ASME Cylindrical Shell Thickness (UG-27) Calculator
Calculate circumferential hoop stress thickness, longitudinal stress thickness, corroded MAWP, and shop hydrostatic test pressure per ASME Section VIII Div 1.
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Frequently Asked Questions
Why does hoop stress dictate cylindrical shell thickness rather than longitudinal stress?
From thin-wall pressure vessel mechanics, the circumferential (hoop) stress is exactly twice the magnitude of the longitudinal (axial) stress (sigma_hoop = P*R/t vs sigma_long = P*R / 2t). Consequently, internal pressure creates double the bursting force across the longitudinal seam, always making hoop stress the governing design criterion.
What is the Lowest Stress Ratio (LSR) in UG-99 hydrostatic testing?
The test factor 1.3 is multiplied by the ratio of allowable stress at test temperature (ambient ~70°F) to allowable stress at design operating temperature: LSR = S_test / S_design. This compensates for metal strength derating at elevated operating temperatures, ensuring the vessel is tested with adequate cold proof margin without yielding.
When does thin-wall UG-27 cease to be applicable?
ASME Section VIII Div 1 UG-27 thin-shell formulas are valid as long as the thickness t does not exceed 0.5 * R (or design pressure P <= 0.385 * S * E). For thick-walled reactors or high-pressure separators where t > 0.5 * R, heavy-wall Lame stress equations (Appendix 1-2) must be used to account for radial stress gradients.