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Calculate required wall thickness for internal pressure per ASME B31.1 Power Piping Code

Design Conditions

Design Pressure (P)

psig

Maximum internal pressure

Design Temperature

°F

Maximum operating temperature

Pipe Material

Nominal Pipe Size (NPS)

Outside Diameter (Do)

Actual pipe OD

Allowable Stress (SE)

psi

From ASME B31.1 Table A-1

Weld Joint Efficiency (E) Per Table 102.4.3

Y Coefficient (Table 104.1.2A)

Material	≤900°F	950°F	1000°F	≥1050°F
Ferritic Steel	0.4	0.5	0.7	0.7
Austenitic Steel	0.4	0.4	0.4	0.4
Other Ductile	0.4	0.4	0.4	0.4

Selected y =

Allowances & Tolerances

Corrosion Allowance (A)

Typically 1/16" for carbon steel

Mill Tolerance Manufacturing undertolerance

Thread/Groove Depth

Mechanical allowance if threaded

Erosion Allowance

For abrasive service

Common Corrosion Allowances

Wall Thickness Comparison (Optional)

Actual/Specified Wall

Pipe schedule wall thickness

Schedule

📋 Notes

Seamless pipe: E = 1.0, standard 12.5% mill tolerance
Carbon Steel: Typically 1/16" corrosion allowance
Stainless Steel: Typically 1/32" or 0" corrosion allowance
y increases to 0.7 for ferritic steels above 950°F

Calculation Results

Minimum Required Wall (t_m)

0.186

inches

Per ASME B31.1 Eq. 104.1.2

Pressure Thickness (t)

0.124

inches

Before allowances

Nominal Wall Required

0.213

inches

Including mill tolerance

Margin / Status

+11%

ACCEPTABLE

Actual vs. Required

Wall Thickness Comparison

Required: 0.213" Actual: 0.237"

Adequate (11% margin)

0" Required Minimum Actual Wall

ASME B31.1 Formula (Equation 104.1.2)

t_m = (P × D_o) / [2(SE + Py)] + A

P Design Pressure 1500 psi

D_o Outside Diameter 4.500 in

S Allowable Stress 15000 psi

E Joint Efficiency 1.00

y Temperature Coefficient 0.4

A Total Allowances 0.0625 in

Pipe Cross Section (Not to Scale)

Allowable Stress Reference (ASME B31.1 Table A-1)

Temp (°F)	A106 B Carbon	A335 P11 1.25Cr-0.5Mo	A335 P22 2.25Cr-1Mo	A335 P91 9Cr-1Mo-V	A312 TP304 18Cr-8Ni	A312 TP316 16Cr-12Ni-2Mo

* Values shown are typical. Verify with current ASME B31.1 code edition for critical applications.

ASME B31.1 Minimum Wall Thickness Calculator

📋 Notes

Wall Thickness Comparison

ASME B31.1 Formula (Equation 104.1.2)

Pipe Cross Section (Not to Scale)