9.1 Clause 9 Stud Welding: Pre-Production Testing, Bend Tests & Flash Acceptance

Clause 9 Stud Welding: Pre-Production Testing, Bend Tests & Flash Acceptance

Clause 9 (Stud Welding) of AWS D1.1/D1.1M:2025 governs the specific equipment, consumable requirements, procedure qualification, operator testing, workmanship, and quality inspection standards for steel studs welded to structural steel components. In structural steel fabrication and bridge construction, studs function primarily as headed shear connectors (transferring composite shear forces between steel beams and reinforced concrete floor slabs per AISC 360), concrete anchors, threaded fasteners, or deformed bar anchors. Because stud welding relies on rapid, semi-automatic electrical timing rather than manual weld manipulation, Clause 9 establishes an inspection and testing regime centered on pre-production verification, flash collar morphology, and non-destructive bend testing.

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1. Scope, Material Classifications & Welding Processes

Clause 9 applies exclusively to the attachment of steel studs to carbon and low-alloy structural steels listed in Table 5.6. Studs welded to unlisted base metals or materials with specified minimum yield strengths exceeding 100 ksi [690 MPa] require comprehensive procedure qualification testing approved by the Engineer.

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|                   AWS D1.1 CLAUSE 9 STUD CLASSIFICATIONS                |
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| Type A Studs:  General purpose fasteners (threaded studs, unthreaded    |
|                pins, tie anchors for sheet metal, lag screws).          |
| Type B Studs:  Headed shear connectors utilized in composite steel-     |
|                concrete structural beams, girders, and bridge decks.    |
| Type C Studs:  Cold-worked deformed steel bars utilized as concrete     |
|                anchorage reinforcement and rebar tie connectors.        |
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Material Requirements (Clause 9.3 & Table 9.1)

New in the 2025 edition: Clause 9 adds Type D studs, made from deformed wire or bar conforming to ASTM A706/A706M Grade 60. Their tension test requirement is 125% of the specified minimum yield strength, and when Type D studs are fillet welded the welds shall comply with AWS D1.4/D1.4M, Structural Welding Code — Steel Reinforcing Bars. Minimum fillet weld sizes for studs are given in Table 9.2.

Studs must be manufactured from cold-drawn carbon steel bars conforming to ASTM A108 (Standard Specification for Steel Bar, Carbon and Alloy, Cold-Finished), Grades 1010 through 1020. Mechanical property minimums depend strictly on stud classification:

• Type A Studs: Minimum tensile strength of 60 ksi [415 MPa], minimum yield strength (0.2% offset) of 50 ksi [345 MPa], and minimum elongation of 20% in 2 inches [50 mm].
• Type B Studs (Headed Shear Connectors): Minimum tensile strength of 65 ksi [450 MPa], minimum yield strength of 51 ksi [350 MPa], and minimum elongation of 20% in 2 inches [50 mm].
• Type C Studs (Deformed Bars): Minimum tensile strength of 80 ksi [550 MPa], minimum yield strength of 70 ksi [485 MPa], and minimum elongation of 10% in 2 inches [50 mm].

Stud Welding Processes (Clause 9.2)

Clause 9 recognizes three primary manufacturing methods for attaching studs to base metals:

1. Arc Stud Welding (Clause 9.2.1): The primary structural process. The stud is inserted into a specialized stud gun, fitted with a disposable ceramic ferrule, and positioned against the base metal. When the trigger is pulled, a solenoid retracts the stud to establish an electric arc. The arc melts the end of the stud and the adjacent base metal while an integral solid flux ball (or centered flux slug at the stud base) deoxidizes the molten pool. At the conclusion of the timed arc cycle, the main spring plunges the stud into the molten pool. The ceramic ferrule contains the molten steel, shapes the fillet weld collar (flash), and shields the puddle from atmospheric contamination.
2. Capacitor Discharge (CD) Stud Welding (Clause 9.2.2): An electrostatic process where energy stored in a capacitor bank discharges across a small projection on the stud base in milliseconds. CD stud welding is typically restricted to lightweight, small-diameter studs (≤ 5/16 in. [8 mm]) and thin sheet materials; it is generally not utilized for heavy structural shear connectors.
3. Fillet-Welded Studs (Clause 9.2.3): When automatic stud welding equipment cannot access a joint, or when broken studs require replacement in the field, studs may be attached using conventional manual or semi-automatic arc welding processes (SMAW, GMAW, or FCAW). Fillet-welded studs fall outside the automatic arc stud rules of Clause 9 and must be fabricated using qualified WPSs conforming to Clause 5 (Prequalification) or Clause 6 (Qualification).

