Which of the following is considered a common welding defect?

Poor penetration is considered a common welding defect because it refers to the inadequate depth of weld metal that fuses with the base material. Proper penetration is essential for ensuring that the weld has sufficient strength and durability. When penetration is insufficient, it can lead to weak joints, resulting in potential failure during service or application.

Common causes of poor penetration can include incorrect electrode angle, insufficient heat input, or improper travel speed. Understanding this defect is crucial for welders in order to adjust their techniques and parameters to achieve the desired weld quality.

In contrast, excessive heat input is not desirable but is distinct from poor penetration; it can lead to other issues such as distortion or burn-through. A stable arc is a sign of good welding conditions, and complete fusion indicates a successful weld joint where the weld metal and base metal are fully integrated without any gaps or defects. These options reflect positive attributes in welding processes rather than defects.