Argon

Linde Austria Argon 5.0 lists 99.999% purity, with maxima of oxygen 2 ppm, nitrogen 5 ppm, water 3 ppm and hydrocarbons 0.2 ppm. The supplier uses ideal volume fractions, equivalent to mole fractions. Compare each impurity limit and delivery specification. Use the gas composition required by the welding procedure. Linde Austria, Argon 5.0

Identity and physical properties

Argon (Ar, CAS 7440-37-1) is separated from air. Air Liquide lists UN1006 for compressed argon and UN1951 for refrigerated liquid. Specify phase and grade separately. Air Liquide, Gas Encyclopedia: Argon

Useful physical values must retain their conditions:

A gas volume is therefore incomplete without temperature and pressure. A liquid litre is not a litre of delivered gas. The values above are supplier physical-property data, not cylinder fill specifications or a conversion rule valid at every delivery condition. Air Liquide, Gas Encyclopedia: Argon.

Shielding role and process boundaries

In gas tungsten arc welding (GTAW/TIG), argon protects both the molten pool and the tungsten electrode from surrounding atmosphere. Miller describes pure argon as the common choice because of stable arc behavior and favorable high-frequency starting. Helium can increase heat input; argon/helium blends trade some starting behavior for a hotter arc. Gas composition consequently belongs to the welding procedure rather than being an independent purchasing choice. Follow the issued welding procedure specification (WPS), including any requirements for shielding beyond the torch. Miller, Best Practices for Proper Shielding Gas in TIG Welding, 11 March 2026.

Pure argon is also used for aluminum GMAW/MIG, while argon/helium blends are another option. This does not make pure argon a universal GMAW gas. Miller's material-based guide instead discusses argon/carbon-dioxide mixtures for mild steel and distinct blends for stainless steel; it excludes carbon-dioxide blends for aluminum. A cylinder suitable for an aluminum MIG job should not be substituted into a steel procedure solely because both machines are called MIG welders. Miller, What Type of Gas Is Best for MIG Welding in DIY Applications?, 30 September 2025.

Purity is not the complete specification

The named Linde Austria Argon 5.0 limits are:

The supplier states these limits as ideal volume fractions, equivalent to mole fractions. Compare them with the applicable delivery specification. Linde Austria, Argon 5.0

A second bounded example is Linde's Liquid Argon, High Tech Quality, material 104807. Its December 2022 sheet specifies at least 99.999 vol.% argon and separately limits oxygen, water, nitrogen and hydrocarbons. Crucially, the sheet says those specifications apply exclusively to deliveries in pressure tanks. It identifies large laboratory and ICP/ICP-MS consumption among its applications. Neither the application description nor the minimum argon percentage makes every other delivery mode equivalent. Linde, Liquid Argon, High Tech Quality, December 2022.

An SDS answers a different question from a grade sheet. Air Products' argon SDS lists 100% nominal concentration for hazard communication but explicitly directs readers to product specifications for exact composition. That nominal entry is not evidence of zero impurities or analytical-grade performance. Air Products South Africa, Argon SDS 003A, revision 6, December 2025, section 3.

Supply and delivered gas quality

Linde offers gaseous and liquid argon in different purities and cylinder, dewar and bulk-tank sizes. Select supply form together with consumption and equipment requirements; the word “argon” alone does not specify a pressure, container connection or delivery arrangement. Linde, Argon: Purity Grades and Supply Modes.

Gas quality at the work can differ from the supplied grade. Linde's TIG guidance emphasizes a high-integrity regulator, torch and gas line and notes that conventional hoses may leak. Its guidance for central distribution also discusses moisture and oxygen control. Thus, a higher-purity source cannot by itself correct air ingress or contamination in downstream equipment. Choose delivery components and any purification controls for the application rather than treating them as universal additions. Linde, TIG Welding: How to Improve Results.

Flow measurement and shielding control

Read the scale for the actual gas and follow the instrument's operating instructions. Smith's H2051B-580 flowmeter regulator has separate scales for argon/argon–carbon dioxide, carbon dioxide and helium. Its rated flow range describes the instrument, not the correct welding flow for a job. Pressure and flow are different quantities: neither a cylinder-pressure reading nor a regulator setting alone establishes shielding coverage at the arc. Smith Equipment, H2051B-580 Flowmeter Regulator.

Excess flow can create turbulence that draws atmosphere into the gas column; too little can leave the weld and hot tungsten exposed. Cup geometry and gas-lens configuration also affect coverage. Set flow and pre/post-flow through the WPS and the actual torch arrangement and surroundings, rather than using a universal litres-per-minute or current-based recipe. Miller, Best Practices for Proper Shielding Gas in TIG Welding.

For a GMAW delivery check, Miller identifies wrong gas connections, a poorly seated gun and spatter-obstructed nozzles as possible faults and suggests an external flowmeter at the gun when troubleshooting. Drafts can remove coverage even when gas arrives correctly. These checks distinguish a delivery or environmental problem from a cylinder-grade problem. Miller, What Type of Gas Is Best for MIG Welding in DIY Applications?.

Compressed gas and cryogenic hazards

Inert does not mean breathable. Air Products' compressed-argon SDS warns of rapid suffocation, pressure hazards and accumulation in confined or low spaces. It calls for oxygen monitoring and ventilation where needed, pressure-compatible equipment, leak checks, secured upright cylinders and proper cylinder carts. Site-specific controls must account for the release and enclosure; there is no universal ventilation rate implied here. Air Products South Africa, Argon SDS 003A, revision 6, December 2025, sections 2, 6–8.

Refrigerated liquid adds cold-contact and vaporization hazards. Air Products' separate liquid-argon SDS requires protection against liquid splashes, appropriate cold-insulating gloves and eye/face protection for relevant transfer work. Liquid trapped in a closed volume can generate very high pressure as it warms; cryogenic vessels use relief devices and can vent during normal operation. Vent discharge also creates an oxygen-displacement risk. Use the actual container's instructions and regional SDS for transfer, venting and storage. Air Products South Africa, Argon Liquid/Refrigerated SDS 003B, revision 6, December 2025, sections 6–8.