Welding Gases

Acetylene  |  Air  |   Argon  |   Carbon Dioxide(CO₂)  |   Helium
Hydrogen  |   Nitrogen  |   Oxygen  |  Propane

Helium
Helium (He) is the second lightest element (hydrogen being the lightest) with a gaseous specific gravity of 0.138.  It is a colorless, odorless, tasteless inert gas at room temperature and atmospheric pressure. Its boiling point is -452.1°F (-268.9°C) at atmospheric pressure. Helium is present in dry air at a concentration of 0.0005%.

Helium is one of the noble gases.  Like the other noble gases, helium is chemically inert. Reactions with other elements occur only with difficulty and the resulting compounds are quite unstable.

Helium is the most difficult of all gases to liquefy and is impossible to solidify at atmospheric pressure. These properties make liquid helium extremely useful as a refrigerant and for experimental work in producing and measuring temperatures close to absolute zero.  Liquid helium can be cooled almost to absolute zero at normal pressure by rapidly removing the vapor above the liquid.

First discovered in the spectrum of the sun's corona during an eclipse in 1868, helium was first isolated from terrestrial sources in 1895. In 1907 British physicist Sir Ernest Rutherford showed that alpha particles are the nuclei of helium atoms.

Helium is the second most abundant element in the universe, after hydrogen; however, it is rare on earth.  Its principal source is natural gas wells where the helium is extracted from pockets in the crude natural gas stream and purified.   It  is so light that once released it escapes the earth's atmosphere and cannot be recovered. 

Helium is widely used as an inert gas in the arc welding process and as an inert gas in the production of reactive materials.  Its permeation rate and ease of detectability make it an ideal medium for leak detection.  Also, its low specific gravity and nonflammability allow its use in lighter-than-air applications such as the filling of balloons and blimps.   To reduce risk of the bends, a mixture of helium and oxygen is used as a breathing gas for deep-sea diving, since helium is less soluble in human blood than nitrogen.  Helium is also used in the pressurizing of rockets before takeoff and the pressurizing of tanks of rocket fuel. Liquid helium is used in superconducting magnet applications, including magnetic resonance imaging (MRI).

 

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