4g Weld Test [extra — Quality]

Write-Up: The 4G Weld Test (Overhead Position) 1. Overview & Definition The 4G weld test (4G = 4th Position, Groove weld) is a qualification test for welders performing overhead groove welding . In this position, the weld axis lies approximately horizontal, but the welder deposits the weld from the underside of the joint . The face of the weld is in a horizontal plane, and the welder must push the molten metal upward against gravity. Standard Reference: AWS D1.1 (Structural Steel), ASME Section IX (Pressure Vessels), API 1104 (Pipelines). Common Joint Design: Single-Vee or beveled groove with a backing bar (or open root with backing gas for pipe). 2. Test Setup & Dimensions

Plate Thickness: Typically 3/8 inch (10 mm) to 1 inch (25 mm). Groove Angle: 60° included (30° per side). Root Opening: 1/4 inch (6 mm) if using a backing bar; 1/8 inch (3 mm) for open root. Backing: Copper or steel backing bar (most common for structural tests) or no backing (open root for pipe/advanced tests). Positioning: The plate assembly is fixed horizontally above the welder’s head. The welder stands or lies under the joint, welding upward.

3. Welding Process & Technique Common Processes:

SMAW (Stick) – Most common for field tests. GMAW (MIG) – Short-circuit or pulse transfer. FCAW (Flux-Cored) – Self-shielded or gas-shielded. GTAW (TIG) – Less common for thick plate, but used for root passes in pipe. 4g weld test

Key Techniques for Overhead Welding: | Parameter | Recommended Setting (SMAW, 1/8" electrode) | |-----------|---------------------------------------------| | Current | Slightly lower than flat position (90–115 amps) | | Electrode Angle | 5–15° upward from perpendicular, pushing into puddle | | Arc Length | Short and tight (prevents drooping) | | Travel Speed | Fast enough to freeze puddle before gravity pulls it down | Stringer beads only – No weaving allowed in most 4G tests (except for cover pass on some standards). 4. Common Challenges & Defects Welding overhead is difficult because gravity works against the welder . Common defects include:

Underfill (concavity) – Molten metal sags away from the top edge. Burnthrough – Excessive heat causes the root to fall out. Slag entrapment – Slag runs ahead of the puddle. Incomplete fusion at the top corner – Arc misses the upper plate edge. Excessive reinforcement – Puddle sags into a convex hump.

5. Inspection & Acceptance Criteria (per AWS D1.1) After welding, the test coupon is cut into transverse face bend and root bend specimens (or reduced-section tensile tests). Visual Inspection (before bending): Write-Up: The 4G Weld Test (Overhead Position) 1

No cracks or incomplete fusion. Reinforcement: 1/8" (3 mm) max, 1/32" (1 mm) min. Undercut: ≤ 1/32" (1 mm) deep.

Bend Test Requirements:

Face bend (weld face in tension) – No discontinuity > 1/8" in any direction. Root bend (weld root in tension) – Same criteria. Side bends (for thick plates > 3/4") – No open defects exceeding 1/8". The face of the weld is in a

Typical causes of bend test failure in 4G:

Lack of fusion near the top plate edge. Slag lines near the root. Porosity clusters from poor gas coverage (GMAW/FCAW).