pressure vessels. a pressure vessel is a container for fluids under pressure between 15 psig to 3000...
TRANSCRIPT
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 VIII Division I sets rules for the design, fabrication, and inspection of pressure vessels
Main PV Components and Configurations
Main PV Components and Configurations
The 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 Configurations
Multiple 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 Configurations
Most heads are curved shape for strength, thinness, and economy
Semi-elliptical shape is most common head shape
Main PV Components and Configurations
Small vertical drums typically supported by legs
> Typically max 2:1 ratio of leg length to diameter
> Number, size, and attachment details depend on loads
Main PV Components and Configurations
Main PV Components and Configurations
Nozzles 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 Configurations
Skirt 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 expansion
Main PV Components and Configurations
Main PV Components and Configurations
Spherical storage vessels are typically supported on legs
Cross- bracing is typically used to absorb wind and earthquake loads
Main PV Components and Configurations
Main PV Components and Configurations
Vessel size limits for lug support:
> 1 to 10 ft diameter
> 2:1 to 5:1 height to diameter ratio
Lugs are bolted to horizontal structure
MATERIAL SELECTION
Material Selection Factors:
> Strength
> Corrosion Resistance
> Resistance to Hydrogen Attack
> Fracture Toughness
> Fabricability
MATERIAL SELECTION FACTORS
Strength – mat’ls ability to withstand imposed loading
Determines req’d component thickness
Overall strength determined by:
> Yield Strength> Ultimate Tensile Strength> Creep Strength> Rupture Strength
MATERIAL SELECTION FACTORS
Corrosion Resistance – Deterioration of metal by chemical action
MOST IMPORTANT factor to consider
Corrosion allowance supplies additional thickness
Alloying elements provide additional resistance to corrosion
MATERIAL SELECTION FACTORS
Resistance to Hydrogen Attack
At 300 – 400 ⁰F, monoatomic hydrogen forms molecular hydrogen in voids
Pressure buildup can cause steel to crack
Above 600 ⁰F, hydrogen attack causes irreparable damage through component thickness
Increased alloy content (i.e. Cr) increase H2 attack resistance
MATERIAL SELECTION FACTORS
Brittle Fracture and Fracture Toughness
Fracture toughness – ability of mat’l to withstand cond’ns that cause brittle fracture
Brittle fracture
> Typically at “low” temperature> Can occur below design pressure> No yielding before complete failure
MATERIAL SELECTION FACTORS
Brittle Fracture and Fracture ToughnessConditions for Brittle Fracture to Occur:
> High enough stress for crack initiation and growth
> Low enough mat’l fracture toughness at temperature
> Critical size defect to act as stress concentration
Brittle Fracture occurs w/o warning and is catastrophic
MATERIAL SELECTION FACTORS
Brittle Fracture and Fracture Toughness
Fracture 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 plate
MATERIAL SELECTION FACTORS
Brittle Fracture and Fracture ToughnessSimplified ASME Evaluation Approach
Material specification classified into Material Groups A to D
Impact 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 CET
MATERIAL SELECTION FACTORS
MATERIAL SELECTION FACTORS
MATERIAL SELECTION FACTORS
MATERIAL SELECTION FACTORS
Brittle Fracture and Fracture Toughness
Additional 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
MATERIAL SELECTION FACTORS
Fabricability
Ease of Construction
Any required special fabrication practices
Material must be weldable