Good and Bad TIG Welds: How to Identify, Fix, and Prevent Defects

What Makes a Good TIG Weld vs. a Bad TIG Weld

It’s late in the shop, and the first bead looks perfect — until the sun hits it from the right angle. A faint line of porosity just became your weekend problem. That moment, when raking light reveals what your helmet missed, is where every TIG welder learns that “looks good” and “is good” are two different things.

Tungsten inert gas (TIG) welding, or gas tungsten arc welding (GTAW), is a precision process. It’s slow, controllable, and unforgiving of dirt, drafts, or a wandering torch hand. Maintain the shielding and keep the surfaces clean, and GTAW produces some of the cleanest, highest-quality welds of any arc process. Let either slip, and the same process quietly buries defects beneath a shiny surface.

The Visual Signature of a Good TIG Weld

A sound TIG bead tells a story you can read without magnification:

• Uniform bead width — steady from start to finish, matching your travel speed and amperage.
• Even ripple pattern — a regular stacked-dime rhythm, not a jagged or wandering edge.
• Proper tie-in — toes blend smoothly into the base metal with no notch, undercut, or cold lap.
• Full penetration — complete fusion through the root, with consistent reinforcement on the back side of an open joint.
• Clean colour — a light straw or gold tint on stainless, not dull grey or black oxidation.

Depth of fusion matters as much as appearance. A bead that sits on top of the joint instead of fusing into it is a reject, no matter how neat it looks.

How a Bad TIG Weld Announces Itself

Rejects rarely look dramatic. They whisper:

• Porosity — pinholes or a peppered surface from moisture, oil, or a shielding gas leak.
• Inconsistent ripple spacing — a sign of fluctuating amperage or an unsteady grip.
• Undercut and overlap — gouged toes or rolled edges where filler was dumped in too cold.
• Incomplete fusion — lack of fusion at the sidewalls, often invisible until bend or X-ray testing.
• Excess reinforcement — a crowned, lumpy bead that concentrates stress instead of distributing it.

Measurable Quality: What the Codes Actually Require

Appearance gets you in the door; acceptance criteria keep you there. The AWS D1.1/D1.1M Structural Welding Code — Steel sets the visual acceptance benchmarks for structural steel: welds must be crack-free, show adequate fusion, and stay within defined limits for profile, undercut, and porosity. For pressure and piping work, ASME Boiler and Pressure Vessel Code, Section IX governs procedure and welder qualification, so the person and the process are proven before the arc ever strikes.

Discolouration and Contamination: The Silent Failures

Colour is a temperature and shielding report card. A light straw tint on stainless steel is acceptable in most work; blue, purple, grey, or sugary black scale means the weld stayed hot too long or lost gas coverage. On aluminium, a sooty black smudge points to inadequate cleaning or the wrong polarity and balance settings. Every one of these is contamination you can see — and where there’s surface contamination, there’s usually porosity beneath it.

Side by side, the differences are obvious once you know what to look for:

What You’ll Learn in This Guide

From here, we’ll work through the defects that sabotage TIG welds and how to fix each one, then cover shielding gas and cleanliness, machine settings and polarity, tricky materials and fit-up, safety, inspection and testing, and the habits that build consistency. You’ll learn to read a bead the way an inspector does — and to catch problems while they’re still cheap to fix. If you want to build the muscle memory behind all of it, our guide to welding practice is a good place to start. Consistency, not one lucky bead, is the real measure of quality.

Common TIG Welding Defects: Causes, Appearance, and Fixes

Every flaw on a TIG bead is evidence of something that happened seconds before you spotted it. The AWS D1.1 Structural Welding Code calls these discontinuities—irregularities that only count as defects once they exceed acceptance limits. Name them, and you can trace each one back to a cause and a fix. Here are the ones that sink acceptance tests most often.

Porosity

Appearance: pinholes scattered or clustered along the bead, sometimes invisible until dye penetrant or a bend test reveals them. Causes: inadequate shielding gas coverage, contaminated base metal or filler, moisture, or flow set so high it turns turbulent. Prevention: clean to bright metal, match cup size to flow rate, hold a steady torch angle, and verify your polarity setup. Repair: grind out to sound metal and reweld.

Lack of Fusion and Lack of Penetration

Lack of fusion leaves a bead sitting on top of the joint instead of blending into the sidewalls; lack of penetration leaves an unfused root. Both point to low amperage, travel too fast, or a gap too tight. They hide inside the joint, so inspectors hunt them with radiography or ultrasonic testing. More heat, a slower hand, and honest fit-up prevent them. Repair means gouging out the defect and starting again.