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|                    AUTOMATIC ARC STUD WELDING SEQUENCE                  |
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| 1. Placement:   Stud + Ceramic Ferrule pressed against base metal       |
| 2. Retraction:  Solenoid lifts stud; pilot/main arc initiates           |
| 3. Molten Pool: Flux ball deoxidizes pool; ferrule shields & vents gas  |
| 4. Plunge:      Spring forces stud into molten base metal pool           |
| 5. Solidify:    Ferrule broken away; 360° solid weld flash remains      |
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Ceramic Ferrule Conditioning & Base Metal Cleanliness (Clause 9.4 & 9.5)

• Ferrule Storage & Rebaking: Ceramic ferrules must remain completely dry. Ferrules exposed to moisture, ambient humidity, or wet conditions shall be rebaked in an oven at 250°F [120°C] for at least 2 hours prior to use.
• Surface Preparation: The base metal surface receiving studs must be free from heavy rust, loose scale, oil, moisture, or any coating that would impede electrical conductivity or generate excessive porosity. Light rust or standard mill scale is permissible if acceptable pre-production test results are demonstrated.

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2. Pre-Production Testing Protocols (Clause 9.7)

Because automatic stud welding does not permit continuous welder adjustment during deposition, pre-production testing is mandatory to prove that the electrical settings, gun adjustments, cable lengths, and environmental conditions will produce sound, ductile welds.

When Pre-Production Testing is Required (Clause 9.7.1)

A pre-production test must be performed under any of the following operational triggers:

1. At the beginning of each work shift.
2. Whenever there is a change in the welding operator.
3. Whenever there is a change in the stud welding gun or controller.
4. Whenever there is a change in the power source (welding generator or rectifier).
5. Whenever there is a change in the stud base diameter or stud material lot.
6. Whenever the total length of welding cables changes by more than 10%.
7. Whenever the welding position changes (e.g., transitioning from flat/downhand to horizontal or overhead).

Pre-Production Test Method & Sample Size (Clause 9.7.1 & 9.7.2)

The operator shall weld two (2) consecutive test studs in the same position, using identical consumables, base metal thickness, and machine settings as will be used in production.

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|                    PRE-PRODUCTION TESTING REQUIREMENTS                  |
+-------------------------------------------------------------------------+
| Sample Size:       2 consecutive studs welded to representative plate   |
| Step 1: Visual     Must exhibit a full 360° flash around stud base      |
| Step 2: Mechanical Bend both studs 30° from original axis using pipe    |
| Step 3: Acceptance Zero cracking or tearing in weld metal or HAZ        |
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Mechanical Bend Testing Procedure (Clause 9.7.2)

1. Visual Flash Verification: Both test studs must exhibit a full 360-degree flash around the entire circumference of the stud base prior to bending.
2. 30-Degree Bend Test: After cooling (studs shall not be quenched in water), each test stud is bent to an angle of 30° from its original longitudinal axis. Bending is executed by slipping a steel pipe over the stud and applying steady leverage or striking with a heavy hammer, or by using a calibrated mechanical bending fixture.
3. Pass/Fail Criteria: Both test studs must withstand the 30° bend without any visual evidence of cracking or tearing in the weld metal or the heat-affected zone (HAZ). Tearing of the base metal plate or slight ductile tearing in the stud shank body away from the weld is acceptable; failure in the weld or fusion line constitutes an immediate failure.
4. Retesting Protocol: If either of the two test studs fails the visual flash examination or exhibits cracking during the 30° bend test, the welding variables (current, arc time, plunge distance, cable connections) shall be adjusted. Two new consecutive test studs shall be welded and tested. Production welding shall not commence until two consecutive studs pass both visual examination and mechanical bend testing.

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3. Production Inspection & Acceptance Standards (Clause 9.8)

Once pre-production testing is accepted, production welding may proceed under strict Quality Control (QC) and Quality Assurance (QA) surveillance.

100% Visual Inspection of Production Studs (Clause 9.8.1)

100% of all production studs must receive visual examination. The primary acceptance criterion is the presence of a complete, visible 360° weld flash around the perimeter of the stud base.

