Ultrasonic Testing – UT (NDT) Questions and Answers for Level III and II exams

Q1. Which of the following factors can affect the accuracy of flaw detection in UT:
  1. Beam divergence
  2. Surface roughness
  3. Frequency of the ultrasonic waves
  4. All of the above

(Explanation: Ultrasonic flaw detection in UT depends on several factors, with frequency selection being the most prominent. However, other factors also play a crucial role in achieving accurate results.

  • Beam Divergence: As sound waves travel through materials, their beam widens, making it harder to detect small flaws or locate them accurately.
  • Surface Roughness: The quality of the material’s surface affects ultrasonic testing’s effectiveness. Rough surfaces scatter ultrasound beams, reducing signal strength and penetration, while smooth surfaces can cause reflections from internal flaws to be missed.
  • Frequency Selection: The frequency of ultrasonic waves used for testing affects the ability to detect specific types of flaws. Higher frequencies offer better detail but less penetration, while lower frequencies penetrate deeper but provide less detail.

Other factors, such as pulse length, transducer design, and receiver circuitry, can also impact the accuracy of ultrasonic flaw detection. To ensure reliable and effective ultrasonic inspections, it’s essential to understand and optimize these factors based on the specific application.)

Q2. In Ultrasonic Testing (UT), what is the purpose of a reference block, and how does it contribute to the calibration process?
  1. To measure the surface roughness of the test material
  2. To provide a standard for adjusting the instrument’s sensitivity
  3. To act as a reflector for ultrasonic waves
  4. To assess the ambient temperature during testing

(Explanation: In Ultrasonic Testing (UT), a reference block is used to provide a standard for adjusting the instrument’s sensitivity during the calibration process. The purpose of the reference block is to ensure that the instrument is accurately detecting flaws in the test material. The block acts as a reflector for ultrasonic waves, allowing the operator to adjust the instrument’s sensitivity until it detects the reflected waves at the same amplitude as the reference block. This ensures that the instrument is calibrated to the correct sensitivity level for the specific material being tested. Surface roughness and ambient temperature are not factors that a reference block is used to assess during the calibration process. However, Option 3 i.e. To act as a reflector for ultrasonic waves is partially correct, but the primary purpose of a reference block is calibration rather than acting as a reflector.)

Q3. What is the purpose of the Time-of-Flight Diffraction (TOFD) technique and how does it differ from conventional pulse-echo ultrasonic testing?
  1. TOFD is used for measuring material thickness, while conventional pulse-echo is for detecting surface flaws.
  2. TOFD provides real-time imaging of internal structures, whereas conventional pulse-echo measures material density.
  3. TOFD is effective for sizing and positioning flaws in welds, while conventional pulse-echo primarily identifies material boundaries.
  4. TOFD is suitable for inspecting metallic materials, while conventional pulse-echo is more applicable to non-metallic substances.

(Explanation: The Time-of-Flight Diffraction (TOFD) technique is distinct from conventional pulse-echo ultrasonic testing in that it focuses on detecting and sizing internal flaws rather than identifying material boundaries or surface defects. Unlike pulse-echo, which measures the amplitude of reflected waves, TOFD determines the time of flight of diffracted waves emitted from the edges of flaws, enabling precise measurements of flaw sizes and positions within welds. Additionally, TOFD can be used during production without interrupting operations, providing digital records for future reference, and delivering quick inspection results.)

Q4. In Ultrasonic Testing (UT), what is the purpose of a wedge in the inspection setup, and how does it contribute to the testing process?
  1. The wedge is used to measure the velocity of ultrasonic waves in the test material, ensuring accurate calibration.
  2. The wedge acts as a reflector, enhancing the detection of surface-breaking flaws.
  3. The wedge helps to direct and focus ultrasonic waves into the test material at a desired angle for better penetration and defect detection.
  4. The wedge is employed for temperature compensation, ensuring consistent testing results under varying environmental conditions.

(Explanation: In Ultrasonic Testing (UT) Level II, the purpose of a wedge in the inspection setup is to direct and focus ultrasonic waves into the test material at a desired angle for better penetration and defect detection. The wedge is used to position the transducer at an angle to the surface of the specimen so that the shear-wave-refraction angle is optimized. This contributes to the testing process by ensuring that the ultrasonic waves are directed effectively into the material, allowing for improved defect detection and accurate inspection results.)

