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PRESSURE VESSELS

Pressure vessels are containers used in holding or processing fluids under

pressure (usually pressures above or below atmospheric).

What are Pressure vessels?

Applications

Examples• industrial compressed air receivers • domestic hot water storage tanks. • diving cylinder, • recompression chamber,• distillation towers,• autoclaves • vessels in mining or oil refineries and

petrochemical plants,

Examples• 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.

Shape• Vertical Drum• Horizontal Drum• Vertical Towers• Spheres

ShapeHorizontal DrumOn Saddles

Shape

Vertical DrumOn Legs

Vertical Toweron Skirt

Shape

ShapeSphere • with legs

reinforced with cross bracing

• For storing gaseous fluids

Construction materials Generally, almost any material with good tensile

properties that is chemically stable in the chosen application can be employed

e.g.

• Steel – carbon steels, stainless steels • composite materials, such as wound carbon fibre

held in place with a polymer• polymers such as PET in carbonated beverage

containers and copper in plumbing.• They may be lined with various metals, ceramics,

or polymers – to prevent leaking and – protect the structure of the vessel from the contained

fluid.

DesignDesign Codes & StandardsMinimum standards used as guides for designe.g.• EN 13445: The current European standard, harmonized with

the Pressure Equipment Directive.• ASME Code Section VIII Division 1: US standard, widely used.• 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: Former British Standard, replaced in the UK by EN

13445 but retained under the name PD 5500 for the design and construction of export equipment.

DesignDesign Codes & Standards• AD Merkblätter: German standard, harmonized with the

Pressure Equipment Directive.• API 510 "Pressure Vessel Inspection Code: In-Service

Inspection, Rating, Repair, and Alteration".• ISO 11439 "Gas cylinders - High pressure cylinders for the

on-board storage of natural gas as a fuel for automotive vehicles

• EN 286 (Parts 1 to 4): European standard for simple pressure vessels, harmonized with Council Directive 87/404/EEC.

• 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)

Failure modes • Stress corrosion cracking• Cracking• Explosion• Rupture• Leakage• Corrosion 

Failure modesHydrogen embrittlement• Creep and stress rupture• Fatigue • Caustic embrittlement.• Brittle fractures• Erosion

Factors Responsible for failure

• Operation above the maximum allowable working and test pressures.

• Improper sizing or pressure setting of relief devices.

• Improper operation of relief devices due to faulty maintenance and failure to test regularly.

• Failure of the vessel due to fatigue from repeated pressurization, general thinning from corrosion or erosion, localized corrosion, stress corrosion cracking, embrittlement, holes and leaks.

Factors Responsible for failure

• Failure to inspect frequently enough.

• Improper repair of a leak or other defect involving welding and annealing that embrittles and further weakens the vessel

• Overpressuring and failure of the vessel due to exothermic reaction or polymerization.

• Vessel exposure to fire.

Design Considerations• Material Selection• Thickness Determination• Weights and Volume Calculations

Design Considerations• Material SelectionDepends on

– Strength: material must be able to withstand high stresses.

– Corrosion Resistance– Resistance to Hydrogen Attack– Fracture Toughness– Fabricability: must be weldable and easy to form

and fabricate.

Design Considerations• Thickness Determination (shells)Vessel must be thick enough to withstand stresses.

Longitudinal design-

Circumferential-

Maximum of the two is chosen.

PSE

PRt o

4.12

PSE

PRt o

4.0

t- thickness; P-Pressure; Ro-Outside radius; S-Design Stress; E-Longitudinal joint factor (for welded joints)

Design Considerations• Thickness Determination (heads)

Note: Corrosion Allowance must be added to the thicknesses obtained.

PSE

PRt o

8.12

Design ConsiderationsWeights Fabricated weight: Total weight as

fabricated in the shop.

• Shipping weight: Fabrication weight plus any weight added for shipping purposes, such as shipping saddles.

• Erection weight: Fabrication weight plus any weight installed for the erection of the equipment, such as any insulation, fireproofing, piping, ladders, platforms.

Design ConsiderationsWeights Empty weight: The overall weight of the vessel

sitting on the foundation, fully dressed, waiting for operating liquid.

• Operating weight: Empty weight plus any operating liquid weight.

• Test weight: This weight can be either shop or field test weight, that is, the vessel full of water.

Design ConsiderationsWeights

• Shell Weight:

• Weight of one 2:1 Semi Elliptical head

tLDW m

tDW m2084.1

Dm =mean vessel diameter (mm)L = vessel length T = vessel thicknessρ = density of material

Design Considerations

Part Volume Surface Area

Shell: (Cylinder)

2:1 Semi Elliptical head

4

2lDV i

DlA

24

3iDV

2084.1 DA

Volumes &Surface Area formulas