Undercut

Appearance: a groove melted into the base metal along the weld toe. It narrows the effective throat, so AWS D1.1 caps its depth and length. Causes: too much amperage, an arc stretched long, a poor work angle, or travel speed that outruns the puddle. Prevention: steady angle, correct heat, a brief pause at each edge. Repair: blend within limits; otherwise grind and reweld.

Overlap

Appearance: a convex bead that rolls onto the base metal without fusing to it—a cold lap. Causes: travel too slow, amperage too low, or the torch held at the wrong angle. Prevention: enough heat to wet the toes, plus consistent travel. Repair: remove the whole bead and reweld. Our guides to the overlap welding defect and to overlapping as a technique versus a defect break down detection in more depth.

Cracks: Hot and Cold

Hot cracks form while the weld solidifies, often along the centerline; cold cracks appear hours or days later, frequently in the heat-affected zone of hardened or thick steel. High restraint, sulfur and hydrogen, or rapid cooling are the usual suspects. Preheat, clean filler, and controlled cooling are the tools. Keep interpass temperature steady, and if a crack does appear, it’s a full removal—not a touch-up.

Tungsten Inclusions

Appearance: small bright specks or a ragged, spitting arc mark where the electrode dipped into the puddle. Causes: touching the tungsten to the puddle or filler, or running a contaminated, balled-up electrode. Prevention: keep a tight arc without contact, regrind or swap the tungsten the moment it’s fouled, and set current per the Miller TIG welding guide. Repair: grind out the inclusion; it won’t melt back into the metal.

Oxidation and Discoloration

Appearance: straw, blue, grey, or black oxide on the bead. Light straw on stainless is normal; heavy grey or black sugaring means the shield failed. Causes: lost gas coverage, too much heat, travel too slow, or no back purge. Prevention: purge the backside, increase flow, and reduce heat input. Repair: light discoloration is cosmetic after pickling; sugaring usually demands a full cut-out. That heat also produces fumes—NIOSH links them to respiratory and neurological risks, and OSHA’s welding ventilation requirements exist for exactly that reason. Ventilation is part of weld quality, not a separate topic.

Reading a bead this way—defect, cause, fix—turns guesswork into a checklist. Sloppy practice builds bad habits that repeat every defect above; deliberate, clean welding builds the opposite, and whether you’re on a foot pedal or automating heavy plate, the acceptance criteria never change.

Shielding Gas, Cleanliness, and Contamination

If there is one rule worth taping above your machine, it is this: the TIG arc does not forgive a dirty surface. Proper shielding gas coverage keeps oxygen and nitrogen out of the molten puddle, and GTAW is uniquely sensitive because the tungsten electrode, filler rod, and weld pool all share one small gas envelope. Break that envelope and you invite porosity, oxidation, and the faint rejects that only show up when sunlight hits the bead at the wrong angle. Follow along with our AC or DC for TIG Welding Steel guide for the polarity side of the equation.

Gas Selection: Argon, Helium, and Blends

Argon is the workhorse for TIG: a stable arc, easy arc starts, and strong AC cleaning action. Helium runs hotter, wets out faster, and shines on thick aluminium or copper where you need deeper penetration. Argon–helium blends, often 25–75% helium, split the difference for heavier steel and stainless. Set flow with a meter, not a guess: 15–20 CFH of argon through a standard cup is typical, while a gas lens or large cup needs a touch more. Turn the flow too high and the jet turns turbulent, dragging room air into the shield. Our friends at Miller’s TIG welding guide make the same point.

Trailing Shields and Back Purge

Stainless and titanium stay reactive long after the arc moves on. A trailing shield extends gas coverage behind the torch, and a back purge floods the underside of the joint with argon, taping and foiling the joint to trap gas where it counts. Keep purging until the metal drops below roughly 800°F; many shops verify with an oxygen meter and aim for less than 1% oxygen. Skip this and you get sugaring — a rough, black, corroded backside that fails inspection.

Surface Prep: Degrease First, Then Remove Oxide

Contaminants — oil, paint, rust, moisture, cutting fluid — break down in the arc and feed hydrogen straight into the puddle, which is exactly how porosity forms. Wipe the joint and filler rod with acetone, then remove oxide with a dedicated stainless brush or a clean grinding disc used on that metal only. Never mix brushes between carbon steel and stainless; embedded steel particles cause rust blooms and contamination.

Filler wire deserves the same respect as the base metal. Rods sit on benches, get handled with bare hands, and pick up oil and dust; wipe them down and store them capped. Oxidized or rusty filler should be cut back, not welded.

