AWS D1.1:2025 · Clause 5.6.4 · GMAW

GMAW Shielding Gas Under D1.1:2025 — Essential Variable, OE Formula, and the ER80/ER90 Rule

Shielding gas is an essential variable for GMAW under AWS D1.1:2025. Clause 5.6.4 gives four compliance paths for prequalified WPSs: match the A5 classification gas, hit the oxygen equivalent range, fall within Table 5.10, or test the combination with the filler manufacturer.

The common shop-floor claim that “a different shielding gas changes your ER80 to ER90” is almost right, and almost right is what fails audits. The A5.28 classifications are fixed properties of the wire chemistry and the tested mechanical properties. What the gas actually does is change whether the deposited weld meets the classification threshold on your actual job — and that is what invalidates your prequalification.

Shielding Gas is an Essential Variable for GMAW

AWS D1.1:2025 Table 6.6 lists shielding gas composition and flow rate as essential variables for GMAW, FCAW-G, and GMAW-S. Table 5.5 carries the equivalent status for prequalified WPSs. In plain terms, if the gas on the production floor is not the gas on the WPS, the WPS is no longer valid — and for prequalified procedures, prequalification is lost.

The consequences flow from Clause 6.8.1: changes beyond the limitations of PQR essential variables for SMAW, SAW, GMAW, GTAW, and FCAW shown in Table 6.6 require requalification of the WPS. That means a new test coupon, new destructive testing, and a new PQR. There is no “minor deviation” clause for gas composition.

The ER80S-D2 / ER90S-D2 Exception in A5.28

AWS A5.28 Section 3.2 is strict: electrodes and rods classified under one classification shall not be classified under any other classification in the specification — with one exception. ER80S-D2 may also be classified as ER90S-D2 provided the product meets the requirements of both classifications. The same physical wire can be labeled either way if the manufacturer demonstrates it passes both the 80 ksi and 90 ksi minimum tensile tests.

This is the kernel of truth behind the common shop claim that gas can “change ER80 to ER90.” It does not — the wire is a wire, and its classification is earned through the A5.28 testing protocol. But for this one dual-classified wire, the manufacturer may ship the same spool to Shop A marked ER80S-D2 and to Shop B marked ER90S-D2. If Shop A and Shop B run it on the same Ar/2% O2 gas the wire was tested on, both classifications stand. If either shop swaps to a different gas, the actual deposited weld properties are no longer what A5.28 measured, and the classification is operationally meaningless for that job.

No other ER80 and ER90 pair enjoys this exception. ER80S-B2 and ER90S-B3 are different wires with different chromium and molybdenum content. ER80S-Ni1, ER80S-Ni2, and ER80S-Ni3 differ in nickel content and are not interchangeable even between themselves. The exception is narrow.

Clause 5.6.4 — The Four Compliance Paths for Prequalified Shielding Gas

AWS D1.1:2025 Clause 5.6.4 governs which shielding gases may be used on a prequalified GMAW or FCAW-G WPS. The clause provides four independent paths, and production gas must satisfy at least one of them:

(1) Match the A5 classification gas. The production shielding gas shall be the gas used for electrode classification under the applicable AWS A5 specification — A5.18/A5.18M, A5.20/A5.20M, A5.28/A5.28M, or A5.29/A5.29M. This is the strictest and safest path.
(2) Fall within the OE range. For electrodes that include an “OE” shielding gas designator in the classification (new under the 2025 edition), the production shielding gas must have an oxygen equivalent within the range listed in the classification. The OE formula is defined in the clause itself and is covered in the next section.
(3) Appear in Table 5.10 for A5.18 electrodes. For electrodes classified per AWS A5.18/A5.18M, Table 5.10 provides acceptable gases regardless of whether the electrode carries an OE designator. This is the convenient path for the most common structural filler — ER70S-6.
(4) Test the combination. If an electrode does not have an OE designator and does not conform to A5.18, the electrode-gas combination that will be used in production must have been tested in accordance with the applicable A5 specification by the filler metal manufacturer or the gas producer. Tests must cover mechanical properties, chemical composition, NDT requirements, and any supplemental designators such as diffusible hydrogen.

If no path applies, prequalification is lost and the WPS must be qualified under Clause 6 with a new PQR. The paths are independent but not permissive — picking whichever is most convenient to the production floor is the right read, but the documentation must show which path was selected and how the gas meets it.

