Welds can fail for several reasons—bad design, sloppy technique, or using the wrong materials. Here are the most common causes and how to fix them in 2026.
Quick Fix Summary:
Check if the weld size matches the load requirements. Make sure you're using the right preheat and filler material. Look for cracks in the HAZ or bits of slag stuck inside. Tweak your voltage and wire feed to get a smooth bead.
What's Happening
Under-designed welds—too small, too short, or stuck in high-stress spots—often crack when stretched, squeezed, or vibrated American Welding Society (AWS). If the heat isn’t controlled properly during welding, the HAZ turns brittle. Using the wrong filler metals doesn’t help either—it just makes the joint less stretchy AWS.
Why did the weld crack?
Imagine a weld that’s supposed to hold 50,000 psi but only gets 30,000 psi of strength. That’s a recipe for failure. Or picture a joint that got blasted with too much heat, turning the area around the weld into a brittle glass-like zone. Even the filler metal matters—if it doesn’t match the base metal, the joint becomes a weak link.
Step-by-Step Solution
- Verify Weld Geometry
- Compare the actual weld size—leg length, throat—to what the engineering drawings say.
- Grab a set of calipers. For fillet welds, the leg length has to match the design exactly.
- If it’s too small, add another pass or switch to a bigger electrode.
- Check Preheat and Interpass Temperatures
- Look up the base metal specs first. For example, 304L stainless needs a preheat between 150–250°F.
- Use an infrared thermometer or temp sticks to check. Both pieces need to be heated evenly.
- If the heat’s dropping too fast, bump up the voltage or slow down your travel speed to keep the heat input steady.
- Inspect for Defects
- Cracking: Hunt for cracks running along the weld, across it, or in the crater. Try dye penetrant testing (Type I, Level 2 per ASNT).
- Slag Inclusion: Chip out the slag, then grind if you have to.
- Porosity: Start with clean base material and make sure your shielding gas flow is right (10–20 CFH for MIG).
- Adjust Welding Parameters
- For MIG: Crank the voltage up to 22–26V when using 0.035" wire (set wire feed between 18–22 ipm).
- For Stick: Go with an E7018 electrode if you need high-impact toughness.
- For TIG: Keep the arc length between 1.5–3mm. If you’re welding aluminum, use an Ar/He mix.
- Confirm Filler Metal Compatibility
- Match the filler to the base metal—ER308L works great with 304 stainless.
- Don’t mix dissimilar metals unless you add a buttering layer first.
If This Didn’t Work
- Post-Weld Heat Treatment (PWHT): Heat the weld to 1100–1200°F for 1 hour per inch of thickness to ease out built-up stress American Nuclear Society.
- Weld Overlay: Got a minor defect? Grind it out, then reweld using a low-hydrogen filler like E7018. Just make sure you get full penetration this time.
- Alternative Joining Method: For parts that can’t afford to fail, bolted joints with Belleville washers can handle vibration better than most welds.
Prevention Tips
| Preventive Action | Checkpoint |
|---|---|
| Review WPS/PQR | Double-check that your welding procedure specs line up with the job requirements (AWS D1.1). |
| Clean Joints | Scrub off rust, oil, and mill scale before you even strike an arc (aim for SA 2.5 cleanliness). |
| Use Positioners | Set up positioners to keep the work flat—it cuts down on wonky out-of-position welds. |
| Monitor Environment | Weld indoors if you can. If you’re outside, block the wind—anything over 10 mph can mess up your gas shielding. |
How do I know if my weld is too small?
Grab a pair of calipers and measure the leg length and throat. If it doesn’t match what the drawings call for, you’ve got a problem. Honestly, this is one of those cases where being off by even a few millimeters can make the difference between a weld that holds and one that cracks under load.
What’s the best way to avoid HAZ cracks?
Start by checking the base metal specs. Some metals, like 304L stainless, need a preheat between 150–250°F to stay tough. Use an infrared thermometer or temp sticks to keep everything even. If the heat drops too fast between passes, bump up the voltage or slow your travel speed. That way, you avoid turning the HAZ into a brittle zone.
Can I reweld a cracked joint?
Start by chipping out the cracked section and cleaning the area. Then, reweld using a low-hydrogen filler like E7018. Make sure you get full penetration this time. If the crack keeps coming back, consider stress-relief heat treatment or switching to a bolted joint instead.
What filler metal should I use for 304 stainless?
This filler matches the base metal’s chemistry, so the joint stays strong and ductile. Avoid mixing dissimilar metals unless you add a buttering layer first—otherwise, you risk creating weak spots.
How do I check for slag inclusion?
Slag inclusion happens when bits of flux get trapped inside the weld. After you’ve finished welding, grab a chipping hammer and go to town. If you see dark spots, grind them out and reweld if needed. You can also use dye penetrant testing (Type I, Level 2 per ASNT) to spot hidden slag pockets.
What’s the right shielding gas flow for MIG welding?
Too little gas, and you’ll get porosity. Too much, and you’re wasting money. Stick with 10–20 CFH for most jobs. If you’re outside, block the wind—anything over 10 mph can blow your shielding away and ruin the weld.
When should I use post-weld heat treatment?
If you’re working with thick materials, heat the weld to 1100–1200°F for 1 hour per inch of thickness. This eases out the built-up stress and keeps the joint from cracking later. Just don’t skip the preheat and interpass temperature checks—those matter too.
What’s the best electrode for high-impact toughness?
This electrode is a go-to for jobs that need to handle sudden shocks or heavy loads. It’s low-hydrogen, so it resists cracking even under tough conditions. Stick with it when you need a weld that won’t let you down.
How do I prevent porosity in my welds?
Porosity shows up when gas gets trapped inside the weld. To stop it, make sure your base metal is spotless—no rust, oil, or mill scale. Then, set your shielding gas flow to 10–20 CFH for MIG. If you’re outside, shield the area from wind. That’s really all it takes to keep your welds solid.
What’s the best way to handle out-of-position welding?
(Honestly, this is the best approach.) Out-of-position welds are tricky because gravity works against you. Positioners tilt the workpiece so you can weld flat or slightly uphill, which gives you better control. If you don’t have a positioner, practice your technique—otherwise, you’ll end up with uneven beads and potential defects.
