The Common Arc Processes and What Each One Buys

Why this matters

Arc processes are usually taught as a list of names, which leaves a shop choosing whichever machine is on the truck. The processes actually differ along two axes only - where the shielding comes from and how the filler is delivered - and those two answers decide everything a shop cares about downstream: whether the process survives a breeze, whether it tolerates mill scale, whether it can be run overhead, and how much metal lands per arc-hour. Process selection is therefore a site-conditions decision before it is a quality decision, and a shop that gets the order backwards ends up screening a parking lot to protect a process it never needed.

Before an arc is struck, and the controls differ by process: every arc burns corneas and skin with ultraviolet at a distance, so screen the arc and use the minimum protective shade for the process and current from OSHA's filter-lens table at 29 CFR 1910.133(a)(5). Fume is an inhalation route in all of them and the load is not equal: self-shielded flux-cored wire puts substantially more fume in the breathing zone than gas-shielded solid wire on the same joint, because its shielding comes from consumed flux rather than from a bottle. Manganese from mild-steel consumables carries a ceiling limit in 29 CFR 1910.1000 Table Z-1 and stainless generates hexavalent chromium under 29 CFR 1910.1026 in general industry or 29 CFR 1926.1126 in construction; either needs local exhaust at the arc or a respirator issued under a written program meeting 29 CFR 1910.134. Grinding a thoriated tungsten electrode for gas tungsten arc work releases a radioactive dust and needs capture at the wheel or a substitute electrode type. Fire prevention, ignition control and the fire watch belong to the hot work permit and the hot work cards in this library, under 29 CFR 1910.252(a) or 29 CFR 1926.352 in construction.

The two axes that actually separate them

Where the shielding comes from. Either a bottle feeds gas through a nozzle, or a flux burns and decomposes to make its own gas and a slag blanket, or a granular flux is poured over the joint. Bottle gas gives the cleanest, most controllable atmosphere and the least tolerance for air movement. Flux-generated shielding is dirtier, leaves slag to remove, and does not care about a breeze.

How the filler arrives. Fed continuously by a wire drive, held as a consumed stick, or added by hand as a separate rod into an arc struck from a non-consumable electrode. Continuous feed buys deposition rate and arc-on time. A hand-fed rod buys independent control of heat and filler, which is what makes thin material and root passes possible.

The processes side by side

The site conditions that make the choice

Air movement at the arc. Gas-shielded processes are commonly derated above roughly 5 miles per hour of air movement at the joint, a figure about the gas column being stripped off the pool rather than about the welder feeling cold. It is a rule of thumb held at constant nozzle size and standard flow; a larger nozzle with a gas lens tolerates more, a long stickout tolerates less, and the coverage mechanics belong to the shielding-gas card. Above that point you either screen the work, change nozzle and flow together, or change to a flux-shielded process.

Surface condition. Mill scale, light rust and traces of oil are tolerated to very different degrees. Covered electrodes and flux-cored wires carry deoxidisers in the flux and cope with more than a solid wire does; gas tungsten arc copes with the least. That does not make cleaning optional on any process, it changes what happens when cleaning is imperfect, which in the field it always is.

Position. Out-of-position work rewards a process whose pool is small and fast-freezing, or one whose slag holds the pool up. This is where flux-cored wires with rutile-type cores earn their place and where spray-transfer solid wire is out of the running entirely.

Arc-on time. The share of an hour a welder spends with the arc lit is far lower than most shops assume. Manual covered-electrode work commonly lands around a quarter of the hour once stub changes, slag chipping and repositioning are counted; semi-automatic wire work commonly lands roughly twice that. That factor multiplies with deposition rate, and the product is what determines how long a run of weld takes.

The completed selection record

The artifact below is the whole procedure: a short record filled in before anyone opens a case. Every line is a site fact, not a preference, and the selection falls out of the lines above it.

Job: replace a corroded kick plate and reweld four support brackets on an exterior loading dock frame.

Gas-shielded processes eliminated on the wind line. The measured 8 mph at the joint is above the roughly 5 mph point at which gas shielding is commonly derated, so gas metal arc and gas-shielded flux-cored come off the list unless the dock face is screened. It is an open face on two sides, and screening it is a half-day of work against a wind that will change direction anyway.