Oxygen Equivalent (OE) — The 2025 Formula

The oxygen equivalent concept was added to D1.1 in the 2025 edition as a way to characterize oxidation potential for mixed gases. Per Clause 5.6.4(2):

Oxygen Equivalent = % oxygen in shielding gas + (0.5 × % carbon dioxide in shielding gas)
AWS D1.1:2025 Clause 5.6.4(2)

The coefficient 0.5 on carbon dioxide reflects that CO2 contributes roughly half the oxidation potential of free O2 at arc temperatures. Some worked values:

100% Ar: OE = 0
Ar / 2% O2: OE = 2.0
Ar / 5% O2: OE = 5.0
Ar / 8% CO2: OE = 4.0
Ar / 25% CO2 (C25): OE = 12.5
100% CO2: OE = 50.0

An electrode classified with an “OE” designator has a permitted OE range listed in its classification. Any gas whose computed OE falls in that range satisfies Clause 5.6.4(2), regardless of whether it is an Ar/O2 blend, an Ar/CO2 blend, or a tri-mix. The OE mechanism replaces having to enumerate every possible gas pairing and gives the fabricator a larger menu at the cost of requiring that the electrode manufacturer has published an OE range for the classification in question.

`Table 5.10` — Prequalified Gases for ER70S-X

For electrodes conforming to AWS A5.18/A5.18M — which covers the entire ER70S family and the E70C metal-cored electrodes — Table 5.10 spares the fabricator from computing oxygen equivalents or matching classification gases. Three gas families are prequalified:

Electrode	Shielding Gas Family	Composition Range
ER70S-X (except ER70S-G) and E70C-X metal-cored electrodes	Ar/CO2 combinations	Ar 75–90% / CO2 10–25%
	Ar/O2 combinations	Ar 95–98% / O2 2–5%
	100% CO2	100% CO2

ER70S-G is deliberately excluded because the G suffix is a manufacturer-specified composition with no required gas. E70C metal-cored electrodes share the spray-transfer behaviour of their solid-wire counterparts and follow the same prequalified gas menu. Any gas outside these three bands requires one of the other Clause 5.6.4 compliance paths.

`Table 6.6` — When a Gas Change Forces Requalification

For procedures qualified under Clause 6 (rather than prequalified under Clause 5), Table 6.6 defines the GMAW essential variables. Key rules for shielding gas:

Any change in nominal shielding gas composition requires requalification. A switch from Ar/25% CO2 to Ar/8% CO2 is a new PQR even though both gases are in Table 5.10 for prequalified use.
Flow rate has a calibration tolerance: + 50% if increased or – 25% if decreased from the documented value. A flow rate of 35 cfh documented on the PQR tolerates 26 to 52 cfh in production without requalification.
Table 5.5 Item (26) applies the same flow rate tolerance to prequalified WPSs.

The Table 6.6 essential variable rule also extends to GMAW-S per Clause 5.5.2 (Code Approved Processes) — Cl. 5.5.1 excludes GMAW-S from prequalification, and Cl. 5.5.2 then requires GMAW-S WPSs to be qualified under Clause 6 with Table 6.6 essential variables applied. Every GMAW-S WPS requires a PQR — the shielding gas rules from Table 6.6 apply identically.

The “Retro-active PQR” Fix

When a shop discovers mid-job that production shielding gas does not satisfy any Clause 5.6.4 path — or that the gas differs from the qualified PQR and exceeds Table 6.6 limits — the standard corrective action is a retro-active PQR, derived from the Clause 6 qualification provisions. The typical shop-practice sequence:

Stop production welding on the affected joints. Document the date, joint IDs, and deviant parameters.
Run a test coupon under the actual production parameters, including the deviant shielding gas. The coupon conforms to Clause 6 joint, thickness, and test-specimen requirements.
Destructive-test the coupon per Clause 6 acceptance criteria: tensile, bend, macro-etch, and where CVN testing is specified, impact.
If the coupon passes, issue a new qualified WPS covering the actual production parameters. The prior prequalified WPS is retired or archived with an effective-date cutoff.
Welds produced under the old WPS remain subject to the Engineer’s disposition under D1.1 Clause 4.1 and Clause 8. The Engineer may require additional NDE, may accept as-is with documentation, or may require removal and replacement per the contract documents.

