Worm Tracking in Welding: Causes, Fixes, and How It Differs From Seam Tracking

Worm Tracking in Welding: Why Your Bead Looks Like a Worm Crawled Through It

You lift your hood after a clean pass and freeze. Instead of the tight, uniform ripples you were expecting, the surface of your bead looks like a tiny worm crawled across the hot metal and left a trail behind. There are little grooves, channels, and hollowed trails running along the face or the toe of the weld. If that’s the scene in front of you, you’ve just met worm tracking — and it’s worth understanding before you strike another arc.

Worm tracking (also called worm tracks or wormholes) describes small, elongated, worm-like gas channels or trails that open up on the face or toe of a weld. Despite the name, it isn’t a ripple pattern that went wrong. Worm tracks are a surface expression of porosity — trapped gas that pushed through the molten weld pool and left a channel behind as it escaped. What looks like a cosmetic blemish is often the visible tip of a gas problem sitting just below the surface.

The defect turns up most often in flux-shielded processes, especially flux-cored arc welding (FCAW) and submerged arc welding (SAW), where the flux itself can become a source of moisture and gas. If you’re still getting comfortable with wire-fed work, our guide to gasless MIG welding covers the flux-cored basics that set the stage for this defect. On the automation side, the same chemistry trips up robotic submerged arc welding just as readily as it does a hand-held stinger.

That naming collision causes genuine confusion, so let’s settle it early. Automated seam tracking is a sensing method; worm tracking is a flaw. Keep those two apart and the rest of the topic falls into place. Two very different problems simply share a nickname.

What This Guide Covers

This is a practical, code-aware walkthrough for hobbyists, fabricators, and pipeline welders alike. Whether you’re running a hobby machine in the garage or laying root passes in the ditch, the fix starts with understanding what’s happening at the arc. Each builds on the one before it. Over the next sections we’ll cover:

• What worm tracking is, how it looks, and where it appears
• The root causes: moisture, contamination, and process parameters
• The science of how gas gets trapped in the weld pool
• How to identify it through inspection and testing, and tell it apart from other defects
• Prevention through flux handling, cleaning, and parameter control
• Repair methods and what acceptance criteria actually require
• How it compares to seam tracking and other common weld defects
• Real-world settings for FCAW, SAW, MIG, and pipeline work

Why it matters beyond looks: worm tracks are a porosity signal. Even visually minor porosity can point to contamination or moisture problems that compromise weld integrity. Trapped hydrogen and gas can reduce ductility and set up cracking down the road. Fabrication codes such as AWS D1.1 treat excessive porosity as a discontinuity that may require repair, and pipeline work is even stricter about defects that can seed a failure under strain.

By the end, you’ll know exactly what causes worm tracking and how to stop it — not just how to make the bead look nicer. Let’s dig in.

What Is Worm Tracking? Definition, Appearance, and Where It Shows Up

Worm tracking is the name welders give to shallow, irregular channels and grooves on or just below a weld bead’s surface that resemble the trail a worm drags through wet ground. The metal around these channels may be gently raised, gently recessed, or a mix of both. The trails usually run along the bead edge, right at the toe line where the weld meets the base metal, which is exactly where gas escaping a covered pool likes to poke through.

A clean bead has ripples: even, repeatable ridges spaced the same distance apart from start to finish. Worm tracks break that rhythm. They branch, wander, stop and restart, or open into small pockets. Instead of a uniform fingerprint pattern you get something scattered and chaotic, as though the surface bubbled and collapsed just before it froze. Reading that difference is a core skill — telling good and bad MIG welds apart starts with the ripple pattern.

The Three Look-Alike Terms: Worm Tracks, Wormholes, and Porosity

These terms get swapped freely on the shop floor, but they describe different things:

• Surface worm tracks — the visible form: open channels on the cap or face, often near the toe, visible to the naked eye under good light.
• Wormholes — the subsurface cousin: elongated, tubular gas cavities that branch or run like a worm instead of forming round bubbles.
• Porosity — rounded gas voids, scattered or clustered, sitting anywhere in the deposit.

Under the hood, both surface worm tracks and wormholes belong to the cavity-type discontinuity family in IIW/AWS defect terminology — the same group as porosity, not the crack or lack-of-fusion groups. That classification matters, because it tells an inspector where to look and points the fix toward gas control and cleaning rather than structural rework.

Sometimes the channels look bright or slightly oxidized, and sometimes they sit nearly flush and are easy to miss in dim light. That subtlety is why worm tracking gets dismissed as cosmetic, right up until a bend test or radiograph exposes the wormholes beneath.

Worm Tracks vs. Wagon Tracks vs. Ripples

A quick side-by-side makes the distinctions easier to hold onto.

