Argon technical data sheet: physical properties IS 5760 status, purity grades and cylinder pressure

Argon is a noble gas that makes up 0.934 % of air by volume and is recovered as a by-product of cryogenic oxygen and nitrogen production. Its boiling point sits between those of nitrogen and oxygen, which is why it is drawn from the middle of the air separation column and purified separately. It is a permanent gas with a critical temperature of −122.46 °C, so it is sold by pressure in cylinders and as liquid in bulk. The physical figures below are from the NIST Chemistry WebBook; the standards position is from the Bureau of Indian Standards catalogue. KIGL argon is supplied in two grades published as KIGL specifications.

Several of these numbers explain argon's uses directly. A ratio of specific heats of 1.67, against 1.40 for nitrogen and oxygen, is the mark of a monatomic gas with no internal rotation or vibration to store energy. A thermal conductivity about two thirds that of air is why it is used to fill insulating glass. An ionisation energy of 15.76 eV, against 24.59 eV for helium, is why the argon arc strikes and holds at low current. And a density 1.38 times air is why it shields a weld pool well and why it collects in low places when it leaks.

The Indian specification is IS 5760, Argon, compressed and liquid, under the CHD 06 Industrial Gases committee. Two editions are live in the BIS catalogue: the 1998 second revision, reaffirmed February 2021 with one amendment, and a third revision published in 2026. IS 309:2023 notes that it harmonised its liquid-oxygen provisions with IS 5760:1998, which is the only clause-level trace of IS 5760 in the standards KIGL holds. Because the text of neither edition is held, KIGL does not quote an IS 5760 grade limit and publishes its argon grades as its own specifications; the corrected product specifications confirm that this is the right treatment.

Internationally, ISO 14175 defines the welding grade, classifying argon as Group I1 with a minimum purity of 99.99 %. The purer grades follow supplier convention, using the same "N" or numeric notation as IS 309 and IS 1747 (4.0 = 99.99 %, 5.0 = 99.999 %).

Purity minima are the grade definitions; the impurity columns are typical market values, not IS 5760 figures, and are shown to indicate scale. KIGL's own limits are on the argon product page, and the regulatory picture is on argon standards.

Argon is filled into seamless steel cylinders to IS 7285 (Part 1):2018 or (Part 2):2017, with IS 3224:2021 valves and a right-hand outlet thread. As a permanent gas it falls under IS 8775:1978, which fixes the filling pressure at 15 °C and checks the developed pressure at 65 °C. Its compressibility factor at 150 bar and 15 °C is about 0.93 (NIST), so a cylinder holds slightly more argon than the ideal-gas calculation suggests.

Mass is real content at 15 °C times 1.690 kg/m³. These are worked examples; the method is on gas cylinder sizes and contents in India. Pressure rises about 0.4 % per °C, so a welding cylinder left in the sun at 50 °C reads about 15 % above its 15 °C fill. A welder using 10 to 15 litres per minute through a TIG torch empties a 7.4 m³ cylinder in roughly 8 to 12 hours of arc-on time; heavy users move to liquid argon or a manifold.

Under IS 4379:2021 the cylinder is peacock blue shade 103 throughout. Argon-based mixtures add a band: light Brunswick green for argon-CO₂, graphite black for argon-oxygen, and a French grey band with a peacock blue shoulder for argon-nitrogen (Table 12). Under GCR 2016 rule 44(b)(ii), up to 200 cylinders of a non-flammable non-toxic gas may be held without a storage licence.

Liquid argon at 1,395 kg/m³ is the densest of the common cryogens and expands about 840 times to gas at 21 °C. Its liquid range at atmospheric pressure is very narrow: it boils at 87.30 K and its triple point is 83.81 K at 0.689 bar. A bulk tank or line depressurised below about 0.7 bar absolute can therefore freeze solid argon in valves and vaporisers, and vacuum on a liquid argon line is avoided. Bulk vessels are licensed under the SMPV (Unfired) Rules 2016; transportable vacuum-insulated vessels up to 1,000 litres are covered by IS 18719 (Parts 1 and 2):2024.