TIG Welding Troubleshooting: Problems, Causes & Fixes

You spend twenty minutes cleaning the joint, dial in what looks like the right amperage, strike the arc, and the puddle still wanders, sputters, and leaves a grey porous bead that no amount of grinding will excuse. Almost every TIG problem looks like a machine fault but usually traces back to one of three things: a contaminated surface, a lost gas shield, or a wrong setting.

Why TIG Welding Troubleshooting Starts Before the Arc

It only takes one bad bead to learn a hard lesson. Imagine a small fabrication job: 1.5 mm stainless sheet for a food-processing enclosure. The joint is deburred, wiped with acetone, the machine is set for 45 amps on DCEN, argon is open to around 15 CFH, and the arc is struck. For a couple of inches, the puddle looks perfect. Then it starts to sputter. By the end of the run, the bead is grey, peppered with pinholes, and the trailing edge has a sugary, frosted look.

The immediate reaction for many is to blame the power source. However, the real culprit was a cracked hose fitting behind the machine, leaking argon before it ever reached the cup. The machine was working exactly as it should. This is the exact reason that tig welding troubleshooting is its own skill, separate from simply laying a bead.

The Nature of TIG Leaves Nowhere To Hide

TIG, or GTAW (Gas Tungsten Arc Welding), is known for its precision. The tungsten electrode doesn’t melt into the puddle, carrying only current to maintain the arc. Any filler used is fed by hand separately, and the entire weld pool relies on a blanket of shielding gas for protection. As Miller’s TIG basics guide states, this makes it one of the cleanest and most controllable arc processes, which is why it’s used for thin stock, cosmetic work, and critical alloys.

With that level of cleanliness comes little mercy. Unlike stick welding with its slag, or MIG and flux-cored with their consumable shielding, TIG produces no covering to hide imperfections. Every pore, discoloration, or break in fusion is visible the moment it forms. This is also why, as noted by OSHA’s welding safety guidance, GTAW generates some of the lowest fume levels of the common arc processes, as there is no consumable being burned off into the plume.

The Three Root-Cause Families

With time, nearly every TIG issue falls into one of three categories:

• Contamination: Oil, mill scale, oxides, moisture, paint, a greasy filler rod, or even a finger print on tungsten can all be pulled into the puddle.
• Shielding loss: Argon not reaching the weld, or being disrupted. This can come from an empty cylinder, a leak, incorrect flow, an oversized cup distance, a damaged O-ring, or even a draft from an open bay door.
• Incorrect settings or technique: Wrong polarity, improper amperage, an arc that is too long, incorrect travel speed, poor torch angle, the wrong tungsten preparation, or untimely filler addition.

Know The Difference Between Defects and Faults

Before troubleshooting anything, it’s important to split the problem into two groups. A weld defect is a discontinuity found in or on the finished weld, such as porosity, lack of fusion, undercut, inclusions, or a crater crack. A machine fault, on the other hand, is when the equipment itself isn’t performing to its settings. This could be a gas solenoid failing to open, a pedal with a dead spot, a rectifier losing current, or a high resistance ground path.

Defects are typically corrected with prep, torch angle, and technique. Faults require testing with a multimeter and replacement parts. The most common pitfall is assuming a defect is a fault, simply because it’s an easier problem to point to than one’s own technique.

A Diagnostic Order That Saves Time

To avoid chasing multiple issues at once, follow this fixed order from evidence to source:

1. Look at the bead. Pay attention to color, texture, porosity patterns, and the toe line. These are your first clues.
2. Check the gas. Verify cylinder pressure, valve position, flow meter, hoses, the cup and diffuser for damage or debris, and that post-flow is actually running.
3. Check the tungsten. Look for contamination, balled ends, burrs, incorrect grind angle, wrong diameter, or the wrong alloy for the material.
4. Check the settings. Confirm polarity, amperage or pedal range, and if applicable, AC balance, frequency, pre-flow, or post-flow times.
5. Check the technique. Assess arc length, travel speed, push or drag, stickout, filler timing, joint fit-up, and overall cleanliness.

For aluminium in particular, this order will almost always lead back to the first and final steps. Its tenacious oxide film will ruin a weld before any amperage can compensate, which is why thorough prep is non-negotiable. More details on this can be found in our Aluminum Cleaner for Welding guide.

With this mindset in place, the work doesn’t start when the pedal is pressed. It starts with the checks that prevent the arc from ever having a chance to fail.

Machine Setup Checks: Polarity, Gas Flow, Tungsten and Cup

Machine setup is unglamorous work, but it solves a large share of TIG complaints. Before you drag the machine in for service, run the checks below in order. More “dead torches” than anyone wants to admit turn out to be a gas cylinder valve left closed, and more “bad machines” turned out to be a ground clamp biting onto paint or mill scale three feet away from the joint.

Polarity: The Single Most Expensive Mistake to Ignore

Polarity decides where the arc’s heat goes, so getting it wrong changes everything downstream. On DCEN (electrode negative, or “straight polarity”), roughly 70 percent of the arc heat concentrates at the workpiece while the remaining share heats the electrode. That split gives deep, narrow penetration and a cool, stable tungsten, which is why DCEN is the standard for steel, stainless steel, titanium, copper and most other metals, as outlined in Miller’s guide to TIG welding basics.

