What may cause indications during a surface wave test?

Indications during a surface wave test can be influenced by a variety of factors that affect the transmission of ultrasonic waves through the material being tested. In this context, each of the options provided contributes to the potential for generating indications.

Surface discontinuities are critical because they can reflect, refract, or scatter the ultrasonic waves, leading to detectable indications. These discontinuities might include flaws such as cracks, inclusions, or any variations in material properties that affect how the waves propagate.

The presence of oil on the surface can also interfere with the coupling of the ultrasonic waves to the test material. Oil can create a barrier that disrupts the energy transmission or may alter the way the waves interact with the surface, potentially causing misleading indications.

Dirt on the surface similarly prevents optimal transmission of the ultrasonic waves. The particles can scatter the waves or form a barrier that affects the integrity of the surface contact, leading to variations in wave amplitude and potentially resulting in false indications.

Because all these factors can independently create challenges in the accurate interpretation of surface wave tests, each one contributes to the overall likelihood of generating indications. Therefore, the choice indicating that all of these elements can cause indications is comprehensive and accurate, highlighting the complexity of surface wave testing in real-world applications.