In welding shielding gas is used to protect the molten weld pool from atmospheric contamination by applying a gas or a blend of gases from a compressed cylinder designed for this purpose.
Most metals, when heated to their melting point become susceptible to the absorption of nitrogen, oxygen, and hydrogen which leads to porosity in the weld. Porosity is an undesirable discontinuity that renders the weld inferior and may inhibit the ability of the weld to meet engineering and quality requirements.
The specification which governs weld shielding gas is AWS A5.32 and ASME SFA 5.32.
GTAW, PAW, GMAW, FCAW, and EGW welding processes rely on compressed shielding gas to be delivered to the weld pool as part of the function of the welding equipment.
SMAW, SAW, and ESW welding processes rely on the gaseous atmosphere created from the flux as it is consumed during the welding process to protect the weld.
In addition to atmospheric protection, shielding gas can also have a pronounced effect on the following welding attributes.
Safety is of high importance when working with weld shielding gas as it can cause asphyxiation. The air we breathe is roughly 21% Oxygen & 78% Nitrogen with the balance being miscellaneous other gases. Breathing air with less than 18% Oxygen will cause dizziness, unconsciousness, and eventually death.
Shielding gas freely enters the localized atmosphere where the shielding gas is being applied. Heavier gases such as Argon can pool, or build up in low areas in much the same way water would. Precautions must be taken to prevent the accumulation of Argon as it displaces Oxygen and will lead to dangerous or deadly breathing conditions. Ensure that adequate ventilation is provided in all work areas, but especially in confined spaces. Follow all safety procedures and best safety practices when working with shielding gases to remain safe and unharmed.