What are common welding defects and how are they detected?

Common welding defects include: Porosity (gas pockets), Lack of fusion (incomplete bonding), Undercut (groove at weld toe), Cracks (hot/cold cracking), Incomplete penetration, and Slag inclusions. Detection methods include: Visual inspection (surface defects), Dye penetrant testing (surface cracks), Magnetic particle testing (ferromagnetic materials), Ultrasonic testing (internal defects), and Radiographic testing (comprehensive internal inspection). Selection of NDT method depends on defect type, material, and criticality.