How to weld stainless steel: TIG, purge and cleaning

Free guide · The Welder's Forge · updated September 2026

Austenitic stainless steel, the kind in commercial kitchens, handrails and food equipment, welds well. What differs from mild steel is that stainless does not forgive dirt, reacts badly to oxygen on the back side of the joint and warps easily. Control those three things and the weld comes out clean and keeps its corrosion resistance.

Why TIG is the preferred process

TIG gives clean beads with no spatter and no slag, and full control of the puddle. It is the process of choice for food and pharmaceutical stainless, where finish and corrosion resistance matter. It runs on DCEN (electrode negative): about 70% of the heat goes into the work, with good penetration and long tungsten life.

The tungsten is ground to a point. Types and grinding are in tungsten electrode colors; the base technique is in TIG welding for beginners. Match the filler to the grade: a 308L-type rod is the usual match for 304, and 316L for 316. Confirm with the filler maker's data.

TIG is not the only option. Pulsed MIG does well on stainless, flux-cored wires and stick electrodes made for stainless exist too, and AWS D1.6 is the structural welding code for stainless steel. But if you want first-rate finish, TIG is the way.

Where stainless sits among steels

Table 11.1 of the e-book The Welder's Forge (excerpt).

Purging the root: stop the "sugaring"

When you weld stainless tube or a vessel, the inside face of the joint (the root) is exposed to air. Heat and oxygen oxidize it hard: the root turns dark, rough and crusty, like burnt sugar. This is sugaring, and it ruins the corrosion resistance that is the whole reason for using stainless.

The cure is a purge: fill the inside with inert gas, usually argon, before and during the root pass.

1. Cap the ends of the tube, leaving one gas inlet and one small outlet vented to open, ventilated air.
2. Let argon flow long enough to push the air out.
3. Confirm with an oxygen monitor: the level must be below 50 ppm before you start the root.
4. On critical piping, the level should be below 20 ppm.

Purge values from section 5.4 of the e-book The Welder's Forge.

Controlling warping

Austenitic stainless expands more and conducts heat worse than mild steel. Heat stays near the bead and, as it cools, pulls the part out of shape. That is why Table 11.1 lists distortion control as the main precaution.

• Clamp parts firmly before welding. A copper backing bar helps pull heat away from thin sections.
• Tack often, with short tacks close together.
• Alternate sides and spread beads around the part.
• Use the lowest current that still fuses, and never dwell in one spot. Pulsed current lowers average heat input. For a starting current, see the TIG welding amperage chart; stainless often runs a little lower than mild steel of the same thickness.
• Let the part cool between passes on thick sections.

Cleaning: do not contaminate the stainless

• Use brushes and discs used only on stainless. A brush that has touched mild steel leaves iron particles that later turn into rust spots.
• Degrease the joint and the filler rod before welding.
• Wear clean gloves: thin goatskin TIG gloves give feel on the rod and keep oils off the metal.
• Heavy straw-to-blue heat tint, or dark gray oxide, means too much heat or poor gas coverage. Pickling and passivation products restore the surface; follow their safety data sheet.

If your bead shows pinholes, discoloration or cracks, compare it to the pictures and causes in common welding defects and how to fix them. Anything that carries a load or holds pressure deserves a qualified procedure and a qualified welder, not just an article.

Frequently asked questions