DCEP (electrode positive, or “reverse polarity”) reverses that split. The electrode absorbs the majority of the heat, the arc becomes shallow and broad, and a pure tungsten will overheat and melt in seconds. DCEP has a few niche uses, but if your bead suddenly looks like a puddle of soup and your tungsten is glowing cherry red, check the leads before you check anything else.

AC is the required polarity for aluminum and magnesium. Their oxide layer melts around 2,050 °C while the base metal melts nearer 660 °C, so the electrode-positive half-cycle has to tear the oxide off before the electrode-negative half can do the actual welding. That balance between cleaning and penetration is covered in depth by Miller here, and Section 6 of this guide deals with it directly. If you are considering MIG or flux-cored alternatives for aluminum work instead, our Aluminum MIG Welding: The Complete Practical Guide explains where those processes pick up the slack.

Shielding Gas: The Right Gas at the Right Flow

For almost everything you will do, 100 percent argon is the correct answer. It starts easily, runs stable on DCEN and AC alike, and is cheap enough that there is no reason to improvise. Argon/helium blends are the step up for thick sections or faster travel, since helium carries more heat into the puddle, but they cost more and demand a properly mixed cylinder.

The gas you must never use is anything with CO₂ in it. CK Worldwide lists wrong gas or CO₂-bearing mixed gas as a primary cause of tungsten and bead contamination. Even a small percentage of CO₂ in an argon/CO₂ MIG mix attacks a tungsten electrode and wrecks arc stability. If you share a shop with MIG welders, label your regulator and keep a dedicated argon cylinder on your cart. Our Airgas Welding Supplies guide walks through cylinder types, regulators and what to ask your gas supplier for.

Flow rate matters more than most beginners think, in both directions:

• Too little flow (under about 10 cfh) lets air creep into the shielding envelope, producing porosity and heavy oxidation colors.
• Too much flow is equally damaging. ESAB warns that exceeding roughly 15 L/min creates turbulence that draws atmospheric air into the weld pool, which is the same enemy you were trying to keep out.

Miller recommends 15–20 cfh for general TIG work. Larger cups and gas-lens setups can run higher because they deliver a calmer, more laminar column of gas, but a plain cup at 40 cfh is usually worse than one at 18 cfh.

Pre-flow and post-flow finish the job. A pre-flow of half a second to one second floods the zone before the arc strikes. For post-flow, a practical rule is roughly one second per 10 amps of weld current, which keeps the hot puddle and the tungsten shielded until they drop below the temperature where oxygen will attack them. On stainless and titanium, short post-flow is a fast route to a grey, sugared bead that has to be cut out.

Tungsten Diameter, Cup, Stickout and Ground

As a starting point, a 3/32-inch tungsten is the general-purpose size for work up to about 220 amps. Drop to 1/16-inch for thin material under roughly 80 amps, and step up to 1/8-inch for heavy current where a thinner electrode will ball, melt back or spit. An undersized tungsten that constantly degrades is one of the most common setup faults, and it masquerades as a machine problem.

Cup size follows the joint. A #6 or #8 covers most bench work; a #10 or #12, ideally on a gas lens, gives a wider calm envelope for stainless and titanium. Keep stickout short, about one cup diameter, so gas coverage stays effective, but long enough that you can see the puddle and dip filler without fouling the electrode. And place the ground clamp on clean metal, as close to the joint as you can get it, directly on the workpiece rather than the table or a fixture. A poor return path forces the machine to compensate and shows up as an erratic arc.

Starting Settings Cheat Sheet

Setting	Steel / stainless (DCEN)	Aluminum (AC)
Shielding gas	100% argon, 15–20 cfh	100% argon, 15–20 cfh (argon/helium for thick stock)
Tungsten	3/32″ ceriated or lanthanated up to ~220A	3/32″ ceriated or lanthanated; balled on transformer machines, sharpened on many inverters
Cup	#6–#8	#8, gas lens preferred
Stickout	About one cup diameter	About one cup diameter
Post-flow	~1 second per 10 amps	~1 second per 10 amps
Work lead	Clean metal, close to joint	Clean metal, close to joint

Before you strike the arc on aluminum, remember that the setup does not stop at the machine: the surface itself has to be scrupulously clean. Our Aluminum Cleaner for Welding guide covers the degreasing and dedicated stainless-brush routine that keeps the oxide from coming back between passes. Once these boxes are ticked, anything that still goes wrong is genuinely an arc, technique, or material problem, which is exactly what the next section diagnoses.

Arc Troubleshooting: Hard Starts, Arc Wander and Unstable Arc

Before a TIG arc ever lays down a bad bead, it usually tells you something is wrong. The torch hisses differently, the arc pops instead of humming, or the tip of the arc skitters sideways like it cannot decide where to land. Arc-side faults are the fastest problems to isolate because they happen in the first second of the weld, and almost always trace back to the same short list: the circuit is not complete, gas is not arriving, the tungsten is wrong, or your settings and technique are fighting each other.