Submerged arc and gas tungsten arc eliminated on position and rate. Submerged arc cannot hold flux overhead, and 10 of the 40 feet are overhead. Gas tungsten arc would run all 40 feet at a deposition rate that makes a 1/4 in fillet a multi-day proposition for no gain, since nothing here is thin or requires a root pass.

Selected: self-shielded flux-cored, with covered electrode as the fallback. Both survive the wind, so the comparison between them is throughput.

Throughput, computed, and what the ratio measures. Take the covered electrode as the baseline of 1.0 on both factors. Self-shielded flux-cored on this joint runs roughly 2 times the deposition rate and roughly 2 times the arc-on-time factor on the roughly-twice operator factor the section above gives, since there is no stub change and much less chipping. Multiply: 2 x 2 = 4 times the metal deposited per hour on site. That is arc-time throughput and nothing else. It is not a ratio of billable hours to effort hours, and it excludes the wire feeder setup and the fume control below.

Correction, printed: the fume control is not the same for the two candidates. The self-shielded wire's shielding comes from consumed flux, so its fume generation on this joint is materially higher than the covered electrode's. That re-bases the throughput finding rather than adding to it: the 4 times multiple was computed on arc time with fume control assumed present, so choosing the higher-fume process makes local exhaust at the arc a condition of the selection rather than an extra. The overhead 10 feet is where this bites, because the plume rises into the breathing zone by geometry.

Check against the sibling rules, with the figures printed. The shielding-gas card gives roughly 5 mph as the derate point for gas coverage; this record's wind figure is 8 mph, and the two gas-shielded processes are struck on that comparison rather than on a preference. The heat-input card states that arc energy is only comparable between procedures holding thickness and geometry constant; this record quotes no heat input and makes no cross-process energy comparison. The lack-of-fusion card names short-circuit solid wire as a fusion risk on heavy sections; solid wire is already off the list on the wind line, so that risk is not carried into the selection.

What would flip it. Move this job into a bay with the doors shut and the wind line disappears: gas-shielded flux-cored then wins on the same throughput arithmetic with a lower fume load, and the record changes on one line. Change the material to stainless and the whole record changes, because hexavalent chromium control under 1910.1026 becomes a condition of doing the work at all and self-shielded wire drops off on metallurgical grounds rather than on exposure grounds.

How to verify you picked on facts rather than on habit

• Did a measured site condition eliminate anything? If nothing was eliminated by a number, you did not select, you defaulted. The wind figure and the position split are the two lines that most often do real work.
• Is the process one your welders are qualified on for these positions? Qualification under AWS D1.1, in the edition the specification invokes, or under ASME Boiler and Pressure Vessel Code Section IX where the work is pressure-retaining, is process-specific and position-specific. A welder qualified on covered electrode is not thereby qualified on flux-cored wire.
• Does the fume control match the process you chose, not the process you usually run? Changing process changes the fume load without changing anything a supervisor can see. Re-check the control when the process changes.
• Did you compare arc-on throughput to arc-on throughput? Deposition rate alone flatters continuous-feed processes and operator factor alone flatters them again. The two multiply, and the product is still not a labour estimate.

References

• 29 CFR 1910 Subpart Q and 29 CFR 1926 Subpart J for welding and cutting; 29 CFR 1910.252(a) and 29 CFR 1926.352 for hot work fire prevention
• 29 CFR 1910.133(a)(5) for minimum protective filter shade; 29 CFR 1910.134 for respiratory protection; 29 CFR 1910.1000 Table Z-1 for manganese and zinc fume; 29 CFR 1910.1026 and 29 CFR 1926.1126 for hexavalent chromium
• ANSI/AWS Z49.1, Safety in Welding, Cutting, and Allied Processes, in the edition your employer's written program adopts
• AWS D1.1 structural welding code for steel, in the edition invoked by the project specification or the adopted building code, for process and position qualification
• See related: What Shielding Gas Is Doing and What Happens When It Stops; What Lack of Fusion Is and Why It Hides; What Heat Input Actually Controls