Causes of poor weld penetration include too low heat setting, travel speed too fast, stick out too long, and improper root gaps.

• A. Distortion
• B. Porosity
• C. Penetration
• D. Burn through

Answer: (C)

Penetration is about how deeply the weld metal fuses into the base metal. When heat input is too low, the weld doesn’t reach the root well enough, so fusion remains shallow. If travel speed is too fast, the arc spends less time in the joint, delivering less heat and producing a shallower weld. A stick-out that is too long spreads the arc arc length and lowers the energy concentrated at the root, again reducing penetration. Improper root gaps prevent proper fusion at the joint root, so the weld cannot penetrate fully to the far side or to the root. Together these conditions specifically degrade penetration depth rather than other weld flaws like distortion, porosity, or burn-through, which are caused by different issues.