strength to weight ratio of the construction material (minimum massdecreases as strength increases[5]).

Scaling of stress in walls of vessel

Pressure vessels are held together against the gas pressure due to tensile forces within the walls of the container. Thenormal (tensile) stress in the walls of the container is proportional to the pressure and radius of the vessel andinversely proportional to the thickness of the walls.[6] Therefore pressure vessels are designed to have a thicknessproportional to the radius of tank and the pressure of the tank and inversely proportional to the maximum allowednormal stress of the particular material used in the walls of the container.Because (for a given pressure) the thickness of the walls scales with the radius of the tank, the mass of a tank (whichscales as the length times radius times thickness of the wall for a cylindrical tank) scales with the volume of the gasheld (which scales as length times radius squared). The exact formula varies with the tank shape but depends on thedensity, ρ, and maximum allowable stress σ of the material in addition to the pressure P and volume V of the vessel.(See below for the exact equations for the stress in the walls.)

Pressure vessel 3

Spherical vessel

For a sphere, the mass of a pressure vessel is

,

whereis mass,

is the pressure difference from ambient (the gauge pressure),is volume,is the density of the pressure vessel material,is the maximum working stress that material can tolerate.[7]

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

Cylindrical vessel with hemispherical ends

This is sometimes called a "bullet" for its shape, although in geometric terms it is a capsule.For a cylinder with hemispherical ends,

,

where•• R is the radius•• W is the middle cylinder width only, and the overall width is W + 2R

2:1 Cylindrical vessel with semi-elliptical ends

In a vessel with an aspect ratio of middle cylinder width to radius of 2:1,

.

Gas storage

In looking at the first equation, the factor PV, in SI units, is in units of (pressurization) energy. For a stored gas, PVis proportional to the mass of gas at a given temperature, thus

. (see gas law)

The other factors are constant for a given vessel shape and material. 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 massto stored gas mass. For storing gases, "tankage efficiency" is independent of pressure, at least for the sametemperature.So, for example, a typical design for a minimum mass tank to hold helium (as a pressurant gas) on a rocket woulduse a spherical chamber for a minimum shape constant, carbon fiber for best possible , and very cold heliumfor best possible .

Pressure vessel 4

Stress in thin-walled pressure vesselsStress in a shallow-walled pressure vessel in the shape of a sphere is

,

where is hoop stress, or stress in the circumferential direction, is stress in the longitudinal direction, p isinternal gauge pressure, r is the inner radius of the sphere, and t is thickness of the cylinder wall. A vessel can beconsidered "shallow-walled" if the diameter is at least 10 times (sometimes cited as 20 times) greater than the walldepth.[8]

Stress in a shallow-walled pressure vessel in the shape of a cylinder is

,

,

where is hoop stress, or stress in the circumferential direction, is stress in the longitudinal direction, p isinternal gauge pressure, r is the inner radius of the cylinder, and t is thickness of the cylinder wall.Almost all pressure vessel design standards contain variations of these two formulas with additional empirical termsto account for wall thickness tolerances, quality control of welds and in-service corrosion allowances.For example, the ASME Boiler and Pressure Vessel Code (BPVC) (UG-27) formulas are:[9]

Spherical shells:

Cylindrical shells:

where E is the joint efficient, and all others variables as stated above.

Winding angle of carbon fibre vesselsWound infinite cylindrical shapes optimally take a winding angle of 54.7 degrees, as this gives the necessary twicethe strength in the circumferential direction to the longitudinal.[10]

Design and operation standardsPressure 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 pressureconstitutes a very significant safety hazard. Because of that, the design and certification of pressure vessels isgoverned by design codes such as the ASME Boiler and Pressure Vessel Code in North America, the PressureEquipment Directive of the EU (PED), Japanese Industrial Standard (JIS), CSA B51 in Canada, Australian Standardsin Australia and other international standards like Lloyd's, Germanischer Lloyd, Det Norske Veritas, SociétéGénérale de Surveillance (SGS S.A.), Stoomwezen etc.Note that where the pressure-volume product is part of a safety standard, any incompressible liquid in the vessel canbe excluded as it does not contribute to the potential energy stored in the vessel, so only the volume of thecompressible part such as gas is used.

Pressure vessel 5

List of standards• EN 13445: The current European Standard, harmonized with the Pressure Equipment Directive (97/23/EC).

