Argon-oxygen shielding mixtures

BOC's UK SPECSHIELD factsheet identifies 2% oxygen, balance argon, as ISO 14175-M13-ArO-2 under BS EN ISO 14175:2008. Linde reports better wetting at 2% than at 1%, with a darker, more oxidized stainless bead. Check the wire, transfer mode and weld requirements before changing the blend. BOC, SPECSHIELD 2% Oxygen, Balance Argon Linde, Argon oxygen mixtures

Air Liquide describes 1–5% oxygen additions to argon for arc stability and wetting in active GMAW shielding. Pure oxygen serves a different process role. Air Liquide, Shielding gas explained

Composition and identification

Specify both components and the concentration basis. Linde describes its common oxygen additions as percentages by volume. A shorthand such as “98/2” without gas names is incomplete. Record the supplier product and specification alongside the nominal composition. Linde, StarGold O-2 and O-5 welding gas blends

The BOC factsheet carries printed code BOC004/Spec2O_Rev2/CST/0123. Use the governing standard and purchase specification for impurity limits and blend tolerances. BOC, SPECSHIELD 2% Oxygen, Balance Argon

Supplier product names also carry useful distinctions:

These are examples from Linde's product family, not a cross-brand naming standard or a universal material approval. Linde notes that its 2% blend gives better wetting than its 1% blend, but produces a darker, more oxidized stainless-steel bead. Linde, Argon oxygen mixtures

Transfer mode, wetting and oxidation

Linde positions its O-2/O-5 blends for conventional and pulsed spray transfer on clean plain-carbon and ferritic stainless steels. Increasing oxygen within the discussed range reduces the minimum spray-transition current, increases puddle fluidity and wetting, and can support faster travel. The product guidance does not recommend these blends for short-circuit transfer, citing increased lack-of-fusion risk. Check a transfer-mode change against the welding procedure. Linde, StarGold O-2 and O-5 welding gas blends

The same guide warns that oxygen above 5% can promote undercut, poor bead appearance and oxide buildup, with reduced puddle control and gap bridging. This is a supplier application boundary. Select the gas with the wire manufacturer's recommendations and the qualified welding procedure; oxygen percentage alone does not specify current. Linde, StarGold O-2 and O-5 welding gas blends

Grade, supply and procedure control

A nominal blend name is not a complete gas-quality specification. Distinguish the intended oxygen addition from unwanted moisture, air ingress or other contamination. Nippon Sanso Matheson describes typical Ar/O₂ blends for pulse/spray GMAW of mild and low-alloy steels, with some stainless applications, while treating demanding stainless and nickel-alloy applications as specific gas-selection problems. Its availability of certificates of conformance for selected shielding gases is useful when procurement requires documented compliance. Request the actual certificate and applicable composition/impurity specification rather than assuming a grade from a trade name. Nippon Sanso Matheson, Shielding gas

Supply can include cylinders, premixed liquid supply or engineered mixing systems; Matheson describes both premixed liquid Ar/O₂ and on-site mixing arrangements. For a mixed-on-site installation, distinguish the incoming component specifications from verification of the delivered blend. Treat a change of supplier, blend or delivery arrangement as something to check against the welding procedure and quality requirements. Neither a nominal composition nor a certificate alone demonstrates the mechanical properties, corrosion performance or appearance of the finished weld. Nippon Sanso Matheson, Shielding gas

Delivery, environment and contamination

More flow does not automatically improve shielding. Hobart identifies restricted, insufficient or turbulent gas flow as possible porosity causes. Excessive flow relative to nozzle size can entrain air; drafts can displace shielding, while spatter in the nozzle or diffuser can restrict or disturb it. Establish flow using the equipment instructions and welding procedure for the actual gun, nozzle, joint and environment. There is no single flow value that follows from “98/2.” Clean base metal and properly stored, dry wire matter too: oil, rust, scale and moisture can produce defects even when the gas blend is correct. Hobart Brothers, MIG troubleshooting for metal-cored and solid wire

When porosity appears, check the flowmeter/regulator, hoses and gun for delivery faults or leaks, inspect the nozzle for spatter, and consider drafts and base-metal contamination. Miller lists these as troubleshooting checks; porosity alone does not identify a wrong oxygen percentage. Record what changed before substituting another blend, since a different gas cannot repair a leaking hose or contaminated joint. Miller, Troubleshooting weld defects

Mixture-specific handling

Use the supplied mixture's SDS and supplier-approved delivery equipment. Purity Cylinder Gases' 98% Argon 2% Oxygen SDS has an actual preparation date of March 3, 2025, despite the PDF's older URL directory. Section 2 classifies it as gas under pressure and requires protection from sunlight and well-ventilated storage; its argon information identifies a simple-asphyxiant hazard. Section 14 lists this mixture under US DOT as UN1956, compressed gas, n.o.s. (argon, oxygen), class 2.2. These are the cited product's statements, not worldwide transport instructions. Purity Cylinder Gases, 98% Argon 2% Oxygen SDS

An oxygen addition that oxidizes weld metal does not make the cylinder interchangeable with pure-oxygen service. Conversely, the cited mixture's nonflammable-gas transport class does not remove pressure or oxygen-displacement hazards. Identify the cylinder contents, connection and approved regulator from the supplier's documentation; keep the mixture SDS separate from component SDSs and from the hazards of welding fumes and the arc. Purity Cylinder Gases, 98% Argon 2% Oxygen SDS

Related reference

Welding methods