On a radiograph, how does lack of root fusion on a single-V-butt weld typically appear?

• A. A light curved line with a dark root
• B. A dark straight line with a light root
• C. A light line with dark patches
• D. An even shade throughout

Answer: (B)

In the context of radiography, a lack of root fusion on a single-V-butt weld typically manifests as a dark straight line with a light root. This appearance is due to the way the weld has penetrated and fused the materials.

When there is insufficient fusion at the root of the weld, the x-rays pass through the unbonded areas differently than they do through well-fused weld material. The poorly fused area does not absorb x-rays as effectively as the surrounding base metal or the fully fused parts of the weld. Consequently, the region of lack of fusion appears darker on the radiograph because it allows more x-rays to pass through, resulting in an image that registers as a dark line. The light root indicates the area where the weld metal did not adequately merge into the parent materials, highlighting the defect effectively.

This interpretation of the radiograph is crucial for weld inspections, as it provides visual feedback on the integrity and quality of the weld, assisting inspectors in identifying potential weaknesses before they result in failure.