| Scenario | Volume (m³) | O₂ start (%) | O₂ target (%) | Efficiency (%) | Safety (%) | Method |
|---|---|---|---|---|---|---|
| Pipe spool purge | 2.5 | 20.9 | 2.0 | 85 | 15 | Continuous flush |
| Small vessel inerting | 12 | 20.9 | 1.0 | 80 | 20 | Continuous flush |
| Enclosed skid purge | 18 | 20.9 | 3.0 | 90 | 10 | Pressurize-vent |
Ct = C0 · e−Vinj/V
So the injected nitrogen volume at site conditions becomes:
Vinj = V · ln(C0/Ct)
Ct = C0 · (Pvent/Ppress)n
Cycles:
n = ln(Ct/C0) / ln(Pvent/Ppress)
Injected gas (per cycle) is approximated by filling from vent to press pressure.
V′ = (Vinj/η) · (1 + SF)
Convert site m³ to Nm³ (0°C, 1 atm) using ideal gas scaling:
Nm³ = V′ · (Psite/Pstd) · (Tstd/Tsite)
- Choose a method: continuous flush for open purges, or cycles for pressurize-vent procedures.
- Enter the system volume and oxygen start/target values from your procedure.
- Set efficiency based on geometry, venting, and expected losses.
- Add a safety factor to cover leakage, dead legs, and uncertainty.
- Provide site pressure and gas temperature to convert to standard volume.
- Optionally enter supply flow to estimate purge time and logistics.
- Press Calculate. Download CSV/PDF for records and planning.
Operational context for inerting and purging
Nitrogen demand planning reduces schedule risk during hot work isolation, pipeline commissioning, tank entry preparation, and confined-space maintenance. By translating oxygen targets into standard volume, crews can size cylinder packs, bulk dewars, or membrane generators before mobilization. This prevents mid-shift changeouts that interrupt permits and increase exposure time.
Key inputs that drive consumption
The dominant drivers are enclosed volume, initial oxygen, target oxygen, and mixing effectiveness. Poor vent placement, dead legs, and short-circuit flow can double consumption, so the calculator includes an efficiency factor to represent real field behavior. A safety factor then covers leakage, instrument uncertainty, and procedural hold points. Use project drawings and temporary works layouts to estimate the true gas space, not just nominal vessel size.
Interpreting results for logistics
Outputs are shown as site cubic meters and Nm³, plus an approximate mass. Standard volume is the best purchasing unit because supplier flows and cylinder capacities are commonly rated at standard conditions. If you enter supply flow, the estimated purge time helps coordinate gas deliveries with crane lifts, valve lineups, and shift handovers. For long purges, plan breaks for analyzer stabilization and document readings at defined milestones.
Method selection for common construction tasks
Continuous flushing suits open-ended purges where gas can exit freely and mixing is reasonably uniform, such as pipe spools, manifolds, and skid piping. Pressurize-vent cycles are useful on closed vessels or assemblies that can be pressured safely, where each cycle reduces oxygen by a predictable pressure ratio. Select the method that matches your approved procedure, pressure ratings, and the available vent path capacity.
Quality and safety checks
Before execution, verify oxygen readings with calibrated instruments and stable sampling points. Confirm vent routing, noise control, and exclusion zones, and ensure permit requirements match the target oxygen. After purge completion, recheck oxygen to confirm it remains below the limit during the planned work window. Record temperature and pressure assumptions so future audits can reproduce the calculation and validate supplier invoices.
FAQs
1) What does Nm³ mean in the results?
Nm³ is gas volume at standard conditions (0°C, 1 atm). It allows fair comparison between suppliers, cylinder ratings, and flow meter specifications.
2) How should I choose the efficiency factor?
Start with 80–90% for well-vented, simple geometry. Use lower values for complex piping, dead legs, or poor vent placement. Calibrate from past jobs when possible.
3) When is the pressurize-vent method appropriate?
Use it when your system can be safely pressurized and vented per procedure. It is common for closed vessels or assemblies where continuous venting is limited.
4) Why is site pressure and temperature included?
Gas volume changes with pressure and temperature. These inputs convert site cubic meters to standard volume so purchasing and flow planning remain consistent.
5) Can I estimate purge duration with this tool?
Yes. Enter the available supply flow in Nm³/h to get an approximate time. Actual duration can change due to analyzer stabilization, vent restrictions, and operational pauses.
6) Is the mass result suitable for lifting plans?
It is a planning estimate for gas requirement, not for rigging. Use supplier manifests and cylinder pack specifications for certified weights and lifting calculations.