Tungsten Inert Gas (TIG) welding is prized for clean, precise welds — but it’s also unforgiving. Small mistakes in gas, torch handling, cleanliness, or machine settings show up immediately in the bead. Below is a practical, engineer-friendly guide to the ten most common TIG problems, why they happen, and how to fix them. At the end you’ll find a short testing checklist and FAQs to help you verify weld quality. (Sources for the technical guidance and testing methods are listed inline.)
Quick overview — the 10 problems:
Poor gas coverage (porosity / contamination)
Wrong polarity or balance when welding aluminum
Grainy or contaminated bead (filler/base contamination)
Lack of fusion (insufficient root penetration)
Craters and crater cracking at weld stop points
Dirty base metal or filler rod contamination
Tungsten contamination or balling
Overheating / burn-through on thin materials
Excessive weld color / oxidation (stainless & aluminum)
Arc wandering or unstable arc (poor arc control)
The list above consolidates common field failures and remedies recommended in industry TIG guides and equipment application notes.
I. For each problem: what to look for and how to fix it
1) Poor gas coverage (porosity, surface contamination)
What you’ll see:
Tiny pinholes or bubbles in the weld bead
Dull gray surface or soot on stainless/aluminum
Arc flickering or unstable
Why it happens:
Incorrect shielding gas or flow rate
Gas leaks at fittings or torch connections
Drafts or excessive gas velocity causing turbulence
Damaged torch components (cracked cup, loose collet body)
Detailed Fix:
Check gas type: Use 100% Argon for TIG on steel, stainless, and aluminum. Helium or Ar/He blends can help for thick aluminum but are unnecessary for most work.
Adjust flow rate: 12–20 CFH is typical for indoor TIG. Too low → porosity; too high → turbulence. For open areas or large nozzles, increase slightly to 20–25 CFH.
Leak test your gas line: Apply a mild soap-water mix at hose joints, regulator, and torch connections. Look for bubbles.
Inspect torch parts: Replace worn O-rings, cracked cups, or bent back caps. Ensure collet body threads are tight.
Shield the weld zone: Block fans or drafts. If outdoors, use barriers or a temporary enclosure.
Post-flow timing: Set 5–10 seconds of post-flow (longer for thicker tungsten). This protects both tungsten and weld pool while cooling.
2) Welding aluminum with wrong polarity / balance
What you’ll see:
Black soot, oxide “islands,” or dull surface
Poor wetting and inconsistent puddle
Tungsten overheating or excessive balling
Why it happens:
Detailed Fix:
Set correct polarity: For aluminum → AC (alternating current); For steel/stainless → DCEN (direct current electrode negative).
Adjust AC balance: Start around 70% EN / 30% EP (Electrode Negative / Positive); Increase EP to 35–40% if oxide remains; Reduce EP if tungsten overheats or balls excessively.
Fine-tune AC frequency: 100–120 Hz gives a narrower, more stable arc for fillet welds; 60 Hz gives a softer, wider arc for thick materials.
Pre-clean aluminum: Remove oxide layer using a stainless brush or mechanical abrasion immediately before welding.
Use proper tungsten: 2% lanthanated or ceriated (blue or gray tip) holds shape better on AC.
3) Grainy / inconsistent bead (filler-metal or feed issues)
What you’ll see:
Why it happens:
Detailed Fix:
Clean filler rods: Wipe with acetone before use; store rods in sealed tubes to prevent oxidation.
Check filler alloy: Match to base metal — e.g., ER70S-2 for mild steel, ER308L for stainless, ER4043 or ER5356 for aluminum.
Feed technique: Feed filler gently into the front edge of the puddle, not directly into the arc. Keep filler tip inside the gas shield.
Control heat input: Overheating creates grainy texture; lower current or increase travel speed slightly.
Arc length: Keep arc tight — about 1–1.5× tungsten diameter away from the puddle.
4) Lack of fusion (root or toe lack of penetration)
What you’ll see:
Why it happens:
Detailed Fix:
Increase amperage: For mild steel, use ~1 amp per 0.001" of thickness as a baseline. Example: 120 A for 1/8" steel.
Shorten arc: Maintain 1–2 mm between tungsten and puddle for a focused, penetrating arc.
Adjust torch angle: Keep 10–15° push angle; direct more heat into thicker material if joint is uneven.