Wagon tracks are a different animal entirely: a single, straight, continuous groove tied to specific processes such as electroslag welding, not to trapped gas. Normal ripples, meanwhile, are uniform and repeatable — texture, not a defect.

Which Processes and Materials Are Prone

Worm tracks show up most often in flux-cored arc welding (FCAW) and submerged arc welding (SAW), where a molten slag layer blankets the pool and can trap gas against the freezing metal. A common gasless flux-cored setup is a frequent offender, and heavy SAW work such as robotic submerged arc welding can develop them too. Self-shielded flux-cored wires are especially guilty because their shielding comes from the flux itself. Gas metal arc (MIG) welding appears occasionally, usually when shielding is poor, the wire is contaminated, or a worn contact tip throws the arc off.

Material matters as well. Free-machining and high-sulfur steels are more prone to gas porosity and worm-track formation, as is rusty, mill-scale-covered, or oily plate. The sulfur and surface contamination give gas extra places to form and hold.

Where They Show Up on the Joint

You can find worm tracks on any pass — root, fill, or cap — but the cap and the toes get them most, because that is where gas has the shortest path out and the least chance to dissipate. On multipass work they sometimes reappear pass after pass, which is a strong hint that the problem is the wire, the flux, or the base metal rather than a one-off glitch.

Root Causes of Worm Tracking: Moisture, Contamination, and Process Parameters

Worm tracks rarely appear out of nowhere. Something injected extra gas into the pool, and the metal froze before it escaped. The causes rank in a rough order: moisture and hydrogen first, contamination second, process settings third. Fix them in that order.

Moisture and Hydrogen: The Number One Culprit

If you chase one cause, chase water. When moisture hides inside flux or an electrode coating, arc heat breaks that water into hydrogen and oxygen. Hydrogen dissolves readily into the liquid pool, but its solubility in solid steel is far lower. As the bead solidifies, the metal can no longer hold the gas, and worm tracks plus porosity form together.

Where does the moisture come from? More places than most welders expect:

• Damp flux or wire. A bag left open or a spool stored in a humid shop absorbs water.
• Electrode storage. Low-hydrogen electrodes need a rod oven; a lukewarm, humid cabinet is useless.
• Wet or rusty base metal. Rust is hydrated iron oxide, and that water becomes hydrogen under the arc.
• Moisture in gas lines. Condensation in shielding gas drags water straight into the arc.

For flux-cored work especially, gas generation is baked into the process, which is why getting the polarity right matters so much. If you are running self-shielded wire, our guide to polarity for flux core welding explains how DCEN vs DCEP changes arc behavior and gas shielding.

Contamination: Oil, Grease, Paint, and Sulfur

Contaminants break down under arc heat and generate trapped gas, while also disrupting pool flow. Watch for oil, grease, paint, rust, mill scale, and the drawing lubricants left on as-received steel. Clean the joint before you strike an arc.

Sulfur deserves its own mention. Free-machining steels contain added sulfur for chip control, and that sulfur is linked to worm tracks and gas porosity. If a job keeps producing tracks no matter how clean and dry you work, check the material spec.

Process Parameters That Open the Door

Settings do not usually start worm tracking on their own, but they make a marginal situation worse. Run through this list:

• Excessive arc voltage. A higher voltage stretches the arc, exposing the pool to more atmosphere and increasing nitrogen pickup, which raises porosity risk. Drop the voltage toward the low end of the range.
• Wrong stick-out (CTWD). Too long and the wire wanders while shielding degrades; too short and you overheat the tip.
• Wrong polarity. Each wire type wants specific polarity; the wrong one changes penetration, arc stability, and gas coverage. Our polarity reference covers the settings.
• Unstable wire feed. A worn drive roll or kinked liner makes the feed stutter, and a stuttering arc pulls in air.
• A worn contact tip. An eroded tip lets the wire wander, widening the arc and weakening shielding; our contact tip maintenance guide covers wear checks.
• Poor inter-run cleaning. Slag and spatter left between passes introduce trapped gas and defects on the next layer.

SSAB lists low and high travel speed, low arc voltage, long stick-out, and a worn contact tip among the causes of fusion and gas-related defects, confirming that unstable arc conditions sit at the center of most trouble.

Environment: Wind, Humidity, and Cold Plate

Your shop and jobsite matter too. Wind blows shielding gas away and lets air reach the pool. Humidity loads the air and your consumables with moisture. A cold plate chills the pool faster, cutting the time trapped gas has to escape. Shield the arc, store consumables properly, and preheat thick or cold steel when the procedure allows.

Quick Troubleshooting: Symptom, Cause, Fix

The Science Behind Worm Tracks: How Gas Gets Trapped in the Weld Pool

Think of a freshly poured glass of soda. While the liquid sits still, the dissolved carbon dioxide stays put. Shake it, warm it, or seal the top, and the gas has to go somewhere: bubbles form, and if they can’t escape, they get stuck. That’s essentially what happens inside a weld pool, except the “sealed top” is a skin of freezing slag and the trapped bubbles leave behind a visible trail.

