What should be applied to the panel flanges prior to welding?

Weld-through primer is specifically designed to be used on panel flanges prior to welding to ensure both protection and functionality during the welding process. This type of primer has properties that allow it to withstand the high heat of welding without burning off or affecting the weld quality. Additionally, it provides corrosion resistance to the bare metal surfaces that are exposed during the welding, helping to prevent rust and other forms of deterioration that could occur after the welding is completed.

The use of weld-through primer creates a barrier that protects the metal and improves the adhesion of the weld while still allowing the weld area to be properly joined. Other paint products like standard paint or clear coats are not suitable for this application because they can burn away or create contaminants that impair the weld's integrity. Hence, using weld-through primer is crucial for maintaining the quality and longevity of the repair.