Which is a common welding defect and its cause?

• A. Slag inclusion — improper joint fit
• B. Porosity — gas entrapment or moisture
• C. Lack of fusion — excessive current
• D. Undercut — large weld bead width

Answer: (B)

Porosity is a common welding defect created when gas bubbles get trapped in the weld metal as it solidifies. The most frequent causes are gas entrapment or moisture. If moisture is present on the electrode coating or the workpiece, or if shielding gas coverage is inadequate, hydrogen or other gases can enter the molten weld and form pores as it cools. Keeping metals and electrodes dry, ensuring good shielding coverage, and controlling heat input help prevent porosity.

Slag inclusion happens when slag from the flux gets trapped in the weld, often due to insufficient slag coverage, improper cleaning, or poor technique between passes. Lack of fusion arises when the weld metal doesn’t fully fuse with the base metal, typically from too little heat input or incorrect joint prep. Undercut is a groove along the weld toe caused by factors like excessive current or improper travel speed, not by moisture-related porosity or wide bead width.