Half the questions on a pigging job are the same question: where is it now, and when does it arrive? The flow meter answers both, as long as the bore is right.
Every cubic metre pumped in displaces a cubic metre of line. So on a constant-bore line:
x = Vpumped / A and V = A × x
For a 12-inch standard wall line, one metre of pipe holds 73 litres, so every 73 m³ pumped moves the pig a kilometre. Working the other way gives the arrival estimate:
| Chainage (km) | Volume to pump (m³) | Time at 263 m³/h (≈1 m/s) |
|---|---|---|
| 1 | 73 | 0 h 17 min |
| 2 | 146 | 0 h 33 min |
| 5 | 365 | 1 h 23 min |
| 10 | 730 | 2 h 47 min |
| 15 | 1,095 | 4 h 10 min |
| 20 | 1,460 | 5 h 33 min |
A single division stops working the moment the line has a 12-inch section and a 10-inch section. Do it section by section: subtract each section's volume from the pumped total until the remainder is smaller than the next section's volume, then divide that remainder by that section's area. The same walk in reverse gives the volume needed to reach a chainage.
This is also why a bore change matters for speed: at constant flow rate, the pig speeds up in the smaller bore in proportion to the area ratio. A 12-inch to 10-inch step at constant flow raises pig speed by about 40 %, which is enough to push an ILI tool out of its window.
Flow that goes through the pig does not move it. If the pig is passing 20 m³/h of the 263 m³/h you are pumping, use 243 m³/h in the position calculation, not 260. Ignore it and your pig will be consistently ahead of where the meter says it is — the most common reason a pig "arrives late".
Cumulative volume, flow rate, launcher pressure, receiver pressure and time — at fixed intervals, from before the launch. The pressure differential trend is the check on the volume calculation: a steady differential and a steady rate means the pig is moving as predicted, a rising differential means it is working harder than planned.
A volume calculation is an estimate, not a confirmation that the pig is in the receiver. The trap is opened on isolation, depressurisation and physical verification — never on the arithmetic alone.
Give it the pumped volume and it returns the chainage; give it a chainage and it returns the volume, the time to get there and the arrival estimate — multi-diameter lines included.
Open the pigging calculatorWho writes this. A mechanical engineer with twelve years in oil and gas — in-line inspection, fired heater and furnace inspection, and pipeline integrity. What is here comes from the published standards and from what those years in the field actually looked like. It is not written by an API-certified inspector.
This is not an assessment. Nothing on this site may be used to justify a decision about real equipment. Assessing plant requires the current editions of the applicable codes, data from a licensed source, and a competent engineer who signs for the answer. · Integrity Field Guide · Pipeline pigging calc & planner