Which NDT method is most effective for detecting internal weld porosity?

• A. Radiographic (X-ray) testing
• B. Visual inspection
• C. Magnetic particle testing
• D. Liquid penetrant testing

Answer: (A)

Internal weld porosity consists of gas pockets inside the weld that aren’t visible on the surface, so you need a method that can image the interior. Radiographic testing uses penetrating radiation to pass through the weld and create an image of what lies inside. Porosity shows up in the radiograph as distinct features—voids or density changes—that reveal their size and location even when they’re not exposed to the surface.

Visual inspection only sees the exterior surface, so it misses internal voids. Magnetic particle testing detects surface or near-surface discontinuities in ferromagnetic materials and may not reveal internal porosity unless it affects the surface or magnetic flux path. Liquid penetrant testing relies on the defect having a pathway to the surface; if porosity is fully enclosed, penetrant won’t indicate it.

Because its imaging capability uncovers internal voids directly, radiographic testing is the most effective method for detecting internal weld porosity.