Original synthetic study
Why the same standard gas rate has different pipe velocity
The same standard gas rate can occupy different actual volumes at different pressure and temperature. Pipe velocity must use that local volume, not the unchanged standard-rate number.
By PetroCalcHub Team · Updated October 24, 2026 · Free to read and use
Preserve gas amount through the conversion
For fixed gas amount, actual-to-standard volume follows the ratio ZT/P on absolute scales. Higher local pressure generally reduces actual volume when the other factors are fixed.
The study holds standard rate, pipe ID, temperature and Z assumptions fixed while varying absolute pressure to isolate that effect.
Divide the actual rate by area
Once local Q is obtained, average speed is Q divided by the pipe ID area. A constant standard rate therefore produces different local speeds along a pressure-changing line.
For a real line, Z and temperature can vary as well, so a coupled profile needs more than this controlled pressure ratio.
Separate average gas speed from multiphase behavior
If liquid is present, phase slip and holdup can make gas velocity differ from a no-slip mixture average.
The downloadable experiment is a single-gas continuity study. It is not a multiphase pressure prediction or an erosional integrity assessment.
Explore the example
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
Select one of 5 recorded scenarios. Intermediate states are not interpolated.
Local absolute pressure (MPa) = 2. Actual gas rate (m³/s): 0.050636127; Gas speed (m/s): 6.44719193.
- Actual gas rate (m³/s)
Worked example
One standard gas rate, different actual speeds
Standard rate 1 m³/s at 101,325 Pa, 288.15 K and Zs = 1. Local T = 320 K, Z = 0.9, pipe ID = 0.1 m.
Relation and unit basis
Qactual = Qstd(ZT/P)/(ZsTs/Ps); v = Qactual/(πD²/4)
All pressures are absolute. Standard cubic metres per second are used here to make the SI state ratio explicit.
1. Define the baseline
Local absolute pressure (MPa) = 2
Standard rate 1 m³/s at 101,325 Pa, 288.15 K and Zs = 1. Local T = 320 K, Z = 0.9, pipe ID = 0.1 m.
2. Select the relation
Qactual = Qstd(ZT/P)/(ZsTs/Ps); v = Qactual/(πD²/4)
All pressures are absolute. Standard cubic metres per second are used here to make the SI state ratio explicit.
3. Substitute the values
At 2 MPa: Q = 1 × 0.9 × 320 × 101,325/(2,000,000 × 288.15); divide by π × 0.1²/4 for speed
Retain intermediate precision. The displayed values are rounded only after evaluation.
4. Read the result
Actual gas rate (m³/s) = 0.050636127; Gas speed (m/s) = 6.44719193
Constant standard rate does not mean constant local volumetric rate or velocity.
Result and interpretation
Actual gas rate (m³/s) = 0.050636127; Gas speed (m/s) = 6.44719193
Constant standard rate does not mean constant local volumetric rate or velocity.
Absolute pressure is the only changing thermodynamic input in the synthetic gas-volume conversion.
Study data and reproduction
Original synthetic teaching calculation. Equations and fixed controls are stated here; these are not field measurements.
| Local absolute pressure (MPa) | Actual gas rate (m³/s) | Gas speed (m/s) |
|---|---|---|
| 0.5 | 0.2025445 | 25.78877 |
| 1 | 0.1012723 | 12.89438 |
| 2 | 0.05063613 | 6.447192 |
| 5 | 0.02025445 | 2.578877 |
| 10 | 0.01012723 | 1.289438 |
Scroll the table to see all columns. The highlighted row is the worked baseline. Downloads retain full numerical precision.
Test your understanding
Work through the question before revealing its answer. Use the stated assumptions and include units in every numerical step.
1. At fixed T and Z, what happens to actual volume and speed when absolute pressure doubles?
Show the worked answer
Both halve for the same gas amount rate and pipe area.
2. Reproduce the baseline Actual gas rate (m³/s) without rounding intermediate values.
Show the worked answer
At 2 MPa: Q = 1 × 0.9 × 320 × 101,325/(2,000,000 × 288.15); divide by π × 0.1²/4 for speed. Actual gas rate (m³/s) = 0.050636127. Constant standard rate does not mean constant local volumetric rate or velocity.
3. Compare the first and last recorded scenarios. Which input changes?
Show the worked answer
Local absolute pressure (MPa) changes from 0.5 to 10. Other controls remain as stated in the premise. Actual gas rate (m³/s) changes from 0.202544508 to 0.0101272254.
4. What would be needed to apply this example to a different physical system?
Show the worked answer
Replace the synthetic controls with compatible documented inputs and check the relation's assumptions. All pressures are absolute. Standard cubic metres per second are used here to make the SI state ratio explicit. Constant standard rate does not mean constant local volumetric rate or velocity.
Before using the result
- Convert standard rate to local rate.
- Use absolute pressure and temperature.
- Do not equate gas speed with no-slip mixture speed.
Constant standard rate does not mean constant local volumetric rate or velocity.
Continue learning
Start with the broader workflow guide · Related method guide
Sources and method
The explanation and synthetic examples are original PetroCalcHub teaching material. The references below support the definitions and model context. They do not supply field validation for the synthetic scenarios.