# Helium

Helium properties, application-specific grades, welding and leak-test controls, delivery measurement and cryogenic handling.

Reviewed: 2026-11-01

Tags: consumables, gases, welding

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*](https://produkte.linde.at/schweiss_schneidgase/helium_5.0.html)

## 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*](https://encyclopedia.airliquide.com/helium)

| Property | Supplier value and reference condition |
|---|---|
| Molar mass | 4.003 g/mol |
| Boiling point | −268.93 °C at 1.013 bar |
| Gas density | 0.1784 kg/m³ at 0 °C and 1.013 bar |
| Liquid density | 124.74 kg/m³ at its boiling point, 1.013 bar |

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*](https://encyclopedia.airliquide.com/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*](https://produkte.linde.at/schweiss_schneidgase/helium_5.0.html)

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*](https://tyczka-airgases.at/content/download/937/8204).

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](https://www.millerwelds.com/en-us/resources/knowledge-hub/tig-welding/how-to/best-practices-for-proper-shielding-gas-in-tig-welding).

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*](https://www.linde-gas.fi/shop/en/fi-ig/buy-gases/gas-1006/laser-gases-1006).

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*](https://www.linde-gas.fr/wcsstore/FR_RES_Industrial_Gas_Store/Attachment/fiche_produits/FR-FPLG-0073.pdf).

## 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*](https://www.linde-gas.com/products-and-services/industrial-service-solutions/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*](https://www.inficon.com/en/news/2023-12-at-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*](https://www.inficon.com/en/news/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*](https://www.smithequipment.com/en-us/equipment/regulators-and-gas-control/flowmeters/medium-duty-single-stage-flowmeter-regulators-m00254/argon-co2-helium-medium-duty-flowmeter-regulator-50-psig-h2051b-580).

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*](https://www.millerwelds.com/en-us/resources/knowledge-hub/tig-welding/how-to/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](https://airproducts.co.za/wp-content/uploads/2026/01/MSDS-061A-APSAP-Helium-GHS-r5-2025-12.pdf).

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](https://static.prd.echannel.linde.com/wcsstore/CA_LINDE_Store/datasheets/E-4600-Helium%2C%20Refrigerated%20Liquid-SDS%20CA-EN-1.1.pdf).