Extensively used in Europe.• ASME Boiler and Pressure Vessel Code Section VIII: Rules for Construction of Pressure Vessels.• BS 5500: Former British Standard, replaced in the UK by BS EN 13445 but retained under the name PD 5500 for

the design and construction of export equipment.• AD Merkblätter: German standard, harmonized with the Pressure Equipment Directive.•• EN 286 (Parts 1 to 4): European standard for simple pressure vessels (air tanks), harmonized with Council

Directive 87/404/EEC.• BS 4994: Specification for design and construction of vessels and tanks in reinforced plastics.•• ASME PVHO: US standard for Pressure Vessels for Human Occupancy.•• CODAP: French Code for Construction of Unfired Pressure Vessel.• AS/NZS 1200: Pressure equipment.[11]

•• AS 3788 Pressure equipment - In-service inspection• API 510.[12]

• ISO 11439: Compressed natural gas (CNG) cylinders[13]

•• IS 2825-1969 (RE1977)_code_unfired_Pressure_vessels.• FRP tanks and vessels.•• AIAA S-080-1998: AIAA Standard for Space Systems - Metallic Pressure Vessels, Pressurized Structures, and

Pressure Components.•• AIAA S-081A-2006: AIAA Standard for Space Systems - Composite Overwrapped Pressure Vessels (COPVs).•• B51-09 Canadian Boiler, pressure vessel, and pressure piping code.•• HSE guidelines for pressure systems.•• Stoomwezen: Former pressure vessels code in the Netherlands, also known as RToD: Regels voor Toestellen

onder Druk (Dutch Rules for Pressure Vessels).

Design Features

Leak before burstLeak before burst describes a pressure vessel designed such that a crack in the vessel will grow through the wall,allowing the contained fluid to escape and reducing the pressure, prior to growing so large as to cause fracture at theoperating pressure.Many pressure vessel standards, including the ASME Boiler and Pressure Vessel Code and the AIAA metallicpressure vessel standard, either require pressure vessel designs to be leak before burst, or require pressure vessels tomeet more stringent requirements for fatigue and fracture if they are not shown to be leak before burst.[14]

Safety ValvesAs the pressure vessel is designed to a pressure, there is typically a safety valve or relief valve to ensure that thispressure is not exceeded in operation.

Pressure vessel closuresPressure vessel closures are pressure retaining structures designed to provide quick access to pipelines, pressurevessels, pig traps, filters and filtration systems. Typically pressure vessel closures allow maintenance personnel toload a sphere or pig into a pig trap for pipeline cleaning purposes.[15]

Pressure vessel 6

Alternatives to pressure vesselsDepending on the application and local circumstances, alternatives to pressure vessels exist. Examples can be seen indomestic water collection systems, where the following may be used:• Gravity controlled systems[16] which typically consist of an unpressurized water tank at an elevation higher than

the point of use. Pressure at the point of use is the result of the hydrostatic pressure caused by the elevationdifference. Gravity systems produce 0.43 pounds per square inch (3.0 kPa) per foot of water head (elevationdifference). A municipal water supply or pumped water is typically around 90 pounds per square inch (620 kPa).

• Inline pump controllers or pressure-sensitive pumps.[17]

History of pressure vessels

A 10,000 psi (69 MPa) pressure vessel from1919, wrapped with high tensile steel banding

and steel rods to secure the end caps.

Large pressure vessels were invented during the industrial revolution,particularly in Great Britain, to be used as boilers for making steam todrive steam engines.

Design and testing standards and a system of certification came aboutas the result of fatal boiler explosions.

In an early effort to design a tank capable of withstanding pressures upto 10,000 psi (69 MPa), a 6-inch (150 mm) diameter tank wasdeveloped in 1919 that was spirally-wound with two layers of hightensile strength steel wire to prevent sidewall rupture, and the end capslongitudinally reinforced with lengthwise high-tensile rods.[18]

Notes[2] NASA Tech Briefs, "Making a Metal-Lined Composite Overwrapped Pressure Vessel" (http:/ / www. techbriefs. com/ component/ content/

article/ 747), 1 Mar 2005.[3][3] Frietas, O., "Maintenance and Repair of Glass-Lined Equipment", Chemical Engineering, 1 Jul 2007.[4][4] "High Pressure Vessels",D. Freyer and J. Harvey, 1998[7] For a sphere the thickness d = rP/2σ, where r is the radius of the tank. The volume of the spherical surface then is 4πr2d = 4πr3P/2σ. The mass

is determined by multiplying by the density of the material that makes up the walls of the spherical vessel. Further the volume of the gas is(4πr3)/3. Combining these equations give the above results. The equations for the other geometries are derived in a similar manner

[8][8] Richard Budynas, J. Nisbett, Shigley's Mechanical Engineering Design, 8th ed., New York:McGraw-Hill, ISBN 978-0-07-312193-2, pg 108[10] MIT pressure vessel lecture (http:/ / web. mit. edu/ course/ 3/ 3. 11/ www/ modules/ pv. pdf)[13][13] .[14][14] ANSI/AIAA S-080-1998, Space Systems - Metallic Pressure Vessels, Pressurized Structures, and Pressure Components, §5.1[15] Pressure Vessel Closure (http:/ / www. gdengineering. com/ bandlock2. asp)[18] Ingenious Coal-Gas Motor Tank, Popular Science monthly, January 1919, page 27, Scanned by Google Books: http:/ / books. google. com/

books?id=HykDAAAAMBAJ& pg=PA13

References•• A.C. Ugural, S.K. Fenster, Advanced Strength and Applied Elasticity, 4th ed.•• E.P. Popov, Engineering Mechanics of Solids, 1st ed.•• Megyesy, Eugene F. "Pressure Vessel Handbook, 14th Edition." PV Publishing, Inc. Oklahoma City, OK

Further reading• Megyesy, Eugene F. (2008, 14th ed.) Pressure Vessel Handbook. PV Publishing, Inc.: Oklahoma City,

Oklahoma, USA. www.pressurevesselhandbook.com Design handbook for pressure vessels based on the ASMEcode.

