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Shielding Gas Selection Chart

A counter chart of the common shielding gases and mixes by welding process and base metal, with the AWS A5.32 and ISO 14175 style of naming them.

Ref WG-0205AWS A5.32

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

Shielding gas protects the molten weld from air and shapes the arc. The right choice depends on the process, the base metal, the transfer mode and the filler. AWS A5.32 classifies welding gases and uses the ISO 14175 system of designators, so a cylinder label or spec may say "M21-ArC-25" instead of "75/25". This chart covers the common choices. The WPS governs on code work.

How to use it

Find the process (GMAW, GTAW or FCAW).
Find the base metal.
Read the common gas. For GMAW, check the transfer mode.
For flux-cored wire, match the gas to the wire's designator (C or M).

Selection chart

Process and base metal	Common gas	Notes
GMAW short-circuit, carbon steel	75% Ar / 25% CO2, or 100% CO2	75/25 runs smoother with less spatter; CO2 gives deeper penetration and lower cost
GMAW spray or pulse, carbon steel	Ar with about 5–10% CO2, or Ar with 1–5% O2	High argon content needed for spray transfer
GMAW, stainless steel	Helium-argon-CO2 tri-mix for short-circuit; 98% Ar / 2% CO2 or 98% Ar / 2% O2 for spray	Keep active gas low to limit oxidation and carbon pickup
GMAW, aluminum	100% argon; argon-helium for thick sections	No CO2 or O2
GTAW, steel, stainless, aluminum, copper	100% argon	Argon-helium for thick aluminum or copper
GTAW, austenitic stainless	Argon; argon-hydrogen mixes in some cases	Never use hydrogen mixes on carbon steel, ferritic or martensitic grades
FCAW gas-shielded, carbon steel	100% CO2 (C wires) or 75–80% Ar / balance CO2 (M wires)	Wrong gas changes weld chemistry and strength
FCAW self-shielded	None	Flux makes its own shielding

Gas naming

Common name	ISO 14175 style
100% argon	I1
100% helium	I2
Argon-helium	I3
100% CO2	C1
75% Ar / 25% CO2	M21
98% Ar / 2% O2	M13

Key points

Flow is set in CFH or L/min per the WPS or the maker's guidance. See the gas flow sheet.
Inert gases displace oxygen. Ventilate confined work areas.
Label is the authority on cylinder contents, never color.

Common mistakes

Using 75/25 for TIG.
Running M-designated flux-cored wire on straight CO2.
Turning up flow to fight porosity caused by drafts or leaks.

Governing standards: AWS A5.32; ISO 14175.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.

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