Helium (He) is an inert, very light monoatomic gas, of atomic weight of 4. It is obtained by separation from natural gas. Helium is refined to a purity of min. 99.99 %. As helium is lighter, it tends to rise around the nozzle andhence to produce equivalent shielding effectiveness, then flow of helium must be two to 3 times of argon. The same general relationship is true for mixtures of argon & helium, particularly those high in helium content.
For given values of welding current and arc length, helium transfers more heat into the work as compare to argon. The greater heating power of the helium arc can be advantageous for joining metals of high thermal conductivity and for high speed mechanisedapplications. Also, helium is used more often than argon for welding heavy plate. Mixtures of argon and helium are useful when some balance between the characteristics of both is desire.