Pressure vessel 7

External links• Use of pressure vessels in oil and gas industry (http:/ / articles. compressionjobs. com/ articles/ oilfield-101/

5130-storage-tanks-vessels-gas-liquids?start=6)• Basic formulas for thin walled pressure vessels; with examples (http:/ / www. mathalino. com/ reviewer/

mechanics-and-strength-of-materials/ thin-walled-pressure-vessels)• Educational Excel spreadsheets for ASME head, shell and nozzle designs (http:/ / www. pveng. com/ ASME/

DesignTools/ DesignTools. php)• ASME Boiler and Pressure Vessel website (http:/ / www. asme. org/ Codes/ International_Boiler_Pressure. cfm)• Journal of Pressure Vessel Technology (http:/ / www. asmedl. org/ PressureVesselTech)• EU Pressure Equipment Directive website (http:/ / ec. europa. eu/ enterprise/ pressure_equipment/ ped/ index_en.

html)• EU Pressure Equipment Directive 97/23/EC categorization software (http:/ / www. hrs-heatexchangers. com/ en/

resources/ ped-calculations/ ped-data. aspx)• EU Simple Pressure Vessel Directive (http:/ / ec. europa. eu/ enterprise/ pressure_equipment/ sector_pressure/

spv_sector/ index. htm)• EU Classification (http:/ / ec. europa. eu/ enterprise/ pressure_equipment/ ped/ guidelines/ guideline2-13_en.

html)

Article Sources and Contributors 8

Article Sources and ContributorsPressure vessel  Source: http://en.wikipedia.org/w/index.php?oldid=541511525  Contributors: 84user, A Softer Answer, Andycjp, Bernoullies, Biscuittin, BoJosley, Brockert, Brutaldeluxe,ChemE50, Cholmes75, ChrisCork, Christoffel K, Correogsk, Crainsworth, DMahalko, Dawnseeker2000, Dispenser, Dodger67, Drilnoth, Drkort, E Wing, EdJogg, Emerson7, Emijrp, EndingPop,Erik9, Exit2DOS2000, FizxGuy, Franamax, Gene Nygaard, Gertdam, Glenn, Glrx, Gproud, Hitesh patel6798, Hooperbloob, Hustvedt, Iain.mcclatchie, JRThro, JaTSIMS, Jamclaassen, Jimp,Johnnie Rico, Jolio81, Jorge Stolfi, KVDP, Katana0182, Khakiandmauve, Khalid hassani, Lorast, M karzarj, Mac, Mark.murphy, Markus Kuhn, MasterXC, Matt.hiskett, Mauls, Mausy5043,Mbeychok, Meaghan, Mikiemike, Mion, Mmeijeri, Nicola.Manini, NigelHarris, Nlaporte, Nopetro, Oilandgas2011, Oilandgas2012, Onursengul, Pashute, Patrikovics, Peter Horn, PeterEasthope,Phasmatisnox, Philipjameshoward, Phoebe, Pietrow, Pranav.priya, R'n'B, Rajendra acharaya, Rememberway, Robina Fox, RoyBoy, Rp8083, Ruud Koot, Shanel, Shoefly, Smartse, Sophus Bie,Ssri1983, Steinsky, Strayan, Sv1xv, Swmmr1928, TStein, Tassedethe, Tjeenkwillink, Tlogmer, Tmariem, WikHead, Wolfkeeper, Yardimsever, Ytrottier, 147 anonymous edits

Image Sources, Licenses and ContributorsFile:Pressure Vessel for Australia.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Pressure_Vessel_for_Australia.jpg  License: Creative Commons Attribution-Sharealike 3.0 Contributors: User:BernoulliesFile:Water well tank.JPG  Source: http://en.wikipedia.org/w/index.php?title=File:Water_well_tank.JPG  License: Public Domain  Contributors: KVDP (talkFile:Propane tanks large.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Propane_tanks_large.jpg  License: Creative Commons Attribution-Sharealike 3.0  Contributors: HustvedtFile:Pressure Vessel.jpg  Source: http://en.wikipedia.org/w/index.php?title=File:Pressure_Vessel.jpg  License: Creative Commons Attribution-ShareAlike 3.0 Unported  Contributors:Exit2dos2000File:Popular Science Jan 1919 p27 - 10,000psi wrapped fuel tank.JPG  Source:http://en.wikipedia.org/w/index.php?title=File:Popular_Science_Jan_1919_p27_-_10,000psi_wrapped_fuel_tank.JPG  License: Public Domain  Contributors: User:DMahalko

LicenseCreative Commons Attribution-Share Alike 3.0 Unported//creativecommons.org/licenses/by-sa/3.0/