Does the longitudinal seam weld in a built-up girder require a separate WPS from the transverse welds?

Yes, if the process, position, or joint geometry differs from the WPS used for transverse fillet and groove welds. Longitudinal seam welds on plate girder web-to-flange joints are almost always SAW or FCAW-G in flat position, while cope, clip angle, and stiffener welds may use SMAW or FCAW in vertical or overhead. A single WPS that covers all positions and processes is unusual — most shops maintain separate WPS documents by process and position.

What joint type is typically used for the flange-to-web weld in a fabricated girder?

The flange-to-web connection in a plate girder is a T-joint, typically a double-fillet weld or a PJP (partial joint penetration) groove weld depending on the design requirement. CJP groove welds at the flange-web intersection are specified only where full-penetration design transfer is required — otherwise double-fillet or PJP is standard and prequalified under AWS D1.1 Clause 5.

How is the longitudinal weld sequence specified on the WPS for a box column?

The WPS or a supplemental weld sequence document (often referenced on the shop drawing) specifies the order of passes and which plates are welded first to control distortion and residual stress. AWS D1.1:2025 does not prescribe a universal sequence for box columns, but the contract documents or engineer's specification may. The WPS must reflect whatever sequence is used, especially for high-restraint heavy-plate box section work.

Can SAW flat-position qualification cover the longitudinal seam in a box column welded in the rotisserie position?

Rotisserie welding of a box column holds the seam in the flat (1F or 1G) position by rotating the assembly. A WPS qualified in 1F or 1G flat position covers this. The welder qualification range also covers flat-position runs. The key is that the actual weld axis is horizontal and the progression is flat at the moment of welding — the manipulator or positioner brings the seam to the flat orientation.

Longitudinal Seam Weld WPS for Fabricated Columns and Girders

WPS requirements, joint design, distortion control, and inspection strategy for longitudinal seam welds in built-up plate girders and box columns under AWS D1.1:2025.

Fabricated plate girders and box columns are among the most common products of a structural fab shop, and their longitudinal seam welds present a specific combination of challenges: long uninterrupted runs, high heat input, significant distortion potential, and dimensional tolerance requirements that are often tighter than for typical connection welds. Writing a WPS that actually controls what matters on these welds — and keeping the documentation straight when SAW or FCAW-G runs hundreds of inches on a single pass — requires a deliberate approach.

Joint Configurations in Built-Up Members

Plate Girder Flange-to-Web (T-Joint)

The most common longitudinal weld in structural fabrication is the double-fillet or PJP (partial joint penetration) groove weld connecting the web plate to the top and bottom flanges in an I-shaped plate girder. Under AWS D1.1:2025 Clause 5, prequalified T-joint geometries are available for both double-fillet and PJP applications. The choice between them is a design decision:

Double-fillet: Used where the fillet size (leg dimension) provides adequate shear transfer per unit length. The web-to-flange fillet in most standard girder designs falls here. The WPS lists fillet weld size range and minimum effective throat.
PJP groove weld: Required when the joint is designed for higher shear load transfer, or when the design engineer specifies minimum weld throat exceeding what double-fillets can provide. PJP joints require documentation of the effective throat and any weld root opening on the WPS.
CJP groove weld: Rarely used for continuous longitudinal flange-web joints except in special seismic applications or transfer plates. CJP requires a PQR and adds cost without structural benefit in standard girder design.

Box Column Seam Welds (Corner CJP or PJP)

A fabricated box column is built from four plates — two webs and two flanges — with four continuous corner joints running the full member length. The joint design may be a CJP groove, a PJP groove, or in some cases a double-fillet depending on the column's structural role and the engineer's specification.

For moment frame applications, corner joints in box columns are often specified CJP because of the high flexural demand and the need for full through-thickness force transfer at connections. This means the WPS must be a tested procedure — no prequalified route for CJP. The PQR test coupon must represent the actual corner geometry, plate thickness, and preheat/interpass temperature used in production.

SAW as the Dominant Process for Longitudinal Seams

Submerged arc welding (SAW) is the preferred process for longitudinal seam welds in plate girder and box column fabrication. The reasons are practical: SAW deposits weld metal at high rates in flat position, the covered arc eliminates spatter and fume concerns, and the deep penetration profile is well-suited to the thick plate common in heavy structural members.

The SAW WPS must specify:

Wire classification and diameter (essential variable)
Flux classification and brand/grade (essential variable under AWS D1.1:2025 — a change in flux supplier or brand that alters the classification triggers requalification)
Current, polarity, voltage, and wire feed speed ranges (or heat input range)
Travel speed range
Preheat and maximum interpass temperature

For details on SAW essential variables specific to structural WPS development, see SAW essential variables and WPS requirements under AWS D1.1.