No Arc Despite High Frequency

You press the switch, you hear the high-frequency crackle, but no arc jumps to the work. This is one of the most reported TIG starting faults, and Miller’s TIG welding guide gives a blunt diagnosis: high frequency present with no arc power points to an incomplete welding circuit, or to no shielding gas reaching the torch. Many machines will not energize arc output until the gas solenoid confirms flow, so a closed cylinder valve, an empty bottle, or a failed gas line looks exactly like an electrical failure.

Check these in order:

• Gas first: open the cylinder valve, confirm remaining pressure, and bump the flow. If you hear nothing at the cup, the problem is upstream. Leaking O-rings, a pinched hose, or a loose fitting are common culprits, and a supplier like AllGas Welding Supply can often pressure-test a questionable line faster than you can chase it.
• Circuit second: a ground clamp biting onto paint, mill scale, or a rusty edge is not a ground. Move it to bare, bright metal and check that the work cable is tight at both ends.
• Polarity third: steel, stainless, titanium and copper run DCEN. If the arc refuses to strike or the tungsten instantly glows cherry red, swap the polarity leads.
• Tungsten fourth: a contaminated, chipped, or wrongly ground electrode will not carry a high-frequency start reliably.

The Isolation Sequence

Work through arc faults the same way every time. The order matters because each step eliminates a whole category of cause.

1. Confirm gas is flowing at the torch with a short trigger pull.
2. Confirm the work lead is attached to clean base metal with continuity back to the machine.
3. Confirm polarity matches the material.
4. Confirm the tungsten is the right diameter for the current and freshly prepared.
5. Set arc length to roughly 1/16 to 1/8 inch above the workpiece and hold it there.
6. Clean the joint and deal with coatings: galvanized spatter, paint, unidentified mill scale and shop dust all destabilize the start.
7. Adjust AC frequency and balance if you are on aluminum.
8. Shield the arc from drafts with a screen or your body position.

Only when all eight hold should you suspect the machine itself.

An Arc That Refuses to Stay Pointed

A wandering or cone-shaped-off-axis arc is almost always mechanical rather than electronic. The three usual suspects are arc length, electrode geometry, and preparation of the base metal. Stretch the arc past about 1/8 inch and it loses stiffness, widens, and begins to drift toward whichever surface is dirtiest or hottest. Shorten it and the arc column stiffens immediately.

Next, look at the tungsten. A jagged, rounded, or faceted-the-wrong-way tip gives the arc no defined path, so it roams. On AC inverter machines, Miller recommends a frequency range of 100–180 Hz for a tighter, more stable arc, and increasing the electrode-negative percentage to roughly 70–90 percent stabilizes the arc while putting less heat into the tungsten. Cranking frequency too far up narrows the arc to a needle and makes travel harder; too low and the arc goes soft and wide.

Finally, check the surface. Mill scale, oxide and zinc coatings divert the arc at the moment of strike. A dedicated cleaning pass with a stainless brush or dedicated cleaner, as covered in Aluminum Cleaner for Welding, fixes more “arc wander” than any machine adjustment ever will.

A Sputtering, Spitting Puddle

Once the arc is established but the puddle pops, spits, or crawls instead of flowing evenly, the list shortens to contamination, gas coverage, and heat. Oil and moisture trapped in the joint, dirty filler rod, and an arc stretched too long all introduce gas and oxides into the pool. Traveling too fast starves the puddle; too much current boils it. Drafts stripped away by an open shop door produce the same grey, peppered surface you would expect from no gas at all, and oversized stickout makes it worse by diluting the shield before it reaches the weld.

Work the isolation sequence once and most arc problems disappear on the first pass. The pattern repeats across every TIG fault in this article: verify gas, verify circuit, verify electrode, verify settings, then verify technique, in that order and no other.

Porosity and Discoloration: Reading What the Bead Tells You

Every bead is a logbook. Before you touch a dial, learn to read it. Porosity forms when gas becomes trapped in the weld pool and has no path out as the metal solidifies, and the shape, location and frequency of those voids point straight at the cause. Scattered pinholes after twenty minutes of welding usually mean a systematic shielding or cleanliness failure. A few holes only at the start of the bead usually mean rushed pre-flow. This is the side of TIG basics that separates a hobbyist weld from code work, because GTAW gives you no flux blanket to hide behind: everything the puddle is exposed to, it feels.

Pinholes, Wormholes and Surface Porosity

• Pinholes are small, round, evenly spaced craters across the face of the bead. Even distribution points to a constant fault: bad gas, a leaky line, or a dirty surface that never got clean.
• Wormholes are elongated, tunnel-like voids that track along the weld. They typically mean gas was generated under the arc from oil, moisture, paint or a coating, or that arc force blew shielding away from the joint ahead of the puddle.
• Surface porosity appears as clustered, rough openings where the pool froze before gas could rise. Usual suspects: travel speed too fast, amperage too low, or an arc length long enough that the shield never fully covered the melt.

