Common TIG welding problems
Gas tungsten arc welding (GTAW), or TIG, is often chosen for projects requiring high aesthetic quality, structural integrity or compliance with strict codes and standards. While TIG delivers precision, it is also the most difficult process to learn. Follow these basic tips to prevent common TIG welding problems.
1. Poor gas coverage
Insufficient shielding gas can lead to contamination and weak welds. This problem often occurs when the shielding gas is not turned on, the flow rate is set too low or too high, or airflow disrupts the gas coverage.
How to fix gas coverage issues
- Verify the gas type: TIG welding typically uses 100% argon or an argon/helium blend for thick aluminum. Avoid argon/CO2 mixes (used for MIG), as they cause immediate contamination.
- Set the proper gas flow rate: Aim for 15–20 cubic feet per hour (cfh). Higher gas flow/pressure doesn’t mean better protection. In fact, excessive gas flow creates turbulence, pulling in unwanted airborne contaminants and causing arc instability. Generally, the lower side of recommended shielding gas rates is preferred to ensure proper shielding coverage without turbulence.
- Check for leaks: Inspect all the fittings and hoses. Any breach may pull air into the shielding gas stream, which can contaminate the weld. Rub soapy water over the hose and all fittings. If bubbles form, you have a leak and need to replace the defective components.
- Rule out cylinder contamination: Rare but possible. If everything else checks out, contact your gas supplier to resolve this issue.
For more details, see TIG shielding gas best practices.
Figure 1: Poor gas coverage leads to contamination.
2. Incorrect polarity or balance settings
Using the wrong polarity when TIG welding aluminum leads to contamination. For example, welding on direct current electrode negative (DCEN) (see Figure 2A) fails to break down the aluminum oxide layer. The filler metal mixes in with the partially melted oxide, creating the contaminated bead seen here.
How to prevent polarity and balance issues
Always use alternating current (AC) for aluminum. AC polarity (see Figure 2B) combines two actions:
- Electrode positive (EP): Cleans the oxide layer.
- Electrode negative (EN): Melts the base metal.
- Adjust AC balance: A feature called AC balance control allows operators to tailor the EP to EN ratio. If you notice a brownish oxidation or flakes that look like black pepper in your weld puddle (Figure 2C), decrease the balance setting to increase the EP time for better cleaning.
- Caution: Too much EP causes the tungsten to ball excessively (Figure 2D) and could provide too much etching.
- Start with a clean puddle: Wait until the puddle has the appearance of a shiny dot before adding filler. This indicates that the oxide has been removed and it is safe to add filler and move forward. Adding filler to the weld zone before removing the oxide layer results in contamination.
Figure 2A: Aluminum welded in DC with argon
Figure 2B: Ideal aluminum weld
Figure 2C: AC balance set too high (insufficient oxide removal)
Figure 2D: Bald tungsten caused by a low balance setting (excess EP)
4. Lack of fusion in the root
Improper fit-up or technique can cause incomplete fusion at the root — discover how to improve penetration. Several factors contribute to a lack of fusion at the root of a T-joint or a fillet weld.
Causes of root fusion problems:
- Improper fit-up
- Holding the torch too far from the joint (increasing arc length)
- Incorrect filler rod feeding techniques
How to prevent lack of fusion in the root
- Reduce arc length: Shorten the arc to maintain better directional control and improve penetration. This is especially important on transformer-based machines, where the arc tends to wander between the sides of the joint as it seeks the path of least resistance.
- Avoid under-filling or rushing: Ensure proper deposition and maintain a steady travel speed to prevent incomplete fusion.
- Use advanced controls when available: Inverter-based machines with advanced output controls such as adjustable frequency and pulsing offer more control over the arc. These settings create a narrower, more focused arc cone, providing deeper penetration and better directional control — often at higher travel speeds.
Figure 4: Lack of fusion in the root
5. Craters
Ending a weld too abruptly creates craters that can crack, such as the one shown in Figure 5A. Avoid with proper finishing techniques. Common issues include:
- Instantly reducing the welding power, which cools the puddle too quickly.
