Porosity and low current on a horizontal fillet
A shop is FCAW-welding a 12 mm mild-steel T-joint in the horizontal fillet position with 1.2 mm E71T-1 wire and CO2. The machine is set at 26 V and 8.5 m/min wire-feed speed; the welder uses a 22 mm contact-tip-to-work distance, 10° drag angle, and 15 L/min gas flow at the regulator. The contact tip is a 1.6 mm bore worn to about 2.2 mm; the liner is 4.5 m long with one sharp bend; the gas hose has a small cut near the feeder. The shop door is open and a fan blows across the bay. Inspection finds clustered porosity along the weld, heavy spatter, a convex bead, and occasional incomplete fusion at the root. The ammeter reads 205 A; the WPS range is 220–260 A, 24–28 V. A new spool was opened three weeks ago and stored uncovered. Production wants to increase gas flow to 25 L/min and continue.
1. Diagnose the likely causes and rank them by contribution.
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Most likely sequence: gas coverage is lost first. The 15 L/min is at the regulator, but a cut hose, a 22 mm CTWD and a fan across the bay reduce shielding at the arc. Porosity clustered along the bead fits that. The worn 2.2 mm tip and the sharp liner bend add poor current transfer and wire-feed fluctuation; the 205 A reading is below the 220–260 A WPS range, which explains the convex bead and incomplete fusion. The open spool stored three weeks near a wash bay can add surface moisture and hydrogen, worsening porosity. Spatter is consistent with long CTWD and low voltage relative to WFS. Increasing gas to 25 L/min alone would waste gas and may create turbulence; it does not fix the leak, draft, tip or current.
2. State the parameter and equipment changes you would make, with justification.
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Set CTWD to 15–18 mm, replace the contact tip with the correct bore for 1.2 mm wire, and replace or reroute the liner to remove the sharp bend. Repair or replace the gas hose, set flow to about 18–20 L/min measured at the nozzle with a flow meter, and screen the bay from the fan or move the work. Adjust WFS and voltage together to bring current into 220–260 A and voltage into 24–28 V, then run a test bead on scrap and check penetration, bead shape and porosity. Use dry wire from a sealed package; if the opened spool has been exposed, do not use it for code work. Record the new parameters and verify with a visual or destructive test before production.
3. What maintenance and storage controls prevent recurrence?
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Daily inspection of tip, liner, drive rolls, gas hose and nozzle; weekly flow test at the nozzle and leak test; calibration of WFS and meters; keep spools sealed with desiccant and off the floor, FIFO; replace damaged hoses; train welders to set CTWD with a gauge and to purge gas before start. Keep a log so repeat failures are visible. Assign the checks to a named person and stop production if the gas flow at the nozzle is below the qualified range.