• Classification of Thick vs. Thin Shell Pressure Vessels:
• In structural mechanics, cylindrical pressure vessels are classified by the ratio of internal diameter to wall thickness ($D/t$):
• Thin shells: $D/t \ge 10 - 20$, where radial stress is negligible and membrane hoop stress is uniform.
• Thick shells: Lamé's equations apply due to pronounced non-uniform stress distribution across the thick wall.
• Official Answer Key: Designated Option 2 (>10) as the credited option.
• Conclusion: >10 (Option 2).

Correct option: (2) >10

• Engineering Acronym UFPV:
• In pressure vessel manufacturing codes (ASME Section VIII, Division 1 and IS 2825), UFPV stands for Unfired Pressure Vessel.
• Refers to closed containers designed to operate under internal or external hydrostatic/pneumatic pressure without direct flame exposure (e.g., milk vacuum deaerators, air surge tanks, plate heat exchanger frames).
• Conclusion: Unfired Pressure Vessel (Option 3).

Correct option: (3) Unfired Pressure Vessel

• Design Foundations of Pressure Vessels:
• Elastic Analysis Basis:
• Design codes (ASME Boiler & Pressure Vessel Code Section VIII and IS 2825) formulate allowable design stresses based primarily on linear elastic analysis.
• Ensures that operating membrane and bending stresses remain strictly within the reversible Hookean elastic regime well below the material yield strength ($S_y$).
• Conclusion: Elastic analysis (Option 1).

Correct option: (1) Elastic analysis