Which inspection method would best detect a lack of filler metal at a joint interior?

• A. Ultrasonic testing
• B. Dye penetrant testing
• C. Radiographic testing
• D. Magnetic particle testing

Answer: (C)

Radiographic testing lets you see inside the weld. By passing X-rays or gamma rays through the joint, you get an image of the interior cross-section, so you can judge whether the weld metal actually fills the joint. A lack of filler metal shows up as a gap or a lighter area along the joint in the radiograph, making incomplete penetration or lack of fusion easy to identify. The other methods focus on surface or near-surface features and aren’t as reliable for confirming interior filler metal presence: dye penetrant is surface-only, magnetic particle targets surface or near-surface flaws in ferromagnetic materials, and ultrasonic testing can detect internal flaws but interpreting the interior filler absence isn’t as straightforward or definitive in all geometries. Radiographic imaging directly reveals the internal continuity of the weld, which is what you need to detect a lack of filler metal at the interior.