Why Dissolved Gas Suddenly Needs Out

Molten steel can hold far more dissolved gas than solid steel ever can. As the pool cools and begins to freeze, that solubility falls off a cliff. Hydrogen is the textbook example, and the reason it drives so much weld porosity research. Its solubility in liquid iron is high, but it plummets the instant iron transforms from liquid to solid. Gas that was comfortably dissolved a moment ago is suddenly forced out of solution, and it has to move fast. Reach the surface and it vents harmlessly. Get caught, and it nucleates a tiny bubble. Those bubbles either freeze as rounded pockets of porosity or stretch into the long, wormlike channels we call worm tracks.

The Slag and Solidification Race

Here’s the heart of it: gas escape and metal freezing are racing on the same clock. A fast-freezing weld, or one blanketed by a viscous, slow-draining slag, can seal the surface before bubbles break through. The molten skin closes over like ice forming on a pond, and gas is trapped just beneath it. The result is those elongated worm tracks — channels frozen in the very act of trying to escape. Slow cooling does the opposite. It gives bubbles time to rise, break the surface, and vent, which is why a hot, slow, flat bead resists worm tracks that a chilled, fast bead invites.

Where the Gas Actually Comes From

Three sources cause most of the trouble:

• Hydrogen from moisture — damp flux, rusty plate, or condensation on the wire. Even a few drops of water are enough.
• Nitrogen from air entrainment — a long arc, weak shielding, or a breeze pulls air into the pool, and nitrogen behaves much like hydrogen.
• Carbon monoxide from poor deoxidation — insufficient deoxidizers in carbon and low-alloy steel consume oxygen poorly, so CO bubbles form and freeze in place.

How Arc Length, Heat Input, and Position Change the Rules

Every variable that changes how long the pool stays molten changes whether gas escapes. A long arc and poor gas coverage invite nitrogen in; a tight arc under solid shielding keeps it out. In GMAW, remember that a worn or recessed contact tip quietly stretches your effective arc length, letting more air into the arc. Heat input matters enormously — hotter, slower welds hold the pool liquid longer, giving bubbles a window to vent, while cold, fast welds slam that window shut. Position does the same thing. Vertical-up welding uses a fast-freeze technique, so the thin, quickly solidifying pool traps gas far more readily than a slow, flat-position bead. High-current welds add another wrinkle: they freeze quickly and can outrun the gas trying to rise out.

Preheat and interpass temperature tip the balance too. A warm base plate slows solidification and lets gas escape before the surface seals, while a cold plate accelerates the freeze and locks gas in. Keep your interpass temperature in the range your procedure calls for, and mind the fit-up and ventilation guidance in standards like OSHA 1910.252 when setting up the job. Understanding this mechanism is step one; controlling it is the skill you build through deliberate welding practice.

How to Identify Worm Tracking: Inspection, Testing, and Telling It Apart From Other Defects

Worm tracks rarely hide. Because they break the weld surface, a sensible inspection sequence catches them fast — and keeps you from misreading them as something more serious or more harmless than they are.

Step 1: Visual Testing (VT)

Visual testing is your first line of defense and the cheapest check you own. Worm tracks are surface-breaking, so a strong light, a magnifier, and a trained eye often finish the job. You’re looking for irregular, winding channels that snake along the bead, often near the toes or the centerline. Low-power magnification, roughly 5x to 10x, makes the fine ones stand out. Clean the joint first, and keep your eyes protected — any grinding or brushing flings debris, so protective eyewear for welding is a given.

Step 2: Surface and Subsurface NDT

Not every track is obvious, so surface and volumetric methods back up the naked eye.

• Liquid penetrant testing (PT) exposes surface-breaking gas tracks too fine to see unaided. The penetrant seeps into the channel and stains it, giving you a clear, low-cost map of the surface network.
• Radiographic testing (RT) looks inside the weld. Subsurface wormholes and porosity appear as darker indications on the film, telling you how deep the gas entrapment really goes.
• Ultrasonic testing (UT) is favored for planar defects like lack of fusion, where a sharp, unbonded plane reflects sound far more strongly than rounded gas pores do.

Step 3: Destructive Confirmation

On coupons, test welds, or cut sections, destructive checks confirm what NDT suspected. A macro etch — polishing a cross-section and etching it with acid — opens the defect so you can size individual wormholes and see whether they connect. A guided bend test stretches the weld and exposes internal porosity as opened pinholes on the tension face. These checks turn a suspicion into documented fact, and they’re the same skills you sharpen through steady welding practice.

Differential Diagnosis: Telling Defects Apart

Where welders get tripped up is the differential diagnosis — several defects look vaguely similar at a glance.