Discoloration Is a Different Diagnosis

Heat tint is not porosity. Straw, gold, blue and purple on stainless or alloy steel are oxidation colors: the surface reacted with air because gas coverage thinned, but the weld underneath may be perfectly dense. A straw-to-blue tint is a coverage nuisance that wire brushing or passivation can address. Dull grey or chalky white “sugaring” is another matter entirely: that is heavy oxide contamination with real depth, and it has to be ground out before anything is re-welded over it.

The pattern of tint is a fast diagnostic. Tint starting mid-bead usually means a draft hit the puddle, a hose got pinched under your arm, or the cylinder ran low. Tint at the very start of every bead points to pre-flow set too short. Tint creeping in just before the arc quits almost always means post-flow too short, leaving hot metal exposed to air the instant you release the trigger.

What Actually Traps the Gas

Group the causes before you chase them:

• On the metal: oil, cutting fluid, moisture, mill scale, paint, galvanized coatings, mill lubricants, layout ink, and welded-on fingerprints. Galvanized and unidentified mill scale are the worst offenders because they release gas directly beneath the arc.
• In the line: wet or off-spec cylinder gas, pinched or perforated hoses, worn back-cap O-rings, loose fittings and leaking regulators. Even a small leak draws air into a low-pressure argon stream. Buying clean, dry gas from a reputable supplier such as a proper welding gas supplier solves half of this before you strike an arc.
• In the technique: excessive travel speed, an arc length too long, a stickout far longer than the cup allows, and current so low the puddle chills before gas escapes.
• In the room: open doors, fans, welding near an air handler. Wind blows the shield away even when your regulator is set perfectly, which is why a screen matters more outdoors than any flow adjustment.

Aluminum’s Moisture Problem

On aluminum, porosity is driven mainly by moisture and oil, not by mill scale. The oxide layer is hygroscopic and grabs water from the air; aluminum soaks up hydrogen readily while molten and rejects it sharply as it freezes, so hydrogen gets pushed ahead of the puddle and trapped. Scrub with a dedicated stainless steel brush, wipe with a fresh solvent, clean the filler rod, and keep everything dry. Our aluminum cleaning guide walks through the prep sequence, and the same discipline applies to hull work where dampness is constant, as covered in aluminum boat welding.

Inspection and Prevention Checklist

1. Grind or brush the joint to bright metal within an inch of the weld zone; store cleaned parts somewhere dry.
2. Wipe filler rod; keep it off the floor and out of the glove.
3. Check hose, O-rings and fittings for leaks with soap solution before the session.
4. Set flow in the 15–20 CFH range for most bench work, then confirm with a bubble meter or flow meter at the torch, not just at the regulator.
5. Set pre-flow and post-flow long enough that gas covers the arc start and the crater through cooling.
6. Position the ground clamp and torch so neither fights the shield, and screen the area from drafts.
7. Slow down enough for gas to escape the pool and the puddle to stay fluid.

Tungsten Contamination, Melting and Inclusions

Almost every TIG welder has dipped their tungsten at some point. One moment the puddle is clean and controlled, the next the arc spits, wanders, and the sharp point of your electrode is gone. A dip is more than just a nuisance, as it can introduce tungsten into the weld itself. With the right awareness, though, most of these issues can be caught and corrected before they become a reject.

Contamination Begins on Contact

Tungsten has a melting point of roughly 3,422 °C, which is why it’s used for GTAW. However, the molten weld pool isn’t a neutral heat source. On steel, iron and carbon can alloy with the tip on contact. On aluminum, the electrode picks up aluminum and forms a lower-melting alloy at the point of contact. This instantly destroys the ground taper and causes the arc to lose its focus.

The filler rod can be just as guilty. If it touches the hot electrode rather than the puddle, it can transfer fragments of tungsten directly into the joint. Once either happens, the electrode should be treated as contaminated until it’s re-ground.

Not All Electrode Issues Are the Same

Before changing your setup, it’s important to identify what you’re actually seeing. These failures all look similar at a glance, but require different fixes:

What you see	What it actually is	Usual cause	Correction
Grey bite, chunk missing, or sputtering arc	Contamination from dipping	Too little arc length or filler rod drift	Stop and re-grind the electrode completely
Tip rounds and shortens over a long run	Excessive consumption	Current too high for the electrode diameter	Drop amperage or step up to a larger tungsten
Fuzzy, bearded, or crumbly deposits on the taper	Oxidation of the hot taper	Poor shielding (short post-flow, draft, turbulence, or oversized cup)	Fix gas coverage first, then re-grind
Bright white spots on X-ray film	Trapped tungsten inclusion	Broken tungsten left in the pool or unground dip	Remove and re-weld; it will not disappear on its own

Why the Tip Melts or Burns

A melting tip is almost never a tungsten defect. The most common culprits are excessive amperage for the electrode diameter, an arc that’s too long spreading heat over the taper, or excessive stickout preventing heat from conducting back into the collet body.

Miller advises keeping the tungsten about 1/16 to 1/8 inch above the puddle during normal welding, and if the tip starts melting, reduce current or step up to a larger tungsten before anything else (Miller’s guide to TIG welding basics). With a foot pedal, this is as simple as backing off heat on starts, pauses, and crater fills where most tips burn the fastest.

