GMAW NC II common mistakes
GMAW NC II · Understand the traps and how to avoid them.
Treating PPE as optional when the helmet is up or the grinder is running, and welding in a short-sleeve shirt or open collar because the arc 'looks small'.
GMAW produces intense UV and infrared that burns skin and eyes even on brief exposure, and spatter enters open collars and cuffs. Candidates who learned in informal shops often copy bad habits, and the short arc of short-circuit transfer makes the hazard feel minor.
What to do instead
Before striking an arc, run a fixed PPE check: welding helmet with correct shade (typically 10–13 for GMAW at common currents), leather gloves with gauntlets, flame-resistant long sleeves and collar closed, leather apron or jacket, safety glasses under the helmet, and hearing/eye protection when grinding. Treat the helmet-up rule as absolute: no arc until the shield is down, and no grinding without a face shield over safety glasses.
Leaving the shop with the shielding gas cylinder unsecured, the regulator left pressurised, or hoses draped across walkways, then calling housekeeping done because the bench is swept.
Candidates equate housekeeping with sweeping and miss the safety-critical items: unsecured cylinders can fall and shear the valve, trapped pressure in regulators damages diaphragms, and hoses across walkways trip people carrying hot metal. Time pressure at the end of a practical test drives this.
What to do instead
Use a 5S close-out checklist: cylinders chained or racked upright with caps on when moved, regulator backed off and valve closed when the station is idle, hoses coiled off the floor, cables and leads routed clear of walkways, hot offcuts in the designated quench or scrap bin, and the work area swept. Practise the close-out as a timed routine so it becomes automatic under exam pressure.
Reading a welding symbol as if the arrow side and other side are interchangeable, or ignoring the tail, size, length, pitch, and supplementary GMAW process reference.
The symbol system is compact and easy to skim: the reference line, arrow side, other side, and tail carry different information, and candidates memorise a few common symbols without practising the full standard. Under time pressure they read the joint drawing and guess the symbol.
What to do instead
Adopt a fixed decoding order: find the reference line, note arrow-side versus other-side placement, read the weld type and size to the left of the symbol, length and pitch to the right, then read the tail for process and specification references. Practise on a set of symbols covering fillet, groove, plug, spot, and backing, and write the decoded instruction in words before welding. Cross-check against the WPS for current, wire, gas, and position.
Welding to the drawing's nominal dimensions without checking the WPS joint preparation, root gap, and fit-up tolerances, then discovering the gap is too wide or the bevel angle is wrong after the root pass.
Candidates treat the drawing as the only authority and skip the WPS, or they assemble parts by eye because the fixture 'looks right'. They also forget that mill scale, oil, and moisture on the faying surfaces cause porosity and incomplete fusion.
What to do instead
Before fit-up, read the WPS for joint type, bevel angle, root gap, root face, and fit-up tolerance, then measure with a gap gauge, bevel protractor, and tape. Clean faying surfaces and 25 mm either side of the joint to bare metal, remove oil and moisture, and tack in the fixture so the gap is held during welding. Record the measured fit-up against the WPS before the first arc.
Setting the machine by memory or by what the last job used, without checking polarity, wire diameter, gas flow, and drive-roll tension against the WPS.
Modern synergic machines make setup look automatic, and candidates assume the displayed settings are correct. They also skip drive-roll tension and spool brake checks, so the wire slips or birds-nests mid-pass, and they set gas flow by ear instead of with a flowmeter.
What to do instead
Run a documented setup sequence: confirm electrode-positive (DCEP) polarity for solid wire GMAW unless the WPS says otherwise, match wire diameter and drive-roll groove to the wire, set drive-roll tension so the wire feeds without crushing or slipping, set the spool brake to prevent overrun, set gas flow with a flowmeter at the torch (commonly 12–20 L/min depending on conditions), and verify current, voltage, and travel speed against the WPS. Record the settings on the job card before welding.
Holding a fixed torch angle and travel speed regardless of position, then blaming the machine when the bead is convex, undercut, or cold-lapped in vertical or overhead work.
Candidates practise mostly flat and horizontal, then carry the same drag angle, work angle, and speed into vertical-up and overhead. They also fail to adjust for the puddle: they watch the arc instead of the puddle edges and the wire entering the pool.
What to do instead
Set work angle and travel angle deliberately for each position: for a fillet, split the work angle between the plates (about 45 degrees) and use a slight push or drag per the WPS; for vertical-up, use a slight upward angle with short, controlled weave or stringer and watch the puddle freeze; for overhead, keep a short arc and lower current to control the puddle. Practise each position on scrap, adjusting current, voltage, and travel speed until the bead profile is flat to slightly convex with toes wetted in, then repeat on the test piece.
Diagnosing a defect by appearance only and grinding it out without confirming depth, or re-welding over porosity and slag without removing the source.
Candidates want to fix the visible symptom fast. Porosity from a draft, moisture, or a dirty surface will return if the cause is not removed, and grinding until it 'looks clean' can leave defect below the surface or thin the section.
What to do instead
Identify the defect class first: porosity (gas source, draft, moisture, dirty wire or base metal), lack of fusion (low heat input, wrong angle, travel too fast), undercut (current too high, angle wrong, travel too fast), spatter (wrong parameters, no anti-spatter, wrong gas mix), or burn-through (gap too wide, current too high). Remove the defect to sound metal, confirm with visual and, where specified, PT or RT, correct the process cause, then re-weld to the WPS and re-inspect. Document the defect, cause, and correction.
Finishing the joint and handing it over without post-weld cleaning, stress relief where specified, or dimensional check, and without completing the WPS and inspection records.
Candidates see the weld as the end of the task and underestimate the documentation requirement. They also skip cleaning spatter and slag, which hides defects and fails the cosmetic acceptance criteria, and they omit heat-treatment or stress-relief steps that the specification requires.
What to do instead
Follow the post-weld sequence in the specification: remove spatter and slag, wire-brush and clean the weld and heat-affected zone, check dimensions and distortion against the drawing, apply stress relief or heat treatment where the WPS or code requires it, and complete the records: WPS number, parameters used, consumable batch, gas, position, welder ID, date, and inspection results. File the records with the job so traceability is complete.
Skipping routine maintenance: never checking the contact tip, nozzle, liner, or drive rolls, and welding with a spattered nozzle or worn tip because the machine still arcs.
A worn contact tip or blocked nozzle still produces an arc, so candidates see no failure. Spatter build-up in the nozzle disrupts gas flow and causes porosity, and a worn liner causes erratic wire feed, but both develop gradually and are easy to miss.
What to do instead
Add a pre-shift check to the routine: inspect and replace the contact tip when the bore is worn or oval, clean or replace the nozzle when spatter restricts gas flow, check the liner for kinks and wear, inspect drive rolls for flat spots, and verify gas flow at the torch. Keep a maintenance log with dates and parts replaced so wear is tracked rather than discovered mid-job.
Ignoring fume control and ventilation because the shop door is open, welding in a confined area without extraction, or positioning the head directly in the plume.
GMAW fume contains metal oxides and ozone, and in confined spaces or on galvanised or painted metal the exposure is worse. Candidates underestimate cumulative exposure and rely on general dilution instead of local extraction.
What to do instead
Use local exhaust ventilation or a fume extraction torch where available, keep the head out of the plume and to the side of the arc, ensure general ventilation moves air across the work area, and use respiratory protection where assessment shows it is needed. For galvanised or coated metal, remove the coating from the weld zone first and increase extraction. Report symptoms such as metal fume fever and record ventilation checks.