Weld Defects and Their Causes
Porosity, undercut, overlap, lack of fusion, slag inclusion, and their prevention.
- Identify common weld defects by appearance and location
- Explain the causes of porosity, undercut, overlap, lack of fusion, and slag inclusion
- Describe prevention methods for each defect type
Lesson 1
Porosity Causes and Prevention
What Is Porosity?
Porosity consists of gas pockets trapped in the solidified weld metal. These voids weaken the weld and are caused by gas being unable to escape before the weld pool solidifies.
Causes of Porosity
Moisture on base metal, electrode, or in atmosphere
Contamination - oil, paint, rust, mill scale
Arc too long - loss of gas shielding
Wet/damaged electrodes
Wind or drafts blowing shielding gas away
Prevention
Clean base metal thoroughly before welding
Use dry electrodes from rod oven
Maintain proper arc length
Shield from wind with barriers
Preheat to remove surface moisture
Types of Porosity
- Scattered porosity - random gas pockets throughout the weld
- Clustered porosity - concentrated group of pores in one area (usually at start or stop)
- Linear porosity - pores aligned along the weld, often at the fusion line
- Piping (wormholes) - elongated gas pockets perpendicular to the weld surface
The Biggest Cause
The most common cause of porosity in SMAW is contaminated base metal (oil, paint, rust, moisture). Always clean the weld area to bright metal for at least 25 mm (1") on each side of the joint.
Porosity is caused by trapped gas from moisture, contamination, or loss of shielding. The primary prevention is cleaning base metal to bright metal and using dry electrodes. Maintain proper arc length and shield from wind.