Non-Destructive Testing (NDT) Practice Test

Which ultrasonic testing method is primarily used for detecting surface flaws?

1. Pulse-echo

2. Through transmission

3. Time-of-flight diffraction

4. Coating thickness measurement

The correct answer is: Pulse-echo

The pulse-echo method is primarily used for detecting surface flaws due to its ability to send ultrasonic waves into a material and receive the echoes that return from the surfaces and any discontinuities within the material. In this technique, a transducer emits a short burst of ultrasonic energy, which travels through the material. When the waves encounter a flaw, such as a crack or void, some of the energy is reflected back to the transducer, allowing the operator to analyze the signals received. This method is particularly effective for identifying defects located near the surface since the echoes from these surface flaws will return to the transducer relatively quickly compared to those from deeper discontinuities. This capability makes pulse-echo a preferred choice in applications where surface integrity is critical, such as in weld inspections, material evaluation, and fatigue assessments. In contrast, while the through transmission method is useful for assessing material thickness and detecting internal flaws, it does not focus specifically on surface flaws. Time-of-flight diffraction is another ultrasonic technique but is more suited for characterizing defects that are not directly on the surface. Coating thickness measurement is a specialized application that does not inherently detect flaws but rather measures the thickness of a coating over a substrate. Therefore, pulse-echo is the most suitable method for