Commercial Gas Calculator

Information and sources

Which standard

This calculator picks the standard by installation volume only (meter + pipes + 10% fittings): IV up to and including 1 m³ uses IGEM/UP/1A, over 1 m³ uses IGEM/UP/1. Note: the published UP/1A scope also mentions MOP up to 40 mbar, supply MOP up to 75 mbar and bore up to 150 mm. The page shows a reminder if the pressures are higher, but it does not change the selection. Very small installations (IV up to 0.035 m³, pipe up to 35 mm) may fall under IGEM/UP/1B instead.

Installation volume

IVt = IVm + IVp + IVf. IVf is taken as 10% of IVp when fittings can't be calculated. IVt is rounded up to 2 significant figures. Diaphragm meter IVs: U6 0.008, U16 0.025, U25 0.037, U40 0.067, U65 0.100, U100 0.182, U160 0.304 m³.

Rotary meters: IV taken as 1 m of pipe at the meter connection diameter (your method). The standard's own formula is 0.79 x d² x L using the flange to flange length, so 1 m is on the safe (larger) side for these meters. Connection sizes are Dresser Roots sizes confirmed by Jim (Dresser codes B4B 2 in, B4C 3 in, B4D 4 in, B4E 6 in, B4F 8 in; 102M 10 in). 9M comes in 3 in and 4 in versions. Sizes can still be changed per job.

Tightness test duration (TTD)

Type A area (inadequately ventilated, used for new work): TTD = GRM x IV x F1.
Type B (adequately ventilated room under 60 m³): TTD = 2.8 x GRM x IV x F1 / RV.
Type C (over 60 m³, external or buried): TTD = 0.047 x GRM x IV x F1.
F1 = 42 natural gas, 67 air or nitrogen. Round up to the next full minute, minimum 2 minutes. If TTD is over the gauge's typical maximum (water / 1dp gauge 30 min, 2dp gauge 15 min, high SG 45 min) use a more sensitive gauge.

MPLR: Type A 0.0014 m³/h, Type B 0.0005 m³/h per m³ room, Type C 0.03 m³/h. New installations: no gauge movement over GRM allowed. Stabilisation: TTD or 15 min, whichever is longer (UP/1 method).

UP/1A existing installations, typical TTD by IV (gas / air): up to 0.15: 2/2; to 0.3: 2/3; to 0.45: 3/5; to 0.6: 4/6; to 0.75: 5/8; to 0.9: 6/9; to 1.0: 6/10 min. Let-by at 50% OP: up to 0.5 m³ 2 min, to 0.8 m³ 3 min, to 1.0 m³ 4 min.

Strength test (pneumatic)

MOP up to 100 mbar: STP = greater of 1.1 x MIP or 2.5 x MOP, stabilise 5 min, STD 5 min.
MOP over 100 mbar to 2 bar: STP = greater of 1.1 x MIP or 1.5 x MOP, stabilise 10 min, STD 5 min.
MOP over 2 bar to 7 bar: STP = greater of 1.1 x MIP or 1.5 x MOP, stabilise 15 min, STD 30 min.
Maximum permitted drop 20% of STP. Hydrostatic test needed where STP would exceed 3.5 bar on pipe over 150 mm, or 10.5 bar on pipe over 25 mm. Typical LP meter installation: MOP 21 to 23 mbar, MIP 75 mbar, so STP 82.5 mbar.

Purge

PV = 1.5 x (IVp + IVf) + meter PV + 1.5 x hose volume. Diaphragm meter PV = 5 x cyclic volume (U6 0.01, U16 0.03, U25 0.05, U40 0.10, U65 0.125, U100 0.285, U160 0.355 m³). Rotary / turbine meter PV = 1.5 x its IV. Hose volume uses the steel pipe volume per metre for the hose bore.

Minimum purge flow by largest nominal pipe size (m³/h): 20 mm 0.7, 25 mm 1.0, 32 mm 1.7, 40 mm 2.5, 50 mm 4.5, 80 mm 11, 100 mm 20, 125 mm 30, 150 mm 38, 200 mm 79, 250 mm 141, 300 mm 216. Sizes not listed use the next larger size (so 65 mm uses 80 mm, 15 mm uses 20 mm). Max purge time = PV x 3600 / flow (seconds). Above 150 mm, IGEM/UP/1 limits purge lengths; check the standard.

Meter only test (no pipework added): IV = meter IV only; purge volume = meter PV + hose. Rotary meters use the flow rate for the meter's connection size. Diaphragm (and manually entered) meters use the 150 mm rate, 38 m³/h, which matches the Commercial Gas Calculator app (U160 meter only = 34 s). The purge size can still be set by hand.

Pipe volumes per metre (m³)

Steel: 15 0.00024, 20 0.00046, 25 0.00064, 32 0.0011, 40 0.0015, 50 0.0024, 65 0.0038, 80 0.0054, 100 0.009, 125 0.014, 150 0.02, 200 0.035, 250 0.053, 300 0.074.
Copper: 15 0.00014, 22 0.00032, 28 0.00054, 35 0.00084, 42 0.0013, 54 0.0021; 67, 76.1 and 108 worked out from the tube bore (marked *).
PE SDR11: 20 0.00019, 25 0.00033, 32 0.00053; bigger sizes and all SDR17 worked out from bore = OD x (1 - 2/SDR) (marked *).

Sources

• IGEM: IGE/UP/1A Edition 2 scope (igem.org.uk resource page) for the UP/1A limits.
• IGEM/UP/1C draft for comment (IGEM/TSP/10/122): Table 5 strength testing, Table 10 purge flow rates, Table 14 meter IV and cyclic volumes, Table 15 pipe volumes, Tables 16 and 17 gauge GRM and F1, TTD = GRM x IV x F1.
• Installer magazine "Nice and tight" (IGE/UP/1 summary): MPLR types A, B, C and TTD formulas.
• RAD Midlands IV and PV calculation sheets: steel pipe volumes, meter IV and PV.
• NICEIC Pocket Guide Gas 2: copper and PE pipe volumes, fittings at 10%.
• heatwizard.co.uk summary of UP/1A existing installation TTD and let-by tables.
• Dresser Roots Series B3 rotary meter data sheet and misl.org / processvalve.com summaries: rotary connection sizes.

This page is a calculator to help with planning. It does not replace the standards, your training, or a site specific procedure.