AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is performing a visual inspection of a Gas Tungsten Arc Welding (GTAW) root pass on a stainless steel pipe. The welder reports difficulty maintaining a consistent arc and notices a 'green glow' from the tungsten electrode. Upon closer inspection, the CWI observes that the tungsten electrode tip appears eroded and discolored, and there are black inclusions in the weld bead. What is the most probable cause of these observations?
- AExcessive electrode stick-out.
- BContamination of the tungsten electrode.
- CToo low welding current for the electrode size.
- DInsufficient shielding gas coverage.
Show answer & explanationAnswer & explanation
Correct answer: B. Contamination of the tungsten electrode.
A 'green glow' from the tungsten electrode, along with erosion, discoloration, and black inclusions in the weld, are classic signs of tungsten contamination. This usually occurs when the hot tungsten electrode touches the molten weld pool or filler metal, transferring base metal elements to the tungsten, which then degrades its performance and contaminates the weld.
Why the other options are wrong
- A. Excessive electrode stick-out would reduce shielding effectiveness and potentially lead to tungsten oxidation, but not directly cause a green glow or black inclusions in the weld bead.
- C. Too low welding current for the electrode size would typically result in an unstable arc, but not necessarily a green glow, erosion, or black inclusions from tungsten contamination.
- D. Insufficient shielding gas coverage would primarily lead to porosity, discoloration (oxidation) of the weld bead and tungsten, and a 'sugared' appearance on stainless steel, but a green glow is specific to tungsten contamination.
GTAW Tungsten Contamination
Tungsten contamination in GTAW occurs when the hot tungsten electrode touches the molten weld pool or filler metal, leading to electrode degradation and weld defects.
- Causes arc instability.
- Electrode tip erodes, discolors, glows green.
- Results in tungsten inclusions (black spots) in weld.
- Prevented by proper technique and electrode maintenance.
Memory trick: Green glow, black spots, tungsten got hot and it lost its plots.