Improve joint fit-up: Bevel thick joints; maintain tight, consistent root gaps.
Use pulse TIG (if available): Set pulse frequency 1–2 Hz for manual control; 30–100 Hz for thin materials to limit heat and improve fusion.
Clean base material: Grind off oxides or coatings that block fusion.
5) Craters and crater cracking at weld stops
What you’ll see:
Why it happens:
Detailed Fix:
Taper current: Use foot pedal or crater-fill function to ramp down current gradually over 2–3 seconds.
Feed filler until crater fills: Keep adding filler while current tapers down; finish slightly above surface.
Overlap weld stop points: When resuming, start a few mm ahead of the crater and backtrack briefly.
Set crater-fill function (if available): Some TIG machines can automatically reduce current at the end of the weld.
Check gas post-flow: Longer post-flow (7–10 s) helps prevent oxidation during cooling.
6) Dirty base metal or contaminated filler metal
What you’ll see:
Why it happens:
Oils, rust, moisture, paint, or oxide contamination
Contaminated filler rods or dirty gloves
Detailed Fix:
Clean before welding: Steel: Degrease → grind → acetone wipe; Stainless: Wire brush (dedicated stainless brush only); Aluminum: Acetone → mechanical oxide removal → immediate weld.
Keep filler rods clean: Store rods in dry, sealed tubes or hangers. Never touch filler tip with bare hands.
Protect tungsten and filler: Keep both inside the gas shield during welding; avoid touching the tungsten to molten pool or filler.
If contamination occurs: Stop, break off the filler, grind the tungsten, and restart clean.
7) Tungsten Contamination or Over-Balling
What you’ll see:
Why it happens:
Tungsten dipped into the puddle or touched filler
Too much EP (electrode positive) on AC
Wrong tungsten size for amperage
Detailed Fix:
| Current (A) | Tungsten Ø (mm) |
|--------------|----------------|
| 50–100 A | 1.6 mm |
| 100–200 A | 2.4 mm |
| 200–300 A | 3.2 mm |
Correct contamination: Stop immediately, break the arc, cut off 5–10 mm of contaminated tungsten, and regrind.
Lower EP balance on AC: If tungsten balls rapidly, reduce electrode positive portion to ~25–30%.
Use proper tungsten type: Lanthanated or ceriated electrodes stay sharper and resist contamination.
8) Overheating / burn-through on thin materials
What you’ll see:
Why it happens:
Excess current
Slow travel
Poor heat dissipation
Detailed Fix:
Reduce current: For 1 mm stainless sheet, stay around 35–45 A; for 2 mm, 55–70 A.
Increase travel speed: Keep the puddle small — move steadily, not hesitantly.
Use pulse TIG: Set peak 1.0× base current, base current 30–40% of peak, pulse frequency 30–100 Hz. This lowers average heat input.
Add backing plate: Clamp workpiece to copper or aluminum plate to dissipate heat.
Skip welding technique: On long seams, weld short sections (1–2 in.) alternating sides to reduce heat buildup.
9) Excessive weld color / oxidation (esp. stainless & aluminum)
What you’ll see:
Brown, blue, or gray discoloration
Loss of corrosion resistance
Dull, oxidized bead edges
Why it happens:
Insufficient shielding during cooling
Too much heat input or poor post-flow
Contaminated or turbulent gas
Detailed Fix:
Optimize gas shielding: Increase post-flow 7–15 seconds. For long beads, use a trailing shield or gas lens.
Reduce current or travel faster: Too much heat = more oxidation.
Back purge stainless tubing: Use argon purge on root side to avoid sugar (oxidation inside).
Use gas lens setup: Improves laminar gas flow and reduces discoloration.
Post-weld cleaning: Stainless: Use passivation or pickling paste to restore corrosion resistance; Aluminum: Use mechanical cleaning if oxide forms.
10) Arc wandering / unstable arc
What you’ll see:
Why it happens:
Improper tungsten grind or shape
Long arc length
Gas turbulence or magnetic arc blow
Contaminated work clamp connection
Detailed Fix:
Grind tungsten tip axially: Grind lengthwise (not sideways) to maintain arc focus.
Keep arc short: 1–2 mm from puddle; longer arcs reduce focus.
Inspect ground clamp: Ensure clean contact with bright metal — no paint, rust, or grease.
