TIG Welding Troubleshooting

TIG Problems Quick Answer

Use this chart when the tungsten, puddle, or tint looks wrong and you want the first fix fast.

1. Tungsten Contamination

What it looks like: Tip turns grey, black, or glassy. Arc gets wide and fuzzy. Beads show tungsten inclusions (hard bright specks on a ground section) or a dirty, sputtering start. On aluminum AC, the ball grows oversized, lopsided, or “flowers” instead of a clean shiny hemisphere.

Why it happens (TIG-only mechanics): The electrode is non-consumable. The instant the tip dips into molten pool — or filler rod touches the tip — base metal alloys contaminate the tungsten. Contaminated tips emit electrons poorly, so the arc wanders and spatters oxide into the puddle. Overheating an undersized electrode (amps above diameter rating) melts the tip the same way.

Visual diagnosis:

• Grey / blackened tip after one bad dip — puddle contact or filler kiss. Cut back and re-prep.
• Purple / blue heat tint far up the electrode — stickout too long, post-flow too short, or amps too high for diameter.
• AC ball oversized or mushroomed — too much electrode-positive (EP) cleaning, or tungsten too small for amps. Not the same as MIG burn-back into a contact tip.
• Point melts into a blob on DC steel/stainless — grinding crosswise, wrong polarity (should be DCEN), or diameter undersized for amps.

Fixes:

• Stop the weld. Break off the contaminated tip past the dirty zone — do not “polish over” contamination.
• DC (steel/stainless): grind a fresh longitudinal point on a dedicated tungsten grinder; never grind across the axis.
• AC (aluminum): re-square or lightly blunt, then let AC form a controlled ball; dial EP down if the ball keeps growing.
• Match tungsten diameter to amps with the TIG calculator. Bump diameter before you bury an undersized tip in the puddle.
• Widen torch-to-work and rod technique so the filler enters the front of the puddle without tagging the tip.

2. Arc Wander / Arc Instability

What it looks like: Arc walks off the joint line, flares to one side of the cup, stutter-starts, or “breathes” wider and narrower without you changing torch height. On AC aluminum, the arc may scrub oxide on one edge of the joint and ignore the other.

Why it happens: TIG concentrates the arc at a prepared tip geometry. Cross-ground tungsten, contamination films, magnetized fixtures, and AC balance that is too soft on EP all widen or deflect that focus. High-frequency or Lift-arc start problems leave you dragging a cold tip until the arc finally grabs.

Likely causes checklist:

• Tungsten ground across the grain or with a blunt, ragged tip for DC work
• Contaminated tip from a prior dip (see above)
• AC balance set with too little EN (soft, wide cleaning arc) or unstable frequency for the joint
• Excessive arc length — torch lifted so the arc balloons inside the cup
• Work clamp far away or on painted/oxidized metal so return path squirms

How to fix it: Re-prep the electrode correctly for polarity. Keep a tight, visible cone under the cup. On aluminum, add a little EN if the arc is washing too wide, or add a little EP if oxide film remains — small steps. Degauss large fixtures if the arc consistently pulls toward one clamp or steel table edge. Settings charts for aluminum balance live in the aluminum TIG guide.

3. Heat-Affected Zone Discoloration (Stainless & Aluminum)

What it looks like:

• Stainless: straw → blue → purple → grey/black HAZ bands; worst case root “sugar” (crumbly oxidized ID on pipe/tube).
• Aluminum: dull grey or black soot veil beside the bead, frosty oxide that never wet into a mirror puddle.

Why it happens: TIG uses inert gas only — no slag blanket. When the cup envelope is broken (bad angle, wind, too-small cup, CFH too high or too low) or you dwell hot and slow, chromium and aluminum oxidize in the HAZ. Pipe without backpurge oxidizes the root while the face still looks acceptable.

