AWS D1.1 is known as a welding code, but Clause 4 is fundamentally a fabrication code — it tells the shop floor and the CWI what is and is not acceptable before, during, and immediately after welding. A CWI who only opens the code to check visual acceptance criteria in Clause 9 is missing half the inspection program. Clause 4 governs the conditions that must exist before the arc strikes.
This overview addresses the Clause 4 requirements most frequently encountered in structural steel fabrication: base metal preparation, joint fit-up, tack welds, and weld profiles.
Rule library based on AWS D1.1:2025; verify against your governing edition.
Base metal preparation
Surface condition. AWS D1.1:2025 Clause 4 requires that base metal surfaces to be welded be free of mill scale that would adversely affect weld quality, rust, moisture, grease, paint, and other foreign material except as specifically allowed. The practical standard: surfaces in the weld zone and adjacent heat-affected zone must be clean enough that the welder is not burning through contamination. Mill scale on the fusion faces of a prequalified joint must be removed if it is loose or flaking.
Thermal cut edges. Oxygen-cut, plasma-cut, and laser-cut edge preparation is permitted. The edge must be free of dross, notches, and gross irregularities. AWS D1.1:2025 Clause 4 sets limits on notch depth and requires grinding to remove gouges or notches that exceed allowable limits. A CWI inspecting groove weld preparation must check the fusion face profile — a smooth, uniform bevel without gouges that would entrap slag or create stress risers.
Weld access holes. When AWS D1.1 or AISC 358 requires weld access holes for moment connection fabrication, Clause 4 specifies minimum dimensions and edge preparation requirements. Access holes that are undersized, have sharp re-entrant corners, or lack adequate thermal cut quality are a Clause 4 nonconformance — not a post-weld cosmetic issue. Inspect access holes before any connection welding begins.
Joint fit-up tolerances
Fit-up is where most pre-weld nonconformances occur. AWS D1.1:2025 Clause 4 provides specific tolerances; the following are the most common inspection points.
Root opening — groove welds. Prequalified joint details in Annex B specify the designed root opening (typically 0 to 1/4 in, depending on the joint type). Clause 4 allows:
- Root openings up to 1/16 in [2 mm] less than the minimum to be accepted as-is
- Root openings up to 1/16 in [2 mm] greater than the maximum to be corrected by buttering the groove face (adding weld metal to build out the face until the gap is within tolerance)
- Root openings greater than 1/16 in [2 mm] beyond maximum: engineering disposition required
Root face (land). The root face dimension affects burn-through risk and root fusion. Clause 4 tolerances for root face depend on the joint type; verify the specific prequalified detail. Undersized root faces risk burn-through; oversized root faces can prevent fusion at the root.
Groove angle. For prequalified V-groove and bevel-groove joints, the groove angle must be within the specified range. Too narrow an angle traps the electrode and prevents complete fusion; too wide an angle wastes filler metal and increases heat input. Inspect with a groove angle gauge before fit-up acceptance.
Fillet weld fit-up — T-joints and lap joints. For fillet welds at T-joints, the gap between the two members at the root is an indirect fit-up measure. AWS D1.1:2025 Clause 4 specifies that when the root gap at a T-joint exceeds 1/16 in [2 mm], the fillet weld leg must be increased by the amount of the gap (to maintain the effective throat). For gaps greater than 3/16 in [5 mm] for material 1/4 in [6 mm] thick or greater, fit-up must be corrected before welding.
Out-of-plumb at T-joints. Clause 4 limits the angular deviation of the intersecting member from the intended angle. Excessive out-of-plumb creates a non-uniform root gap around the fillet weld perimeter.
Tack welds
Tack welds are an area where shops routinely operate below the Clause 4 standard. The requirements:
Process. Tack welds must be made by a qualified welder using a qualified WPS — or a prequalified process. A certified tack welder qualification under AWS D1.1:2025 Clause 6 is the minimum credential. Structural tack welding is not a job for whoever has a hood.
Size and length. Tack welds that will be incorporated into the final weld must meet a minimum size (typically 1/2 in [13 mm] minimum length for structural work) and must be sound. Undersized, cracked, or porous tack welds incorporated into the weld are a nonconformance in the finished product.
Defective tack welds. Cracked tack welds must be removed before the final weld pass. This is a Clause 4 requirement, not optional — a cracked tack in the root zone of a CJP groove weld will likely propagate into the root of the finished weld. Inspect tack welds before welding begins and direct removal of any cracked tacks.
Tack weld position. Some structural details require tack welds in specific locations; others prohibit tacks in certain areas (tension zone, base metal with high carbon equivalent). Confirm the contract or project-specific WPS requirements for tack placement.
Weld profiles and Clause 4 dimensional requirements
Post-weld profile requirements appear in both Clause 4 and Clause 9. The Clause 4 provisions address:
Convexity limits. Excessive weld reinforcement (convexity) on groove welds creates stress concentration at the weld toe and can interfere with ultrasonic testing. AWS D1.1:2025 establishes maximum convexity as a function of weld width. Inspect with a bridge cam gauge after each pass on multipass welds where profile is critical.
Undercut. Undercut along the weld toe is a Clause 4 and Clause 9 defect. For statically loaded structures, the limit is typically 1/32 in [1 mm] depth for welds transverse to tensile stress and 1/8 in [3 mm] for welds parallel to tensile stress — verify with the applicable edition. For cyclically loaded structures, the limits are more restrictive.
Overlap. Weld metal rolled onto the base metal surface without fusion at the toe is not acceptable. It creates a crevice that acts as a notch under load.
Weld sequencing and distortion. Clause 4 addresses distortion control by requiring that welding sequences minimize restraint and locked-in stress. The WPS or separate welding sequence document must address weld sequence for highly restrained joints; a CWI sign-off on sequence compliance is part of the inspection hold point before and during welding.
The CWI's pre-weld checklist under Clause 4
Before arc ignition on any Clause 4-governed joint:
- Joint identification. Confirm the correct WPS is applied to this joint type, process, position, and base metal
- Surface preparation. Check fusion faces for cleanliness, dross, and notches
- Fit-up. Measure root opening, root face, and groove angle; document against Clause 4 limits
- Tack weld condition. Inspect every tack weld; direct removal of cracked tacks
- Preheat. Verify preheat is applied and within WPS range before the first arc is struck — not during or after
- Access hole condition (for moment connections). Inspect geometry and edge quality
After welding:
- Visual acceptance per Clause 9 (convexity, undercut, overlap, cracks, craters)
- Profile measurement with appropriate gauge
- Dimensional check — weld size, fillet leg, groove weld reinforcement
A CWI who documents both the pre-weld and post-weld checks creates an audit trail that covers the full Clause 4 and Clause 9 inspection lifecycle of the joint.
For inspection checklists that link Clause 4 hold points to specific WPS parameters and NDE requirements, see wpswelding.com/pricing. Related reading: CWI pre-weld inspection checklist under AWS D1.1, weld quality control plans for AWS D1.1 compliance, and groove weld fit-up tolerances under AWS D1.1.