The lack of parallelism between the entry surface and the back surface in ultrasonic testing may result in which outcome?

• A. Will decrease the penetrating power of the test
• B. May result in a screen pattern that does not contain back reflection indications
• C. Usually indicates that a porous condition exists in the metal
• D. Makes it difficult to locate discontinuities that lie parallel to the entry surface

Answer: (B)

When the entry surface and the back surface are not parallel, the ultrasonic beam that would normally reflect straight back from the far surface is redirected as it travels to the back wall. The transducer is positioned to receive echoes that return along the same path, so if the back surface is tilted relative to the entry surface, the reflected energy is sent off at an angle and may not return to the probe. As a result, the back-wall echo can be weak or absent on the screen, leading to a pattern that does not show back reflection indications. This effect is a direct consequence of how the beam reflects and refracts at inclined interfaces, rather than a change in penetration power or material porosity.