On formed or rolled parts over 75 mm where straightening still does not meet tolerance, what revised fit-up tolerance can be used if a sealing weld or backing plate is employed?

• A. 5 mm (3/16 inch)
• B. 8 mm (5/16 inch)
• C. 3 mm (1/8 inch)
• D. 10 mm (3/4 inch)

Answer: (B)

When parts are formed or rolled and are over 75 mm, straightening may not bring them into the required fit-up tolerance. In these cases, using a sealing weld or a backing plate allows a larger, controlled gap at the joint while still achieving a sound weld. The revised fit-up tolerance for this scenario is 8 mm (5/16 inch). This allowance recognizes that the sealing or backing approach helps maintain weld integrity, root fusion, and a proper seal despite the bigger misalignment. Smaller gaps (5 mm or 3 mm) would be too restrictive for these larger formed parts, and a 10 mm gap is not the specified revision for this situation.