NDT Ultrasonic Testing 2 — Questions and Answers
Question 1: What is the primary purpose of a couplant in ultrasonic testing?
- To increase the frequency of the sound wave
- To eliminate the air gap between the transducer and test material (Correct answer)
- To harden the surface of the material being tested
- To amplify the received signal on the display
Correct answer: To eliminate the air gap between the transducer and test material
Couplants fill the air gap between the transducer and material surface, enabling efficient transfer of ultrasonic energy since air is a poor acoustic conductor.
Question 2: In ultrasonic testing, what does 'beam spread' refer to?
- The divergence of the ultrasonic beam as it travels through a material (Correct answer)
- The width of the transducer crystal
- The range of frequencies emitted by the transducer
- The attenuation rate of the signal over distance
Correct answer: The divergence of the ultrasonic beam as it travels through a material
Beam spread is the natural divergence of an ultrasonic beam as it travels away from the transducer, which affects lateral resolution and coverage area.
Question 3: Which ultrasonic testing method uses two separate transducers — one for sending and one for receiving?
- Pulse-echo technique
- Pitch-catch technique (Correct answer)
- Immersion testing
- Resonance testing
Correct answer: Pitch-catch technique
The pitch-catch (or through-transmission) technique uses separate transmitter and receiver transducers, allowing detection of flaws that might not produce strong reflections.
Question 4: What is the 'near field' (Fresnel zone) in ultrasonic testing?
- The region beyond the transducer where the beam is fully diverged
- The region close to the transducer where sound pressure varies irregularly (Correct answer)
- The area immediately behind a detected flaw
- The calibration reference zone on the A-scan display
Correct answer: The region close to the transducer where sound pressure varies irregularly
The near field (Fresnel zone) is the region close to the transducer face where constructive and destructive interference cause irregular sound pressure variations.
Question 5: When performing angle beam UT on a weld, what is the 'skip distance'?
- The distance the ultrasonic beam travels before entering the material
- The surface distance traveled for one complete V-path (down and back up) (Correct answer)
- The depth at which the refracted beam travels horizontally
- The gap between two adjacent transducer positions
Correct answer: The surface distance traveled for one complete V-path (down and back up)
Skip distance is the surface distance covered in one full V-path of an angle beam, from entry point to where the beam returns to the surface after reflecting off the back wall.
Question 6: Which material property most significantly affects ultrasonic attenuation?
- Electrical conductivity
- Grain size and structure (Correct answer)
- Tensile strength
- Surface hardness
Correct answer: Grain size and structure
Coarse grain size scatters ultrasonic waves, greatly increasing attenuation and making inspection of coarse-grained materials like cast iron more difficult.
Question 7: In immersion ultrasonic testing, why is a water column maintained between the transducer and test piece?
- To cool the transducer during extended operation
- To provide a consistent, bubble-free couplant path and allow precise beam angle control (Correct answer)
- To increase the frequency of the emitted pulse
- To prevent electrical interference from the test piece
Correct answer: To provide a consistent, bubble-free couplant path and allow precise beam angle control
The water column acts as an acoustic couplant and, combined with transducer angle adjustment, allows precise control of the refracted beam angle entering the test piece.
NDT Ultrasonic Testing 2
What is the primary purpose of a couplant in ultrasonic testing?