Mastering the welding process takes time, but running into a sudden weld defect can slow down any project. Whether you are using mig welding, TIG, or stick, issues like a porous weld bead or an unstable arc happen to everyone.
This comprehensive welding troubleshooting guide breaks down exactly why these issues happen and how to fix them to keep your fabrication on track.
Troubleshooting Matrix: Quick Fix Guide
| Symptom | Primary Root Cause | Fast Solution |
| Porosity | Contamination or lost gas coverage | Clean metal; check gas flow & lines |
| Arc Blow | Magnetic interference in DC welding | Alter ground position; switch to AC |
| Undercut | High current or fast travel speed | Lower voltage/amps; slow down |
| Burnback | Erratic wire feeding or wrong stick-out | Replace contact tip; adjust wire tension |
| Warping | Excessive heat concentration | Use intermittent welding |
Why are my welds porous?
Porosity in welding occurs when tiny gas bubbles get trapped inside the molten weld pool as it cools. This creates a sponge-like structure that results in dangerously weak welds.
The Cause
Porosity is usually triggered by moisture, oil, rust, or paint on your base metals. It also occurs if your shielding gas is blown away by a breeze or if your gas flow rate is set incorrectly.
How to prevent porosity in welding
Always grind your weld joint down to bright, clean metal before starting. If you are working indoors, verify that your gas lines are free of leaks and that you aren’t using a worn-out torch nozzle.
Why is my arc unstable?
An unstable or erratic arc makes it incredibly difficult to maintain a consistent weld bead.
The Cause
If you are experiencing a straying arc on DC settings, you are likely dealing with arc blow in welding. This happens when a magnetic field builds up in the steel and pulls the arc away from its path. It is often referred to as a magnetic arc blow.
How to reduce arc blow in welding
Move your work lead clamp to another location on the workpiece, weld toward the ground connection, or switch your machine to alternating current (AC) to break up the magnetic interference.
Why is my weld cracking?
Weld cracking is one of the most critical structural failures, rendering a component unsafe for use.
The Cause
Cracks develop due to rapid expansion and contraction stresses during the cooling phase. They can occur as hot cracks (during solidification) or cold cracks (hours later due to hydrogen embrittlement).
How to prevent crack in welding
Select a filler metal that perfectly matches your base metals. For high-carbon steels or thicker sections, preheat the metal to slow down the cooling rate and reduce internal stress.
Why is my weld undercutting?
An undercut in welding is a grooved indentation left in the base metal right at the toe of the weld, reducing the material’s thickness and strength.
The Cause
This is caused by excessive welding current or a travel speed that is too fast. The arc melts away the edge of the base metal, but the fast movement doesn’t allow the filler metal to drop in and fill the void.
How to prevent undercut
Lower your amperage or voltage settings and maintain a consistent torch angle to prevent undercut from forming.
How to repair undercut in welding
Use a grinder to clean the groove completely, then run a targeted, lower-amperage stringer bead directly over the undercut zone to restore the profile.
Why does my wire keep burning back?
Welding burnback occurs when the welding wire fuses directly inside the copper contact tip of your MIG gun, cutting off your feed entirely.
The Cause
This happens if your wire feed speed is set too low for your voltage, causing the arc to jump backward into the gun. It can also be caused by excessive tip-to-work distance.
The Fix
Increase your wire feed speed or replace a worn out, oversized contact tip. Ensure your drive rolls have the correct tension to avoid wire slippage.
Why is my tungsten turning black?
If you are TIG welding and your tungsten electrode changes colour, it is an immediate sign of atmospheric contamination.
The Cause
A black or heavily discoloured tip means the hot tungsten was exposed to oxygen without adequate protection from your shielding gas.
The Fix
Follow fundamental tungsten welding tips: check for gas post-flow time (ensure it runs for at least 1 second per 10 amps used) and keep your torch steady over the weld end until the gas completely stops flowing.
Why are my welds weak?
Weak joints often present visually with a low profile or lack of reinforcement, indicating a structural lack of fusion.
The Cause
Lack of fusion occurs when the weld metal fails to completely bond with the edges of your weld joint. This is typically a result of cold lapping from insufficient heat input or incorrect torch angles.
The Fix
Turn up the amperage/voltage settings on your machine, slow down your travel speed, and focus your arc directly on the root of the joint.
How do I stop warping?
Warping in welding distorts your assembly, pulling flat plates out of alignment and throwing off square frames.
The Cause
Metal naturally expands when heated and contracts as it cools. Concentrated, continuous heat input creates localised pull zones.
The Fix
To minimise distortion, use clamping fixtures, stagger your passes, and implement intermittent welding (stitch welding) rather than running long, continuous beads.
Why is slag trapped in my weld?
Trapped welding slag (slag inclusions) weakens multi-pass welds by creating pockets of non-metallic debris inside the metal matrix.
The Cause
This is common when using stick or flux-cored welding techniques. It occurs when you fail to clean a previous pass or when your torch angle causes the molten slag to run out in front of the weld pool.
The Fix
Always use a chipping hammer and wire brush to remove every bit of welding slag before laying down your next pass. Keep your arc ahead of the slag cloud while welding.
Need High-Quality Consumables?
Eliminate erratic wire feeds and shielding issues by upgrading your setup. Choose the right contact tips and liners to keep your machine feeding smoothly and minimise downtime. Contact our team for expert advice or to request a quote.