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.
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.
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