Does switching from 75/25 Ar/CO2 to 80/20 Ar/CO2 require WPS requalification?

Yes, if the change falls outside the tolerance allowed by your WPS and AWS D1.1:2025 Table 6.6. A change in gas composition — even a modest shift in blend ratio — is an essential variable for GMAW and FCAW that requires PQR requalification or a new WPS entry if it exceeds the stated allowable range.

What is AWS A5.32 and why does it appear on a WPS?

AWS A5.32 is the AWS specification for welding shielding gases. It assigns classification codes (e.g., SG-AC for argon-CO2 mixtures) that precisely identify gas composition. Listing the A5.32 classification on the WPS creates a traceable, unambiguous record of the qualified gas — which is required documentation under AWS D1.1.

Is shielding gas an essential variable for SMAW?

No. SMAW does not use an externally supplied shielding gas, so it has no shielding gas essential variable. Shielding gas is an essential variable for GMAW, FCAW-G, GTAW, and PAW.

Can the same WPS cover both CO2 and a 75/25 Ar/CO2 blend?

Only if the WPS was qualified on a PQR using a gas within the allowable range that covers both. Pure CO2 and an argon blend are different classifications under A5.32 and different positions in AWS D1.1:2025 Table 6.6 — qualifying on one does not automatically cover the other.

Sep 3, 20267 min read

AWS A5.32 Shielding Gas Classification and WPS Compliance

How AWS A5.32 classification codes identify shielding gas mixtures, which changes are essential variables under AWS D1.1:2025 Table 6.6, and what CWIs must document.

WPS GMAW FCAW shielding gas AWS D1.1 essential variables CWI

Walk the floor of any busy fab shop running GMAW or FCAW-G and you will find gas cylinders labeled with blend percentages written in marker: "75/25," "90/10," "C25." Welders and foremen usually know what gas they are running, but whether that knowledge makes it onto the WPS — and whether it matches the PQR — is another matter. When a CWI or a third-party auditor opens the welding procedure package and finds a vague entry like "CO2 or mix" in the shielding gas field, the WPS has a deficiency. AWS A5.32 exists to close exactly that gap.

What AWS A5.32 Classifies

AWS A5.32, Specification for Welding Shielding Gases, provides a standardized classification system for shielding and backing gases used in arc welding. The specification defines a shorthand code built from letters representing the constituent gases:

A — Argon
C — Carbon dioxide
O — Oxygen
H — Hydrogen
N — Nitrogen
He — Helium

Mixtures are identified by combining the letters of their components, along with balance-gas fractions. A common 75% Ar / 25% CO2 mixture carries the classification SG-AC-25, where "AC" indicates an argon-CO2 blend and "25" identifies the CO2 percentage. Pure CO2 is SG-C. A tri-mix argon-CO2-oxygen blend would appear as SG-ACO with the respective percentages appended. Pure argon used as a TIG back-purge gas is SG-A.

The value of this system on a WPS is precision. "Argon mix" is ambiguous — SG-AC-25 is not. When the WPS lists an A5.32 classification, anyone reading it knows exactly what gas composition was used on the qualifying PQR, and inspectors can verify that the cylinder tag on the floor matches.

Shielding Gas as an Essential Variable: AWS D1.1:2025 Table 6.6

Under AWS D1.1:2025, shielding gas is an essential variable for GMAW, FCAW-G, GTAW, and PAW. Essential variables are listed in Table 6.6 (Rule library based on AWS D1.1:2025; verify against your governing edition). A change in shielding gas type or composition beyond the limits established on the qualifying PQR requires either a new PQR or a separate WPS.

The code distinguishes several categories of shielding gas change:

A change in gas type — for example, moving from a CO2-based shield to an argon-based blend — is always an essential variable requiring requalification. These are fundamentally different arc and chemistry environments. CO2 produces a more oxidizing atmosphere and typically wider, more penetrating weld profiles; argon-rich blends yield a narrower bead with reduced spatter and a different droplet transfer mode at equivalent parameters.

A change in gas classification — for example, switching from SG-AC-25 to SG-AC-20 — is also an essential variable. Even a modest shift in the CO2 fraction changes the shielding chemistry, arc voltage behavior, and weld metal oxygen content. A WPS qualified with 75/25 Ar/CO2 does not automatically cover 80/20 Ar/CO2.

A change beyond the allowable compositional tolerance stated in the WPS is treated as an essential variable even when the blend ratio change appears minor. If the WPS states the qualified gas as SG-AC-25 and production cylinders come in at SG-AC-22 without a corresponding PQR or WPS amendment, the production weld is being made under an unqualified condition.

For FCAW-S (self-shielded) processes, there is no external shielding gas, so this essential variable does not apply. For SMAW, the same logic holds — the flux coating provides shielding. But for any gas-shielded process, the shielding gas entry on the WPS is load-bearing information, not a formality.

What Must Appear on the WPS

A conforming WPS for GMAW or FCAW-G should include:

The AWS A5.32 classification of the qualified shielding gas (e.g., SG-AC-25)
The flow rate range in cubic feet per hour (or liters per minute) at which the process was qualified, if flow rate is listed as a variable in the procedure
A notation for backing gas if applicable (common in GTAW root passes on stainless; see the D1.6 requirements for stainless structural welding)

The PQR that supports the WPS must document the actual gas used during test coupon welding. If the test was run with SG-AC-25, the PQR records SG-AC-25 and that classification defines the qualified condition.

