What is the major disadvantage of using reactive gases in MIG welding?

The primary disadvantage of using reactive gases in MIG welding lies in their potential for causing welding defects. Reactive gases, such as oxygen or carbon dioxide, can lead to oxidation and contamination of the weld pool, negatively affecting the quality and integrity of the weld. This can result in issues such as porosity, inclusions, or a weak weld structure. When these gases are introduced during the welding process, they can create conditions that compromise the overall performance of the weld, making it crucial for welders to carefully control their use and ensure proper shielding to minimize these risks.

In contrast, the other options, while they may present challenges in specific contexts, do not encapsulate the immediate and critical concern regarding weld quality associated with reactive gases. For instance, cost, complexity, and setup time may vary based on other factors, but the direct impact on weld integrity from using reactive gases is a more pressing issue.