Is weathering steel prequalified under AWS D1.1?

A588 (Grades A, B, C, K) and A709 Grade 50W are listed as approved prequalified base metals in AWS D1.1. High-performance grades such as A709 HPS 70W and HPS 100W are not prequalified — they require a PQR-qualified procedure.

What filler metal should I use for weathering steel joints left unpainted?

For SMAW, use a low-hydrogen electrode with a weathering designation such as an A5.5 E8018-W2. For FCAW, AWS A5.20 or A5.36 weathering-grade wires (W-designator) are available. For GMAW, ER80S-Ni1 (A5.28) is widely used. If the joint will be painted, a standard matching-strength low-hydrogen electrode is mechanically acceptable.

Do I need CVN impact testing for weathering steel welds under AWS D1.1?

Not automatically. CVN testing is only required when the project specification, AISC 341 (seismic), or AASHTO specifies it. If CVN is required, Table 6.8 supplementary essential variables apply on top of Table 6.6.

Can I use a standard E7018 on A588 or A709 50W if the joint will be painted?

In most cases yes — the mechanical properties are compatible with the base metal. In a painted joint the filler is not exposed to the wet/dry corrosion cycle, so a non-weathering electrode is mechanically acceptable. Verify with the engineer of record before substituting.

Weathering steel WPS: A588, A709 50W, and HPS 70W basics

A588 and A709 Grade 50W are prequalified base metals. HPS 70W and HPS 100W require a PQR. Here's what changes on your WPS when you weld weathering steel.

Weathering steel — sold under designations like ASTM A588, A709 Grade 50W, and the high-performance bridge series A709 HPS 70W — is designed to form a stable, adherent oxide layer that slows further corrosion without paint. That metallurgy changes what goes on your WPS.

What makes weathering steel different

Weathering-grade alloys achieve corrosion resistance through controlled additions of copper, chromium, nickel, and phosphorus. These additions raise the carbon equivalent slightly compared to plain A36 or A572 Grade 50, which can tighten preheat requirements. More importantly, when a welded joint is left bare and exposed to the same wet/dry cycles as the base metal, a non-matching filler will rust at a different rate — creating a visible discoloration stripe and a potential crevice where water collects.

That's why the WPS must specify not just process and filler classification, but whether the joint will be painted or left bare. Filler selection depends on the answer.

Prequalified grades vs. grades that require a PQR

AWS D1.1 lists approved base metals eligible for prequalified procedures. A588 (Grades A, B, C, K) and A709 Grade 50W fall within the prequalified list. You can use these base metals with a prequalified joint design and a conforming WPS without running a PQR test weld — no lab fees, no wait time.

The high-performance bridge steels A709 HPS 70W and HPS 100W are not in the prequalified base metal list. Any WPS covering these materials requires a qualified PQR. Because HPS 70W has a minimum 70 ksi yield and HPS 100W has a minimum 100 ksi yield, filler selection, preheat, and heat-input limits all tighten considerably. If your shop is moving from structural building work on A588 into bridge fabrication on HPS grades, budget for PQR testing before the job starts.

See PQR vs. prequalified: cost comparison for a practical breakdown of when the testing investment pays off.

Filler metal selection for bare, exposed joints

When joints will be unpainted and exposed, filler metal must provide matching corrosion resistance:

SMAW: AWS A5.5 electrodes with the W-designator (e.g., E8018-W2) contain the copper/chromium/nickel additions that form a matching oxide layer alongside the base metal.
FCAW: AWS A5.20 and A5.36 both have weathering-grade wire classifications carrying a W-designator. Note that A5.36 now has updated designator rules under AWS D1.1:2025 — see the new A5.36 designator rules for details.
GMAW: AWS A5.28 ER80S-Ni1 is widely used for weathering steel GMAW. Confirm corrosion-resistance data with the wire manufacturer's product data sheet for your specific service environment.
SAW: Weathering-grade wire/flux combinations are available from major manufacturers; verify the corrosion-test data.

When joints will be painted, a standard matching-strength low-hydrogen electrode (E7018, E8018-C3, etc.) is mechanically acceptable. Record the paint system on the WPS or the accompanying engineering note so there's no ambiguity about intent if the WPS is reviewed years later.

Preheat and interpass temperature

Preheat on A588 and A709 Grade 50W follows the same carbon-equivalent approach used for other structural steels. In practice, these grades often require preheat similar to or slightly higher than A572 Grade 50 at the same thickness because of the alloy additions. For HPS 70W and HPS 100W, FHWA bridge research publications provide recommended preheat values — use those alongside your PQR heat-affected-zone characterization, not just the D1.1 table minimum.

For the underlying CE calculation methodology, see carbon equivalent and preheat under AWS D1.1.

Essential variable requalification triggers

Weathering steel WPSs use the same essential variable framework as other structural procedures — Table 6.6 of AWS D1.1:2025 (and Table 6.8 when CVN testing is required). The changes most likely to trigger requalification in practice:

Filler classification change: Switching from an E8018-W2 to a standard E8018-C3 (or vice versa) is a change in AWS A-specification classification — an essential variable under Table 6.6.
Base metal group change: Moving from A588/A709 50W (a prequalified group) to A709 HPS 70W (a non-prequalified grade requiring its own PQR) is a base metal essential variable change.
Heat input: Engineers on HPS bridge jobs frequently impose tighter heat input limits than the code minimum to protect HAZ toughness. Document the upper limit on the WPS and monitor it at the machine — see heat input control and documentation.

Rule library based on AWS D1.1:2025; verify against your governing edition.

What CWIs find on weathering steel jobs

A recurring nonconformance on weathering steel jobs: welders pull standard structural electrodes from the rod oven because "it's the same strength." If the contract requires matching corrosion resistance, that substitution is a nonconformance, regardless of the mechanical property compatibility. Check the electrode label, the rod oven tag, and the heat-number cert against the WPS filler specification.

Also watch for primer or paint overspray on joints designed to remain bare. Contaminated faying surfaces affect weld quality and long-term corrosion performance — both are your inspection scope.

For how filler documentation flows from WPS to heat number to material test report, see welding consumable cert traceability.

Managing WPS filler requirements across multiple weathering steel jobs in a shared library — not a folder of PDFs — keeps these nonconformances from happening. See how a structured WPS library works.