Pipe Flow Area Calculator

Nominal Inside Diameter (ID):

Flow Area:

Thermal Expansion Adjustment:

1. Nominal Flow Area

Uses specified OD and wall thickness per ASME B36.10M. Includes thermal expansion at operating temperature. Use for design-basis calculations.

2. Effective Flow Area

Accounts for corrosion allowance (thicker effective wall = smaller ID) and pipe ovality per API 5L Table 10. Represents design flow area for service life calculations.

3. Maximum Flow Area

Uses minimum wall thickness (nominal -12.5% per API 5L tolerance) giving maximum ID. Use for conservative pressure drop calculations where larger area = lower velocity = less conservative.

• Manufacturing Tolerance: API 5L / ASTM A530 permit -12.5% to +12.5% wall thickness variation. Thinner wall = larger ID = larger flow area.
• Ovality (Out-of-Roundness): Per API 5L Table 10: 1.0% for OD <8.625", 1.5% for ≥12.75". Area reduction = ovality² (small second-order effect).
• Corrosion Allowance: Typical: 0.0625" (1/16") gas service, 0.125" (1/8") liquid service. Added to wall, reducing ID for design life calculations.
• Thermal Expansion: Carbon steel: 6.5×10⁻⁶ /°F per ASME B31.1. At 200°F: ~0.09% increase vs 60°F reference.
• Velocity Check: Use V = Q/A. Gas transmission: 20-60 ft/s typical. API RP 14E erosional: V_e = C/√ρ (C=100-150).