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 Toughness
Conditions 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 Toughness
Simplified ASME Evaluation Approach
Material specification classified into Material
Groups A to D
Impact test exemption curves
For each material group
Acceptable 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