Hoop Stress Calculator

Pipe Geometry

Outside Diameter (OD)

Nominal Wall Thickness

Operating Conditions

Internal Design Pressure

psig

Operating Temperature

°F

T ≤ 250°F: Factor = 1.00
T > 250°F: Derating applies

Material Properties

SMYS

psi

Common grades:
• X42: 42,000 psi
• X52: 52,000 psi
• X60: 60,000 psi
• X65: 65,000 psi
• X70: 70,000 psi

Design Factors (ASME B31.8)

Location Class

Longitudinal Joint Factor (E)

Location class based on population density within 220-yard corridor

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Design Formulas

σ_h = (P × D_m) / (2 × t_min)

σ_h = Hoop stress (psi)

P = Internal pressure (psig)

D_m = Mean diameter (OD - t)

t_min = Min. wall (87.5% nominal)

S_allow = SMYS × F × E × T

F = Design factor (location class)

E = Joint efficiency factor

T = Temperature derating

Engineering Notes

Mean Diameter: Used for accuracy instead of OD. Reduces error by ~3%.
Manufacturing Tolerance: API 5L allows -12.5% wall thickness. Calculator uses minimum thickness for conservative design.
Thin-Wall Validity: Barlow's formula valid when t/D < 0.1. Thick-wall pipes require Lamé equations.
End Effects: Longitudinal stress assumes closed-end (capped) conditions. Restrained pipes have additional thermal stresses.
Von Mises: Combined stress criterion for ductile failure. Must be < yield strength.

Design Guidelines

Class 1 (Rural): F = 0.72 (72% SMYS). ≤10 buildings per mile.
Class 2 (Fringe): F = 0.60 (60% SMYS). 10-45 buildings per mile.
Class 3 (Suburban): F = 0.50 (50% SMYS). >45 buildings or near assembly areas.
Class 4 (Urban): F = 0.40 (40% SMYS). Multi-story buildings prevalent.
Hydro Test: Minimum 1.5× MAOP for Class 1-2, 1.4× for Class 3-4.

Limitations

Valid for steady-state internal pressure only
Does not include cyclic fatigue or external loads
Assumes uniform corrosion allowance if applicable
Does not account for defects, dents, or damage
Results are preliminary - final design requires PE review

Standards & References

ASME B31.8-2020
Gas Transmission and Distribution Piping Systems
49 CFR Part 192
Transportation of Natural and Other Gas by Pipeline
API 5L-2018
Specification for Line Pipe
API 1104
Welding of Pipelines and Related Facilities