TIG welding gas: what to use, and how much
Which shielding gas TIG welding needs, how much of it, and when helium or a purge gas earns its place — plus what never belongs on a TIG torch.
Every TIG weld sits under a shield of gas, and the choice is narrower than the gas rack suggests. For almost all work the answer is pure argon. What actually needs deciding is how much of it, when something other than argon earns its place, and where a second supply is needed on the back of the joint.
Why TIG needs an inert gas at all
The I in TIG stands for inert, and that is the whole requirement. A tungsten electrode runs at temperatures where it will happily combine with oxygen — an unshielded tip oxidizes within seconds and stops conducting properly. The molten pool behaves the same way: exposed to air, it takes up oxygen and nitrogen and solidifies porous and brittle.
Other processes solve this differently. Stick and flux-cored wire carry their own flux, which burns to form a protective slag and gas. TIG has neither. The gas is the entire shielding system, which is why it is worth getting right.
That also explains why the gas that works beautifully on a MIG torch ruins a TIG weld — more on that below.
Argon: the default, and usually the answer
Welding-grade argon at 99.996% purity (grade 4.6) covers the overwhelming majority of TIG work — carbon steel, stainless, aluminum, nickel alloys, copper, titanium. It is fully inert, heavier than air so it blankets the pool rather than drifting off it, and it ionizes at a low enough voltage to make arc starting easy and the arc stable at low current.
For reactive metals — titanium, zirconium, tantalum — step up to 99.999% (grade 5.0). Those metals take up whatever the shield lets through, and the difference between 4.6 and 5.0 is the difference between a silver weld and a scrapped part. The same applies to the purge on the back side.
One thing argon is not: a cleaning agent. It protects what is already clean. Oil, moisture, mill scale, and oxide have to come off before the torch arrives, whatever gas is in the bottle.
How much gas — flow rate
Too little flow leaves the pool exposed. Too much is worse than people expect: past a certain point the stream turns turbulent, drags surrounding air into the shield, and produces exactly the contamination the gas was meant to prevent.
A widely used starting point is roughly twice the cup number in cubic feet per hour:
| Cup size | Starting flow |
|---|---|
| No. 6 | 5–6 l/min |
| No. 8 | 7–8 l/min |
| No. 10 | 9–11 l/min |
| No. 12 | 11–14 l/min |
Four things push the real figure away from the table:
- A gas lens smooths the flow and usually lets you run less gas while shielding a wider area — often the single cheapest improvement to a TIG setup.
- Drafts. An open shop door will strip a shield that works perfectly on the bench. Screen the work rather than turning the flow up.
- Position. Overhead and vertical work lose gas that flat work keeps.
- Post-flow. The gas has to keep running until the tungsten and the crater have cooled. A second per 10 A of welding current is the usual rule; on titanium, considerably longer.
Whatever the table says, a qualified procedure governs. On code work the WPS specifies gas and flow, and that is the number that counts.
When helium earns its place
Helium has a higher ionization potential than argon, which means a hotter arc at the same current — more penetration, faster travel, a broader bead. It is the standard answer for two situations:
- Thick aluminum and copper, where argon alone cannot get the heat in fast enough before it conducts away.
- Mechanized welding, where the extra travel speed pays for the gas.
It has real drawbacks. Helium is lighter than air, so it needs roughly two to three times the flow to maintain the same shield, and it costs considerably more. Arc starting is harder, and the arc is less forgiving at low current.
Most shops that use it do not use it neat. Argon-helium mixtures — commonly 25 to 75% helium — give part of the heat benefit while keeping argon’s easy starting and lower flow.
A third option shows up on austenitic stainless: argon with up to about 5% hydrogen. It runs hotter and cleaner and lets the weld move faster. It is strictly limited: never on carbon steel, duplex, martensitic stainless or titanium, where hydrogen causes cracking and embrittlement.
The gas on the other side: backing and purge
On a full-penetration weld the root sees the same air the face does. Two material groups make a back purge non-negotiable:
- Stainless steel and nickel alloys, where an unpurged root oxidizes into what the trade calls sugaring — a rough, dark, corrosion-prone surface that no amount of face-side technique fixes.
- Titanium, where the requirement is stricter again and the trailing shield matters as much as the purge.
Purge with argon, and displace the air properly before striking the arc. For stainless root passes the usual target is oxygen below about 50 ppm in the purge volume; on titanium, lower still. An oxygen meter is worth more than guesswork here — the color of the finished root tells you afterwards what you should have known before.
For pipe, an inflatable or mechanical purge dam keeps the volume small. Purging an entire length of pipe to clean out one joint wastes an extraordinary amount of gas.
What never belongs on a TIG torch
- CO₂. It dissociates in the arc and releases oxygen, which attacks the tungsten and contaminates the pool.
- Argon-CO₂ and argon-oxygen mixes. These are MIG gases. The small oxygen additions that stabilize a MIG arc destroy a TIG electrode.
- Nitrogen as a shielding gas. It is not inert towards most weld metals; it is used as a backing gas in some duplex procedures, which is a different job entirely.
- Industrial or balloon-grade argon. The purity is not specified for welding, and the moisture content shows up as porosity.
The TIP TIG angle
TIP TIG is a hot wire TIG process, and it runs on the same shield as any other TIG work: 100% argon, on every weldable metal — carbon and stainless steels, duplex, nickel alloys, titanium, aluminum, copper. There is no special mixture to buy and no change to the gas rack.
Where it differs is consumption. Because the process welds substantially faster, the arc is open for less time per meter of weld, and less gas goes into the same joint. In the keyhole variant, which fuses the full thickness in a single pass instead of building a multi-pass groove, gas use drops to a fraction of the conventional figure — there are simply fewer passes to shield.
In short
Pure argon at 99.996% answers nearly every TIG question; go to 99.999% for titanium and other reactive metals. Set the flow from the cup size, then correct for gas lens, drafts, and position — and remember that too much flow contaminates as surely as too little. Add helium when you need heat that argon cannot deliver, and a little hydrogen only on austenitic stainless. Purge the back of any full-penetration weld in stainless, nickel alloys or titanium. And keep the MIG gases on the MIG machine.