The retro-active PQR is a standard shop practice precisely because shielding gas drift is common — a supplier change, a cylinder swap, or an equipment retrofit can introduce a deviation that nobody catches until the inspector asks to see the WPS alongside the gas analysis certificate. The retro-active PQR does not punish past welds; it legitimizes the current production parameters and re-establishes a compliant paper trail.

Cross-Standard Note — ASME IX and API 1104

Other gas-shielded welding codes treat shielding gas similarly. ASME Section IX groups shielding gas changes under the QW-408 variable family: QW-408.2(a) covers addition or omission of shielding gas, and QW-408.2(b) covers a change in shielding gas composition. Both require a separate procedure qualification — with one exception that parallels D1.1. Electrodes classified to SFA-5.18, SFA-5.20, SFA-5.28, or SFA-5.29 that include an OE designator (for example, ER70S-6 OE 50/4) do not require a separate qualification when the shielding gas OE is within the classification range. ASME IX uses the same formula as D1.1:2025: oxygen equivalent = % oxygen + (0.5 × % carbon dioxide). The two codes are harmonized on the OE mechanism.

API 1104:2021 Section 5.4.2.7 specifies three distinct shielding gas essential variables: (a) a change in shielding gas classification in accordance with AWS A5.32, (b) a change in flow rate greater than 20 percent below the nominal flow rate recorded during procedure qualification, and (c) deletion of or change in nominal composition of backing gas when backing gas is used during qualification. All three trigger requalification for both Category I (standard) and Category II (hardness and/or toughness) WPSs. API 1104 does not yet adopt the OE concept.

The headline: all three codes agree that shielding gas is a qualification event, not a minor adjustment. D1.1:2025 and ASME IX are aligned on the OE formula as a quantitative equivalence mechanism. API 1104 still requires explicit enumeration of gas combinations.

Read the full prequalified WPS rules →

Related Standards Guides

Frequently Asked Questions

Is shielding gas an essential variable for GMAW under D1.1:2025?

Yes. AWS D1.1:2025 Table 6.6 lists shielding gas composition and flow rate as essential variables for GMAW, FCAW-G, and GMAW-S. Table 5.5 carries the same status for prequalified WPSs. Any change in gas composition beyond the documented WPS range invalidates prequalification and, for non-prequalified procedures, requires requalification with a new PQR per Clause 6.2.1. Flow rate has an explicit tolerance of plus 50 percent if increased or minus 25 percent if decreased. The rule applies identically to GMAW-S per Clauses 5.5.1 and 5.5.2 — 5.5.1 excludes GMAW-S from prequalification, and 5.5.2 requires every GMAW-S WPS to be qualified under Clause 6 with Table 6.6 essential variables applied. In practice, this means any documented supplier change, cylinder swap to a different blend, or regulator recalibration outside the tolerance band requires a WPS amendment before production welding continues.

Can ER80S-D2 really be classified as both ER80 and ER90?

Yes, but only for that specific wire. AWS A5.28 Section 3.2 states that electrodes and rods classified under one classification shall not be classified under any other classification in the specification, except that ER80S-D2 and ER55S-D2 may also be classified as ER90S-D2 and ER62S-D2 provided the product meets the requirements of both classifications. This dual classification means the same physical wire can be labeled either way if the manufacturer demonstrates it passes both the 80 ksi and 90 ksi minimum tensile tests on the required shielding gas. No other ER80 or ER90 pair enjoys this exception — ER80S-B2 and ER90S-B3 are chemically different wires with distinct chromium and molybdenum content, and the ER80S-Ni1, Ni2, and Ni3 series differ in nickel content and are not interchangeable. The practical consequence is that a spool labeled both ER80S-D2 and ER90S-D2 is one wire with two valid classifications on the paperwork.

What is the Oxygen Equivalent (OE) formula in D1.1:2025 Clause 5.6.4?

