Shielding gas consumption and cylinder life
How much gas the job needs, how long the cylinder will last and what the gas costs per weld. Arc time is what counts here, not the length of the shift.
Short answer
Typical flow: MAG, steel — 10–16, TIG, steel and stainless — 6–10, Root purging in a pipe — 4–8 l/min. A 40 l cylinder at 200 bar holds 8000 litres of gas — at 12 l/min that is about eleven hours of arc time. The calculator below works out the reserve and the consumption per shift.
How it is worked out
Consumption is flow rate multiplied by arc time. The gas left in a cylinder is its water volume multiplied by the gauge pressure: a 50-litre cylinder at 200 bar holds about 10 m³ of gas at atmospheric pressure. Cylinder life is that volume divided by the flow rate.
The figure that surprises people is arc time. A welder who works a full shift has the arc lit for perhaps two hours of it — the rest is fitting, tacking, grinding and moving. Feeding the shift length into the calculation instead overstates gas use by a factor of three or four.
Setting the flow rate
Ten to sixteen litres per minute for MIG/MAG, six to twelve for TIG, and more only when there is a draught. Turning the flow up does not improve shielding beyond a point: too high a flow makes the stream turbulent and pulls air into the pool, which is exactly the failure it was meant to prevent. If the welds are porous, look for the draught, the leaking hose and the blocked nozzle before touching the flowmeter — see porosity in welds.
| Process | Gas | Flow, l/min |
|---|---|---|
| MAG, steel | CO₂ or Ar+18 % CO₂ | 10–16 |
| MIG, stainless | Ar+2 % CO₂, Ar+He | 12–16 |
| MIG, aluminium | Ar, Ar+He | 14–20 |
| TIG, steel and stainless | Ar 99.99 | 6–10 |
| TIG, aluminium (AC) | Ar 99.99 | 8–12 |
| Root purging in a pipe | Ar, N₂+H₂ | 4–8 |
For a 12–16 mm nozzle with no draught. In a draught do not turn the flow up — screen the bay instead: too strong a stream turns turbulent and pulls air in by itself.
Frequently asked questions
How much gas is in a 20-litre cylinder?
The water capacity times the pressure: 20 l at 200 bar is about 4000 l of expanded gas, or 4 m³. At 12 l/min that is a good five and a half hours of arc time — not five and a half hours of work.
Why is the consumption higher than calculated?
Pre-flow, post-flow and the surge that shoots down the hose when the valve is opened. On many short welds more goes that way than into the welding itself — which is why a shorter pre-flow pays off on tacking work.
How far down can the cylinder be run?
To about 10 bar. Below that the pressure at the valve becomes unstable and the flow wanders, and the cylinder should not be emptied completely because of moisture. The rest is paid for and stays inside.
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