The important thing is to separate the cosmetic from the critical. Lack of fusion is one of the most serious weld defects because it creates a sharp notch effect that concentrates stress — a far bigger deal than a few gas tracks. It often traces back to low or high travel speed, low arc voltage, long stick-out, or a worn contact tip, so checking your contact tip condition is a smart first move, and understanding how your polarity affects the arc helps too (see polarity for flux core welding: DCEN vs DCEP). Wagon tracks are a separate linear defect, while worm tracks are irregular and gas-formed; confusing the two sends you chasing the wrong fix.

Why Accurate Identification Matters

Identification drives both the repair decision and the code call. A cluster of worm tracks that exceeds the acceptance criteria in your governing standard is a repair; a faint cosmetic track within limits may pass as-is. Misreading lack of fusion as porosity, or porosity as worm tracking, changes the repair method, the re-inspection level, and the paperwork. And knowing what a sound bead looks like is your baseline for spotting when something is off. Document every finding: location, size, depth, the method used, and photos.

Preventing Worm Tracking: Flux Handling, Cleaning, and Parameter Control

Worm tracks are stubborn, but they’re also predictable. Nearly every case traces back to one of three things: a moisture source, a dirty joint, or a parameter that pushed gas into the pool faster than it could escape. Fix those three and the worms disappear. What follows is a practical checklist you can run before, during, and after any job.

Consumable Handling: Keep It Dry, Keep It Clean

Moisture pickup in a humid shop is a leading cause of hydrogen-driven worm tracks, so treat every consumable like it matters — because it does.

• Store flux and electrodes dry and per the manufacturer’s instructions. Follow their temperature and humidity limits exactly.
• Use heated ovens for low-hydrogen electrodes and keep them there until the moment of use. Rods left out overnight can pick up moisture.
• Never recycle wet, contaminated, or dirty submerged arc welding flux. Sieve out fines, discard clumped flux, and never sweep floor flux back into the hopper.
• Check wire cleanliness. Rusty, oily, or drawing-lubricant-coated wire drags contamination straight into the pool. Wipe a sample and look.
• Rotate your stock. Use the oldest sealed consumables first, and never leave an open package sitting in a damp corner.

Joint Preparation: Clean to Bare Metal

Clean the joint to bare metal before welding. Contaminants decompose in the arc and release the gases that form porosity. Remove rust, mill scale, oil, grease, paint, and lubricant from the faying surfaces and at least an inch into the heat-affected zone. Use a grinder, wire brush, or solvent wipe as appropriate, and re-clean if the part sits exposed for long. Use dedicated brushes for stainless and carbon steel so you don’t smear one alloy’s contamination onto another. Sulfur-bearing steels deserve special attention — sulfur raises hot-cracking and porosity susceptibility, so confirm the grade and adjust your WPS rather than guessing.

Process Control: Voltage, Stick-Out, and Hardware

Excessive voltage or long stick-out increases nitrogen pickup and porosity. This is one of the most common self-inflicted causes of worm tracks, especially in FCAW. In the field, most parameter-driven worm tracks show up when someone chases speed and cranks the voltage.

• Set correct arc voltage and current within the WPS range for your wire diameter and position.
• Keep stick-out (CTWD) within range — too long lets shielding weaken and atmosphere enter.
• Replace worn contact tips and liners to keep current and wire feed stable. A wobbling wire throws the arc off.
• Verify polarity. Running the wrong polarity changes penetration, arc stability, and gas behavior — see our guide to polarity for flux core welding.
• Maintain stable wire feed. Inconsistent feed creates voltage swings that mimic porosity defects.
• Check the gun liner and drive rolls. A kinked liner starves the arc of wire and destabilizes the pool.

Environment, Shielding, and Preheating

Verify shielding gas flow and quality. Moisture or air in the gas line causes porosity in gas-shielded FCAW, so check the regulator, drain your lines, and confirm the cylinder is the right grade. Control drafts around the arc — a fan or open door can blow shielding away, and airflow also matters for fume control under OSHA’s welding standard. Set flow rate to the WPS recommendation; too much flow causes turbulence that sucks air into the stream, and too little leaves the pool exposed. On thick or cold, damp steel, use preheat to drive off surface moisture and slow cooling so gas can escape before the weld freezes. Gasless processes sidestep shielding-gas moisture entirely; read more in our gasless MIG welding guide.

The WPS Discipline Loop: Test, Measure, Adjust, Record

Prevention only sticks when it’s documented. Treat your WPS as a feedback loop: weld a test coupon, test it (visual, then dye-penetrant or radiography if the code requires), measure the result, adjust one variable at a time, and record what worked. One change per trial keeps you honest. Log holding temperatures, ambient dew point, and the batch numbers of the flux and wire you used so a repeat failure is easy to trace. Shop layout, airflow, and storage practice matter too, so it pays to plan them deliberately — see our guide to setting up welding facilities. That loop turns a one-time fix into a habit that keeps worm tracks out of your production.