D1.1:2025 Clause 5.6.4(2) defines Oxygen Equivalent as the percentage of oxygen in the shielding gas plus half the percentage of carbon dioxide in the shielding gas. The formula is written Oxygen Equivalent equals percent oxygen plus 0.5 times percent carbon dioxide. A gas of Ar/8% CO2 has an OE of 4.0 percent. A gas of Ar/2% O2 has an OE of 2.0 percent. A gas of 100% CO2 has an OE of 50.0, and 100% argon has an OE of zero. For electrodes that carry an OE designator in their classification, the production shielding gas OE must fall within the range listed in the classification. The 0.5 coefficient on carbon dioxide reflects that CO2 contributes roughly half the oxidation potential of free O2 at arc temperatures because CO2 partially dissociates to CO and O in the arc plasma, and the OE concept was introduced in the 2025 edition specifically to give fabricators a larger menu of equivalent gases without needing to enumerate every possible blend.

Which shielding gases are prequalified for ER70S-6 under D1.1:2025?

D1.1:2025 Table 5.10 lists prequalified shielding gases for GMAW electrodes conforming to AWS A5.18/A5.18M, which covers ER70S-6. Three gas families are acceptable: argon and carbon dioxide combinations at 75 to 90 percent argon with 10 to 25 percent carbon dioxide, argon and oxygen combinations at 95 to 98 percent argon with 2 to 5 percent oxygen, and 100 percent carbon dioxide. Any gas outside these ranges requires either an OE designator match under Clause 5.6.4(2) or filler-metal-manufacturer testing under Clause 5.6.4(4). ER70S-G is excluded from Table 5.10 because the G suffix denotes a manufacturer-specified composition with no required gas, and E70C metal-cored electrodes share the same prequalified gas menu as their solid-wire counterparts. Using the popular 90/10 and 75/25 blends or any Ar/O2 mix inside those percentages requires no further compliance action under Clause 5.6.4 for an A5.18 electrode.

If I substitute a different shielding gas, does my prequalified WPS still apply?

Only if the substitute gas falls within one of the four Clause 5.6.4 paths. The new gas must either match the AWS A5 classification gas for that electrode, fall within the OE range of an OE-designated classification, be listed in Table 5.10 for an A5.18 electrode, or have been tested by the filler metal manufacturer or gas producer as a qualified combination. If the substitute gas meets none of those four paths, prequalification is lost. The WPS becomes non-prequalified and must be qualified per Clause 6 with a new PQR before production welding can continue. The documentation burden matters: the WPS should cite which path was selected and show the evidence, because an inspector asking which Clause 5.6.4 compliance path applies is a common Part C exam style and a common audit finding in shops that swap gas suppliers mid-project.

What is a retro-active PQR and when is it required?

A retro-active PQR is a procedure qualification record written and tested after production welding has already occurred on a non-compliant WPS. It is the standard corrective action when a shop discovers a shielding gas, filler metal, or process variable deviation from Clause 5 prequalified limits partway through a job. The sequence is: stop production on the affected joints, run a test coupon under the actual production parameters including the deviant gas, destructive-test the coupon per Clause 6 acceptance criteria, and if the coupon passes, issue a new qualified WPS that covers the production variables. Welds produced under the old WPS remain subject to the Engineer's disposition and may require additional NDE or repair depending on the contract documents.

What are the flow rate tolerances for shielding gas on a D1.1:2025 WPS?

AWS D1.1:2025 Table 5.5 specifies that shielding gas flow rate on a prequalified WPS may increase by up to 50 percent above the documented value or decrease by up to 25 percent below the documented value without requiring WPS revision. Larger deviations require a new prequalified WPS if still within all Clause 5 limits, or requalification under Clause 6. Flow rate changes outside these bands are a frequent cause of porosity because reduced flow lets atmospheric gas contaminate the puddle and excessive flow creates turbulence that sucks air in past the nozzle. As a worked example, a WPS documenting 35 cfh tolerates production readings from 26 cfh to 52 cfh without any amendment. The Table 6.6 rule for qualified WPSs sets the same tolerance band, so the flow-rate envelope is identical regardless of whether the procedure is prequalified or PQR-qualified.

CWI Exam Tip: Part C questions on Clause 5.6.4 often compare two WPSs that list the same filler (ER70S-6) but different gas ratios — only one falls inside Table 5.10. Memorize the three Table 5.10 bands verbatim (Ar/CO2 75–90/10–25, Ar/O2 95–98/2–5, 100% CO2). The 2025 addition of Clause 5.6.4(2) oxygen equivalent is a new Part C topic area that seminar study guides published before 2025 do not cover.