Check for drafts: Wind or fans cause arc instability; block airflow.
Use gas lens: Improves arc stability and focus for thin joints.
If arc still unstable: Verify machine’s HF start and current control circuit — faulty spark gap or inverter board can cause erratic arc starts.
II. Quick Reference Table — Problem & Fix Summary
| Problem | Common Cause | Field Fix Steps |
|---|
| Poor gas coverage | Wrong gas, leaks, turbulence | Use 100% Argon, 15–20 CFH, leak test hoses, block drafts |
| Wrong polarity | DC used on aluminum | Switch to AC, 70/30 balance, clean oxide |
| Grainy bead | Dirty filler / overheat | Clean filler, shorten arc, steady feed |
| Lack of fusion | Low heat / poor angle | Increase current, shorten arc, use pulse |
| Crater cracks | Abrupt stop | Taper current, fill crater, overlap ends |
| Dirty base metal | Oil / rust / oxide | Grind, degrease, acetone, stainless brush |
| Tungsten issues | Tip dip / too much EP | Regrind tungsten, reduce EP, use lanthanated |
| Burn-through | Too hot / slow | Lower amps, pulse mode, copper backup |
| Oxidation | Poor post-flow | Increase post-flow, gas lens, clean finish |
| Arc wander | Long arc / turbulence | Grind tip axially, short arc, clean ground |
III. How to Test Your TIG Welds for Quality
After fixing visible issues, test weld integrity using these quick and formal methods:
Visual Inspection: Look for uniform bead width, smooth ripples, no porosity, consistent color.
Penetrant Test: Apply dye penetrant, wipe off, and develop to detect surface cracks or pores.
Bend or Break Test: For sample welds — check if the bead cracks or delaminates under bend.
Radiography or Ultrasonic Test: For structural or pressure welds, these methods detect internal flaws or lack of fusion.
Macro Etch Test: Cross-section a weld and polish/etch to visually inspect penetration and fusion.
IV. Welding best-practice checklist (pre-weld & post-weld)
Confirm joint fit-up and root gap.
Clean base metal and filler rods; keep consumables dry.
Verify shielding gas type and flow; check for leaks.
Set machine mode and polarity according to material (AC for aluminum with correct balance).
Match electrode size/type to current and workpiece thickness.
Use consistent torch angle and maintain steady filler addition.
Observe starts/stops carefully; use crater-fill features or manual taper.
Inspect visually immediately and sample test per quality plan.
V. FAQs (short, practical answers)
Q: What shielding gas should I use for TIG?
A: For most steels and stainless: 100% argon. For thicker aluminum you can use argon/helium blends to increase heat. Avoid CO₂ mixes used for MIG. Always confirm the gas per procedure.
Q: My aluminum weld has black specks — what caused it?
A: Those are often oxide or contamination. Ensure AC balance is set to provide enough cleaning (electrode positive) and that the parts and filler are clean and dry.
Q: How do I stop crater cracking?
A: Either use a machine crater-fill function, reduce current slowly at the end, or keep adding filler while tapering current; alternatively add a short stitch pass to fill the crater.
Q: Quick test to know if my shielding gas is OK?
A: Soap-water leak check on hoses and fittings, and watch for visual signs (porosity, gray bead). If everything else is correct, try a brief increase then decrease of flow to see the bead change — turbulence at too-high flow will worsen results.
Q: Which NDT should I use for production verification?
A: Start with visual and penetrant for surface defects. For internal flaws or safety-critical parts use ultrasonic testing or radiography as dictated by your code or quality plan. Develop a sample plan with periodic NDT for batches.
Conclusion — build these controls into production
Prevention beats repair. Put these items into your welding procedure (WPS) and operator checklists: gas flows, electrode specs, polarity/machine modes, cleaning steps, and end-of-weld technique. Train operators on what a “good puddle” looks like and how to adjust AC balance for aluminum. When product safety or certification matters, write an NDT sampling plan and include destructive tests for initial qualification.
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1. TIG Welding: A Guide to Top-Quality Connections
2. MIG/MAG, MMA, TIG Welding: Choosing the Right Technique
3. MIG VS TIG Welding: What are the Differences?
4. TIG Welding Stainless Steel: A Beginners Guide
5. TIG Welding: What is Scratch-Start, Lift-Arc and HF Ignition?
