Can I use an AWS D1.1 WPS to weld ASTM A709 HPS 70W?

No. ASTM A709 Grade HPS 70W is a bridge structural steel governed by AWS D1.5, not AWS D1.1. A WPS qualified under D1.1 does not automatically satisfy D1.5 requirements. If the project calls for D1.5, the WPS must be written and qualified under that code.

What makes HPS 70W different from regular Grade 50W weathering steel?

HPS 70W has a minimum yield of 70 ksi versus 50 ksi for Grade 50W. Beyond strength, HPS 70W has stricter composition limits, controlled rolling or thermomechanical processing to achieve higher toughness, and AASHTO-mandated CVN impact requirements. The filler metal, preheat, and heat input controls for welding are more demanding as a result.

What CVN requirements apply to HPS 70W weld metal under AWS D1.5?

AWS D1.5 requires that weld metal for HPS 70W joints achieve minimum Charpy V-notch impact values at low temperature, typically tested at −20°F [−29°C] or lower. The specific CVN values and test temperature depend on the project's fracture control plan (if applicable) and the D1.5 table requirements. Filler metals must be verified to meet these requirements through the PQR or through pre-approved qualification.

Is a prequalified WPS path available for HPS 70W under AWS D1.5?

AWS D1.5 allows certain base metals to use preapproved procedures without a full PQR for some joint types, but HPS 70W is generally treated as requiring PQR-backed qualification due to its strength level, CVN requirements, and heat input sensitivity. Consult the published D1.5 code to confirm what preapproved route, if any, applies to the specific joint, process, and plate thickness.

ASTM A709 HPS 70W Bridge Steel WPS Under AWS D1.5

ASTM A709 Grade HPS 70W demands CVN-qualified filler metals, specific preheat controls, and AWS D1.5 qualification — not D1.1. Here's what a WPS for HPS 70W bridge fabrication requires.

High Performance Steel — the HPS designation in ASTM A709 — represents a generation of bridge structural steel developed jointly by FHWA, AASHTO, and the steel industry to reduce bridge weight and improve durability. HPS 70W, the most widely deployed grade in the family, delivers a 70 ksi minimum yield with toughness and corrosion resistance characteristics that go beyond what ordinary Grade 50W or A572 steel can achieve. For the welding engineer or CWI setting up a fabrication procedure, HPS 70W is a step change in demands, not just a higher-strength version of familiar work.

AWS D1.5 — Not D1.1

The first point that separates HPS 70W work from routine structural fabrication: the governing code is AWS D1.5 Bridge Welding Code, not AWS D1.1 Structural Welding Code. State DOT projects, AASHTO standard bridge specifications, and FHWA-administered projects uniformly require D1.5 for bridge structural steel welding. A WPS qualified under D1.1 does not transfer to D1.5 projects — the essential variable tables, preapproved base metal lists, PQR test requirements, and acceptance criteria differ between the two codes.

Shops that primarily handle building structural steel and encounter a bridge subcontract should confirm whether D1.5 procedures are in place before welding begins. Applying a D1.1 WPS to HPS 70W bridge steel is a qualification gap that an owner's QC inspector or FHWA reviewer will identify, and remediation after fabrication is underway is expensive.

What HPS 70W Is — and Is Not

ASTM A709 covers several bridge structural steel grades from Grade 36 through HPS 100W. Grade HPS 70W is defined by:

Minimum yield strength: 70 ksi [485 MPa]
Minimum tensile strength: 85 ksi [585 MPa]
Atmospheric corrosion resistance meeting weathering steel performance (the "W" suffix)
AASHTO M270 grade equivalence for bridge procurement
Composition limits controlled to achieve thermomechanical processing (TMCP) or quenched-and-self-tempered (QST) properties
CVN impact requirements: minimum values at −10°F [−23°C] or colder depending on fracture criticality zone

The "high performance" in HPS comes from the combination of strength and toughness, achieved by cleaner steel chemistry (lower sulfur, phosphorus, carbon) and controlled mill processing rather than post-rolling heat treatment. This is what separates HPS 70W from A514 — HPS is not a quenched-and-tempered steel, but it is microstructurally sensitive to welding heat input in a way that ordinary Grade 50 steel is not.

Filler Metal Requirements

AWS D1.5 maintains a list of approved filler metals for each base metal group. For HPS 70W, filler metals must satisfy two conditions simultaneously:

Strength match. Weld metal tensile strength must meet or exceed 85 ksi to match the base metal. For SMAW, this means E8018 class electrodes (AWS A5.5) rather than the E7018 common in structural building work. For FCAW-G, E8XT-x or E8XT-K2 class (AWS A5.29) is appropriate. For SAW, a wire-flux combination tested to 80 ksi deposit class is required.

