Learn about the most common welding defects including porosity, cracking, undercut, and incomplete fusion. Discover causes and prevention strategies for each.
Introduction
Welding defects compromise joint integrity and part quality. Understanding causes and prevention is essential. At Fulei Metal, our quality system catches and prevents defects.
Defect 1: Porosity
Gas trapped in the weld pool. Appears as small holes or bubbles.
Causes: contaminated material, insufficient gas coverage, wet or oily surface, wrong gas type, excessive gas flow causing turbulence, dirty filler wire.
Prevention: clean material thoroughly, verify gas flow and type, store filler properly, check for drafts, clean all surfaces.
Defect 2: Cracking
Cracks in or near the weld. Most serious defect.
Hot Cracking
Occurs during solidification. Caused by high sulfur or phosphorus, excessive concavity, rapid cooling. Prevention: use correct filler, maintain proper bead shape, control cooling rate.
Cold Cracking
Occurs after cooling. Caused by hydrogen, residual stress, martensitic structure. Prevention: use low-hydrogen consumables, pre-heat, control heat input, post-weld heat treatment.
Defect 3: Undercut
Groove melted into the base metal adjacent to the weld. Reduces cross-section. Stress concentrator.
Causes: excessive amperage, excessive travel speed, incorrect torch angle, excessive arc length.
Prevention: reduce amperage, slow travel speed, correct torch angle, maintain short arc.
Defect 4: Incomplete Fusion
Weld metal does not fuse with base metal or previous passes.
Causes: insufficient amperage, excessive travel speed, incorrect torch angle, dirty surfaces, improper joint preparation.
Prevention: increase amperage, slow travel, correct angle, clean surfaces, prepare joints properly.
Defect 5: Incomplete Penetration
Weld does not reach through the full joint thickness.
Causes: insufficient amperage, excessive travel speed, excessive root gap, wrong joint preparation, wrong bead sequence.
Prevention: increase amperage, reduce speed, correct root gap, prepare joint correctly, use proper sequence.
Defect 6: Spatter
Metal droplets expelled from the weld. Stick to surrounding surface.
Causes: excessive amperage, low voltage, wrong gas mixture, dirty wire, wrong wire feed speed.
Prevention: optimize parameters, use correct gas, clean wire, consider pulsed transfer.
Defect 7: Overlap
Weld metal flows onto the base metal surface without fusing.
Causes: excessive deposition, slow travel speed, incorrect torch angle.
Prevention: increase travel speed, correct torch angle, reduce deposition rate.
Defect 8: Distortion
Excessive warping of the part.
Causes: excessive heat input, poor sequence, inadequate clamping, wrong joint design.
Prevention: control heat input, proper sequence, adequate clamping, consider joint design.
Inspection and Detection
Visual inspection: undercut, overlap, surface porosity, bead shape, size. Dye penetrant: surface cracks and porosity. Radiography: internal defects, porosity, lack of fusion. Ultrasonic: internal cracks, lack of fusion. Magnetic particle: surface and near-surface cracks (ferromagnetic only).
Defect Repair
Assess extent of defect. Remove defect by grinding or gouging. Clean the repair area. Re-weld with correct parameters. Re-inspect the repair. Document the repair.
Conclusion
Welding defects are preventable with proper procedures, parameters, and skill. At Fulei Metal, our quality system and experienced welders minimize defects and ensure weld integrity.