Which gas is denser than air and beneficial in deep groove welding?

The correct choice, argon, is a noble gas that is denser than air. In the context of deep groove welding, argon provides essential benefits for shielding the weld area from atmospheric contamination. Its density allows it to effectively envelop the molten weld pool and the tungsten electrode, preventing oxidation and other reactions that can compromise the integrity and quality of the weld.

Using argon as a shielding gas is particularly advantageous in deep groove welding applications, where managing thermal and gaseous environments is critical due to the increased exposure of the weld pool. This helps in achieving a clean weld across the often challenging geometry associated with deep grooves.

In contrast, while oxygen, helium, and nitrogen may have specific uses in welding processes, they do not offer the same level of shielding effectiveness for this particular application as argon does. For example, oxygen can actually contribute to oxidation of the weld, whereas helium, while lighter than argon, provides less of the necessary shielding properties in deep grooves. Nitrogen, although inert, does not have the density or the shielding effectiveness required for optimal results in argon-based shielding applications.