Q5. In Ultrasonic Testing (UT), describe the purpose of a couplant in the inspection process, and how does it contribute to the effectiveness of ultrasonic wave transmission?
  1. The couplant is used to clean the surface of the test material, ensuring better contact with the ultrasonic probe.
  2. The couplant serves as a corrosion inhibitor, preventing degradation of the test material during inspection.
  3. The couplant acts as a sound reflector, enhancing the sensitivity of the ultrasonic waves to internal flaws.
  4. The couplant facilitates the transmission of ultrasonic waves by eliminating air gaps between the probe and the test material.

(Explanation: The purpose of a couplant in the inspection process is to facilitate the transmission of ultrasonic waves by eliminating air gaps between the probe and the test material. The couplant serves as a medium to ensure efficient transfer of sound energy from the transducer to the test specimen, enhancing the sensitivity of the ultrasonic waves to internal flaws. It does not clean the surface of the test material or act as a corrosion inhibitor, nor does it serve as a sound reflector.)

Q6. Explain the significance of the Near-Field and Far-Field regions during an inspection, and how do these regions impact flaw detection in UT?
  1. The Near-Field region is where surface flaws are primarily detected, while the Far-Field region is critical for assessing internal defects.
  2. The Near-Field region is characterized by reduced resolution, making it suitable for shallow flaw detection, whereas the Far-Field region provides better depth penetration.
  3. The Near-Field region is where calibration is performed, ensuring accurate instrument settings, while the Far-Field region is where actual flaw detection takes place.
  4. The Near-Field and Far-Field regions are interchangeable terms describing the same phase of ultrasonic testing with no distinct impact on flaw detection.

(Explanation: The Near-Field and Far-Field regions are significant during an inspection. Near-Field (also known as the near zone or Fresnel zone) and Far-Field (also known as the far zone or Fraunhofer zone) regions are crucial aspects of ultrasonic testing. The Near-Field region is characterized by extensive fluctuations in sound intensity near the source (reduced resolution and a higher concentration of energy), making it challenging to evaluate flaws accurately . On the other hand, the Far-Field region is where the ultrasonic beam is more uniform, provides better depth penetration and is essential for detecting flaws at greater depths within the material. Hence, optimal detection results are obtained when flaws occur in this area . The transition between the Near-Field and Far-Field regions occurs at a distance, which is determined by the transducer diameter, frequency, and sound longitudinal velocity in the medium through which waves are transmitted. The Far-Field region is where most ultrasonic inspection procedures are designed to occur, and the intensity of the sound beam in this region falls off exponentially as the distance from the face of the transducer increases. The Near-Field and Far-Field regions are not interchangeable terms and have a distinct impact on flaw detection.)

Q7. What is the significance of the dead zone, and how does it impact flaw detection in UT?
  1. The dead zone is where no ultrasonic waves can penetrate, making it ideal for calibrating instruments.
  2. The dead zone is an area near the surface where flaws cannot be detected, affecting the reliability of inspections.
  3. The dead zone indicates a region where material thickness is too low for accurate measurements.
  4. The dead zone is a term used to describe the time delay in ultrasonic testing, ensuring precise depth calculations.

(Explanation: Dead zone refers to the region close to the transducer where echoes from the initial pulse are still being received. During this time, the system is unable to detect flaws accurately. The dead zone can impact the reliability of flaw detection, especially for cracks which are on the surface of the material being tested.)

Q8. In Ultrasonic Testing (UT), why is the selection of an appropriate probe or search unit crucial, and how does it impact the inspection process?
  1. The probe determines the color contrast in the ultrasonic display, enhancing flaw visibility.
  2. The probe influences the calibration process, ensuring accurate measurement of material thickness.
  3. The probe or search unit affects the frequency and beam characteristics, influencing flaw detection capabilities.
  4. The probe is responsible for cleaning the test material surface, improving contact for better wave transmission.

(Explanation: The selection of an appropriate probe or search unit is crucial because it determines the frequency and beam characteristics of the ultrasonic waves. These factors directly impact the system’s ability to detect and characterize flaws within the inspected material. Different probes are chosen based on the specific inspection requirements, material properties, and the depth of flaws that need to be detected.)

Q9. Why angle probes are used, and how do they contribute to the inspection of materials in Ultrasonic Testing (UT)?
  1. Angle probes are designed for surface cleaning, improving contact between the ultrasonic waves and the test material.
  2. Angle probes facilitate temperature compensation during inspections, ensuring consistent results under varying environmental conditions.
  3. Angle probes are used to adjust the frequency of ultrasonic waves, enhancing the accuracy of calibration.
  4. Angle probes enable the inspection of materials at oblique angles, improving the detection of defects beneath the surface.

