AWS A5.28 · AWS D1.1:2025 · GMAW

ER80 vs ER90 — When Shielding Gas Breaks Your WPS

If your WPS calls for ER90-class Métal Fondu but production swaps shielding gas, you can silently fall below ER90 properties. The gotcha lives in A5.28 §3.2 (a narrow ER80/ER90 exception) and D1.1:2025 Clause 5.6.4 (Préqualifié shielding gas must match classification rules or you need a PQR).

Why this fails audits

The failure mode is simple: a WPS (or purchase spec) assumes “ER90” as a Résistance guarantee, but the wire’s classification and the Code’s prequalified-gas rules are written around the tested combination of wire + shielding gas. If you keep the wire but change the gas, you can change the Soudure metal properties you actually achieve — and you can also step outside what the code allows for prequalified procedures.

“It sounds dumb but your shielding gas can change an ER80 to an ER90 or vice versa.”
— @BadderBanana on r/StructuralEngineering (source)

A5.28 is strict — with one narrow ER80/ER90 exception

AWS A5.28 builds classification around the chemical and Propriétés mécaniques it specifies, and it generally does not allow a product to be classified as two different strength classes. The key rule is §3.2:

Electrodes and rods classified under one classification shall not be classified under any other classification in the Spécification.
Exception: ER80S-D2 may also be classified as ER90S-D2 if the product meets both classifications.

This is why you will sometimes see the same wire marketed as “ER80/ER90 D2” — but it does not mean “any ER80 becomes ER90 when you change gas.” The exception is narrow and explicitly named in A5.28 §3.2.

D1.1:2025 Article 5.6.4 ties production gas back to classification

For prequalified WPSs using GMAW or FCAW-G, AWS D1.1:2025 Clause 5.6.4 governs what shielding gas is allowed. One of the Conformité paths is explicit: the production shielding gas shall be the gas used for Classification des électrodes under the applicable AWS A5 specification. That is the bridge between “what the wire label means” and “what the code allows you to do on a DMOS préqualifié.”

Operationally, that means if your WPS calls ER90S-D2 and you are relying on prequalification, you cannot treat shielding gas as a casual shop substitution. You must be able to point to the Clause 5.6.4 compliance path that makes your production gas valid for that classification — or you are outside prequalification and the procedure belongs in Clause 6 qualification territory.

A quick decision Tableau for the shop

What changed?	Risk	What to do
Wire classification changed (ER80 ↔ ER90)	Strength assumption drift	Update the WPS and Vérifier the selected filler is still matching/allowed for the Groupe de métal de base.
Shielding gas blend changed	Outside `Clause 5.6.4` for prequalified WPS; weld metal properties may shift	Document the new gas and confirm which `Clause 5.6.4` path makes it valid. If none, qualify under Clause 6.
Project requires a guaranteed Minimum strength level	Paper classification ≠ production reality	Qualify the WPS by test under Clause 6 using the exact wire+gas you will use in production.

Frequently Asked Questions

Can the same ER80S-D2 wire also be ER90S-D2?

Sometimes. AWS A5.28 §3.2 states that electrodes and rods classified under one classification shall not be classified under any other classification, except that ER80S-D2 may also be classified as ER90S-D2 provided the product meets the requirements of both classifications. That exception is narrow and does not apply to other ER80/ER90 pairs.

If my WPS says ER90 but we changed shielding gas, is that a nonconformance?

It can be. For prequalified procedures, AWS D1.1:2025 Clause 5.6.4 requires the production shielding gas to follow one of the permitted compliance paths, including using the shielding gas used for electrode classification under the applicable AWS A5 specification. If the production gas does not satisfy an allowed path, prequalification is lost and the procedure must be qualified under Clause 6.

Does shielding gas change the wire’s classification?

The wire classification is defined by AWS A5.28, but shielding gas affects what mechanical properties the deposited weld metal achieves in practice. A5.28 §3.1 notes that certain classifications depend on the shielding gas employed, and D1.1:2025 Clause 5.6.4 ties prequalified production gas back to the classification gas. The operational risk is treating the label as a guarantee while running a different gas than the one used for classification testing.

What is the safest way to avoid the ER80/ER90 gas gotcha?

Document the exact shielding gas on the WPS and treat any change in nominal gas composition as a controlled change requiring review. For prequalified WPSs, explicitly state which D1.1:2025 Clause 5.6.4 compliance path applies (for example, ‘classification gas per A5.28’). If the project requires a specific strength level, verify the wire+gas combination against the applicable A5.28 requirements and qualify the WPS by test under Clause 6 when in doubt.

Where does D1.1 tell me which shielding gas is allowed?

For prequalified GMAW and FCAW-G WPSs, AWS D1.1:2025 Clause 5.6.4 is the controlling clause. It includes the ‘classification gas’ rule and other allowed mechanisms (for example, Table 5.10 for certain A5.18 electrodes). If your production gas does not fit an allowed mechanism, you are outside prequalification and need to qualify under Clause 6.

Reference data from AWS D1.1/D1.1M:2025 and AWS A5.28/A5.28M. Not affiliated with the American Soudage Society.