Porosity in Welds

Porosity in welds refers to the presence of voids or gas pockets within the welded joint. It is a defect that can weaken the weld and reduce its integrity. Several factors can contribute to the formation of porosity in welds, including trapped gases, chemical reactions, and contaminants. However, the lack of fusion is not a cause of porosity in welds.

Trapped Gases:
- One of the primary causes of porosity in welds is the presence of trapped gases. During the welding process, gases such as oxygen, nitrogen, and hydrogen can become trapped within the molten weld pool.
- These gases can originate from various sources, such as the shielding gas, flux, or atmospheric air. When the weld solidifies, these trapped gases result in the formation of voids or gas pockets, leading to porosity.

Chemical Reactions:
- Certain chemical reactions can also contribute to the formation of porosity in welds. For example, if the base metal or the filler material contains elements or compounds that are prone to react with the surrounding environment, porosity can occur.
- These reactions can release gases that become trapped within the weld, leading to the formation of porosity.

Contaminants:
- Contaminants present on the surface of the base metal or filler material can also cause porosity in welds.
- These contaminants may include rust, oil, grease, moisture, or any other foreign substances that are not properly cleaned before welding.
- When these contaminants are subjected to the high temperatures during welding, they can release gases, which in turn contribute to the formation of porosity.

Lack of Fusion:
- The lack of fusion, which refers to incomplete bonding between the base metal and the weld metal, is not a cause of porosity in welds.
- Lack of fusion can result in other defects such as incomplete penetration or lack of sidewall fusion, but it does not directly contribute to the formation of voids or gas pockets.

In conclusion, porosity in welds can be caused by trapped gases, chemical reactions, and contaminants. However, the lack of fusion is not a cause of porosity.