Arc Welding 101: Use and identify tungsten electrodes correctly

PRACTICAL WELDING TODAY® NOVEMBER/DECEMBER 2013

April 22, 2014

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Q: Can you tell me how to identify tungsten after the paint is worn off?

Anonymous

A: The two most common processes that use a nonconsumable tungsten electrode are gas tungsten arc welding (GTAW) and plasma arc welding (PAW). These electrodes come in a variety of compositions or alloys, and each composition serves a specific purpose:

  • Pure tungsten electrodes (AWS classification EWP) contain 99.50 percent tungsten. They provide good arc stability for AC welding on aluminum and magnesium. Their color designation is green.
  • 2 percent thoriated tungsten electrodes (AWS classification EWTh-2) contain 1.70 to 2.20 percent thorium and are the type most commonly used. Unlike pure tungsten, they work exceptionally well for DC electrode negative or straight polarity on carbon and stainless steels. Their color designation is red.
  • 2 percent ceriated tungsten electrodes (AWS classification EWCe-2) contain 1.80 to 2.20 percent cerium. They perform best in DC welding at low current settings but can be used in AC processes as well. Their color designation is orange.
  • 1.5 percent lanthanated tungsten electrodes (AWS classification EWLa-1.5) contain 1.30 to 1.70 percent lanthanum, or lanthana. These have many of the same advantages as ceriated electrodes and closely resemble the conductivity characteristics of 2 percent thoriated tungsten. Their color designation is gold.
  • Zirconiated tungsten electrodes (AWS classification EWZr-1) contain 0.15 to 0.40 percent zirconium. Although ideal for AC welding, under no circumstance is zirconiated recommended for DC welding. Their color designation is brown.

All of these electrodes placed side by side look identical. For that reason, a color code system has been developed to designate each. Short of sending them to a lab for analysis, which can be expensive, once the color designation is gone, there is no way to tell what type of tungsten you're holding.

As the hack TIG welder that I am, I keep short, unmarked tungstens in old military stick match containers. Each container is clearly marked as to the type of tungsten inside. Along with that, I always break down my torch when I'm done and store the tungsten in its designated container.

This works for me in my garage. This would not be a good practice in a manufacturing or code environment. Once the marking is removed, the tungsten is not traceable, and you just lost control of your weld process.

Long story short (and it's a little late for that), your best bet is to replace the unmarked electrodes and then begin a practice of maintaining traceability.



Paul Cameron

CWI, Welding Specialist
Element Materials Technology
662 Cromwell Ave.
St Paul, MN 55144
Phone: 507-269-7142

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