Gas Leak Equivalent Hole Diameter
The equivalent orifice (hole) diameter behind a measured gas leak rate.
Example
You enter
- Measured leak rate (ft³/hr) 7.72
- Upstream gauge pressure (psi) 0.25
- Gas natural_gas
- Discharge coefficient 0.7
You get
- Equivalent orifice diameter 0.05 in
- Orifice area 0.00196 in^2
Checked against published worked examples from: BCcampus Open Education.
Details, formula, and sources
Scoped = sqrt( 4 Q / (8706 c pi sqrt(dP / SG)) ), from the orifice equation. A 7.72 cfh natural-gas leak at 0.25 psi with c 0.7 is about a 0.050 in hole. Turns a clocked or metered leak into a hole size. An estimate of the effective hole, not a code leak-test method; any leak is a hazard - find and repair it. Uses the gas orifice-flow form, not the water one.
Formula or tabled = sqrt( 4 Q / (8706 x c x pi x sqrt(dP / SG)) ), the inverse of Q = 8706 x c x (pi d^2 / 4) x sqrt(dP / SG); orifice area A = Q / (8706 c sqrt(dP/SG)).
Source and editionClassical orifice-flow leak approximation (incompressible, small leak at low pressure), solved for the diameter; the 8706 coefficient is the orifice equation in these units (25 sqrt(2 x 144 x 32.174 / 0.0764)); gas specific gravity bundled.
Free accessThe orifice-flow leak relation is public; the gas specific gravity is a bundled property.
What governsEstimate. AHJ and licensed plumber / gas fitter govern. Verify against the IPC / IFGC edition adopted in your jurisdiction.
API field namesleak_rate_cfh, upstream_psi, gas, c, orifice_diameter_in, orifice_area_in2
- Discharge coefficient c 0.7 default for a rough-edged crack or fitting leak; a sharp-edged orifice is about 0.6 (Eclipse prints 0.60)engineering practice
- Gas specific gravity bundled natural-gas / propane specific gravityengineering reference
- Estimate only the small-leak orifice approximation, not a code leak-test methodscope of this tile