Repairing Worm Tracking and Meeting Acceptance Criteria

Worm tracks can be cosmetic, but the metal underneath is what decides whether you reach for the grinder. Before you choose a fix, measure the defect: how deep the channel runs, how many pores sit beneath it, and what the applicable code actually permits. Shallow surface ripples with no visible porosity may be acceptable as-is. A track that opens into subsurface gas pockets must come out.

Step-by-Step Repair

Running a hot pass straight over the top is a trap — you cap gas under fresh metal and bury a defect you’ll regret. Worm-track repairs typically require grinding or gouging out the affected metal to sound weld, then re-welding with a corrected procedure. The order matters:

1. Locate and mark the affected length with soapstone or paint.
2. Grind or gouge down past the tracks until you reach clean, sound weld — no dark streaks, no pinholes.
3. Clean the excavated area, blowing out every trace of grinding dust.
4. Correct the root cause — dry the flux, clean the base metal, retune the parameters.
5. Re-weld using a procedure that’s been verified for that joint.

Grind depth is where judgment counts. Take the channel down until a dye-penetrant check or a flashlight-and-mirror look shows only clean metal, then a little more to be safe. On thicker sections a carbon arc gouge is faster, but grind back the heat-affected layer afterward, because gouging can leave a carburized skin that seeds new porosity.

That fourth step is the one people skip. Skip it and you simply reproduce the same worm a second time. If you’re chasing settings, our guide to polarity for flux core welding is a good place to confirm you’re running the right polarity for your wire.

What the Codes Accept

Acceptance is defined by the standard that governs your job, not by how the bead looks.

• AWS D1.1 (visual acceptance): welds must be free of cracks, with porosity limits that depend on weld type and loading.
• API 1104: governs pipeline girth welds and sets workmanship acceptance limits for porosity and related defects.
• ASME: sections like B31 and Section VIII set their own porosity and repair rules, so check the one called out on your drawings.

The AWS D1.1 documentation is worth knowing before you argue about a reject. Bottom line: cracks are always rejectable; porosity limits vary, so read the actual clause.

Pipeline work adds a twist. The Canada Energy Regulator cautioned that girth welds meeting API 1104 can still be prone to failure under longitudinal strain, which underlines that passing visual limits isn’t enough if technique is poor.

Repair Limits and Rejection

Every code caps how many times you can repair a joint. Repeated repairs beyond the allowed number can reduce toughness and stack up residual stress, so the whole weld or component may have to be rejected and replaced. Reject and replace is cheaper than a failed weld in service. When in doubt, document each repair and let the engineer decide — don’t quietly add a fourth pass.

The real lesson sits in your paperwork. A documented root-cause and corrective action — drying flux, cleaning base metal, adjusting parameters — is what stops worm tracks from returning after the weld is fixed. Writing down what changed turns a one-off repair into a permanent fix, and that habit is what separates a professional from someone grinding the same defect twice. Many fabricators photograph each repaired area and attach the grind-out evidence to the inspection report, so everyone learns which parameter drifted. If you want to build those habits deliberately, our welding practice guide and the piece on overlap defects both drill the discipline of doing it right the first time.

Worm Tracking vs Seam Tracking vs Other Weld Defects: Clearing Up the Confusion

Few words cause more confusion in a weld shop than “tracking.” Depending on who is saying it, tracking is either the smart sensor that steers your torch or the ugly, wormy groove ruining your bead. The two share a name and almost nothing else. Here is the clean split.

Seam Tracking Is a Tool, Not a Defect

Automated seam tracking, also called joint or weld tracking, is a sensing technology that guides the torch along the joint in robotized and automated welding. It is a tool, not a defect. Two approaches dominate.

Thru-arc seam tracking (TAST) reads the welding arc itself. As the torch weaves across the joint, arc current and voltage shift, and the controller uses that feedback to steer the torch left, right, up, and down. ABB’s WeldGuide IV samples arc impedance at 25 kHz and can correct both vertical and horizontal position to within 0.01 mm.

Laser-vision tracking is the optical cousin. It projects a laser line just ahead of the torch, and a camera reads the reflected profile to triangulate the joint’s position. Lincoln Electric notes laser systems can track joints on material under 1 mm thick at weld speeds up to 100 ipm. In short, TAST works best where optics cannot see, while laser tracking excels on clean, visible seams and thin material.

In field work, a published study demonstrated real-time girth weld tracking for X80 pipeline steel using arc sensors and feature-region fusion, targeting narrow-gap, all-position welding. You will see seam tracking most in high-volume robotic cells, such as robotic submerged arc welding, where consistent torch position beats a human’s steady hand.

