Which type of flaw is best detected with ultrasonic testing?

Ultrasonic testing is particularly effective for detecting internal and subsurface flaws due to the nature of how ultrasound waves interact with materials. This method involves sending high-frequency sound waves into a material and measuring the waves that are reflected back. When these sound waves encounter a discontinuity, such as a void, crack, or inclusion beneath the surface, a portion of the sound waves is reflected back to the transducer, allowing for precise identification and evaluation of the flaw's size, shape, and location.

The capability of ultrasonic testing to penetrate materials helps it to find flaws that would not be detectable through other methods that primarily focus on surface conditions. Surface flaws, while they can also be detected, are more easily identified by different testing methods like magnetic particle testing or dye penetrant testing, which are specifically designed for detecting surface-breaking discontinuities. Other types of flaws, such as corrosion on surfaces or circular flaws, may not be as effectively characterized by ultrasonic methods, as these often exhibit characteristics that can be more easily identified by alternative non-destructive testing techniques.

Thus, ultrasonic testing's ability to examine internal and subsurface structures gives it a distinct advantage in assessing the integrity of materials where hidden flaws may exist.