Tungsten Inclusions and Their Impact

A tungsten inclusion is a fragment of electrode trapped in solidified weld metal. Since tungsten doesn’t fuse to the puddle, it acts as a hard discontinuity. These fragments are nearly impossible to see on the surface and can only be reliably found with volumetric inspection. Due to tungsten absorbing X-rays far more strongly than steel or aluminum, it appears as a bright white spot against the darker weld metal.

ISO 6520 classifies tungsten inclusions as solid inclusions, grouping them with oxides and other trapped particles.

Repairing a Contaminated Electrode

When a dip does happen, speed and discipline are key:

1. Cool safely: Break the arc and allow post-flow to cool the electrode. Never wave a hot tip through open air.
2. Check the filler: Inspect your filler rod. If tungsten transferred to it, cut that contaminated end off before continuing.
3. Re-grind: Remove the electrode and grind off all contaminated material with a dedicated diamond or bonded diamond wheel. Never use a conventional stone wheel, as it can embed abrasive grit.
4. Dress the taper: Re-grind to a point with longitudinal grind lines parallel to the electrode. Circumferential scratches can cause erratic arc starts.
5. Restart fresh: Begin welding on clean, ground material. If tungsten made it into the puddle, the contaminated weld metal will need to be removed before rewelding.

Choosing the Right Tungsten

Electrode selection can drastically cut down on dips, especially when paired with proper AC balance. The most common shop options are as follows:

Alloy	Colour code	Best suited to	Note
Pure tungsten	Green	AC on aluminum and magnesium, older transformer machines	Forms a stable ball on AC, but is soft and dips easily
Ceriated	Grey	AC and DC, thin sections, frequent arc starts
Lanthanated	Blue	AC and DC across most shop work	Starts easily at low current, survives AC balance mistakes better
Thoriated	Red	DC on steel and stainless, higher currents	Radioactive dust when grinding, needs ventilation and dust control

If you are welding AC aluminum and the tip balls up and burns faster than you can dress it, Miller recommends switching from pure green tungsten to a ceriated or lanthanated electrode (Miller’s AC balance control guide). Modern AC machines with balance control let you limit the electrode-positive portion of the cycle to what cleaning actually requires, which keeps less heat in the tip. The cleaning half-cycle does real work on aluminum oxide, and the trade-off between cleaning action and tungsten heat is covered in detail in the AC section above, along with the prep habits that reduce how much cleaning you need in the first place. A cleaner joint, better gas coverage and a shorter arc between the tip and the puddle will prevent more dips than any electrode upgrade alone.

Aluminum TIG Troubleshooting: AC Balance, Frequency and Cleaning

Aluminum is the most common source of TIG frustration, and almost every issue comes down to three settings: cleaning, balance, and frequency. Unlike steel, the metal itself fights the arc, so dialing these in is more important than maxing out amperage.

AC: The Only Way to Break the Oxide Barrier

The culprit is aluminum’s oxide layer. It forms the moment the metal is exposed to air and melts at roughly 3,700°F, while the base aluminum melts near 1,220°F. No amount of heat can bridge that gap alone. As Miller’s TIG welding basics guide explains, alternating current is required for aluminum and magnesium for this exact reason.

AC splits its duties across the cycle. Electrode-negative (EN) melts and penetrates the puddle, while electrode-positive (EP) provides cathodic cleaning to remove the oxide. Using DCEN won’t strip it, and DCEP will ball the tungsten into a blob almost instantly. Both will prevent proper wetting with no machine fault to blame.

Balance Control: Cleaning Versus Penetration

AC balance determines how much time is spent on each half of the cycle. Most machines show this as a percentage of EN, meaning a higher percentage gives more penetration and less cleaning. Miller recommends starting around 75 percent EN for clean, new aluminum, and dropping to around 65 percent EN for older, dirtier, or heavily oxidized material.

The trade-off is strict:

• Too much EP (low EN percentage): Excessive cleaning dumps heat into the tungsten, causing it to ball, wander, or spit with grey speckles. The arc spends its energy etching rather than melting, resulting in a shallow bead.
• Too little EP (high EN percentage): Oxide survives the cycle. The puddle will look dull and grey instead of mirror-bright, struggle to start, fail to wet into the toes, and can hide lack of fusion or gas porosity.

A bright, quiet, mirror-clean puddle is the goal. If you don’t see the faint, frosty white band of etching outside of it, your cleaning half-cycle isn’t doing its job.

AC Frequency: Arc Shape and Control

Frequency dictates how quickly the arc cycles between EN and EP, directly changing the arc cone. Higher frequencies between 120 and 200 Hz narrow and stiffen the arc, offering greater control for tight joints and thin sheet. Lower frequencies between 80 and 100 Hz widen the cone, spreading heat over a larger area which can be more forgiving on dirty material or heavier sections.

On thin stock, a bump up in frequency is often more effective than dropping amperage. On thicker plate, a lower frequency can help with heat spread. Every inverter machine differs, so test adjustments on a scrap coupon before committing to the joint.

