Most structural HSS sections in a typical fab shop are cold-formed, electric resistance welded (ERW) products made to ASTM A500 or ASTM A1085. The manufacturing process introduces characteristics — a longitudinal weld seam, cold-worked corner radii, and variable chemistry across the cross-section — that are invisible on a WPS but matter when you are welding to the HSS surface in the field or shop.
AWS D1.1:2025 governs your fabrication welds. It does not govern the mill seam, and it does not specify HSS product quality beyond listing acceptable base metal specifications. Understanding the gap between what the product standard controls and what your WPS controls will prevent inspection surprises, NDE re-runs, and cracking in corners.
How ERW HSS Is Made
Flat-rolled coil steel is slit to width, roll-formed into a round tube, and the seam edges are joined by resistance welding. The tube is then sized — pushed through a die to final cross-sectional shape. For square and rectangular HSS, this final sizing step is what creates the cold-worked corners.
The ERW seam typically runs along the center of one face of the finished section. The seam is heat-treated in-line by the mill, but it remains identifiable metallurgically — slightly different grain structure, possibly higher hardness than the adjacent base metal, and a predictable linear orientation. On a CMTR, you will not see the seam called out. It is simply part of the product.
Seamless HSS (extruded) avoids the seam entirely but is less common in structural sizes and generally more expensive. ASTM A1085 can be either ERW or seamless; A500 is exclusively cold-formed, usually ERW.
AWS D1.1:2025 Base Metal Coverage
A500 Grade B (Fy = 46 ksi), A500 Grade C (Fy = 50 ksi), A1085 Grade A (Fy = 50 ksi), and A847 (weathering) are all listed as prequalified base metals under AWS D1.1:2025. For tested WPS qualification, these specifications fall into base metal groups in Table 6.9. Matching the correct group determines how far your PQR extends in terms of base metal coverage.
Before writing your WPS:
- Confirm the specification on the contract drawings. A1085 has tighter thickness tolerances and a guaranteed yield; some engineers specify it for demanding connections where A500's wider chemistry range is a concern.
- Pull the CMTR and check actual carbon equivalent (CE). A500 permits wide chemistry ranges, and heats near the upper CE limit warrant a preheat increment above the minimum the table specifies.
- Check whether the contract distinguishes ERW from seamless. Most structural specifications do not, but a contract referencing AWS D1.6 for stainless overlays on HSS might carry different requirements.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Preheat at HSS Corners
The corner of a cold-formed HSS section has been bent under high pressure. This cold work raises local hardness and residual stress — conditions that increase susceptibility to hydrogen-induced cracking if preheat is marginal.
Practical points for your WPS and inspection plan:
Measure on the flat face, not on the corner. The corner radius has lower thermal mass and heats faster under a contact thermometer. A reading taken directly on the corner can be 20–30°F higher than the flat face 2 inches away. Preheat is measured 3 inches minimum from the weld. Position the thermometer on the flat face for a representative reading.
Connections that wrap the corner become part of the weld path. When a brace-to-chord connection requires a full-wrap fillet, the weld must transition around the corner. Travel speed that works on the flat face may generate excess heat at the corner (short path, same speed) or insufficient fusion if the welder slows abruptly. Note this in your WPS technique section, or address it in a welding technique qualification trial on a mock-up before production.
When CE is at the upper end of the heat's range, consider applying the next thickness-category preheat, not just the minimum. This is engineering judgment — document the rationale in your weld quality plan. See heat input control and documentation for how to capture these decisions traceably.
ERW Seam and NDE Interpretation
The ERW seam runs longitudinally and can produce a linear reflector detectable by UT. In a T-joint where the brace welds across the face containing the seam, the UT scan path may intersect the seam and flag it as a linear indication.
Steps to manage this before NDE begins:
- Mark the ERW seam location with a paint pen or scribe before fit-up. The seam location can be identified visually by the slight external bead that some ERW products show, or by the mill marking orientation.
- Record the seam face orientation in the ITP and on the weld map. Note it as "ERW seam on [north/top/left] face" relative to the connection.
- Brief the UT or RT technician before they scan. A linear indication on the seam face at the expected seam depth is not a fabrication weld defect — it needs to be correlated to position, not just called by reflector amplitude alone.
For RT of groove welds at HSS T-joints, the seam can produce a density variation in the film or digital image. Document the seam location in the radiographic technique sheet. See NDE documentation and audit packets for how to capture this in your closeout package.
Filler Metal Selection
For A500 and A1085 connections, matching-strength fillers (70 ksi minimum tensile) cover both specifications:
- SMAW: E7018 (H4 or H8 for low hydrogen control), E7018-1 for improved CVN toughness
- FCAW-G: E71T-1C/M or E71T-12M where toughness requirements apply
- GMAW: ER70S-6 for fillet welds in non-demand-critical applications; ER70S-3 acceptable but less forgiving of mill scale
If the WPS is for demand-critical welds under a seismic specification (AWS D1.8 or AISC 341), the filler must carry CVN toughness data and the WPS must be qualified under the supplementary essential variables in AWS D1.1:2025 Table 6.8. A WPS qualified without CVN testing cannot be extended to demand-critical welds by administrative revision alone — a new PQR is required. See CVN supplementary essential variables under AWS D1.1 Table 6.8 for the full requalification path.
Welder Qualification Scope
For groove welds at HSS (TKY connections, field-welded moment connections), a welder qualified in 2G position on pipe or tube qualifies for groove welds in flat and horizontal positions. For overhead groove welds on HSS, 4G or 6G qualification is needed.
For fillet welds on HSS — the most common case in braced frames and connection plates — 2F qualifies flat and horizontal; 4F qualifies overhead. A welder who is qualified only for plate groove welds is not automatically qualified for tube groove welds. Confirm the qualification record against the work before issuing the job card.
Keep track of your welders' 6-month continuity under AWS D1.1:2025 Clause 6.4.1. HSS connection work done at irregular intervals on field projects is one of the most common places shops discover a continuity lapse. AWS D1.1 welder continuity six-month lapse covers the documentation and requalification steps.
Common Defects at HSS Connections and WPS Controls
Overlap at the heel of a T-joint: The acute-angle side of a brace-to-chord joint requires slow, deliberate travel with correct work angle. Amperage on the lower end of the WPS range combined with too-fast travel causes cold lap. Specify heel-pass parameters separately in the WPS when the angle is less than 45°.
Undercut along the toe at the corner transition: The corner radius changes the effective arc gap and heat distribution. A work angle appropriate for the flat face may direct the arc toward the toe rather than the root at the corner. Address in the WPS technique note: adjust work angle 5–10° toward the HSS face through the corner transition.
Lack of fusion on the flat face adjacent to a corner start: If the welder starts the pass at the corner, the flat face HAZ may be below preheat when the arc reaches it. Always start on the flat face and weld toward the corner.
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