- Pulling the filler rod away too soon at the end of the weld.
How to prevent crater cracking
- Continue feeding filler rod: Gradually reduce current while still adding filler at the end of the weld to avoid leaving a crater.
- Use crater control feature: TIG welders with crater control automatically reduces the current at the end of a weld, producing a good-looking weld bead as seen in Figure 5B.
Figure 5A: Poorly filled weld craters
Figure 5B: Weld crater filled
6. Dirty base and/or filler metal
Contaminated materials compromise TIG weld integrity — cleanliness is critical for strong, defect-free joints. Figure 6A shows the results of welding hot-rolled mild steel without removing mill scale first.
How to keep materials clean for TIG welding
- Clean all base and filler metals: Remove mill scale, aluminum oxide, dirt, grease and other contaminants on filler metals.
- Use proper tools: Grind, brush and wipe away all potential contaminants. For cleaning aluminum, dedicate a stainless-steel brush to the task to prevent contamination from other metals.
Figure 6B shows what happens when a weld on mild steel has been properly cleaned before welding. Figure 6C shows a weld made on uncleaned chromoly tubing, while Figure 6D shows a weld made on clean material.
Figure 6A: Uncleaned steel weld
Figure 6B: Clean steel weld
Figure 6C: Uncleaned chromoly
Figure 6D: Cleaned chromoly
7. Poor color on stainless steel
Overheating stainless steel not only changes its color but also reduces corrosion resistance and weakens mechanical properties. Figure 7A shows discoloration caused by excessive heat input. Unfortunately, once this occurs, it cannot be reversed — prevention is the only solution.
How to prevent overheating
- Reduce amperage: Lower heat input to avoid discoloration and maintain corrosion resistance.
- Increase travel speed: Move slightly faster or shorten the arc length to limit heat buildup.
- Use pulses welding: If your welding equipment features pulsed welding capabilities, take advantage of it — pulsed welding reduces heat input and offers excellent puddle control.
Proper stainless coloration is shown in Figure 7B.
Figure 7A: Poor color on stainless steel
Figure 7B: Good color on stainless steel
8. Sugaring on stainless steel
Oxidation on the backside of stainless welds — known as sugaring — weakens the joint and compromises corrosion resistance. Figure 8 shows this common TIG welding problem, which occurs when the weld when it is exposed to oxygen during welding. The best way to prevent sugaring is to back purge the weld with argon shielding gas or reduce welding amperage.
How to prevent sugaring
- Back purge the weld with argon: Shield the backside of the weld with argon gas to eliminate oxygen exposure.
- Reduce amperage: Lower heat input to minimize oxidation and prevent sugaring.
Figure 8: Sugaring on stainless steel
9. Too much amperage on aluminum
Excessive amperage can distort the weld and even cause burn-through. Figure 9 shows an aluminum weld with heat input set too high, resulting in a wide, ill-defined profile and poor bead appearance.
How to prevent excessive amperage on aluminum
- Lower amperage: Reduce heat input to avoid ill-defined beads and prevent burn-through.
- Increase travel speed: Moving faster helps control heat buildup and maintain a cleaner weld profile.
- Monitor bead appearance: Compare your weld to an ideal profile (see Figure 2B) and adjust settings as needed.
Figure 9: Excessive amperage/heat input
10. Proper arc length control
Maintaining a steady arc length is critical for consistent penetration and bead appearance. Figure 10 shows how an increase in arc length changes the weld bead color and profile. Arc length, which is the distance between the electrode and the base metal, directly affects TIG welding voltage and heat input.
How to prevent arc length issues
- Maintain a steady distance: Keep the electrode at a consistent arc length to ensure uniform penetration and bead appearance.
- Practice control techniques: Use a comfortable torch angle and steady hand movement to avoid drifting away from the joint.
Figure 10: Change in arc length
Avoid TIG pitfalls
Mastering TIG welding takes practice and attention to detail. By recognizing these common problems and applying the right solution, you can achieve cleaner, stronger and more reliable welds.
This article originally appeared in The Fabricator Magazine and is shared with permission.