(Explanation: Angle probes are designed to allow the inspection of materials at oblique angles, enhancing the detection of defects located beneath the surface. These probes are particularly useful for inspecting welds and other components where the geometry may require testing at angles other than perpendicular to the surface.)

Q10. In Ultrasonic Testing (UT) of welds, what is the primary purpose of employing a phased array probe?
  1. To measure the surface roughness of the weld material.
  2. To enhance the sensitivity of the ultrasonic waves to internal defects.
  3. To facilitate temperature compensation during the inspection.
  4. To allow for the inspection of welds at multiple angles without moving the probe.

(Explanation: A phased array probe allows for the inspection of welds at multiple angles without physically moving the probe. This capability improves the flexibility and efficiency of the inspection process, especially in complex weld geometries.)

Q11. What is the name of the curve that shows the relationship between amplitude and distance traveled to reflectors of the same area in ultrasonic testing?
  1. BAC curve
  2. DAC curve
  3. DGS curve
  4. TTT curve

(Explanation: The Distance Amplitude Correction (DAC) curve is a graph that shows the relationship between the amplitude of an ultrasonic signal and the distance traveled by the signal to a reflector of a specific size and shape. The DAC curve is used to adjust the instrument’s sensitivity to ensure that signals from reflectors of different sizes and depths are detected and displayed accurately.)

Q12. A weld inspection is conducted using an angle beam probe with a frequency of 5 MHz. If the velocity of the ultrasonic wave in the material is 3000 m/s, What will be the the wavelength of the ultrasonic wave?
  1. 0.0006 meters
  2. 0.0007 meters
  3. 0.0008 meters
  4. 0.2 milimters

(Explanation: The wavelength can be calculated using the formula λ = v/f, where λ is the wavelength, v is the velocity of the wave, and f is the frequency of the wave. Substituting the given values, we get λ = 3000/5 x 10^6 = 0.0006 meters or 0.6 millimeters. Therefore, the wavelength of the ultrasonic wave is 0.0006 meters.)

Q13. During ultrasonic weld inspection, a technician uses a straight beam probe with a frequency of 10 MHz. If the ultrasonic waves travel through the weld material at a velocity of 2500 m/s, what will be the wavelength of the ultrasonic wave?
  1. 0.21 mm
  2. 0.15 mm
  3. 0.06 mm
  4. 0.00025 m

(Explanation: The wavelength can be calculated using the formula: wavelength (λ) = velocity (v)/ frequency (f). Putting the values, we get: wavelength (λ) = (2500 m/s) / 10 MHz = 0.25 mm = 0.00025 m. Therefore, the wavelength of the ultrasonic wave is 0.00025 meters.)

Q14. In Ultrasonic Testing (UT), what term describes the phenomenon where ultrasonic waves deviate from a straight path when encountering an interface between two different materials?
  1. Beam divergence
  2. Acoustic impedance
  3. Refraction
  4. Attenuation

(Explanation: When ultrasonic waves pass through an interface between two different materials, they change direction, and this phenomenon is known as refraction. The angle of refraction depends on the angle of incidence and the difference in acoustic impedance between the two materials. Refraction is an essential concept in ultrasonic testing, as it allows the operator to direct the ultrasonic beam to specific areas of the material being inspected and detect flaws that may be hidden from a straight beam inspection.)

Q15. Why is the concept of “beam divergence” important, and how does it affect the inspection process in UT?
  1. Beam divergence ensures proper calibration of the ultrasonic instrument.
  2. Beam divergence influences the color contrast of the ultrasonic display.
  3. Beam divergence determines the spread of ultrasonic waves, impacting coverage and flaw detection.
  4. Beam divergence compensates for temperature variations during inspections.

(Explanation: The concept of “beam divergence” is important because it determines the spread of ultrasonic waves, which can impact coverage and flaw detection. Beam divergence refers to the spreading out of the ultrasonic beam as it travels through a material. This can cause the beam to become wider and less focused, which can reduce the sensitivity of the inspection and make it more difficult to detect flaws. The angle of the beam and the frequency of the ultrasonic waves can also affect beam divergence. Therefore, it is important for technicians to consider beam divergence when selecting the appropriate probe and settings for an ultrasonic weld inspection to ensure accurate and reliable results.)