Some WPSs attempt to list a range of acceptable gases, such as "SG-C or SG-AC-25." This is only permissible when the PQR tests were conducted on the most restrictive condition within that range, and when the code supports that coverage. In general, if you want a WPS that covers both pure CO2 and an Ar/CO2 blend, you need a PQR on each — or a PQR demonstrating that coverage, which AWS D1.1 does not automatically grant by blanketing a gas "family."

Why Shielding Gas Deficiencies Show Up in Audits

Shielding gas entries are one of the most commonly deficient fields in WPS packages reviewed during AISC certification audits and third-party project reviews. The pattern typically follows one of three paths:

Outdated WPS after a gas switch: A shop qualifies a WPS years ago using C25 (SG-AC-25). At some point, purchasing switches to a 90/10 Ar/CO2 blend for spatter reduction. The WPS is never updated, and for months or years the shop has been running production welds outside the qualified gas condition.

Generic gas entries: The WPS field reads "CO2" or "inert mix" with no A5.32 classification. While the intent is clear, it does not constitute a documented qualified condition — there is no traceable reference to what was tested.

Backup gas omissions: GTAW procedures for stainless structural work under AWS D1.6 that list the shielding gas but omit the backing (purge) gas. Both can be essential variables, and the backing gas must be documented.

For shops reviewing their existing WPS library, the shielding gas field is a low-effort correction with high audit value. See AWS D1.1:2025 Table 6.6 Explained for the full essential variable framework, and Shielding Gas Essential Variables Under AWS D1.1 for a process-by-process breakdown.

Documenting Gas in Production

Documentation does not stop at the WPS. During production, a conforming welding program under AWS D1.1 requires that the actual shielding gas used can be traced back to the qualified condition. In practice this means:

Cylinder manifolds or supply lines should be labeled with the A5.32 classification and lot/heat number of the gas supply
The production parameter log (where maintained) records the gas specification used per shift or per weld joint type
When multiple gas blends are in use in the same shop for different processes (argon for TIG, C25 for wire feed, 100% CO2 for some FCAW applications), each storage area should be segregated and labeled to prevent the wrong gas from being connected

The CWI's pre-weld checklist should confirm that the gas on the line matches the WPS. For a practical walk-through of pre-arc inspection, see CWI Pre-Weld Inspection Before Striking an Arc.

Shielding Gas in GTAW and Combined Processes

GTAW WPSs require documentation of both the torch shielding gas (almost always argon, sometimes helium or a mixture for specific applications) and any backing gas used on the root side of a joint. For structural carbon steel under AWS D1.1, GTAW root passes with open roots are uncommon but do occur in certain tubular and pipe applications. In those cases, the backing gas must be documented on both the PQR and the WPS.

Combined process WPSs — where GTAW is used for the root pass and GMAW or FCAW-G for fill and cap passes — must document the shielding gas for each process separately. A change in the GTAW backing gas is an essential variable for the root pass, even if the fill-pass gas is unchanged. See AWS D1.1 Multiprocess WPS Essential Variable Scope for how essential variables apply across process transitions within a single WPS.

Building a Compliant Shielding Gas Record

For shops building or updating their WPS library, a defensible shielding gas record requires:

Confirming the A5.32 classification of the gas that was actually used during PQR testing (not what was assumed — get the certificate from the gas supplier)
Updating all WPS documents to list the A5.32 classification rather than a colloquial descriptor
Establishing purchasing controls that flag any gas specification change for engineering review before a cylinder change is made on the shop floor

If your current gas and your WPS qualification don't match, you have two options: requalify a new PQR with the current gas, or switch back to the originally qualified gas. Neither is particularly expensive compared to the cost of discovered nonconformance during a project audit.

For help managing your WPS library and tracking qualified conditions across processes and base metals, see our pricing page — the WPS editor stores qualified shielding gas by A5.32 classification and flags any production deviation.

Rule library based on AWS D1.1:2025; verify against your governing edition. The AHJ or contract may specify 2020 or an earlier edition with different table numbering.

FAQ

Frequently asked.

Does switching from 75/25 Ar/CO2 to 80/20 Ar/CO2 require WPS requalification?: Yes, if the change falls outside the tolerance allowed by your WPS and AWS D1.1:2025 Table 6.6. A change in gas composition — even a modest shift in blend ratio — is an essential variable for GMAW and FCAW that requires PQR requalification or a new WPS entry if it exceeds the stated allowable range.
What is AWS A5.32 and why does it appear on a WPS?: AWS A5.32 is the AWS specification for welding shielding gases. It assigns classification codes (e.g., SG-AC for argon-CO2 mixtures) that precisely identify gas composition. Listing the A5.32 classification on the WPS creates a traceable, unambiguous record of the qualified gas — which is required documentation under AWS D1.1.
Is shielding gas an essential variable for SMAW?: No. SMAW does not use an externally supplied shielding gas, so it has no shielding gas essential variable. Shielding gas is an essential variable for GMAW, FCAW-G, GTAW, and PAW.
Can the same WPS cover both CO2 and a 75/25 Ar/CO2 blend?: Only if the WPS was qualified on a PQR using a gas within the allowable range that covers both. Pure CO2 and an argon blend are different classifications under A5.32 and different positions in AWS D1.1:2025 Table 6.6 — qualifying on one does not automatically cover the other.