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Hoop Stress Calculator

49 CFR 192.105 & ASME B31.8-2022 Compliant

Professional Hoop Stress Calculator
Calculates circumferential stress per Barlow's formula. Supports ASME B31.8 (Gas Transmission), B31.3 (Process Piping), and 49 CFR 192. Includes design factors, joint efficiency, and temperature derating.

Design Code

Gas transmission and distribution piping. Design factor based on location class.

Pipe Geometry

in
in

Operating Conditions

psig
°F

T ≤ 250°F: T = 1.00
T > 250°F: Derating per Table 841.1.8-1

Material Properties

psi

Common API 5L grades:
• Grade B: 35,000 psi
• X42: 42,000 psi
• X52: 52,000 psi
• X60: 60,000 psi
• X65: 65,000 psi
• X70: 70,000 psi
• X80: 80,000 psi

Design Factors (ASME B31.8)

Location class based on building count within 220-yard sliding mile per 49 CFR 192.5

Calculated Parameters

Stress Analysis:
Hoop Stress (Barlow's), Longitudinal Stress, Von Mises Stress, % SMYS (Yield Strength).
Pressure Design:
MAOP (Maximum Allowable Operating Pressure), Burst Pressure, Hydrotest Pressure (1.5x).
Design Factors:
Location Class Factor (F), Joint Efficiency (E), Temperature Derating (T).

Learn the Engineering Theory

Understand hoop stress principles, Barlow's derivation, and code requirements

Read Engineering Guide →

Design Formulas (ASME B31.8 / 49 CFR 192)

S = (P × D) / (2 × t)
S = Hoop stress (psi)
P = Internal pressure (psig)
D = Outside diameter (in)
t = Wall thickness (in)
P = (2 × S × t × F × E × T) / D
F = Design factor (0.40–0.72)
E = Longitudinal joint factor
T = Temperature derating factor

Technical Notes

  • Mean Diameter Method: This calculator uses mean diameter (D − t) for more accurate stress calculation. The difference from OD method is approximately t/D × 100% (~2-4%).
  • Manufacturing Tolerance: API 5L PSL2 allows −12.5% on wall thickness for t ≤ 0.197" and −10% for thicker walls. Calculator applies this for stress verification.
  • Thin-Wall Validity: Barlow's formula is accurate for D/t > 20. For D/t < 10 (thick-wall), use Lamé equations.
  • Von Mises Stress: For internal pressure only, σvm = 0.866 × σh. Used for yield prediction per distortion energy theory.

Location Class Definition (49 CFR 192.5)

  • Class 1: ≤10 buildings within 220-yard corridor per sliding mile. Rural areas.
  • Class 2: 11–46 buildings. Fringe areas around cities or industrial zones.
  • Class 3: ≥46 buildings, or within 100 yards of buildings with 20+ occupants.
  • Class 4: Areas with prevalent 4+ story buildings (hospitals, schools, etc.).

Hydrostatic Test Requirements (49 CFR 192.505)

  • Class 1 & 2: Minimum 1.25× MAOP for 8 hours
  • Class 3 & 4: Minimum 1.40× MAOP for 8 hours
  • Industry Practice: 1.5× MAOP is common for new construction
  • Maximum Test: Should not exceed 90% SMYS during test

Limitations & Assumptions

  • Valid for steady-state internal pressure only (no surge/water hammer)
  • Does not include external loads, cyclic fatigue, or residual stresses
  • Assumes uniform wall thickness (no corrosion, dents, or defects)
  • Longitudinal stress assumes closed-end condition (capped or dead-end)
  • For restrained (buried) pipe, additional thermal stresses may apply
  • Results are for preliminary design—final design requires PE review

Standards & References

  • 49 CFR Part 192
    Transportation of Natural and Other Gas by Pipeline (DOT/PHMSA)
  • ASME B31.8-2022
    Gas Transmission & Distribution Piping Systems
  • API 5L (46th Ed.)
    Specification for Line Pipe
  • ASME B31G
    Manual for Determining Remaining Strength of Corroded Pipelines

Frequently Asked Questions

What is SMYS in pipeline engineering?

SMYS stands for Specified Minimum Yield Strength. It is the minimum stress at which a pipe material will begin to permanently deform. Common grades include Grade B (35,000 psi), X52 (52,000 psi), and X70 (70,000 psi).

How do you calculate hoop stress?

Hoop stress is calculated using Barlow's Formula: S = (P × D) / (2 × t), where S is stress, P is internal pressure, D is outside diameter, and t is wall thickness.

What is the MAOP design factor?

The Design Factor (F) is a safety multiplier used to calculate MAOP. For gas pipelines under 49 CFR 192, factors range from 0.72 (Class 1, Rural) to 0.40 (Class 4, Urban).

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