Green, Pure Tungsten Electrode is unalloyed tungsten, so it lacks the dopants that boost electron emission and current-carrying capacity. That means starting and maintaining a stable arc is harder, and the tip wears more quickly when used at higher amps. Despite that, it can be used with alternating current, since the AC cycle helps refresh the tip and re‑activate the surface, making it suitable for welding metals with AC (like aluminum). So this description highlights the trade-off: poorer electron emission and arc-start behavior, but compatibility with AC.

Edge preparation for pipe welding focuses on creating a clean, properly shaped joint that allows full fusion and proper penetration. Contaminants on the mating surfaces—oil, moisture, rust, or oxide—can trap gas or cause porosity and lack of fusion if not removed, so cleaning must cover both sides of the edge, not just one. Grooving or beveling the edges provides the necessary groove geometry for the weld to fill and for root fusion to occur reliably. Without a groove, the weld may not reach the root properly, leading to weak penetration or incomplete joint fusion. Cleaning to at least an inch on both sides ensures the cleaned surface extends into the bevel area, giving a clean, robust base for the root and subsequent passes and helping prevent recontamination during weld deposition. So, the prepared edges should be cleaned on both sides to at least an inch and should be appropriately grooved. This combination addresses cleanliness and joint geometry to promote sound, penetration-friendly TIG root passes.

Direct current electrode negative (DCEN) minimizes tungsten degradation by keeping the tungsten tip as the negative electrode. When the electrode is negative, the arc heat is directed more to the workpiece and the tungsten experiences less oxidation and erosion. Alternating current or keeping the electrode positive on the arc causes the tip to oxidize and erode more quickly during the positive half-cycle, speeding wear. A smaller tungsten diameter concentrates heat and current at the tip, increasing degradation, while not cooling the system allows excessive heat at the electrode. Not using water cooling would also raise temperatures and wear. So, DCEN is the best practice for extending tungsten life and reducing degradation.

Lanthanated tungsten electrodes are non-radioactive and provide higher current-carrying capacity than pure tungsten, which helps arc stability and allows welding at higher amperages without rapid electrode wear. The lanthanum oxide coating improves electron emission and reduces tip contamination, making starting and maintaining the arc easier. They’re suitable for both AC and DC welding, including DCEN, so the idea that they’re not suitable for DCEN isn’t accurate. Arc voltage isn’t a fixed property of the electrode type; it depends on current, gas, and arc length, not the electrode alone. So the statement that best fits EWLa is that it is not radioactive and improves current carrying capacity.