How to calculate shielding gas consumption
Shielding gas use is the flow rate multiplied by actual arc-on time, not by the length of the shift. At 38 CFH over an 8 hour shift with 35% arc-on time, the arc burns for 2.8 hours and consumes about 117 cubic feet with a 10% allowance, which is roughly half of a size 300 cylinder.
Arc-on time runs about 20% to 30% for manual welding, 30% to 50% for semiautomatic wire processes and 60% or more for mechanized cells. The purge allowance covers pre-flow, torch changes and gas left in the hose; 5% to 15% is typical. Leaking hoses and sticking solenoids can push real usage far above the calculated figure, so check the gas train regularly.
A size 300 argon or mixed-gas cylinder holds roughly 251 cubic feet and a size 150 about 125 cubic feet, while liquid CO2 cylinders are rated by weight at roughly 8.7 cubic feet of gas per pound. Verify the rating on the cylinder label, and measure flow at the nozzle rather than trusting the regulator dial. In confined spaces, displaced oxygen is a real hazard, so review ventilation with your safety officer before welding.
Frequently Asked Questions
Short-circuit and spray GMAW usually run 30 to 45 CFH, and GTAW runs 15 to 30 CFH. Outdoors, a windscreen works better than turning up the flow, because excess flow creates turbulence that pulls air into the shielding envelope and causes porosity.
Arc-on time is the share of the shift when the arc is actually burning. Manual stick and TIG work typically runs 20% to 30%, semiautomatic wire welding 30% to 50%, and mechanized or robotic cells 60% or more. Use your own shop records when you have them.
A common size 300 argon or mixed-gas cylinder holds about 251 cubic feet, and a size 150 holds about 125 cubic feet. Liquid CO2 cylinders are rated by weight, with roughly 8.7 cubic feet of gas per pound. Check the cylinder label for the exact rating.