Calculators›Percent SMYS
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Percent SMYS

Yield Strength · Operating Stress · Safety Margin

Percent SMYS Calculator
Calculate operating hoop stress as a percentage of Specified Minimum Yield Strength using Barlow's formula. Supports ASME B31.8 (gas), B31.4 (liquid), B31.12 (hydrogen), and B31.3 (process piping) with code-specific design limits. Essential for MAOP verification, integrity management, and compliance assessment.
Applicable Code:
49 CFR 192 location class limits: 72%/60%/50%/40% SMYS (Class 1/2/3/4)
Calculation Mode:

Calculate % SMYS

psig
in

Pipe Specifications

in
psi

Advanced Factors

Note: Joint factor (E) and temperature factor (T) are typically 1.0 for most applications. Adjust only if required by specific design conditions.

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Understand percent smys principles, calculations, and industry applications

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Formulas (ASME B31.8 / 49 CFR 192)

Hoop Stress (Barlow's Formula):
σh = (P × D) / (2 × t)
Percent SMYS:
%SMYS = (σh / SMYS) × 100
MAOP (Maximum Allowable Operating Pressure):
MAOP = (2 × S × t × F × E × T) / D
σh = Hoop stress (psi)
P = Operating pressure (psig)
D = Outside diameter (in)
t = Wall thickness (in)
S = SMYS (psi)
F = Design factor (0.40–0.72)
E = Joint factor (1.0 seamless)
T = Temp factor (1.0 at ≤250°F)
Key Insight: The design factor (F) sets the allowable %SMYS limit by location class. Actual %SMYS depends only on P, D, t, and SMYS. The factors E and T apply when calculating MAOP.

Engineering Notes

  • %SMYS = actual hoop stress ÷ SMYS × 100. This is independent of design factors.
  • Design Factor (F) sets the allowable %SMYS limit based on the applicable code.
  • B31.8 (Gas): Location class system per 49 CFR 192 — Class 1: 72%, Class 2: 60%, Class 3: 50%, Class 4: 40%.
  • B31.4 (Liquid): Category system per 49 CFR 195 — General: 72%, Crossings: 60%, Fabricated: 54%.
  • B31.12 (Hydrogen): Location class system + hydrogen compatibility factor (Hf) for material derating.
  • B31.3 (Process): Uses allowable stress methodology, not %SMYS directly. S = min(UTS/3, SMYS/1.5), effectively ~67% SMYS equivalent.
  • Joint Factor (E): 1.0 for seamless/ERW; 0.80 for furnace butt-weld.
  • Temperature Factor (T): 1.0 for ≤250°F; derates at higher temps.
  • Barlow's formula uses thin-wall approximation (valid when D/t > 20).
  • This calculation is for internal pressure only. External loads, thermal stress, and bending require separate analysis.

ASME B31.8 / 49 CFR 192 Design Limits

Class F Max %SMYS Description
Class 10.7272%≤10 buildings per mile
Class 20.6060%11–46 buildings
Class 30.5050%≥46 buildings
Class 40.4040%4+ story buildings

Standards & References

  • ASME B31.8
    Gas Transmission Piping Systems
  • ASME B31.4
    Liquid Pipelines
  • ASME B31.12
    Hydrogen Piping
  • ASME B31.3
    Process Piping
  • 49 CFR 192/195
    Pipeline Safety Regulations
  • API 5L
    Specification for Line Pipe

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