Repair of Studs Lacking Full 360° Flash (Clause 9.8.3)

When a production stud exhibits an incomplete weld flash (e.g., 270° or 300° flash caused by arc blow, gun tilt, or minor surface mill scale), the stud is not automatically rejected or cut off. Clause 9.8.3 provides a specific repair remedy:

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|                 CLAUSE 9.8.3 STUD REPAIR REQUIREMENTS                   |
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| 1. Permitted Processes: SMAW (low-hydrogen E7018), GMAW, or FCAW        |
| 2. Minimum Fillet Size: 5/16 in. [8 mm] fillet weld                     |
| 3. Application:         Deposited completely around the circumference   |
|                         (or spanning the missing flash zone)            |
| 4. Verification:        Inspector may mandate a 15° bend test           |
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If a repair fillet weld is applied, it must have a minimum leg size of 5/16 in. [8 mm]. The weld metal must blend smoothly into the stud base and the structural plate. For high-strength or critical applications, the inspector may require the repaired stud to be bent 15° in the direction opposite the original flash deficiency to verify metallurgical integrity.

Policy on Bent Studs in Production (Clause 9.8.4)

During testing or accidental job-site impact, studs may be bent. Clause 9.8.4 states that studs bent during testing or construction that show no signs of failure shall be left in the bent position. Straightening a bent stud introduces severe cold-work strain, micro-cracking, and strain-age embrittlement, significantly increasing the probability of brittle failure under service loads. Studs shall only be straightened if specifically required by the Engineer or if the bent geometry physically interferes with reinforcing rebar or concrete formwork.

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4. Production Failure Investigation & Sampling Rules (Clause 9.8.5)

If a production stud is tested (due to lack of flash or at the direction of the Verification Inspector) and fails by fracture in the weld or HAZ, the contractor must immediately execute a containment protocol:

1. Adjacent Testing: The two studs immediately adjacent to the failed stud in the production sequence shall be bent to 15°.
2. Escalation to 100% Testing: If either of the two adjacent studs fails, all studs welded by that specific machine and operator since the last acceptable pre-production test shall be bent to 15°.
3. Corrective Reset: The welding unit must be immediately shut down, inspected, recalibrated, and re-qualified via a new pre-production two-stud test before resuming production.

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Summary Matrix: Stud Welding Clause 9 Requirements

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Worked Engineering Example

Problem Scenario

A structural steel erector is installing 3/4 in. [19 mm] diameter Type B headed shear connectors on the top flanges of ASTM A992 W24x68 composite floor beams. At 7:00 AM, the operator sets up the stud gun, welds two pre-production studs on a test coupon, and conducts a 30° bend test. Both studs pass without cracking. At 10:30 AM, after welding 450 studs, the power generator stalls and is replaced with a backup unit. The operator adjusts the cables and immediately continues welding production studs. During QA inspection, the Verification Inspector notes:

1. No pre-production test was performed following the generator replacement.
2. Stud #482 and Stud #510 exhibit only 220° of visible weld flash.
3. The contractor's foreman attempts to straighten a bent stud with a pipe cheater bar.

What specific nonconformances exist under AWS D1.1:2025 Clause 9, and what mandatory corrective actions must be taken?

Technical Resolution & Clause Analysis

1. Generator Replacement Violation (Clause 9.7.1):
   • Replacing the power source is an essential variable change that alters arc voltage and current output characteristics.
   • Mandatory Action: The operator was required to perform a new pre-production qualification test (two consecutive studs welded and bent 30°) immediately upon switching generators before welding any production studs. All studs welded after the generator change (Studs #451 through #550) are suspect and subject to containment testing.
2. Incomplete Flash Disposition (Clause 9.8.1 & 9.8.3):
   • Studs #482 and #510 lack the mandatory full 360° flash.
   • Mandatory Action: The contractor must repair these studs by depositing a minimum 5/16 in. [8 mm] fillet weld completely around their circumference using a qualified SMAW (E7018) or GMAW/FCAW process, or bend-test them 15° away from the missing flash side. If the bend test passes without weld/HAZ tearing, the stud is acceptable.
3. Straightening Violation (Clause 9.8.4):
   • Clause 9.8.4 explicitly forbids straightening bent studs that exhibit no cracking, as straightening causes strain-age embrittlement.
   • Mandatory Action: The foreman must cease straightening. The bent stud shall remain in its bent state unless it physically violates concrete cover or clearances.