Which non-destructive testing method is commonly used to detect internal flaws not visible on the surface?

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Finding hidden internal flaws requires a method that probes beneath the surface. Ultrasonic testing uses high-frequency sound waves that are sent into the material; when these waves encounter internal defects like cracks or voids, part of the wave is reflected back to the detector. By analyzing the travel time and strength of those echoes, you can determine the flaw’s location and size. This gives real-time results and can inspect through coatings or complex shapes, making it a practical, common choice for detecting internal flaws without disassembly or radiation safety concerns. Visual inspection only sees surface conditions, magnetic particle testing targets surface or near-surface discontinuities in ferromagnetic materials, and radiography can reveal internal flaws but requires safety controls for ionizing radiation.