Torch Angle and Draft Control

Hold a 10–15° push angle and keep the cup close to the work; lifting the torch stretches the shielding envelope until it thins out. Open shop doors, fans, and HVAC vents quietly murder gas coverage, so weld behind a screen or curtain. If the bead suddenly greys halfway down a joint, look for a draft before you blame your settings. Building repeatable habits here is the same discipline covered in our guide to welding practice.

Reading Oxidation Colors

On stainless, color is a report card. A light straw or gold tint is generally accepted; blue and purple mean the metal got too hot or the shield was too thin; grey, black, or sugared surfaces signal serious oxidation and usually require removal. If you cannot hold a consistent color, drop the amperage or nudge gas flow up in small steps and test on scrap first. Colors are a fast field check, but code still governs — AWS D1.1 sets acceptance criteria, and ASME Section IX qualifies the procedures behind them.

Shielding gas also displaces oxygen in enclosed spaces, so ventilation is a safety issue, not an afterthought. OSHA 1926.353 requires adequate ventilation and respirators where needed, and NIOSH notes that welding fumes carry manganese and other metals with real health consequences. Argon itself is inert but asphyxiating in a confined tank or vessel.

Settings, Polarity, and Equipment Setup

Here’s the uncomfortable truth about TIG: most bad welds aren’t caused by bad hands. They’re caused by bad numbers. The torch angle can be textbook and the travel rhythmic, and the joint still fails because the machine was dialed in for 1/8-inch plate while you’re welding 16-gauge sheet. Settings are the invisible variable that decides whether your arc behaves like a precision instrument or a blunt object.

Amperage: The Rule of Thumb That Saves Metal

Amperage controls penetration and heat input. Too low and the arc barely wets the toes of the joint, producing cold lap and lack of fusion. Too high and you get burn-through on thin material, undercut along the edges, and a crater that sags on the backside.

A practical starting point for steel is roughly one amp per 0.001 inch of thickness — about 125 amps for 1/8-inch plate — then adjust for joint design. A square-groove butt on thin sheet needs far less heat than a T-joint that acts as a heat sink. Forced gaps demand less amperage and faster travel, not more.

Polarity: DCEN, DCEP, and AC

DCEN (electrode negative) pushes heat into the workpiece, delivering deep penetration on steels and stainless. DCEP runs hot at the tungsten, balls the tip, and offers a strong cleaning action that rarely suits manual TIG. AC splits the difference and is the go-to for aluminum because the positive half-cycle breaks up the tenacious oxide layer, whose melting point sits far above the base metal. Without that cleaning phase you get arc wander, soot, and dull, poorly fused beads. Our guide to TIG welding polarity explains when each mode earns its place, and DC aluminium welding is worth understanding if you chase penetration on thick aluminum.

AC Balance and Frequency

On AC, balance is the time split between cleaning (electrode positive) and penetration (electrode negative). More cleaning helps dirty or oxidized aluminum but widens the etch zone and consumes tungsten; less cleaning gives deeper penetration and a tighter bead but can trap oxides. Frequency controls the arc cone. Higher frequency narrows it for precise work on thin material, while lower frequency widens coverage for broader beads and better tie-in on thicker sections. Most manufacturers publish baseline ranges in their TIG welding guides; start there, then tune to your material.

Tungsten, Cup Size, and Gas Flow

Tungsten type and preparation matter more than beginners expect. Thoriated (red) and lanthanated (gold or blue) electrodes hold a sharp point on DC, while pure or zirconiated tungsten suits AC aluminum. A longitudinally ground, tapered point stabilizes the arc; a contaminated or blunt tip causes wandering and tungsten inclusions, and grinding sideways across the tip channels the arc unpredictably.

Cup size and gas flow go hand in hand. Larger cups at higher flow cover wider beads and resist drafts, but too much flow creates turbulence that pulls air into the shielding envelope. Post-flow — the gas that keeps flowing after the arc stops — protects the hot tungsten and cooling crater from oxidation. Cut it short and you’ll see a sugared gray crater and a discolored electrode tip.

How Bad Settings Show Up

• Burn-through: amperage too high, travel too slow, or a gap that never should have passed fit-up.
• Lack of fusion: heat too low to melt the sidewalls, often hidden under a pretty bead.
• Balling and arc wander: the wrong polarity for the job, or a tungsten that’s been dipped.
• Oxidation: post-flow or gas coverage too low, leaving a gray, sugared surface.