Fixes:

• Use a larger gas lens / cup for stainless and aluminum when reach allows; keep a short stickout.
• Set CFH for the cup (often 15–20 CFH on small cups; more on large lenses) and confirm post-flow covers the cooling tip and puddle. Use the shielding gas flow calculator.
• Torch angle ~15° or less off vertical; push gently — extreme travel angles blow gas off the puddle.
• Travel fast enough to limit HAZ width; pulse or pedal down on thin stainless instead of parked high amps.
• Stainless pipe/tube: purge the ID to low O₂ before the root pass — sugar means purge failure, not “need more face amps.” Details: stainless TIG guide.

4. Foot Pedal / Amperage Control Issues

What it looks like: Penetration jumps thick-to-thin along one pass. Starts under-fused, middles blow through, ends crater-crack. Sound of the arc rises and falls with ankle jitter, not with the joint. Hand-remote users get similar “pumping” if they feather the knob mid-puddle.

Why it happens: TIG expects continuous amp modulation. The machine’s panel max is a ceiling — the pedal is the actual heat. Late pedal ramp dumps full amps into a cold start; early drop freezes the pool mid-joint; laggy or sticky pedals make you overshoot while waiting for heat.

Fixes:

• Set panel amps slightly above the calculated need, then live in the mid-pedal band where you have room up and down. Get the number from the TIG calculator.
• Practice a repeatable ramp: torch in position → pre-flow → ramp in on scrap of the same thickness → feather to maintain a wet dime → slope out into a crater fill.
• If the machine has slope/crater settings, use them for ends so you are not exclusively relying on a twitchy ankle finish.
• Inspect pedal: sticky pots and damaged cables feel like “heat lag.” Swap pedals on shop machines before blaming your technique.

5. Weld Puddle Contamination from Filler Rod Technique

What it looks like: Each time you dab filler, the puddle flickers dirty, leaves a dark streak, or pops a string of pores. The rod tip looks black/crystallized. Aluminum rods form a sooty ball; stainless rods get a crusty oxidized tip that refuses to wet.

Why it happens: MIG feeds wire inside the shielding continuously. TIG filler spends time outside the envelope. If you withdraw the rod into shop air while it is still molten, the tip oxides — and the next dip dumps that oxide into the puddle. Touching the tungsten transfers tip metal; stirring slaggy oxide from dirty plate does the same.

Fixes:

• Keep the hot rod tip inside the gas cone between dabs — “in the shadow of the cup.”
• Clip off any oxidized tip before you re-enter; store aluminum rods sealed and wipe stainless with acetone.
• Dip into the leading edge of the puddle — do not jab the crater under the tungsten.
• If contamination started from a tungsten kiss, re-prep the electrode before more filler dabs. Contaminated tungsten will keep re-poisoning every dab.
• → TIG Tungsten Electrode Selector
• → TIG Tungsten Electrode Guide
• → TIG Tungsten Troubleshooting
• → Which Tungsten Type to Use

6. Porosity Specific to TIG

What it looks like: Surface pinholes, elongated worm tracks, or subsurface pores on a break or grind. On stainless pipe, face looks fine while the root is porous or sugared.

Why TIG porosity is different from MIG: There is no slag system and no continuous wire feed. Coverage lives or dies on cup geometry, CFH, draft control, post-flow, base-metal cleanliness, and — on closed sections — backpurge integrity. Wind that MIG sometimes “fights through” with higher CFH will strip a TIG envelope instantly. Moisture or oily fingerprints that a flux-core rod might tolerate will seed pores under argon.

Cause → fix:

• Draft / fan / open door: block air or use a gas lens and larger cup; raise CFH carefully without creating turbulence.
• Cup / nozzle issues: cracked cups, spatter-packed lenses, and huge stickout beyond the envelope.
• Contamination: mill scale, oil, paint, shop grit — clean to bright metal; dedicated stainless brush for SS and aluminum.
• Backpurge failure (pipe/tube stainless): purge plugs leaking, O₂ too high, purge killed too early — fix purge before stacking cover passes.
• Leaks upstream: torch gasket, hose fittings, empty cylinder — verify gas at the cup with a quick pre-flow feel/test.

Related calculator: Shielding Gas Flow Rate Calculator