AWS Certified Welding Inspector — FundamentalsWelding ProcessesMedium
A CWI is reviewing a Weld Procedure Specification (WPS) for Gas Tungsten Arc Welding (GTAW) of thin-gauge titanium aerospace components. The WPS specifies direct current electrode negative (DCEN) polarity. Which of the following tungsten electrode types is generally NOT recommended for use with DCEN polarity in GTAW?
- APure Tungsten (EWP)
- B2% Lanthanated (EWLa-2)
- C2% Thoriated (EWTh-2)
- D2% Ceriated (EWC-2)
Show answer & explanationAnswer & explanation
Correct answer: A. Pure Tungsten (EWP)
Pure tungsten (EWP) electrodes are generally not recommended for DCEN welding. While they can be used, they have a lower current carrying capacity and poor arc starting characteristics compared to alloyed tungsten electrodes (thoriated, lanthanated, ceriated), which are specifically designed to improve electron emission and arc stability for DCEN applications.
Why the other options are wrong
- B. 2% Lanthanated (EWLa-2) is an excellent all-around electrode, suitable for both AC and DCEN, offering good arc starting and electrode life.
- C. 2% Thoriated (EWTh-2) is a very common and effective electrode for DCEN due to excellent electron emission and current carrying capacity.
- D. 2% Ceriated (EWC-2) is also a good general-purpose DCEN electrode, especially for low-current applications, offering good arc starting.
GTAW Tungsten Electrode Selection (DCEN)
Selecting the correct tungsten electrode type for DCEN GTAW is crucial for arc stability, current capacity, and preventing contamination.
- DCEN concentrates heat on the workpiece.
- Alloyed tungstens (Th, La, Ce) improve electron emission.
- Pure tungsten is less efficient for DCEN.
Memory trick: DCEN needs doping, pure tungsten is a dud.