Equipment Matters Too

Settings only work as well as the machine behind them. An inverter with stable arc control, adjustable AC balance and frequency, a quality torch, and the right collet body change what’s possible; cheap gear with coarse amperage steps makes consistency a fight. When a bead fails, check the dials first — nine times out of ten the fix is a number, not a new technique. Deliberate practice with known settings is how feel and numbers eventually agree.

Materials, Joints, and Fit-Up Challenges

You can nail your torch angle and watch a clean puddle, but still hand over a reject. Often, the material and the gap you inherited decided the outcome before the arc ever struck. TIG gives you total control — and with it, total responsibility.

Steel, Stainless, and Aluminum Behave Very Differently

Mild steel is the most forgiving. Run DCEN, remove mill scale from joint faces, and wipe off oil or coolant. Contamination burns straight into porosity. Light rust may pass, but grease, paint, or cutting fluid won’t.

Stainless punishes excess heat. It conducts poorly, warps easily, and can “sugar” on the backside — a rough, oxidized grain that destroys corrosion resistance. On sanitary tubing for food, dairy, or pharmaceutical work, purge the inside with argon until an oxygen meter reads under 100 ppm. Without that shield, a flawless outside can hide an interior failure. Our Welding Practice guide covers purge setup in detail.

Aluminum rewrites the rules. Its oxide layer melts near 3,700°F, while the base metal melts around 1,220°F — so that oxide must be removed mechanically and electrically. AC handles both, which is why AC polarity is standard for aluminum. Thick sections may call for DC with helium instead. Brush with a stainless brush dedicated to aluminum, wipe with acetone, and weld soon after — the oxide regrows within hours.

Thickness also drives strategy. Sheet under 1/8 inch demands low amperage, a tight arc, a sharp electrode, and often a copper backing plate to sink heat. Go too hot, and it tears. Thick plate requires a beveled prep, sometimes preheat, and enough amperage to fuse the full wall — not just the surface.

Joint Types and Root Gaps

Joint geometry shapes your heat path. Square-butts work for thin sheet, but as thickness rises, switch to a single-V, double-V, or U-groove so the arc reaches the root without over-melting the sidewalls. T-joints and lap joints are especially tricky — lack of fusion often hides beneath the top plate or in the corner, so TIG fillets warrant extra scrutiny.

Root gap makes or breaks the job. Too tight, and the arc can’t reach the bottom, leading to lack of penetration or cold lap. Too wide, and you risk burn-through, a dropped root, and distortion. Inconsistency is the worst offender: a gap that wanders mid-joint forces constant travel and amperage changes. For structural steel, AWS D1.1 sets strict fit-up tolerances for this reason. Tube work only raises the stakes, as outlined in our guide to weld tube fittings.

Backing, Purge, and Distortion Control

Backing bars are your heat insurance. Copper, steel, or aluminum chill bars behind the root control penetration, shape the backside bead, and draw heat away. Consumable inserts serve a similar role on pipe roots by melting into the gap. Even simple purge dams, foil tape, or purge boxes turn a sugared root into a clean one. On code work, these methods must follow the qualified procedure under ASME BPVC Section IX.

Distortion is often a fit-up issue in disguise. Every extra amp used to bridge a sloppy gap turns into shrinkage stress elsewhere. Tack in a balanced sequence, backstep your bead, clamp to chill blocks, and let each pass cool before adding more heat.

Fit-Up Habits That Prevent Defects

• Tack on the side of the joint that moves least, and check alignment after every tack.
• Gap consistently — a uniform 1/16 inch beats a random 1/32 inch.
• Clean the mating faces to bare metal before you tack, not after.
• Dry-fit the whole assembly first, especially on tubing runs where a twist becomes a field problem.

Get material, joint, and fit-up right, and most defects never get the chance to form.

Health, Safety, and Workplace Hazards

TIG welding looks clean from across the shop. There is no spatter spraying off the puddle and no thick smoke plume rolling over the bench the way you get with a wire process. That tidy appearance is exactly why GTAW welders skip safety steps that every other process gets by default. The hazards do not disappear — they just get quieter, and they work on a longer timeline.

Welding Fumes and Manganese Exposure

GTAW produces less fume than stick or flux-cored welding, but less is not none. NIOSH identifies welding fumes as a potential occupational respiratory hazard and singles out manganese, a common alloying element in steel and filler rods, as a specific concern because prolonged overexposure has been linked to neurological effects. Stainless steel adds hexavalent chromium and nickel to the mix — recognized carcinogens — while aluminium brings ozone and fine particulate into your breathing zone.

