That pinhole at the end of a TIG weld is one of the most irritating things to chase. A TIG pinhole at end of weld usually means the puddle didn’t get enough filler or shielding when the arc stopped, and the cause is often in your stop technique, gas settings, or material prep.
The good news is that this failure is predictable. Per the American Welding Society’s D1.1 code, crater voids and porosity count as weld discontinuities, so they matter for strength, not just appearance. As of 2026, most inverter machines include current taper and adjustable post-flow, which makes many of these pinholes preventable once you know which branch to follow.
Let’s work through the diagnosis step by step.
Quick Answer: What Causes a Pinhole at the End of a TIG Weld?
A TIG pinhole at end of weld forms when the crater shrinks without enough filler. It can also form when shielding gas leaves before the metal cools. Fix it by filling the crater and holding post-flow.
Then inspect the hole shape to rule out contamination.
Read the Pinhole First: Shape, Location, and What It Tells You
Before you change machine settings, look at the hole. The shape, location, and pattern around it point to the root cause. This is where most welders skip ahead and waste an afternoon guessing.
A single, clean hole in the center of the crater usually means crater shrinkage. A cluster of tiny pits near the end usually means gas or contamination. Dark discoloration around the hole points to shielding loss.
Bright, shiny edges suggest the puddle collapsed while molten.
Also check the color of the surrounding weld. Blue or gray discoloration near the hole often means the gas cutoff too early. Clean silver metal with a single hole points back to crater fill.
If you need to, zoom in with your phone camera. The difference between a smooth funnel and a rough gas pore is easier to see when you enlarge it.
Crater Pinholes vs. Gas Porosity: How to Tell the Difference
| Feature | Crater Pinhole | Gas Porosity |
|---|---|---|
| Location | Center of the weld crater | Along the weld, often clustered near the end |
| Shape | Round, open funnel | Small, round pits |
| Number | Usually one | Usually several |
| Primary cause | Arc removed too fast, no filler added | Gas loss, contamination, or moisture |
| Visual cue | Puddle collapsed inward | Bubbles frozen in the metal |
If the hole looks like a small volcano, treat it as a crater issue. If it looks like pop marks, treat it as gas or contamination. That simple check tells you which branch to follow.
Branch 1: Crater Shrinkage – Why It Happens and How to Fix It
Crater shrinkage is the number one cause of a TIG pinhole at end of weld. If you’re still learning the process, the fundamentals of TIG welding are worth a quick read. When you snap the arc off, the molten puddle cools fast and the metal shrinks as it solidifies.
Without enough filler, the center collapses into a void. On thicker material, that void can become a crater crack.
Here’s the pattern to look for:
- One hole, right in the middle of the crater.
- The weld looks otherwise clean and bright.
- No surrounding soot or oxidation.
If that matches, the fix is mostly about how you finish the weld.
Fill the Crater Properly
The most direct fix is to add filler metal before you stop. As you approach the end, dip the filler into the center of the puddle once or twice. Keep the arc on for a second or two, then ease off.
That extra material offsets the shrinkage and leaves a dome instead of a hole.
On a fillet weld, try a slight back-step before stopping. Move the arc back into the previous weld bead, add a small dab of filler, then kill the arc. This gives the hot spot enough volume to solidify without sinking.
Use Current Taper or Pedal Dwell
Modern machines often have a current taper or crater fill function. Set it to ramp the amperage down over 3 to 5 seconds. If you’re on a foot pedal, roll back gradually and hold the heat low for a moment.
The goal is a controlled freeze, not an abrupt cutoff.
Manufacturer specs on most inverter machines list taper time in tenths of a second. Start at 3 seconds and adjust from there. For thin wall tubing, go shorter.
For thick plate, go longer. The pinhole at the end is your feedback signal.
Adjust Your Stop Technique
Your physical stop matters just as much. Pulling the torch away while the crater is liquid is a guaranteed way to get a pinhole. Keep the torch still, keep the same torch angle, and wait until the puddle visibly solidifies.
Then move away. If you’re unsure about your torch setup, the torch setup and consumables page covers the parts that affect this.
Branch 2: Gas Shielding Failures – Post-Flow, Gas Lens, and Travel Speed
If the pinholes show up as a cluster, or if the end of the weld looks oxidized, suspect gas shielding. The puddle needs argon coverage until it cools below its solidus temperature. Losing coverage a split second too early is enough to pull air in.
Argon coverage plays the same role in other processes, which is why it helps to understand the basics of argon shielding before you change hardware. The same principle applies to MIG welding as a process. Then work through these three checks.
