What is the purpose of tack welds in fit-up?

• A. To hold joint alignment before final weld.
• B. To increase strength permanently.
• C. To seal openings after welding.
• D. To decrease material thickness.

Answer: (A)

Tack welds are used to temporarily hold the pieces in the correct position during fit-up so the final weld can be laid down accurately. By anchoring the joint at several points, they prevent shifting or opening up gaps as heat is applied during the full weld, helping keep the pieces square and aligned and preserving the intended gap along the seam. They’re small, easy to remove or grind away if needed, and their purpose is to facilitate accurate final welding, not to add permanent strength, seal openings, or alter material thickness.