Pre-Cleaning and Contamination

No balance or frequency setting can compensate for oils, fingerprints, or embedded iron. Start with a dedicated stainless steel wire brush used only for aluminum, never steel, to remove bulk oxide. Follow with acetone or a dedicated aluminum cleaner for welding. Avoid chlorinated degreasers near the arc.

For heavily oxidized or outside-stored aluminum, a light heat pass followed by brushing can help. This is especially critical for cast parts, as alloy wheel welding demands strict cleaning to combat the extra surface contamination they hold.

Filler, Moisture, Heat Input, and Distortion

Porosity in aluminum is almost always hydrogen based. Moisture on the plate, condensation on cold stock, or damp filler rod will all feed it into the puddle. Let cold metal warm up, store rod dry, and wipe it down before use. For filler, 4043 flows smoothly and resists cracking, while 5356 is stronger and clearer, but more crack-sensitive and prone to porosity if contaminated.

Aluminum also expands and contracts far more than steel. To limit distortion, clamp to a rigid fixture, keep interpass temperatures down, and use staggered stitch passes over a long, continuous bead. Pulsing can be a massive asset here. On structural applications, such as aluminum boat welding, this discipline is just as critical as amperage control.

Cracks, Craters, Lack of Fusion and Penetration Problems

Porosity and contaminated tungsten wreck a weld’s appearance, but the defects in this section quietly wreck its strength. A bead can look acceptable on the surface and still hide an unfused line along the root or a crater crack that starts as a hairline and grows under load. This is where TIG troubleshooting stops being cosmetic and becomes structural, and where the difference between a practice coupon and a pressure part, a hull joint, or an aerospace assembly shows up.

The encouraging news: almost every one of these defects traces back to a short list of causes you can control. Wrong filler alloy, travel speed too fast, current too low, arc too long, a root opening that will not let the puddle in, oxides left on the joint, or an arc that was simply switched off instead of wound down.

Hot cracking and centerline cracking

A crack running down the middle of the bead is usually solidification cracking. The weld pool freezes from the outside in, and if the shrinking solid shell gets pulled apart in the final moments, it opens a centerline split. The usual suspects are a filler alloy that freezes too narrow for the base metal, sulfur-bearing steel, high travel speed, and too much heat in one place. The fix is metallurgical before it is mechanical: matching filler to base metal matters more than dialing amperage, because a filler with a wider freezing range bridges the shrinking movement instead of resisting it. Slow the travel slightly, keep the bead width reasonable, and avoid stopping and restarting in the middle of a run.

Crater cracks: the defect you create in the last second

Crater cracking is probably the most common structural defect beginners produce, and it happens in the final second of the weld. Crater cracks commonly result from breaking the arc while the pool is still large and shrinking rapidly; the shrinking metal tears at the center of the crater, sometimes leaving a visible star or a hidden fissure. CK Worldwide recommends reversing direction and welding back into the previous bead to seal craters, or using a foot control for downslope so the current fades while the puddle is still fed. If your machine has a downslope timer, set it and add filler during the ramp. If it does not, a quick back-step of about a quarter inch and a last滴 of rod will close it.

Lack of fusion and lack of penetration

Lack of fusion is the weld sitting on the material instead of becoming part of it. It shows at the toes, between passes in a multi-pass joint, or along the sidewall of a fillet. The causes are familiar: oxides and mill scale left on the joint, travel speed too fast for the heat, arc too long so the force scatters, current too low, or a puddle that never wets the edge. An unfused area behaves like a crack and may be hidden inside the joint, which is why ultrasonic or radiographic testing is specified on critical work.

Lack of penetration is often a joint-design problem rather than a settings problem. In a butt joint, a root gap that is too tight or a root face that is too large physically blocks the arc from reaching the bottom, no matter how much amperage you apply. Open the gap slightly, reduce the root face, or increase amperage modestly and slow down at the start of the run. In corner and T-joints, aim the arc at the joint corner rather than the middle of the fillet, and let the puddle tie into both legs before adding rod.

Undercut, overlap and burn-through

Undercut is a groove melted into the base metal at the toe that the filler never filled, usually from too much current, too long an arc, or travel speed outrunning rod feed. Overlap is the mirror image: cold filler laid on top of unwelded metal, caused by too little heat or too much rod. Burn-through happens on thin material when current is too high or the arc dwells in one spot, and it is common when welding thin aluminum boat panels where the puddle runs away from you. Reduce amperage, shorten the arc, slow the puddle’s travel rather than your hand, and use the backstep technique, welding short segments in reverse order so each pass is supported by the one before it.

How these defects are found

Visual inspection catches surface-breaking cracks, craters, undercut and overlap, and it is the first gate in most work. For anything loaded or pressure-bound, the weld is ground flush and examined by dye penetrant, which reveals tight surface cracks the eye misses, or by radiography and ultrasonic testing, which expose internal lack of fusion and porosity inside the joint. The practical lesson for the person holding the torch: the defect you cannot see is usually the one that came from the joint preparation or the settings you skipped checking, so fix the cause on the next coupon rather than grinding the evidence off this one.