Ventilation and Respiratory Protection

OSHA’s welding standard, 1926.353, requires sufficient ventilation or respiratory protection to keep airborne contaminants out of the welder’s breathing zone during welding operations. In practice that means local exhaust ventilation or a fume-extraction torch positioned close to the arc, your head outside the rising plume, and — for stainless, chrome-bearing alloys, confined spaces, or long shifts — a fitted respirator or powered air-purifying respirator. In tanks and vessels, a permit-required confined space program applies as well. Design the airflow in from day one; our guide to planning a safe shop covers exhaust and layout choices.

UV, Infrared, and Eye Protection

Arc burn, or photokeratitis, feels like sand in your eyes hours after the fact, and it comes from UV rather than heat. TIG runs bright on aluminium and stainless, so match your lens shade to the amperage and never flip the hood up to inspect the puddle while the arc is live. Wear safety glasses with side shields under the helmet for grinding and wire brushing, and cover exposed skin, because UV passes through thin sleeves. Our guide to protective eyewear for welding explains shade numbers and options that fit under a hood.

Electrical and Confined Space Risks

High-frequency starts and open-circuit voltage turn wet gloves, standing water, and a poor work-lead ground into real shock risks. Inspect cable insulation, never weld in the rain, and keep gloves dry. A ground clamp resting on painted or rusty steel is a common, avoidable cause of erratic arcs and shock risk. In confined spaces, fume and shielding gas accumulate quickly; argon and helium are heavier than air and can displace oxygen in a pit or tank before you notice.

Heat, Burns, and Ergonomics

TIG is slow, which means long minutes with your hands close to a hot joint. Contact burns from a stub or hot filler happen to everyone eventually; keep a quenching area and don’t grab rods by feel. Position work at a comfortable height to avoid neck and back strain, and take real breaks.

PPE: The Full Kit

Buy once, fit it properly, and replace damaged gear before it fails you. The baseline kit:

• Auto-darkening helmet with a shade matched to your process and amperage
• Leather gauntlet gloves thick enough to block heat and UV
• FR clothing, a leather apron or jacket, and closed shoes
• Safety glasses with side shields, worn even under the hood
• A respirator or PAPR for stainless, chrome, or confined work

Who Faces Higher Risk

Pregnant welders carry added concerns from fume, heat, and awkward positions, and the honest answer is that risk depends on exposure and control measures — read can you weld while pregnant before assuming it’s fine or impossible. Apprentices and anyone welding chromium-bearing alloys eight hours a day deserve the same scrutiny. The point of all this gear and airflow isn’t paperwork; it’s staying able to weld for thirty years.

Inspection, Testing, and Acceptance Criteria

A weld isn’t good because it looks good to you at midnight. It’s good when it passes the same inspection everyone else’s work passes — which means knowing your code, your inspection sequence, and what “acceptable” actually looks like.

Visual Inspection (VT) Comes First

VT is the cheapest, fastest, and most powerful test you have — and it catches the majority of TIG problems. Before anyone drags out a radiography rig, a certified inspector examines the joint under good light with a magnifier and a weld gauge.

Under AWS D1.1, the Structural Welding Code for Steel, visual acceptance criteria are both detailed and specific. For statically loaded joints, the code requires:

• Cracks: none. Any crack, regardless of size or location, is a reject.
• Undercut: depth limited by material thickness, commonly capped around 0.03 in. (1 mm) on thinner steel.
• Porosity: surface pores are limited in size, spacing, and frequency — not waved through as “a little.”
• Profile and size: the bead must meet the specified leg or throat dimension, with no overlap and no excessive reinforcement that hides incomplete fusion.

That last point matters. A fat, humped cap can mask lack of fusion underneath, which is exactly why profile limits exist. TIG welders who chase a pretty stack of dimes sometimes pass the eye test and fail the code.

NDT: When Visual Isn’t Enough

VT only sees the surface. For critical joints — pressure vessels, bridges, aerospace hardware — non-destructive testing supplements it, each method tuned to different flaw types:

• Penetrant Testing (PT): dye seeps into surface-breaking defects such as cracks and pinholes; excellent on stainless and aluminum TIG work.
• Magnetic Particle Testing (MT): a magnetic field and iron particles expose surface and near-surface defects in ferromagnetic steel — but not in austenitic stainless or aluminum.
• Radiographic Testing (RT): X-rays or gamma rays reveal internal porosity, inclusions, and incomplete fusion; strongest on volumetric flaws.
• Ultrasonic Testing (UT): high-frequency sound catches planar defects like cracks and lack of fusion that RT can miss, especially in thick sections.

