Weld Discontinuities and Defects
Porosity, undercut, lack of fusion, incomplete penetration, slag inclusions, hydrogen cracking, and spatter.
- Identify the causes and prevention of porosity and undercut
- Distinguish between lack of fusion and incomplete penetration
- Explain hydrogen-induced cracking and the three required factors
- Describe spatter, back gouging, and peening
Lesson 1
Porosity and Undercut
Porosity
Porosity is gas pockets or voids in the weld metal caused by gas trapped during solidification. It commonly appears as spherical or elongated holes distributed throughout the weld or concentrated in specific areas.
Porosity is commonly caused by contamination, moisture, or inadequate shielding gas. Specific causes include dirty base metal (oil, rust, paint), moisture on the electrode or base metal, insufficient shielding gas flow, excessive wind disturbing the gas shield, and too-long an arc length.
Scattered Porosity
Appearance: Random voids throughout weld
Cause: General contamination or gas
Fix: Clean base metal, check gas flow
Clustered Porosity
Appearance: Group of pores in one area
Cause: Localized contamination
Fix: Remove weld, clean area, re-weld
Piping (Wormhole) Porosity
Appearance: Elongated tubular voids
Cause: Gas channeling during solidification
Fix: Reduce moisture, preheat
Undercut
Undercut is a groove melted into the base metal adjacent to the weld toe. It reduces the effective cross-section of the base metal at the most stressed point of the joint.
Undercut is caused by excessive current, incorrect angle, or too fast travel speed. The arc melts a groove into the base metal that is not filled by weld metal because the pool moves too quickly or is directed improperly.
Undercut Prevention
Reduce current, slow travel speed, and use proper electrode angle. Pause briefly at the toes of a weave bead to allow filler metal to fill the groove edges.
Porosity is caused by contamination, moisture, or inadequate shielding gas. Undercut is caused by excessive current, incorrect angle, or too fast travel speed. Both are common exam topics requiring you to match the defect to its cause.