Which two methods are used to protect against atmospheric contamination during welding?

The correct answer highlights two methods: back purging and fluxing, both of which are effective in protecting against atmospheric contamination during welding.

Back purging involves introducing an inert gas, typically argon, into the area behind the weld joint. This process displaces air and prevents oxidation or contamination that can occur from atmospheric exposure. It is especially crucial in processes like GTAW (Gas Tungsten Arc Welding), where maintaining a clean environment is vital for achieving quality welds.

Fluxing, on the other hand, is a method that involves applying a flux material to the weld area. The flux serves to protect the molten weld pool from atmospheric gases, particularly oxygen and nitrogen, which can cause defects such as porosity or brittle intermetallic formations in the weld metal. The flux forms a barrier that prevents these contaminants from reacting with the molten weld.

Both of these methods are essential practices for welders to ensure the integrity and quality of the welded joint in environments where atmospheric contamination can compromise the results.