Can I use a D1.1-qualified WPS on a bridge project?

Generally no. AWS D1.5 is the governing code for highway bridge fabrication under AASHTO, and it requires WPS qualification under D1.5 procedures. A D1.1-qualified procedure does not transfer — essential variables, base metal groupings, and CVN requirements differ between the two codes.

Does D1.5 allow prequalified WPS?

No. Unlike D1.1 Clause 5, which allows prequalified WPS based on prequalified joint details, D1.5 requires all welding procedures to be qualified by test. There is no prequalified option under D1.5.

What is a fracture-critical member in bridge welding?

A fracture-critical member (FCM) is a primary tension member whose failure would be expected to result in collapse of the bridge. FCMs require additional CVN impact testing, tighter heat input controls, and more stringent NDE than non-FCM welds.

What base metals does D1.5 cover?

AWS D1.5 uses AASHTO M-number designations. The primary structural steel is ASTM A709/AASHTO M270 in grades 36, 50, 50W, HPS 50W, HPS 70W, and HPS 100W. HPS grades above 70 ksi carry specific preheat and heat-input constraints tied to their thermomechanical-controlled-process rolling.

AWS D1.5 bridge welding WPS: how it differs from D1.1

DOT and AASHTO bridge projects run under AWS D1.5, not D1.1. Key differences in WPS qualification, fracture-critical members, and essential variables.

AWS D1.5 is the Bridge Welding Code — the governing standard for highway bridge fabrication and erection in the United States under AASHTO contracts and FHWA oversight. If your shop welds primary structure for state DOT projects, D1.5 is your code, not D1.1.

The two codes share welding physics, but their WPS requirements diverge in ways that catch fabricators off guard when they move between building and bridge work.

No prequalified WPS under D1.5

This is the single biggest procedural difference. AWS D1.1 Clause 5 lets a shop write a WPS to prequalified joint details without running qualification test plates — provided all essential variables meet prequalified limits.

D1.5 has no equivalent provision. Every welding procedure must be qualified by test. You run test plates, run the mechanical tests (tensile, bend, macroetch), and the resulting PQR supports the WPS. For a refresher on how test-based qualification compares to prequalified in cost and lead time, see PQR vs. prequalified WPS: cost comparison.

For a fab shop transitioning from building-structural work to bridge work, this means your existing WPS library probably cannot be carried forward. You are starting qualification from scratch under D1.5 procedures — even if your D1.1 PQRs cover the same base metals and processes.

Fracture-critical member (FCM) requirements

Bridge members that carry primary tension — girder flanges in positive-moment zones, tension chord members — are often designated fracture-critical. D1.5 imposes additional requirements for welds on or connecting FCMs:

CVN impact testing on the PQR. FCM qualification requires CVN (Charpy V-Notch) testing of the weld metal and HAZ at the temperature specified by the owner. This is conceptually similar to how AWS D1.1's Table 6.8 supplementary essential variables add tightening rules on top of Table 6.6 when CVN is required — but in D1.5, the FCM requirements are woven throughout the standard rather than isolated in a single supplementary table.

Heat input tracking. FCM welds require production heat-input records. The WPS states the qualified range; production records confirm every weld stayed within it. If a welder's heat input drifts — shorter arc length, changed travel speed — that is an FCM nonconformance, not a minor deviation.

Personnel qualification. In some states and for some owners, welders on FCM work must be qualified specifically under FCM procedures, not just standard welder qualification. Check the owner's project specification before assuming standard WPQ coverage extends to FCM work.

Under D1.1, CVN-required work is triggered by the contract or AHJ specifying CVN and invokes Table 6.8. Under D1.5, FCM requirements follow the FCM designation on the structural drawings — the inspector checks drawings, not just the WPS.

Base metals: M-numbers vs D1.1 groups

AWS D1.1 groups base metals by type for WPS qualification purposes. D1.5 uses AASHTO M-number designations, which align with specific ASTM standards:

ASTM A709 Gr 36 = AASHTO M270 Gr 36
ASTM A709 Gr 50, 50W = AASHTO M270 Gr 50, 50W
ASTM A709 HPS 50W, HPS 70W, HPS 100W = AASHTO M270 HPS grades

High Performance Steel (HPS 70W, HPS 100W) grades carry specific preheat requirements and heat-input ceilings that reflect their microalloyed, thermomechanical-controlled-process rolling. A WPS for HPS 70W must stay within narrower voltage, amperage, and travel-speed ranges than a comparable A572 Gr 50 WPS.

Qualification on one HPS grade does not automatically cover another. The M-number groupings in D1.5 are more granular than D1.1 base-metal groups for the high-strength grades.

Filler metal selection differences

D1.5 limits filler metals more narrowly than D1.1 for some processes. Some self-shielded FCAW electrodes permitted under D1.1 for structural work are not in the D1.5 approved list for bridge applications. Your existing FCAW-S procedures that pass D1.1 scrutiny may not qualify under D1.5.

For FCM welds, diffusible hydrogen requirements are tighter. Most FCM procedures specify H8 or H4 electrode designations. Using a high-hydrogen electrode on an FCM weld is a qualification failure even if the test plates pass tensile and bend tests. For a primer on hydrogen designations, see low-hydrogen electrode conditioning: H4, H8, H16.

Inspection requirements for bridges

D1.5 inspection requirements for bridge work are more prescriptive than D1.1 for comparable structural applications:

Radiographic testing (RT) is more common as the primary NDE method for full-penetration groove welds in primary members. Many owner specifications mandate 100% RT on FCM welds.

Ultrasonic testing (UT) is permitted under D1.5, but the acceptance criteria and attenuation correction methods differ from D1.1. A UT procedure qualified to D1.1 Annex S is not automatically valid under D1.5 — the calibration blocks and reference reflectors differ.

MT and PT are used for secondary members and repair verification, generally on the same basis as D1.1.

A shop that relies on UT under D1.1 for building structural work will need to re-qualify or re-certify its UT procedures before bridge work. This is often overlooked when shops bid their first DOT project.

Running a dual shop: D1.1 and D1.5

Many fabricators that work across both markets maintain separate WPS libraries — one for D1.1 building work, one for D1.5 bridge work. The essential variable frameworks are different enough that a single WPS cannot satisfy both codes.

In practice, some base-metal and process combinations will appear in both libraries (A36, A572 Gr 50, SMAW, GMAW). The PQR test plates are still run separately under each code's qualification procedures. You cannot cite a D1.1 PQR on a D1.5 WPS, even when the base metal and filler classification are identical.

A well-organized procedure library tags each WPS and PQR with the governing code, the edition, and the FCM designation where applicable. Mixing D1.1 and D1.5 documents in the same folder without code tagging is an audit finding waiting to happen.

For more on how essential variables work in the D1.1 world, AWS D1.1 Table 6.6 explained covers the PQR essential-variable framework that D1.1-only shops rely on. If you're evaluating WPS management software that supports both code environments, see pricing.

Rule library based on AWS D1.1:2025; verify against your governing edition. D1.5 requirements vary by edition — confirm against the edition specified by your DOT contract or owner specification.