Worm Tracks vs the Other Usual Suspects

Now back to defects. Worm tracks are gas-driven: trapped gas escapes as the pool freezes and carves channels across the surface. Each defect leaves its own signature once you know what to look for. Compare them to the other usual suspects.

Notice the pattern: wagon tracks, overlap, and undercut are mechanical or geometric, while worm tracks and porosity share a gas mechanism. That distinction matters because the fixes are completely different. Overlap, for instance, is covered in our guides to the overlap welding defect and overlapping welding technique vs defect.

Which Process Tracks Worms the Most?

Risk comes down to how much gas each process can trap and how much moisture its consumable brings to the arc.

In practice, flux-based processes dominate worm-track complaints. Severity ultimately depends on your acceptance criteria, whether that is AWS D1.1, ASME, or a pipeline standard, not just on appearance.

One more myth to clear up: “tracking” does not mean one thing. A pipeline girth-weld tracker and a worm-track defect are unrelated ideas that forum chatter constantly blurs. Separate the automation feature from the defect, match the right tool to the job and the right diagnosis to the defect, and you will troubleshoot the real problem.

Practical Tips and Settings: FCAW, SAW, MIG, and Pipeline Welding

Worm tracks rarely come from a single bad habit. They come from a stack of small ones: damp wire, wrong polarity, a gas line that surged, or a travel speed that outran the pool. The fix is process-specific, so here is how to tune each setup.

Self-Shielded (Gasless) FCAW

The flux inside a self-shielded wire does the shielding itself, so anything that degrades that chemistry shows up fast. Store electrodes in a dry, ideally heated cabinet, and never leave spools open overnight in a damp shop.

Polarity matters enormously. Many self-shielded wires are designed to run on DCEN (electrode negative), while gas-shielded flux-cored wires commonly run DCEP (electrode positive). Get it backwards and you raise spatter while driving porosity straight into the bead. Our polarity for flux core welding guide breaks down DCEN vs DCEP, and the gasless MIG welding guide covers the full process picture.

Keep contact-tip-to-work distance (CTWD) inside the wire manufacturer’s range. Too long and you lose current density and shielding, which promotes the trapped gas that becomes worm tracks. Hold a steady drag angle and stop the nozzle from climbing as you move. Tip position is covered in our contact tip welding guide.

Gas-Shielded FCAW and MIG

With gas, your job is keeping the shield clean and steady. Verify flow at the nozzle, not just the regulator, and check for leaks, kinked liners, and clogged tips. Drafts from open doors, fans, or a neighbouring grinder will blow the shield away and let nitrogen and oxygen into the pool. A quick pre-flow and post-flow check is cheap insurance against the shielding gaps that start worm tracks.

Match travel speed to position. Too fast freezes the pool before gas escapes; too slow overheats it and disrupts shielding. Keep the arc on the leading edge of the puddle. If you want to brush up on current types, the TIG welding polarity guide is a useful refresher, though MIG polarity is fixed by the process.

Submerged Arc Welding (SAW)

SAW lives or dies on flux condition. Store flux in heated ovens, and recycle only clean, dry flux. Wet flux is a classic source of wormholes because trapped moisture flashes to steam under the arc. Control current and voltage to the specific wire-flux combination named in your procedure. For high-deposition work, robotic submerged arc welding adds a consistency manual travel struggles to match.

Pipeline and Girth Welding

Field conditions are hostile: wind, humidity, and cold pipe. Procedure discipline wins here. Follow preheat requirements so hydrogen has a chance to escape, and use seam-tracking tools like arc-sensing systems to hold the joint consistently. Consistency beats aggression on a pipeline. Girth weld failures are often traced to construction and procedure issues, as documented in this CER safety advisory.

A Settings Troubleshooting Starter

Test and Log

Change one variable at a time, run a coupon on scrap, and write down exactly what you changed. Log wire type, polarity, CTWD, gas flow, voltage, amperage, and travel speed. When worm tracks return, the culprit is usually one line you touched, and the log isolates it in minutes. That habit builds skills far faster than raw arc time, as we explain in our welding practice guide. Keeping a written procedure also lines you up with recognised practice, like the AWS welding procedure form.

Conclusion: Taming the Worm and Welding Cleaner Beads

Worm tracks look mysterious the first time they show up on an otherwise decent bead. A wandering, worm-like groove appears along the toe or face of the weld, sometimes branching, sometimes threading through the surface like a burrow. Worm tracks go by several names, including wormhole porosity, wormhole defects, and surface porosity, but they all describe the same thing: gas that could not escape the weld before the metal froze. It shows up across processes, from flux-cored to MIG, whenever shielding gas or vapor gets trapped. The truth is reassuring. Worm tracking is a defect you can diagnose, and it almost always traces back to something you can control. Moisture, contamination, or parameters that drifted out of range account for the overwhelming majority of cases welders actually see in the shop. Random bad luck rarely earns a spot on that list.

