Pressure Vessels. A Pressure Vessel is a container for fluids under pressure between 15 psig to 3000 psig ASME Boilers and Pressure vessel Code Section

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Pressure Vessels

Pressure VesselsA Pressure Vessel is a container for fluids under pressure between 15 psig to 3000 psig

ASME Boilers and Pressure vessel Code Section VIII Division I sets rules for the design, fabrication, and inspection of pressure vessels

Main PV Components and Configurations

Main PV Components and ConfigurationsThe shell is the primary component that contains the pressure. Curved shape

Vessel may be cylindrical, spherical, or conical

The Vessel is always closed by heads

The components are typically welded together

Main PV Components and ConfigurationsMultiple diameters, thicknesses or materials are possible

The Saddle supports used for horizontal drums (1) Spreads load over shell; (2) One support is fixed, the other slides

Main PV Components and Configurations

Main PV Components and ConfigurationsMost heads are curved shape for strength, thinness, and economy

Semi-elliptical shape is most common head shapeMain PV Components and ConfigurationsSmall vertical drums typically supported by legs

> Typically max 2:1 ratio of leg length to diameter

> Number, size, and attachment details depend on loadsMain PV Components and Configurations

Main PV Components and ConfigurationsNozzles used for:

> Piping systems> Instrument Connection> Manways> Attaching other equipments

Ends are typically flanged, may be welded

Main PV Components and Configurations

Main PV Components and ConfigurationsSkirt Supports typically used for tall vertical vessels

GENERAL support design

> Designed for weight, wind, earthquake

> Pressure is not a factor

> Temperature is also a consideration for material selection and thermal expansionMain PV Components and Configurations

Main PV Components and ConfigurationsSpherical storage vessels are typically supported on legs

Cross- bracing is typically used to absorb wind and earthquake loadsMain PV Components and Configurations

Main PV Components and ConfigurationsVessel size limits for lug support:

> 1 to 10 ft diameter

> 2:1 to 5:1 height to diameter ratio

Lugs are bolted to horizontal structureMATERIAL SELECTIONMaterial Selection Factors:

> Strength

> Corrosion Resistance

> Resistance to Hydrogen Attack

> Fracture Toughness

> FabricabilityMATERIAL SELECTION FACTORSBrittle Fracture and Fracture ToughnessConditions for Brittle Fracture to Occur:

> High enough stress for crack initiation and growth> Low enough matl fracture toughness at temperature> Critical size defect to act as stress concentration

Brittle Fracture occurs w/o warning and is catastrophicMATERIAL SELECTION FACTORSBrittle Fracture and Fracture ToughnessFracture Toughness Varies with:> Temperature> Type and Chemistry of steel> Manufacturing and Fabrication processes> Arc strikes, esp. if over repaired area> Stress raisers or scratches in cold formed thick plateMATERIAL SELECTION FACTORSBrittle Fracture and Fracture ToughnessSimplified ASME Evaluation Approach

Material specification classified into Material Groups A to DImpact test exemption curvesFor each material groupAcceptable MDMT vs. thickness where impact testing not required> If combination of Material Group and thickness not exempt, then must impact test at CETMATERIAL SELECTION FACTORS

MATERIAL SELECTION FACTORS

MATERIAL SELECTION FACTORS

MATERIAL SELECTION FACTORSBrittle Fracture and Fracture ToughnessAdditional ASME Code Impact Test Requirements

Required for welded construction over 4 in. thick, or non-welded construction over 6in. thick, if MDMT < 120 F

Not Required for Flanges if temperature -20 F

MDMT reduction if calculated stress < allowable stress