CVN qualification. This is the distinguishing requirement for HPS 70W. Filler metals must be pre-qualified or tested to demonstrate that the weld deposit achieves the required Charpy impact values at the test temperature specified for the bridge's fracture control classification. AWS D1.5 includes tables and procedures for verifying filler metal toughness either through preapproval classification testing or through the PQR itself.

The combination of these two requirements eliminates common E70XX and standard E71T-1 products from consideration. A filler metal that works on every A572 Grade 50 job in a structural shop will not be correct for HPS 70W bridge work. Fabricators new to this material consistently underestimate the filler qualification process.

Preheat and Interpass Temperature

AWS D1.5 provides preheat tables for its covered base metals. For HPS 70W, minimum preheat values depend on plate thickness and the welding process. Key practical points:

Minimum preheat climbs with thickness. For thin-to-medium sections (under 3/4 in [19 mm]), minimum preheat for HPS 70W is typically lower than for high-carbon structural steels of equivalent thickness, because HPS 70W is formulated with low carbon equivalents. For sections above 1-1/2 in [38 mm], preheat requirements rise meaningfully.

Maximum interpass temperature is a constraint, not just a floor. Unlike mild structural steel work where the only preheat concern is reaching minimum temperature, HPS 70W work has maximum interpass temperature limits. Exceeding the interpass cap can degrade toughness in the HAZ by coarsening the grain structure. AWS D1.5 tables and the WPS must document both the minimum preheat and the maximum interpass temperature, and field QC must verify both.

Preheat maintenance. For thick multi-pass welds, sustained preheat throughout the weld is required. This has scheduling implications for large box girder assemblies where a pass may take hours — the steel cannot be allowed to cool below minimum preheat between passes.

Heat Input Control

Heat input — calculated as (amps × volts × 60) ÷ (travel speed in in/min), expressed in kJ/in — is an essential variable for HPS 70W WPS qualification. The concern is HAZ toughness: very high heat input produces coarse grain structure in the HAZ adjacent to the fusion line, and coarse HAZ grains degrade CVN impact values. For a bridge on a fracture control plan, HAZ toughness is as important as weld metal toughness.

The WPS must document the qualified heat input range — minimum and maximum — established during PQR testing. During production, the welder's recorded parameters must fall within that range. This is why production parameter logging is not optional on HPS 70W work: the QC record must demonstrate that heat input stayed within the qualified range.

PQR Requirements Under D1.5

For HPS 70W, a PQR under AWS D1.5 typically includes:

Transverse tensile specimens (two)
Guided-bend specimens (root and face, or side bends for material over 3/4 in [19 mm])
Charpy V-notch impact specimens from the weld metal and the HAZ, tested at the specified temperature
Visual and macroetch examination

The Charpy specimens in the HAZ are tested at locations prescribed by the code to capture the coarse-grain heat-affected zone — the region most vulnerable to toughness degradation. The PQR test report must document the actual test temperatures, individual values, and the average. A single low outlier can require the entire test series to be rerun after corrective process adjustment.

Because CVN testing adds cost and time, coordination with the testing lab is important. The test plate, specimen extraction, machining, and impact testing should be planned before the qualification weld is made, not after, to avoid delays from improperly sized plates or missing documentation.

Connection to the WPS Document

An HPS 70W WPS under AWS D1.5 must document all parameters that were established during the PQR, including the heat input range, filler metal designation and CVN classification, minimum preheat, maximum interpass temperature, position of welding, joint geometry tested, and base metal specification. The WPS then becomes the binding procedure document on the shop floor and in the field.

Shops using WPS management software should confirm the system can accommodate D1.5 essential variables, which differ from the D1.1 Table 6.6 framework. The essential variable tables in D1.5 have some differences in scope, particularly around filler metal and heat input. Check the qualification matrix for D1.5 parity before using a D1.1-designed tool on bridge projects.

Practical Recommendations for Shops New to HPS 70W

For a fabrication shop moving from routine A572 Grade 50 structural work into bridge fabrication with HPS 70W, the path forward involves deliberate qualification effort:

Obtain the current edition of AWS D1.5 and verify which provisions apply to the project's contract requirements.
Select filler metals with demonstrated CVN qualification at the required temperature — request the manufacturer's published test data before writing the WPS.
Plan a PQR with full mechanical testing including Charpy tests at both weld metal and HAZ locations.
Establish a heat input monitoring plan for production work and train welders on the interpass temperature limits.
Review WPQ (welder qualification) requirements under D1.5 — welder performance qualification under D1.1 does not automatically transfer.

The upfront investment in proper qualification for HPS 70W is real. So is the exposure from skipping it: rejected welds on a bridge project carry cost and schedule consequences that dwarf the qualification cost many times over.

Rule library based on AWS D1.1:2025; verify against your governing edition. AWS D1.5 bridge fabrication is a separate code — always confirm the edition and contract-specified revision before writing or applying any WPS for bridge structural steel.