Which factor can lead to porosity in welding?

Porosity in welding is primarily caused by the presence of gas bubbles trapped within the solidifying weld metal, impairing the integrity of the weld. Impurities in the base metal can significantly contribute to porosity, as these impurities may include contaminants like oil, rust, or moisture that release gases during the welding process. When these gases aren't properly vented, they can become trapped, leading to the formation of porosity in the finished weld.

In contrast, while factors like high ambient humidity, windy conditions, or an incorrect arc length can also affect the overall quality of a weld, they are less directly related to the introduction of gases from impurities in the base metal. High humidity might increase the likelihood of moisture in the weld area, but it primarily affects the weld's surface rather than directly causing porosity from internal contaminants. Windy conditions can blow away shielding gas, which could lead to other defects but is not as directly tied to gas entrapment as the impurities present in the base metal. Similarly, using too short of an arc can lead to other defects like arc inclusions but is not a primary cause of porosity.

Thus, impurities within the base metal are the most significant factor leading to porosity in welding, as they can