FCAW-G Porosity at Restarts and Along One Side
A shop is welding a 1/2 in A36 column-to-base-plate groove weld in the 3G uphill position using FCAW-G. The WPS lists 0.045 in E71T-1 wire, 75% Ar/25% CO2 at 35 cfh, 26 V, 240 A, a 5/8 in nozzle, and 3/4 in contact-tip-to-work distance. The shop door is open for ventilation, and a fan is running 10 ft away. The first 20 in of weld show scattered porosity concentrated at restart points and along the left side of the joint. The welder says the wire is new and the gas solenoid is working. Visual inspection also shows spatter bridging the nozzle. The inspector must decide whether to stop production and what to check first.
1. List the likely causes of the porosity pattern and rank them.
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The pattern points first to shielding-gas disruption: an open door and a fan 10 ft away can create a draft across the nozzle, and spatter bridging the nozzle distorts gas flow. The 3/4 in contact-tip-to-work distance is at the high end for FCAW-G and worsens draft sensitivity. Restart porosity suggests inadequate gas preflow and poor restart technique. Left-side porosity suggests the welder’s travel angle or nozzle position is favoring one side, or the gas stream is being deflected. Ranked: (1) draft and nozzle spatter, (2) excessive CTWD or poor nozzle position, (3) wire/liner or consumable moisture, (4) gas supply or solenoid issue. The welder’s statement that the solenoid works does not rule out flow restriction or leaks.
2. Describe a field check sequence to separate gas-shielding from wire/consumable causes.
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First, eliminate the obvious shielding problem: close the door, stop the fan, clean the nozzle, and reset CTWD to about 3/4 in or less per the WPS. Check gas flow at the nozzle with a flowmeter, not just at the regulator, and inspect the hose, fittings, and solenoid for leaks. Run a test bead on scrap with the same parameters and watch for smooth gas coverage and spatter behavior. If porosity persists, check the wire for rust, contamination, or poor feed; inspect the liner and drive rolls; confirm the wire diameter and classification. If the wire and feed are good, check gas mix and moisture. A clean test bead with corrected draft and nozzle condition confirms shielding as the dominant cause.
3. If production must continue, what immediate controls should be imposed?
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Do not simply increase gas flow; excessive flow can create turbulence and entrain air. Provide windbreaks, relocate the fan, and keep the nozzle clean. Set gas flow within the WPS range, verify at the nozzle, and use adequate preflow before starting. Reduce CTWD if the WPS allows it, keep the nozzle angle consistent, and improve restart technique by starting on scrap or using a run-off tab. Monitor the first production welds visually and by a quick destructive or NDT check if permitted. If porosity continues after these controls, stop and troubleshoot the wire and gas supply rather than continuing to weld suspect production.