The Ten Most Common TIG Mistakes and How to Correct Them

After a few hundred hours under the hood, most welders learn that failures rarely come from exotic conditions. The same handful of habits repeat themselves on bench after bench, and each one shows through a predictable bead symptom. Read the list as a diagnostic shortcut: find your symptom, match the cause, apply the correction, then re-test on a scrap coupon before touching the real joint.

The Ranked List: Symptom, Cause, Correction

# & Mistake	Symptom	Cause	Correction
1. Skipping cleaning	Grey porous bead, soot, puddle that sputters instead of wetting out	Oil, mill scale, paint, galvanizing or oxide left on the joint	Solvent wipe, then grind or brush to bright metal right before striking the arc
2. Wrong polarity	Tungsten balls up and melts on DC, or arc stutters with shallow penetration	DCEP chosen for steel or stainless, or torch and work leads reversed	DCEN for steel, stainless, titanium and copper; AC only for aluminum and magnesium
3. Wrong or no shielding gas	Porosity, heavy heat tint, tungsten that crumbles or greys	Empty cylinder, closed valve, leaky line, or an argon/CO2 MIG mix used as a substitute	100 percent argon, roughly 15–20 cfh, leaks checked with soap solution
4. Arc length too long	Wide flat bead, wandering arc, weak penetration, cloudy etched zone on AC	Standing off the puddle for comfort or visibility	Hold the tungsten about one electrode diameter from the work, and shorten as amperage drops
5. Wrong tungsten size or dull grind	Balling, spitting, arc wander, grey fuzzy tip	Diameter not matched to amperage, rounded or sideways grind, contaminated tip reground casually	Match diameter to current, grind longitudinally on a dedicated wheel, re-dress the tip after every dip
6. Forgetting post-flow	Discoloured crater and heat zone, tungsten that tarnishes between stops	Post-flow set too short or trigger released off the crater	Hold the arc over the crater until gas clears; about one second of post-flow per 10 amps is a starting point
7. No back purge on stainless	Grey-black crusted, sugared root; corrosion later in service	Root face exposed to oxygen inside the pipe, tube or vessel	Purge with argon, dam the ends, then grind all sugaring out and re-weld the root
8. Wrong filler rod	Cracking along the bead, brittle or sooty welds, black spot inclusions	Rod alloy not matched to the base metal; oily, oxidized or wrong-diameter rod	Match filler to the base metal alloy, clean it, and size it to the joint thickness
9. Cranking amperage instead of fixing technique	Burn-through, undercut, flat lifeless bead, melted electrode	Heat used to compensate for a long arc or hesitant travel	Fix arc length and travel speed first, then fine-tune with the pedal or pulse
10. Re-welding over contamination	Porosity or cracks reappear under the new bead; inclusions on NDT	Original defect sealed beneath fresh metal	Gouge or grind back to sound metal, re-clean, then weld

Why Gas and Purge Errors Cost the Most Rework

Mistake three surprises people, because it looks like a machine fault. A shielding mix meant for MIG, anything carrying CO2, destroys GTAW electrodes and contaminates the puddle; it should never be substituted for pure argon, however convenient that cylinder looks. As Miller’s TIG basics guide outlines, argon alone is the default for nearly every ferrous and non-ferrous metal TIG welders handle, with helium blends reserved for specialized thick-section work. Check your supply through a proper shielding gas supply reference so the wrong bottle never reaches the rack.

Stainless without a back purge is the quiet version of the same failure. The root oxidizes on the inside where you cannot see it, forming the rough, sugared crust that defect guides treat as rejectable contamination. Sugaring has to be ground or cut back to sound metal and then re-welded with purge gas in place. There is no acceptable overlay fix.

Filler Metal and the Temptation to Overheat

Filler selection is the other recurring trap: the rod must be matched to the base metal alloy, and an incompatible rod is one of the most common sources of cracking. Start with the fundamentals in our all-position welding rod guide, then move to alloy-specific procedures such as Alloy 20 welding procedures, where filler choice is prescribed rather than guessed. Aluminum prep is equally unforgiving, so review the steps in aluminum cleaner for welding before blaming the machine. On the heat side, turning the dial up usually masks a long arc or timid travel speed; the bead gets wider, flatter and more under-penetrated while the tungsten erodes faster.

Tungsten that has picked up steel does not forgive a casual regrind either. Reground tungsten contaminated with steel still carries that contamination forward and can vaporize under the arc, leaving discolouration near the weld instead of a clean surface.

None of these ten mistakes requires a new machine to fix. Cleaning discipline, correct polarity and gas, a tight arc, dressed tungsten, matched filler and honest gouge-and-rework habits clear most of what walks through the shop door. In aerospace and code work, where procedures are audited and every repair is documented, these habits are the difference between a weld that passes first time and one that fails under aerospace TIG welding scrutiny. Learn them on coupons, log your settings, and the same ten errors will stop reappearing in your bead.

Safety, Practice Drills and a Final Troubleshooting Checklist

Troubleshooting TIG is mental work in a shop that can hurt you faster than any bad bead. One hazard below changes how you re-test.

