Helium

Linde Austria Helium 5.0 lists 99.999% purity, with maxima of oxygen 2 ppm, nitrogen 3 ppm, water 3 ppm and hydrocarbons 0.2 ppm, on an ideal volume-fraction basis equivalent to mole fraction. Check individual limits even for another 5.0 supply. For leak testing, record tracer concentration and the instrument's correction method. Linde Austria, Helium 5.0

Identity and reference conditions

Helium (He, CAS 7440-59-7) has transport designations UN1046 for compressed gas and UN1963 for refrigerated liquid. Specify the grade and delivery form separately. Air Liquide, Gas Encyclopedia: Helium

Keep temperature and pressure attached to gas-density and volume data. A litre of refrigerated liquid and a litre of gas are different quantities; even a stated gas volume changes with its reference state. The table describes physical properties, not a cylinder fill pressure, flow setting or inventory conversion valid under arbitrary conditions. Air Liquide, Gas Encyclopedia: Helium.

Grade selection and impurity limits

For the named Linde Austria grade, compare individual impurity limits on the stated volume-fraction basis. Linde Austria, Helium 5.0

Supplier specifications can differ at the same nominal purity. Tyczka's helium sheet lists Helium 5.0 at ≥99.999 vol.% with oxygen <1 ppm, nitrogen <5 ppm, water <2 ppm and hydrocarbons <0.5 ppm. These differ from the Linde example; neither product can be declared universally better from the purity headline. Tyczka separately lists balloon gas at ≥97 vol.%, showing why an application nickname is not a substitute for a technical specification. Its sheet carries document code TAG 057/8-02/26; that code is retained rather than inferring an exact issue day. Tyczka Air Gases, Helium Product Data Sheet.

For procurement, record the supplier product/grade, minimum helium fraction, relevant impurity maxima, supply form and required delivery conditions. The examples here are bounded product specifications, not a declaration of brand equivalence or permission to replace a specified gas.

Welding and laser applications

For GTAW/TIG, helium provides higher thermal conductivity than argon and can increase heat input, helping applications involving thicker material. Its higher ionization potential makes arc starts less consistent than with argon. Argon/helium blends combine these characteristics; Miller describes the balance as hotter arcs with increasing helium but less favorable high-frequency starting and stability. Keep gas composition tied to the material, equipment and welding procedure specification (WPS). A blend percentage alone does not define welding current or heat input. Miller, Best Practices for Proper Shielding Gas in TIG Welding, 11 March 2026.

Laser service has distinct gas roles. Linde lists Laser Helium 4.6 as one of the resonator gases used with carbon dioxide and nitrogen in CO₂ lasers. A resonator gas participates in the laser-source system; this listing does not make helium the assist gas for every cutting head, nor establish a requirement for other laser architectures. Use the specific resonator manufacturer's gas specification. Linde Finland, Laser Gases.

As a separate example, Linde France's Laser Hélium sheet describes shielding for laser welding, principally CO₂ lasers, where high ionization energy reduces plasma formation. That named product specifies helium ≥99.996 vol.%, water ≤5 ppmv, oxygen ≤5 ppmv and hydrocarbons ≤1 ppmv. Its footer identifies CD-26761, version 12, effective 11 November 2022. These limits describe that product and application, not every helium laser gas or resonator mixture. Linde France, Laser Hélium Product Sheet.

Leak testing: concentration and calibration

Helium can serve as a tracer rather than the entire test fill. Linde describes helium leak detection using a helium tracer, usually with nitrogen as carrier, and a sensitive helium detector to locate leaks. The tracer mixture and detector arrangement belong to the test method; a helium supply specification alone does not establish a leak-rate acceptance threshold. Linde, Leak Detection and Pressure Testing.

INFICON explains that a detector responds to the helium portion of a diluted tracer gas. Its example uses 10% helium: concentration moving from 10% to 9% or 11% produces a ±10% relative change in detected leak rate. Dilution therefore requires adequate detector sensitivity and concentration compensation in the applicable calibration or trigger arrangement. Follow the instrument's method rather than applying a correction twice. INFICON, How to Save Helium in Vacuum Leak Testing.

Background is another control variable. INFICON warns that helium released during repeated tests can raise and vary the local background, interfering with calibration. Its calibration guidance emphasizes a distinguishable reference-leak signal and adequate detector linearity. A nominal ambient background is not evidence that the test cell remains at that concentration during production. INFICON, The Top 5 Mistakes in Calibration and How to Avoid Them.

Delivery and flow measurement

Use gas-service-compatible delivery equipment and the correct flowmeter scale. Smith's H2051B-580 regulator has separate scales for helium, carbon dioxide and argon/argon–carbon dioxide. Its helium range is an equipment capability, not a prescribed welding or purge flow. Read flow using the manufacturer's specified gas and operating conditions; a pressure gauge reading is not itself a flow measurement. Smith Equipment, H2051B-580 Flowmeter Regulator.

For welding, establish shielding with the actual torch, consumables and surroundings. Miller describes excessive flow as a turbulence/contamination risk and insufficient flow as inadequate protection. Cup geometry, gas lenses, hose integrity and pre/post-flow also matter. Increasing flow cannot substitute for correcting a delivery fault or disrupted shielding envelope, and the selected grade does not guarantee purity at the arc. Miller, Best Practices for Proper Shielding Gas in TIG Welding.

Compressed and refrigerated handling

Air Products' compressed-helium SDS classifies it as gas under pressure and warns of suffocation hazards. Its handling provisions require pressure-compatible equipment, leak checks, secure upright cylinders, suitable cylinder transport and protection against damage. Oxygen-displacement controls must address the actual enclosure and potential release; helium's low density does not establish that an occupied space is safe. Air Products South Africa, Helium SDS 061A, revision 5, December 2025.

Refrigerated helium adds extreme cold and pressure-management hazards. Linde's liquid-helium SDS warns of severe frostbite, pressure buildup in closed containers and oxygen-deficiency risks. It also notes that air can condense on exposed cold surfaces, leaving oxygen-enriched condensate as nitrogen evaporates. This is a cryogenic-system hazard despite helium itself being inert. Use the actual vessel's transfer, relief, protective-equipment and venting instructions and the applicable regional SDS; do not treat a liquid vessel as a compressed-gas cylinder. Linde Canada, Helium, Refrigerated Liquid SDS E-4600, version 1.1, revised 2 October 2023.