Check Post-Flow Time
Post-flow is the timer that keeps argon flowing after the arc stops. A solid rule of thumb is one second per 10 amps. At 150 amps, set about 15 seconds.
At 200 amps, close to 20. If your post-flow is under 10 seconds, that’s likely your problem.
Also set your flow rate around 15 to 20 cubic feet per hour with a gas lens. Too much flow creates turbulence and draws air in. Too little flow leaves the cooling weld exposed.
Inspect Gas Lens and Cup Condition
A damaged gas lens or chipped cup turns smooth gas flow into turbulence. That turbulence pulls in air at the end of the weld. Check the lens screen for dings, holes, or spatter buildup.
Replace the cup if it’s cracked. Also check the gas hose for leaks and loose fittings.
A simple trick is to press the torch trigger and feel the gas flow at the cup. It should feel soft and even. If it hisses or sounds harsh, something in the gas train is wrong.
Watch Your Torch Angle at the End
When you finish, keep the torch angle steady. Lifting the torch while the puddle is still hot creates a low-pressure zone that sucks air in. Hold position for a few seconds after the arc stops, then move away.
This single habit fixes more end pinholes than any machine setting.
Branch 3: Contamination Issues – Tungsten, Base Metal, and Filler Rod
If you have filled the crater and confirmed gas coverage, contamination is the next suspect. This branch is sneaky because the source can be the tungsten, the base metal, or the filler rod. A quick check of all three usually solves it.
Contamination control is one of the biggest practical differences between welding processes. If you want the full picture, the different process setups page explains those differences clearly.
Tungsten Condition and Contamination
If your tungsten touched the puddle, it contaminates the weld with tungsten oxide. That oxide can create a pinhole at the end or anywhere along the bead. Grind the tungsten with the grind lines running lengthwise on a clean wheel.
If you see even a tiny ball on the tip, stop and fix it before you continue.
Tungsten contamination often shows up as a stray spark or an arc that wanders. Catch that early, and you avoid chasing pinholes later.
Base Metal Cleanliness
Oil, grease, rust, mill scale, and even the oil from your fingers turn into gas at welding temperature. On aluminum, that gas shows up as pinholes near the end. Clean the joint with acetone, then brush it with a stainless wire brush dedicated to that material.
For steel, remove all paint, rust, and coatings before you strike the arc.
Do not use a brush that has touched carbon steel on stainless steel. That transfers iron contamination and causes its own weld imperfections.
Filler Rod Quality
Dirty filler rod causes pinholes more often than most welders think. A rod that has been dragged across the floor or handled with oily gloves carries contamination straight into the puddle. Wipe the rod with a clean cloth.
If it’s pitted or oxidized, sand it lightly or cut off the damaged section.
For aluminum, the filler should look bright and free of heavy oxide. For steel and stainless, a clean, dry rod is usually enough. That’s one of the reasons TIG gets chosen over MIG for cleaner weld results.
Step-by-Step Troubleshooting Workflow for End-of-Weld Pinholes
Work this checklist in order. It takes about two minutes and removes the guesswork.
- Inspect the pinhole shape. One clean hole in the center means crater shrinkage. Multiple pits mean gas or contamination.
- Set post-flow correctly. Use one second per 10 amps. At 180 amps, give it at least 18 seconds.
- Check gas flow rate. Aim for 15 to 20 CFH with a gas lens. Adjust more only if the weld discolors.
- Inspect the tungsten and cup. Look for a balled tip, tungsten inclusions, or a chipped cup. Fix anything suspect.
- Clean the base metal and filler rod. Wipe with acetone, brush with a dedicated stainless brush, and wipe the rod.
- Adjust your stop technique. Add a filler dab, hold the torch still, ramp down with the pedal, then move away.
If the hole persists, repeat the steps with fresh consumables. Most fixed shops find the culprit on step 3 or 4.
Common Mistakes That Cause TIG Pinholes at the End
These are the usual offenders we see in weld repair forums and shop floors.
- Snapping the arc off. This kills the puddle instantly and leaves a void.
- Lifting the torch too soon. The gas leaves before the metal cools.
- Short post-flow. Anything under 10 seconds on a high-amp weld is a gamble.
- Contaminated tungsten. Touching the puddle transfers oxide into the weld.
- Dirty base metal. Oil and moisture boil out as gas.
- Skipping the final filler dab. The crater needs extra metal to shrink into.