Because SAW is almost exclusively run flat, the position qualification on the WPS is limited to 1G (groove) or 1F (fillet). This is not a constraint in practice because the work is either horizontal on a flat table or the member is rotated to keep the seam in flat position.

Heat Input and Distortion on Long-Run Welds

Longitudinal seam welds accumulate substantial heat input over their length, and on plate thicknesses above about 1 inch the thermal gradient across the web and flange can induce camber, sweep, or twist that, if uncontrolled, requires flame straightening after fabrication.

The WPS should specify:

Preheat temperature — for A572 Grade 50 and similar steels, the prequalified preheat table in AWS D1.1:2025 Clause 5 starts at 50°F for steel with carbon equivalent below approximately 0.40. For A514 or A709 Grade HPS70W, preheat requirements are higher and must be calculated or specified.
Interpass temperature maximum — the maximum interpass temperature is an essential variable under Table 6.6 (an increase beyond the qualified maximum requires requalification). On longitudinal seam welds in thick plate, the member absorbs heat and the interpass temperature can creep up on multi-pass runs. The WPS maximum should be stated, and production must verify it.
Welding sequence — for a plate girder, common practice is to complete the web-to-flange fillet welds before adding stiffeners, then return for stiffener-to-web and stiffener-to-flange welds. This sequence is not always mandated by the WPS but may appear on the fabrication drawing or a supplemental sequence document that is referenced by the WPS.

For a broader discussion of distortion control methods, see weld distortion control in structural fabrication WPS documentation.

Qualification Range: Thickness Coverage

Under AWS D1.1:2025 Table 6.6 (essential variables), the test coupon thickness determines the qualified production thickness range. For groove welds tested at thickness T:

If T < 3/4 in (19 mm): production range is T to 2T
If T ≥ 3/4 in (19 mm): production range is 3/4 in (19 mm) to unlimited thickness (above)

For longitudinal seam welds in heavy plate girders — web plates often 1/2 in to 1-1/2 in, flanges potentially 2 in to 4 in in heavy columns — you need a PQR run at representative thickness to cover the full production range. Running a 3/4 in test plate for a procedure intended to cover 3 in flanges does not work; 3/4 in qualifies unlimited above, but you still need PQR mechanical test results that demonstrate the weld metal and HAZ properties at the actual heat input conditions used on thick plate.

The interaction between heat input and HAZ grain coarsening in SAW is a real concern on thick plate — see SAW high heat input and HAZ grain coarsening with CVN requirements under AWS D1.1 for how to address this in your PQR program.

Weld Profile and Acceptance Criteria

For the double-fillet web-to-flange weld, the WPS should define the minimum and maximum fillet weld size. The minimum is set by the design — usually the engineer's drawing. The maximum is constrained by the throat that can be deposited in a single pass without exceeding the heat input limit; multi-pass fillets on large legs are common for thick flanges.

AWS D1.1:2025 visual acceptance criteria (Clause 9) apply: no cracks, no undercut exceeding 1/32 in on primary members in tension zones, weld profile within the convexity and concavity limits. For longitudinal seam welds in tension flanges (the bottom flange of a simply supported girder), the undercut limit is the tighter 1/32 in value, not 1/16 in.

Rule library based on AWS D1.1:2025; verify against your governing edition — the AHJ or contract may specify 2020 or earlier.

NDE Requirements for Longitudinal Seam Welds

For statically loaded structures, visual inspection is typically the primary NDE method on longitudinal fillet welds unless the owner spec requires additional testing. For dynamically or cyclically loaded girders (crane girders, bridge members under AWS D1.5), or when specified by the EOR, UT or MT of the web-to-flange zone may be required.

For CJP corner joints in box columns on moment frames, UT is almost always required — either per AWS D1.1 Clause 9 sampling requirements or by the owner's QC plan. The UT procedure must reference the approved WPS, and the acceptance criteria must match the applicable annex (Annex F for structural UT).

For NDE documentation requirements and how they tie back to the WPS, see NDE documentation in the audit packet for WPS.

Keeping the WPS and Shop Practice Aligned

Long-run SAW welds present a specific traceability challenge: the travel speed, current, and voltage may drift over the length of a 60-foot girder flange, and if the operator makes adjustments during the run, the production weld parameters may depart from the WPS essential variable ranges without anyone catching it until the CWI reviews the weld traveler.

A well-run shop addresses this by:

Recording weld parameters at start, mid-run, and end of each long pass
Including parameter ranges on the WPS — not just nominals — that reflect realistic operating windows
Having the CWI verify that recorded parameters are within the WPS range before signing off on each seam

For built-up plate girder WPS setup and the pass sequence documentation specific to large I-shapes, see built-up plate girder WPS pass sequence and camber control.

If you're developing a WPS library that includes SAW procedures for plate girder and box column longitudinal seams, WPS software with process-specific essential variable tracking can help ensure your documentation stays current with production realities and AISC audit requirements.