AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is reviewing a Weld Procedure Specification (WPS) for Gas Tungsten Arc Welding (GTAW) of thin-gauge stainless steel. The WPS specifies a pure tungsten electrode (EWP) for AC welding. What is the primary concern with using a pure tungsten electrode for AC GTAW on stainless steel, and what would be a more appropriate substitute?
- APure tungsten has poor electron emission, leading to arc instability; a thoriated tungsten (EWTh-2) would be better.
- BPure tungsten is prone to spitting and electrode degradation with AC; a zirconiated tungsten (EWZr-1) offers better arc stability.
- CPure tungsten has a low melting point, causing contamination; a ceriated tungsten (EWCe-2) would be more suitable.
- DPure tungsten promotes excessive penetration on thin material; a lanthanated tungsten (EWLa-1.5) provides a shallower arc.
Show answer & explanationAnswer & explanation
Correct answer: B. Pure tungsten is prone to spitting and electrode degradation with AC; a zirconiated tungsten (EWZr-1) offers better arc stability.
Pure tungsten (EWP) is known for forming a balled end when used with AC, but it can spit and degrade more readily than alloyed tungstens. Zirconiated tungsten (EWZr-1) is specifically designed for AC welding, providing a very stable arc, good resistance to contamination, and maintaining a balled tip without excessive spitting.
Why the other options are wrong
- A. Pure tungsten's electron emission is adequate for AC, but its stability and spitting are the main issues, especially compared to alloyed options.
- C. While pure tungsten can contaminate, its main issue on AC is spitting/degradation. Ceriated tungsten (EWCe-2) is typically preferred for DC welding at lower amperages.
- D. Penetration is more controlled by current and travel speed. The primary concern with EWP on AC is arc stability and electrode integrity, not inherently excessive penetration.
GTAW Tungsten Electrode Types (AC)
Different types of tungsten electrodes are alloyed to optimize performance for specific welding currents (AC/DC) and materials, affecting arc stability and electrode life.
- Pure Tungsten (EWP): AC only, balls easily, lower current capacity, prone to spitting.
- Zirconiated Tungsten (EWZr-1): Excellent for AC, very stable arc, resists contamination, good current capacity.
- Thoriated Tungsten (EWTh-2): Primarily DC, high current capacity, good arc start, radioactive.
- Ceriated/Lanthanated Tungsten: DC/AC (non-balled), good for low amps, non-radioactive.
Memory trick: Tungsten's purpose is pure, but AC needs a zircon-cure.