TIG welds tend to fail in predictable ways. Tungsten inclusions show up on radiographs as dense, bright specks. Porosity appears as scattered round indications. Lack of fusion reads as a straight dark line — and it’s one of the most common reasons a weld that looked flawless gets cut out.

WPS, Welder Qualification, and ASME Section IX

Acceptance criteria don’t exist in a vacuum. The work follows a Welding Procedure Specification (WPS), backed by procedure qualification records. ASME Section IX governs the qualification of welding procedures and welder performance for pressure equipment, and its test-a-coupon, bend-it, radiograph-it logic underpins most welder certification systems in use today.

Your qualification covers specific positions, thicknesses, and processes. Weld out of position on a joint your cert doesn’t list, and the weld is nonconforming before the arc even starts — no matter how clean it looks.

A controlled shop — steady shielding gas flow, no drafts, dry filler, organized consumables — makes passing inspection far easier. Our guide to welding facilities covers layout, ventilation, grounding, and the environmental details that quietly drive defect rates. And if you’re still sharpening fundamentals, welding practice is the discipline that turns code compliance into muscle memory.

Reading a Rejection Correctly

When an inspector flags a weld, get the exact code reference before you grind. “Undercut” under D1.1 might be within limits on one job and out of limits on a cyclically loaded member. The inspector isn’t being difficult — the code is the contract. Document the repair, re-inspect the area, and never assume the fix passed just because it looks better.

Finally, remember that inspection is a feedback loop, not a verdict. Every rejected bead tells you something about your gas, your travel speed, your amperage, or your cleanliness. Log it, adjust it, and the next weld is better because the last one failed.

Practical Tips to Get Consistent Good TIG Welds

Ask a welder why one bead looks crisp and the next looks like a caterpillar, and you’ll usually hear a shrug: “Bad day.” Usually it isn’t luck — it’s a small drift in setup or technique you can catch before it costs you a part. Consistency is buildable, and it starts with a repeatable routine.

Prep First, Weld Second

Most TIG troubles begin before the arc ever starts. Wipe base metal with acetone, grind or brush mill scale to bright metal, and keep stainless brushes separate from carbon-steel ones. A dedicated stainless brush that touched mild steel will drag iron into your aluminium and leave black smut that looks like contamination. Match filler to base metal, cut it clean, and wipe it too.

• Grind tungsten to a clean, lengthwise point — and use a dedicated wheel for aluminium so you don’t cross-contaminate.
• Check gas flow at the cup: 15–20 CFH, sealed with a gas lens for tube work.
• Confirm polarity before you strike — see our guide to TIG welding polarity for DCEN, DCEP and AC setups.

Let Settings Do Their Job

Don’t chase the pedal all day. Dial amperage so the puddle forms in two or three seconds, then hold a steady travel speed — Miller’s TIG welding guide frames this as reading the puddle rather than the numbers. Consistent travel speed and torch angle produce uniform ripples and penetration; a wandering hand produces wandering heat. For thin material, a quick tack every few inches keeps the gap from closing before you get there.

Technique: Angle, Speed, Filler, Puddle

Hold the torch 10–15° off vertical, tilted back in the direction of travel. Push forward at a steady pace, and add filler to the leading edge of the puddle, not into the arc. Then watch the puddle, not the arc — the puddle tells you everything.

• Torch angle: too much lean washes the edges; too upright buries heat.
• Travel speed: too fast gives cold lap and overlap; too slow overheats and sags.
• Filler addition: dab, withdraw, dab again — timing creates the ripple rhythm.
• Puddle control: ease off the pedal on keyholes, then walk it out.

Troubleshooting at a Glance

The most common mistakes are the boring ones: a contaminated filler rod laid on a dirty bench, a tungsten dipped in the puddle and re-struck without re-grinding, a gas lens knocked loose. Each has a one-minute fix and an hour-long cost if you ignore it. Check tungsten condition every time you stop.

Before a critical job, burn a few beads on scrap using the exact same material, filler, and settings. If the scrap welds well, your machine and technique are dialled in; if it fights you, you’ve found the problem cheaply instead of on the finished part. This habit — the core of our guide to welding practice — is the single biggest divider between welders who improve and welders who plateau.

One shop learned this the hard way on a run of thin-wall stainless tube. Everything was clean and the machine was set right, yet three parts in a row showed porosity at the stop. The culprit was an open bay door pulling shielding gas away at the worst moment. A cheap welding screen fixed a defect that no amount of pedal control would have cured.