In practical terms, the worm is simply trapped gas. As the molten pool solidifies, dissolved hydrogen or nitrogen, often carried in by moisture or contamination, comes out of solution and pushes toward the surface. If the metal freezes before that gas reaches the air, it leaves a channel behind. That is why the fix is rarely about welding prettier; it is about removing the gas source or giving the gas time to escape.

Once you accept that, the problem stops feeling like a mystery and starts feeling like a checklist. The welder who understands why the worm appears can fix it in minutes. The one who only memorizes a single cure keeps meeting it again in a slightly different disguise.

The Diagnostic Path That Works

Stop guessing and follow the same sequence every time: identify the defect, find the root cause, fix it, then verify the result. Skipping straight to a fix is why so many welders chase the worm in circles: they change shielding gas, then wire, then technique, and never learn which change actually mattered.

Identify means confirming you are looking at worm tracks and not a mechanical scratch, a slag inclusion, or a simple arc mark. Real worm tracks are elongated, irregular, and often appear in clusters or wander across the bead face. A scratch from a grinder or a stray tool follows a straighter, more predictable line. Good light and a magnifier make the call much easier.

Find the root cause means checking the usual suspects in order, cheapest and fastest first. Start with damp flux or wire, because moisture is the most common driver. Move to dirty steel: mill scale, oil, rust, and paint all release gas as they burn. Then check whether a voltage or travel-speed change crept into the settings, and finish by inspecting a worn contact tip or a loose liner that lets feed stutter. Write your findings down as you go, because memory blurs after a long shift.

Fix means correcting that one variable and nothing else, so you know exactly what worked. Verify means welding a test piece, letting it cool, and inspecting it under good light before you commit the rest of the run to production. Keep the coupon from your verified test and re-run it whenever a similar defect appears, because a known-good reference speeds up every future diagnosis and turns tribal knowledge into a repeatable process. This identify-fix-verify workflow resolves most worm-track issues without repeated rework, and it teaches you something useful every single time.

A few traps derail this process. One is changing several variables at once, which erases the information you need. Another is trusting a single test bead on scrap that is dirtier than the real part. A third is assuming the wire is dry because the bag was sealed; bags get opened, and opened bags absorb moisture. Treat every assumption as something to check, and the diagnosis speeds up dramatically.

Prevention Fundamentals to Lock In

None of this is exotic or expensive. Prevention comes down to a handful of habits you can lock in today and repeat on every job:

• Dry consumables: store flux and wire sealed with desiccant, rotate your stock so nothing sits for months, and never leave spools out in humid shops overnight.
• Clean base metal: remove mill scale, oil, rust, and paint, and wipe the joint down with a clean rag before you strike an arc.
• Controlled parameters: hold voltage and stick-out steady from one pass to the next, since both shift how gas behaves in the pool and how easily it escapes.
• Correct polarity: confirm your setup for DCEN vs DCEP on flux-cored wire, because flipping polarity changes shielding behavior and penetration.
• Stable wire feed: inspect and size contact tips so feed stays smooth, and keep drive-roll tension right so porosity stays low.

Together these five habits remove the moisture, dirt, and instability that feed worm tracks, and they cost almost nothing to maintain.

Worm Tracking Is Not Seam Tracking

One last distinction worth keeping straight: worm tracking is a defect in the weld itself, while seam tracking is a technology for following it. Say the two out loud and the confusion disappears.

Seam tracking uses sensors and software, like arc sensing, to steer a torch along a joint automatically, and it is common in automated setups such as robotic submerged arc welding. The system watches arc current, voltage, or a laser line and nudges the torch left or right to stay on the seam. When it works, it keeps a long, straight weld centered for hours.

Worm tracking has nothing to do with that. When you diagnose a wormy bead, you are chasing gas entrapment: moisture, contamination, or unstable parameters pushing gas into the molten pool faster than it can escape. Mixing the two up sends you looking for a machine problem that does not exist, while the real cause sits quietly in a damp bag of flux. In manual welding there is no seam tracking at all; the operator is the tracking system. That is exactly why worm tracks on a hand-held bead have nothing to do with automation and everything to do with gas, moisture, and technique. Knowing which term you actually mean keeps you from wasting an afternoon troubleshooting the wrong system.

Your Next-Step Action List

When a wormy bead stops you, work through this list in order:

1. Confirm the defect and photograph it, so you can compare before and after.
2. Check moisture first: flux, wire, and storage conditions.
3. Clean the joint down to bare, dry metal.
4. Re-verify voltage, stick-out, travel speed, and polarity.
5. Inspect the contact tip and liner; replace them if worn or loose.
6. Run a test coupon and inspect it before production.

