1. Pressure Vessels

2. 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

3. Main PV Components and Configurations

4. 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

5. 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

6. Main PV Components and Configurations

7. Main PV Components and Configurations
Most heads are curved shape for strength, thinness, and economy
Semi-elliptical shape is most common head shape

8. 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

9. Main PV Components and Configurations

10. Main PV Components and Configurations
Nozzles used for:
> Piping systems
> Instrument Connection
> Manways
> Attaching other equipments
Ends are typically flanged, may be welded

11. Main PV Components and Configurations

12. 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

13. Main PV Components and Configurations

14. Main PV Components and Configurations
Spherical storage vessels are typically supported on legs
Cross- bracing is typically used to absorb wind and earthquake loads

15. Main PV Components and Configurations

16. 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

17. MATERIAL SELECTION Material Selection Factors: > Strength
> Corrosion Resistance
> Resistance to Hydrogen Attack
> Fracture Toughness
> Fabricability

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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

25. MATERIAL SELECTION FACTORS

26. MATERIAL SELECTION FACTORS

27. MATERIAL SELECTION FACTORS

28. 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

29. MATERIAL SELECTION FACTORS
Fabricability
Ease of Construction
Any required special fabrication practices
Material must be weldable