Build the checklist into your routine and consistency follows: prep, set, tack, brace, watch the puddle, and log what changed when something goes wrong. Acceptance standards like AWS D1.1 don’t care how good the bead looked in the moment — they care what the test says. Good TIG welds aren’t a gift; they’re a process you repeat on purpose.

Comparisons, Costs of Bad Welds, and When to Repair/Reject

Every welder eventually faces the same quiet math: is this bead good enough, or will it come back to cost me? The answer depends on the process, the code, and how late the defect surfaces. Understanding where TIG sits against MIG — and what a reject really costs — turns that gut feeling into a decision you can defend.

TIG vs. MIG: Quality, Speed, and Cost Compared

TIG typically delivers higher precision and cleanliness than gas metal arc welding (GMAW), producing cleaner, more controlled beads with minimal spatter — ideal for thin material, stainless, aluminium, and code-critical root passes. The trade-off is speed: manual TIG deposition rates are far lower, often a fraction of MIG’s, so labour cost per metre climbs quickly. MIG wins on productivity and is easier to automate, which is why high-volume shops lean on it while aerospace, tube, and sanitary work stay with TIG.

If you came up on wire feed, our breakdown of Good and Bad MIG Welds: How to Tell the Difference gives you the matching set of visual cues. The practical takeaway: neither process is “better.” The expensive weld is the one that fails inspection, regardless of how fast it was laid down.

The Real Cost of a Bad Weld

A defect found at the bench costs a grinding disc and fifteen minutes. The same defect found in the field after coating, assembly, or commissioning can multiply that cost by ten or more — scaffolding, mobilisation, NDT re-testing, and downtime all stack on top of the repair itself. Structural rework late in a project is routinely cited as one of the largest avoidable line items in fabrication.

Liability and Safety Implications

Bad welds are not just a cost problem. On pressure and structural work, they are a legal one. AWS D1.1 sets acceptance criteria for steel structures, and fabricated assemblies that fall outside those limits can expose a shop to liability if a joint later cracks or fails. Safety matters too: undersized or cracked welds on lifting gear and load-bearing frames create genuine injury risk, and welding activities themselves fall under OSHA 1926.353 ventilation and protection requirements.

Repair or Reject: Working to Code

When a defect is confirmed, the question becomes repair versus cut-out. Most minor discontinuities — surface porosity, isolated undercut, small spatter-related inclusions — can be repaired by grinding out the defect to sound metal, re-preparing the joint, and re-welding. The repair must restore full cross-section, not just cap the flaw.

Some defects are less forgiving:

• Cracks generally require complete removal of the cracked region plus a length of surrounding metal, because a partial repair rarely arrests propagation.
• Lack of fusion or penetration on a critical joint often means cut-out rather than surface repair.
• Contaminated repairs (base metal or filler mismatch) may demand full requalification under ASME Section IX procedures before re-welding.

A simple decision guide:

1. If the defect is shallow, isolated, and outside a critical section — grind and re-weld.
2. If it is a crack, or repeats in the same location — investigate root cause, then cut out.
3. If the part carries code status or pressure duty — consult the WPS and inspector before touching it.

The best repair, though, is the weld that never needed one. Controlled polarity and setup, covered in our TIG polarity guide, plus deliberate, repetitive welding practice, are what keep the reject pile empty. Treat every bead as if the inspector is already standing behind you, and the costly conversation about rework never has to happen.

Conclusion: Building a Quality-First TIG Mindset

Back to that late-night bead. You caught the porosity only when the light shifted — but that moment of catching it, diagnosing it, and knowing how to fix it is exactly what separates a welder who guesses from one who controls the outcome. Every section of this guide pointed the same direction: quality is not a lucky arc. It is the predictable result of preparation, settings, shielding, technique, and inspection working together.

Define Quality Before You Chase It

A good TIG weld is not merely pretty. It is a joint that satisfies its drawing, its code, and its service conditions: clean toes, even ripples, full fusion, no porosity, no undercut, no cracks. On structural steel the governing standard is often AWS D1.1, while procedure and welder qualification frequently fall under ASME BPVC Section IX. Learn which document applies to your job, then treat it as the target rather than an afterthought.

The Four Habits That Prevent Defects

• Prepare and clean: strip mill scale, oil, moisture, and oxide from both sides of the joint before the arc ever starts.
• Control the process: match polarity, amperage, and travel speed to the material — the difference between AC and DC is not optional.
• Protect the puddle: the right cup, gas flow, and trailing shield keep oxygen and nitrogen out of a reactive weld.
• Inspect as you go: catch a defect after one pass, not after the whole joint is welded and painted.