- Excessive gas flow. High flow creates turbulence and pulls air in.
- Poor torch angle at the stop. Tilting the torch draws atmospheric air into the trailing shielding.
Each of these creates a slightly different pinhole signature. Learn to read the signs and you’ll stop chasing your tail.
Prevention Setup: Settings, Equipment, and Technique That Eliminate Pinholes
Get the setup right and pinholes become rare. This table reflects common shop settings that work across most materials.
| Parameter | Recommended Setting | Notes |
|---|---|---|
| Post-flow | 1 second per 10 amps | Use 15–20 seconds for heavy plate |
| Gas flow | 15–20 CFH | Use a gas lens for laminar flow |
| Current taper | 3–5 seconds | Ramp down gradually at the end |
| Tungsten | 2% lanthanated or ceriated | Keep a sharp point for DC welding |
| Cup size | #6 to #8 | Larger cups give better coverage |
| Filler rod | Clean, dry, matched to base metal | Wipe before each use |
Pair those settings with a steady stop. Dip filler into the crater, let the puddle freeze, count to three, then raise the torch.
One more thing. On aluminum, bump the post-flow higher. Aluminum holds heat longer and needs coverage until the crater solidifies fully.
Real Scenarios: What Fixed the Pinhole in Practice
Real-world fixes break down to a few common patterns.
Scenario 1: Mild steel, 1/8-inch plate, 150 amps. The welder saw a single center hole. Short post-flow was the cause. Increasing it from 8 to 15 seconds fixed the problem completely.
Scenario 2: Aluminum, 1/4-inch tube, 190 amps. Pinholes clustered at the end. The base metal had not been cleaned. Wiping with acetone and using a dedicated stainless brush eliminated every pit.
Scenario 3: Stainless steel, 3/32-inch wall, 110 amps. The craters looked clean but one hole appeared each time. The torch angle was lifting during the stop. Holding position for five seconds after arc cutoff solved it.
Scenario 4: Steel pipe, root pass, 120 amps. Repeated pinholes traced back to a contaminated filler rod. Switching to a fresh, clean rod stopped the issue.
These patterns match what we see in aggregate reviews across welding forums. A single root cause is almost always the answer.
Frequently Asked Questions
Why do I get a pinhole at the end of my TIG weld?
You lose heat and gas coverage at the same time. The crater shrinks and pulls in air. Add a small filler dab, ramp down slowly, and hold post-flow until the puddle freezes.
Does post-flow time really matter?
Yes. Post-flow protects the weld as it cools. Per manufacturer specs, the rule of thumb is one second per 10 amps.
Shorten it, and you risk porosity at the crater.
Can a bad tungsten cause pinholes?
Absolutely. A contaminated tungsten injects tungsten oxide into the weld. That oxide takes the form of tiny pits or a visible pinhole.
Grind the tungsten clean with the lines lengthwise.
Should I add filler at the end of every TIG weld?
Not every weld, but most of them. Adding a final dab fills the crater and compensates for shrinkage. On thin material, you can often skip it and just taper the current.
What causes multiple pinholes instead of one?
Multiple pinholes point to gas or contamination. Look for dirty base metal, wet filler rod, or a leak in the gas line. Also check the gas lens for spatter buildup.
How do I fix a pinhole without restarting the weld?
Grind out the pinhole and weld over it with a fresh start. Do not just arc over the hole. That leaves porosity trapped underneath.
Final Decision Guide: Your Next Step Based on the Pinhole Type
Here is your quick decision tree. Follow the branch that matches what you see and you will fix the problem in one or two tries.
| If you see… | Do this first |
|---|---|
| One clean hole in the crater center | Add a filler dab, ramp down over 3 seconds, hold post-flow longer |
| A cluster of tiny pits near the end | Check post-flow, gas flow, and cleanliness of the base metal |
| Dark or blue discoloration around the hole | Increase post-flow and keep the torch angle steady at the stop |
| Bright weld with one hole | Focus on crater fill and current taper settings |
| Soot or black residue inside the hole | Clean the tungsten and check for contamination |
Think of it in three layers. First, fix the crater. If the hole disappears, you are done.
If not, move to gas. Check post-flow, flow rate, and torch movement. If pinholes remain, clean everything.
Tungsten, base metal, and filler rod. One of those three layers will match your situation.
The pinhole at the end of a TIG weld is rarely a mystery once you slow down the stop. The metal gives you clues. Read them, make one change at a time, and test.
You will find that most fixes take less than a minute of adjustment. That is the whole secret.
