For welds at transitioning thickness longer than 10 inches, how many IQIs are required and where?

• A. Two IQIs on the thicker plate and one on the thinner
• B. Two IQIs on the thinner plate and one on the thicker
• C. Three IQIs on the thinner plate
• D. One IQI on the joint

Answer: (A)

When radiographic inspection covers a weld with a thickness transition longer than 10 inches, the thicker section attenuates more radiation, which can reduce defect detectability if you’re relying on a single IQI. To ensure the radiographic sensitivity is verified across both sides of the transition, you need three IQIs: place two on the thicker plate to guarantee adequate coverage and redundancy in the thicker region, and place one on the thinner plate to confirm sufficient sensitivity there as well. This arrangement helps confirm that defects would be visible throughout the weld area despite the thickness change.

Other options don’t provide this balanced verification across both sides of the transition: placing more IQIs on the thinner plate ignores the critical thicker region, placing all on the thinner plate misses the thick-side assurance, and using too few IQIs would fail to demonstrate the required radiographic sensitivity across the weld.