Get all four right, and most common TIG defects simply never get the chance to form.

Quality Includes Safety

A quality-first mindset is also a safety mindset. The same contamination that ruins a weld — chlorinated solvents, zinc fumes, improper shielding — is the same contamination that harms the welder. OSHA’s ventilation requirements for welding, cutting, and heating exist because those hazards are real. Clean fume extraction, proper PPE such as welding-specific protective eyewear, and disciplined housekeeping in a well-planned shop are not extras; they are part of producing good work. A welder who protects the puddle and protects themselves is working from the same principle: control the variables.

Your Final Good-Weld Checklist

Run through this before signing off any TIG joint:

• Correct polarity and amperage for the material thickness
• Clean base metal, filler, and tungsten
• Gas flow, cup size, and no drafts
• Consistent bead profile with no undercut, porosity, or overlap
• Post-weld inspection and, where required, testing

If any line fails, stop and correct it before the next pass — a rejected part always costs less than a failed one in service.

Keep the Skill Growing

Good TIG welding is a perishable skill. Thirty minutes of deliberate practice beats three hours of production welding for building muscle memory, and reviewing your codes keeps your judgment sharp as standards evolve. Cross-process work helps too — the wire-feed control you learn from a MIG or flux-cored setup transfers straight back to TIG. Our How to Use a Wire Welder: Complete Beginner’s Guide and Welding Practice guide are good next steps. Staying current with code revisions and new processes — from robotic submerged arc to DC aluminium techniques — keeps your judgment sharp and your welds sound.

A Look Ahead

So the next time the sun catches a bead and a faint line of porosity appears, you will not panic — you will read it. You will know whether it is gas flow, moisture, or technique, and you will know whether to grind it out or reject the part. That calm, repeatable confidence is what a quality-first mindset feels like. The welders who get hired, trusted, and promoted are rarely the ones with the prettiest beads alone; they are the ones whose work passes inspection the first time, every time. Keep your tungsten sharp, your metal clean, and your standards high, and good TIG welds stop being lucky and start being routine.

Frequently Asked Questions

What does a good TIG weld look like?

A good TIG weld has uniform, stacked ripples, smooth transition to base metal (good tie-in), consistent width, proper penetration, no cracks/porosity/undercut, and minimal discoloration. Code acceptance (e.g. AWS D1.1) defines specific limits.

How can I tell bad TIG welds from good ones?

Look for cracks, porosity, undercut, lack of fusion/penetration, overlap, tungsten inclusions, or heavy oxidation. Use good lighting and magnification; critical welds require inspection per governing code.

Why is my TIG weld full of porosity?

Porosity is usually caused by inadequate shielding gas coverage, drafts, contaminated base/filler, moisture, or leaks. Check gas flow, cup size, post-flow, surface prep, and torch angle.

What causes lack of fusion in TIG welding?

Common causes include insufficient heat input/amperage, wrong torch angle, poor joint fit-up, slow travel in wrong direction, or oxide contamination. Match settings to thickness and ensure clean joint.

Is TIG welding safe for your health?

TIG produces fewer fumes than some processes but still emits hazardous metals/fumes. Follow OSHA 1926.353 ventilation requirements, use respiratory protection when needed, and wear proper PPE including eye/face protection.

What codes govern TIG weld acceptance?

AWS D1.1 is common for structural steel; ASME Section IX governs WPS/welder qualification; other codes apply by industry. Always follow the code specified for your work.

Can bad TIG welds be repaired?

Many surface defects can be repaired by grinding out and re-welding per approved WPS/procedure. Cracks typically require complete removal and evaluation. Follow code requirements for repair.

When should I use AC vs DC for TIG?

Use DCEN for most steels and stainless (deep penetration). Use AC for aluminum to remove oxide (with appropriate balance/frequency). Material and joint design determine polarity.

Authoritative Sources & Further Reading

• https://www.aws.org/standards-and-publications/technical-standards/d1-1-d1-1m-structural-welding-code-steel
• https://www.osha.gov/laws-regs/regulations/standardnumber/1926/1926.353
• https://www.cdc.gov/niosh/topics/welding/
• https://www.asme.org/codes-standards/find-codes-standards/bpvc-section-ix-welding-brazing-fusing-qualifications
• https://www.ansi.org/
• https://www.nfpa.org/
• https://www.cdc.gov/niosh/npg/npgd0379.html
• https://www.lincolnelectric.com/en/welding-and-cutting-resource-center/welding-articles/
• https://www.millerwelds.com/resources/welding-guides/tig-welding-guide