Q16. Which ultrasonic test frequency would probably provide the best penetration in a 300 mm thick specimen of coarse-grained steel?
  1. 2.25 MHz
  2. 10 MHz
  3. 5 MHz
  4. 1 MHz

(Explanation: In ultrasonic testing, higher frequencies generally provide better resolution but less penetration, while lower frequencies offer deeper penetration but lower resolution. Since, we have 300 mm thick specimen of coarse-grained steel, which requires good penetration, a lower frequency would be more suitable. A 1 MHz frequency would have a longer wavelength compared to higher frequencies, allowing it to penetrate deeper into the material.)

Q17. What leads to the attenuation of ultrasonic wave energy as it traverses through a material during testing?
  1. Composition and contrast
  2. Reflection and refraction
  3. Dispersion and diffraction
  4. Absorption and scattering

(Explanation: Attenuation in ultrasonic waves refers to the loss of energy as it travels through a material. This loss occurs mainly because of absorption and scattering. Absorption refers to the conversion of sound energy into heat as the wave travels through the material, while scattering involves the redirection of sound waves in different directions due to irregularities or inhomogeneities in the material.)

Q18. Angle beam testing of plate will often miss:
  1. Incomplete penetration at the root.
  2. Inclusions that are randomly oriented.
  3. Laminations that are parallel to the front surface.
  4. A series of small discontinuities.

(Explanation: When laminations run parallel to the front surface of a plate, the sound waves can travel along them smoothly without encountering obstacles that would create reflections. This makes it possible for these defects to go undetected during angle beam testing. The way the defect aligns with the sound beam’s direction is a key factor in determining whether it can be detected effectively using this testing method.)

Q19. What characteristic of particular materials enables them to convert electric energy into mechanical energy and conversely, mechanical energy into electric energy?
  1. Piezoelectric effect
  2. Gamma-Beta effect
  3. Acoustic Impedance
  4. Attenuation effect

(Explanation: Certain materials have the unique ability to convert electrical energy into mechanical energy and vice versa, which is referred to as the piezoelectric effect. This phenomenon allows piezoelectric materials to transform mechanical stress into electricity or vice versa. That is why these materials are used in the probes or search units of a Ultrasonic Testing equipment.)

Q20. In ultrasonic testing using an angle probe for weld scanning, if the angle of the probe is 45 degrees and the sound velocity in the material is 3000 m/s, what is the depth of a flaw detected at a time interval of 10 microseconds?
  1. 1.5 mm
  2. 21.2 mm
  3. 4.5 mm
  4. 6 mm

(Explanation: The depth (d) of a flaw detected using ultrasonic testing can be calculated using the formula;

d = (V x t)/(2 x cos)

  • Sound velocity in the material
  • Time interval
  • Angle of the probe

Given values are;

  • Sound velocity = 3000 m/s
  • Time interval = (which is 10×10^−6 seconds)
  • Angle of the probe

Putting the values d =(3000×10×10^−6)/(2 x cos

Now, expressing in millimeters (1 m = 1000 mm)

Q22. Which parameter is calculated by multiplying the density () of a material by its longitudinal wave velocity (VL) in ultrasonic testing?
  1. Ultrasonic Impedance ()
  2. Acoustic Conductivity )
  3. Acoustic Impedance ()
  4. Density Velocity Product ()

(Explanation: In ultrasonic testing, the parameter that is calculated by multiplying the density (ρ) of a material by its longitudinal wave velocity (VL) is called Acoustic Impedance (AI). Acoustic impedance plays a crucial role by determining how much sound energy bounces back when it encounters different materials. This bouncing back of energy affects how well we can find defects and understand the properties of the material being tested. When there is a big difference in acoustic impedance between materials, more energy reflects back, which can make the testing process less effective in detecting flaws accurately.)

Q23. Consider a steel specimen with a density of 7,850 kg/m³ and a longitudinal wave velocity of 5,900 m/s. Calculate the acoustic impedance of the steel specimen and explain its significance in the context of ultrasonic testing.
  1. 46,415,000 kg/(m²s)
  2. 35,000,000 kg/(m²s)
  3. 52,150,000 kg/(m²s)
  4. 40,000,000 kg/(m²s)

(Explanation: Acoustic Impedance (Z) = Density (ρ) X Longitudinal Sound Velocity (VL)

Given:

  • Density of steel specimen (ρ) = 7,850 kg/m³
  • Longitudinal wave velocity of steel specimen (VL) = 5,900 m/s

Substitute the values into the formula:
Z = 7,850 kg/m³ X 5,900 m/s
Z = 46,415,000 kg/(m²s)