Safety Limits That Change How You Troubleshoot

The GTAW arc is one of the most intense ultraviolet sources in a shop. OSHA states that inert-gas metal-arc welding produces ultraviolet radiation five to thirty times that of shielded metal arc welding, so an unhooded peek at a TIG arc is a far bigger dose than the same glance at stick. Every re-test is another exposure event, so re-test shielded. OSHA’s welding, cutting and brazing safety and health information publication carries the full hazard summary.

Ventilation is the second constraint. OSHA requires local exhaust or general mechanical ventilation whenever welding takes place in a confined space. Argon blends are heavier than air, so they pool in pits, tanks and hulls and displace oxygen with no warning smell. For repeated test welds inside a vessel, ventilation is a working condition rather than a comfort choice. OSHA 1926.353 sets out those rules and 1910.252(a)(2) covers general industry.

Three rules matter directly to the fixes described earlier:

• Stainless steel and chromium alloys. Grinding or welding stainless can generate hexavalent chromium. OSHA’s permissible exposure limit is 5 micrograms per cubic meter as an 8-hour time-weighted average, with monitoring and respiratory protection above it, and grinding the same coupon out eight times is exposure a production welder would never create.
• Chlorinated solvents. OSHA requires chlorinated solvents kept at least 200 feet from the arc, or thoroughly dried or shielded, because arc heat breaks them into phosgene and hydrogen chloride. That kills the worst porosity fix in the shop: wiping a joint with degreaser, then welding it minutes later.
• Eye and skin protection for bystanders. TIG’s UV output is high enough that a curtain containing stick welding may not contain it, so anyone past an open arc needs shade protection too.

A Deliberate Practice Regimen

Guessing at settings builds bad habits; controlled tests build skill. Four drills to run weekly:

1. Coupon tests with a written settings log. For every test plate, log material, thickness, tungsten, cup size, stickout, amperage, frequency, balance, gas flow and travel speed, then note the result. Six logged coupons beat sixty unlogged ones, and the habit underpins any formal Aluminium Welding Course.
2. The no-filler trial bead. Run a bead on clean scrap with no filler metal. Pure melted surface metal shows oxidation colours and porosity immediately if coverage is poor, and stays bright if it is good.
3. The aluminum cleaning-only test pass. Run a low-current pass with enough electrode-positive balance to clean, without building a puddle, and read the etched white band. Even and bright means cleaning zone and gas coverage are right; patchy or dull means fix pre-cleaning and balance first. A stainless brush and proper Aluminum Cleaner for Welding prep matters more than any knob.
4. Deliberate contamination tests. Weld one coupon with a fingerprint, one with mill scale, one clean. A known-bad reference bead beside your good work is the fastest way to recognise defects later.

The Symptom-to-Fix Checklist

Print this and keep it near the machine. Work left to right and resist skipping to the most expensive explanation.

Symptom	Check first	Most likely cause	First fix
No arc despite high frequency	Ground, gas, contact	Open circuit, empty tank	Reclamp ground, open valve
Lift or scratch start hard	Polarity, tungsten prep	Wrong polarity, balled tip	Switch to DCEN, re-grind
Arc wanders off target	Arc length, drafts	Long arc, air currents	Shorten arc, shield it
Sputtering arc on AC	Balance, tungsten size	Too much EP balls tip	Reduce EP, upsize tungsten
Grey porous bead	Base metal, gas, rod	Contamination, lost gas	Clean bright, check flow
White crusty aluminum	Cleaning half-cycle	Too little EP for oxide	Increase cleaning, pre-brush
Tungsten dipped, arc pink	Technique	Electrode touched pool	Stop, re-prep tungsten
Crater crack at stop	Downslope, post-flow	Arc cut on full crater	Use downslope, back-feed
Undercut on vertical uphill	Amperage, weave width	Too hot, travel too fast	Pause at toes, drop 5 amps
Lack of fusion at root	Root gap, oxides	Tight joint, oxide skin	Open root, clean, slow travel
Burn-through on thin sheet	Heat input, fit-up	Too much current or a gap	Pulse amperage, tighten fit-up
Cracking in finished weld	Filler alloy match	Wrong rod for base metal	Match filler, re-weld

Conclusion: Build Habits, Not Heroics

Almost every TIG problem traces back to three families: contamination, shielding loss, or a wrong setting. Look at the bead, check gas, tungsten and settings, then change one variable at a time so you learn what fixed it. An Aerospace TIG Welding standard reminds us that professional shops solve these problems with procedure and documentation, not instinct. Treat every defect as a diagnosis rather than an insult. The welders with consistently clean results are not luckier than you; they are simply more repeatable.

Frequently Asked Questions

Why is my TIG arc unstable and wandering?

Why does my TIG weld have porosity?

What gas flow rate should I use for TIG welding?

How do I stop dipping the tungsten into the weld puddle?

Why is my tungsten melting or balling up?

What AC balance setting should I use for aluminum TIG?

How do I prevent crater cracks at the end of a TIG bead?

Why does my stainless steel weld look grey, sugary, or rainbow colored on the back?