Most welders find the culprit in the first three steps. If you get to step six with no change, go back to the callout above and question your consumable storage again.

Cleaner beads are not a talent. They are a habit built one variable at a time. Every welder who has beaten worm tracking did it by building consistency: the same dry consumables, the same clean prep, the same checked settings, run after run. That consistency is what makes the defect stand out instantly when it finally shows up, because the only thing that changed is obvious.

To sharpen the underlying skills, spend time on deliberate welding practice instead of just running production passes. Understand your setup from the wire up, including how gasless MIG welding behaves differently from solid-wire work, and how shielding choice changes the way gas escapes the pool. Keep a simple log of settings for each job so a drifting voltage or a tired contact tip announces itself early, and re-check your consumable storage every week rather than every season. It also helps to slow down the variables you can see. Keep a scrap coupon of the same material next to every job so you can test a change without risking a finished part, and inspect your weld as soon as it cools rather than after the whole assembly is built.

Tame the worm once, and you will recognize it in seconds for the rest of your career. The mystery disappears the moment you stop treating worm tracking as bad luck and start treating it as a signal that points straight to moisture, dirt, or a setting that slipped out of range.

Frequently Asked Questions

What is worm tracking in welding?

Worm tracking (also called worm tracks) is a surface gas/porosity defect that leaves small, elongated, worm-like channels or trails on a weld bead, most often in flux-shielded processes like FCAW and SAW. It occurs when gas trapped in the molten pool escapes through or under the slag as the weld solidifies. It is a cavity-type discontinuity, not a cosmetic ripple pattern.

What causes worm tracks on a weld?

The leading causes are moisture and hydrogen from damp flux or electrodes, contamination such as oil, grease, rust, paint, and mill scale, and out-of-range parameters including excessive arc voltage, wrong polarity, and long stick-out (CTWD). Sulfur in the steel and poor inter-run cleaning also contribute. Correcting the source is more effective than chasing the symptom.

Is worm tracking the same as porosity?

Worm tracks are a specific, elongated surface form of porosity caused by gas escaping as the weld solidifies. General porosity appears as rounded gas voids, while wormholes are elongated subsurface gas cavities. All are cavity-type discontinuities, but their appearance and location help determine severity and repair.

Can worm tracks be repaired?

Yes. The usual repair is to grind or gouge out the affected metal back to sound weld, clean the area, correct the root cause, and re-weld with a verified procedure. Simply welding over worm tracks will not remove the trapped gas. Always document the root cause so the problem does not return.

Will worm tracks fail a weld under AWS D1.1?

It depends on the extent and weld type. AWS D1.1 requires welds to be free of cracks, and porosity limits for visual inspection vary with weld type and loading. Even when worm tracks are within limits, they often signal a contamination or moisture problem that should be corrected to protect overall weld quality.

Which welding process is most likely to produce worm tracks?

Flux-cored arc welding (FCAW) and submerged arc welding (SAW) are the most common culprits because a molten slag layer covers the pool and can trap gas. Gas-shielded FCAW, MIG/GMAW, and SMAW can also produce them when moisture, contamination, or parameter problems are present.

How do I stop worm tracks in flux-cored welding?

Store wire and electrodes dry, clean the joint to bare metal, keep contact-tip-to-work distance within the manufacturer’s range, verify polarity, and control arc voltage and travel speed. Check for drafts and confirm shielding gas quality on gas-shielded wire. Test parameter changes on scrap and log what works.

Is worm tracking the same as weld seam tracking?

No. Worm tracking is a weld defect caused by trapped gas. Seam tracking (sometimes called weld tracking) is an automation technology that guides the torch along the joint using arc sensors, lasers, or cameras. The two share a name similarity but describe completely different things.

Authoritative Sources & Further Reading

• https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.252
• https://www.cdc.gov/niosh/topics/welding/
• https://www.ssab.com/en/support/how-to-process/how-to-weld/welding-defects-and-discontinuities/lack-of-fusion
• https://www.ndt.net/article/wcndt00/papers/idn403/idn403.htm
• https://pmc.ncbi.nlm.nih.gov/articles/PMC10747874/
• https://pmc.ncbi.nlm.nih.gov/articles/PMC12552434
• https://www.lincolnelectric.com/en/Welding-and-Cutting-Resource-Center/Process-and-Theory/Intelligent-Robotic-Arc-Sensing
• https://www.abb.com/global/en/areas/robotics/products/equipment/arc-welding/weldguide
• https://www.cer-rec.gc.ca/en/safety-environment/industry-performance/information-safety-advisories/safety-advisory/2020/safety-advisory-sa-2020-01-girth-weld-area-strain-induced-failures-pipeline-design-construction-operation-considerations.html
• https://pubs.aws.org/content/free_downloads/Form_N1.pdf