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A thin stainless steel T-joint looks simple, but it is one of the easiest TIG joints to overheat. The intersecting sheets create a corner that holds heat, while the small fillet weld has little metal available to absorb it. The result can be burn-through, distortion, sugaring on the backside, or a weld that looks clean but has barely fused the upright piece.
This method suits stainless sheet and tube roughly 0.8 to 1.5 mm thick. Thicker material allows more heat and a larger fillet; thinner material may need pulse control, copper backing, or a different joint design.
Materials and equipment
Use a DC TIG welder with high-frequency start and a foot pedal or fingertip amperage control. Stainless steel is welded with DC electrode negative (DCEN), not AC. Pure argon is the correct shielding gas; start around 15 to 20 cubic feet per hour (7 to 9 litres per minute), then adjust for drafts and cup size.
A small, gas-efficient torch is easier to control than a large torch on thin sheet. A gas lens and a 6 or 7 ceramic cup provide a stable shield with the tungsten held slightly farther away. A TIG gas lens kit is a worthwhile upgrade if your torch currently produces a narrow, turbulent gas stream.
Use 1.0 or 1.6 mm, 2% lanthanated tungsten, ground to a sharp point with the grinding marks running lengthwise. For common 304 stainless, use 308L filler. For 316 stainless, use 316L filler. Filler diameter should usually be 0.8 to 1.0 mm for thin sheet. Do not use carbon-steel filler, and avoid touching stainless with dirty tools that have been used on mild steel.
| Material thickness | Starting amperage | Tungsten | Filler |
|---|---|---|---|
| 0.8 mm | 25–40 A | 1.0 mm | 0.8 mm |
| 1.0 mm | 35–50 A | 1.0 or 1.6 mm | 0.8–1.0 mm |
| 1.5 mm | 50–70 A | 1.6 mm | 1.0 mm |
These are starting ranges, not guaranteed settings. Joint fit, torch angle, heat sinking, and travel speed can change the required amperage substantially. A TIG foot pedal is more useful than extra maximum amperage for this job because it lets you reduce heat at the end of each run.
Prepare and fit the joint
Cut both pieces square and remove burrs without rounding the edges. Clean at least 25 mm on either side of the joint with acetone or a dedicated stainless cleaner. Use a fresh stainless-only wire brush or abrasive pad. Wipe filler rod as well; oil and fingerprints can create porosity.
Set the upright sheet against the face sheet with the edges aligned. A tight, consistent fit is important. A gap larger than about 0.25 mm makes thin stainless much more likely to sag or burn through. Clamp the pieces to a copper, brass, or thick aluminum fixture when possible. The backing metal draws heat away and supports the root of the fillet.
Tack the joint at both ends and then add tacks every 25 to 40 mm on a longer seam. Keep tacks small and fully fused. Check squareness after tacking because stainless moves as it heats. If the joint pulls out of position, more clamps and shorter weld segments are better fixes than simply increasing amperage.
Set up the TIG welder
Set polarity to DCEN, post-flow to roughly 5 to 8 seconds, and start with a 1.0 to 1.5 second pre-flow. Set peak amperage near the upper end of the range, then control actual heat with the pedal. A 1.0 mm tungsten with a 15 to 20 mm stick-out and a medium gas cup is a practical starting setup.
Pulse can help, but it is not a substitute for good travel speed. Try 1 to 2 pulses per second with a peak current near your normal welding current and a background current around 30 to 50 percent of peak. Use a short peak time, such as 20 to 35 percent. Some welders produce a smoother bead without pulse, particularly on a short fillet, so compare both on scrap.
Make a practice T-joint from the same thickness and test your settings. The aim is a small, even fillet with fusion into both pieces—not a tall bead sitting on top. For a 1 mm sheet, a fillet around 1 to 1.5 mm is often adequate. Oversized fillets add heat and distortion without automatically adding strength.
Welding technique
Hold the torch about 70 to 80 degrees to the face sheet, with the tungsten aimed into the corner but not touching either wall. Keep the arc short, usually 1 to 1.5 mm. Point the torch slightly toward the direction of travel and keep the filler rod low in the front edge of the molten puddle.
Start on a tack and establish a small puddle on both pieces before adding filler. Feed tiny amounts of rod—roughly 0.5 to 1 mm at a time—then move forward. Do not dab large amounts of filler into a cold joint. Travel quickly enough to keep the puddle small, but pause just long enough at each wall to ensure sidewall fusion.
Weld in short 25 to 50 mm sections, alternating sides or allowing the joint to cool until it can be touched with a gloved hand. For a long seam, skip around rather than running continuously from one end. Keep the torch moving after releasing the pedal so the post-flow shields the cooling tungsten and weld crater.
If the design permits it, weld only the required length instead of automatically welding the entire joint. Intermittent welds reduce distortion and heat input, but they are unsuitable where the joint must be sealed or where a drawing specifies a continuous weld.
Inspect and fix common problems
A good weld is smooth, consistently sized, and lightly straw-colored at most. Bright silver is better. Dark gray, blue, or black oxidation means excessive heat, poor shielding, contamination, or drafts. Discoloration should be removed with stainless-only abrasive methods or an appropriate chemical passivation process; do not leave heavy oxide on a corrosion-sensitive joint.
| Problem | Likely cause | Correction |
|---|---|---|
| Burn-through | Too much heat, excessive gap, slow travel | Lower current, use backing, tighten fit, shorten welds |
| Bead sitting on one wall | Arc aimed away from the cold piece | Center the puddle and pause briefly on both walls |
| Black or gray weld | Poor gas coverage or contamination | Check leaks, cup, flow, drafts, cleaning, and post-flow |
| Warped joint | Continuous welding and oversized fillet | Use more tacks, shorter sections, lower heat, and clamps |
| Porosity | Oil, moisture, dirty filler, or gas turbulence | Reclean everything and reduce excessive gas flow |
Safety and finishing
Wear a properly rated TIG helmet, gloves, nonflammable clothing, and eye protection while grinding. Stainless welding fumes can contain hazardous compounds, so use local fume extraction and avoid breathing the plume. Argon can displace oxygen in small spaces; never weld in an enclosed area without verified ventilation and an appropriate confined-space procedure. A welding fume extraction setup is preferable to relying on a shop fan that simply moves contamination around.
After welding, remove heat tint and sharp edges. Inspect both legs of the fillet and, when accessible, the backside. If the joint will hold liquid, pressure, or structural load, visual inspection alone is not enough; use the specified leak or nondestructive test. The cheapest TIG machine can make this weld if it has stable low-amp control, but a pedal, clean gas delivery, and disciplined fit-up usually matter more than a higher advertised maximum amperage.