Questions -

Question 1 - An aluminum component with a thickness of 20 mm is tested using full immersion. The probe is positioned at a distance from the aluminum sample, with the aim of receiving the following echoes when no flaw is present in the order given:

first water echo;

first back wall echo;

second back wall echo;

second water echo;

Assuming that the velocity of compression waves in aluminum is 6374 m/s and in water is 1480 m/s, suggest a distance from the sample at which the probe should be placed to achieve the desired goal. Include a diagram of the set-up in your solution.

Using the set-up above, calculate the time at which the 4 echoes will arrive if there are no flaws.

Again, using the set-up above, calculate the time at which an echo will arrive if a small flaw such as a gas pore is present at a depth of 6 mm in the sample.

Question 2 - A 0.5 MHz, 12.7 mm diameter single crystal probe is used to produce a compression wave in water for an immersion test on 20 mm thick aluminum. The probe is placed 20 mm away from the sample. Assume that the velocity of the wave in water v = 1.48 x 10⁶ mm/s and the velocity in steel is 6.374 x 10⁶ mm/s. The acoustic impedance of water 1.482 kg/m2s and the acoustic impedance of aluminum is 17.21 kg/m²s.

Assuming that the beam is vertical, how much of the beam is reflected at the surface of the aluminum and how much is transmitted?

On these percentages alone, what is the relative size of the first 4 echoes in the immersive test? Assume that 100% of the beam is reflected at the back wall.

Question 3 - A 0.5 MHz, 12.5 mm diameter single crystal probe is used to produce a compression wave in water for an immersion test on 20 mm thick aluminum. The probe is placed 20 mm away from the sample. Assume that the velocity of the wave in water v = 1.48 x 10⁶ mm/s and k = 1.22 for full beam width.

What is the length of the near zone?

What is the area of the beam at the end of the near zone?

Question 4 - A DAC line is produced using 4 mm diameter flat bottomed holes.

What is the area of a reflector that produces an echo that is 6 dB below the DAC line?

Assuming the reflector is circular, what is its diameter?

Question 5 - A single 'V' butt weld in 12 mm plate is inspected using Method 1 from the standard EN ISO 11666 which uses a DAC curve for a 3 mm diameter side-drilled holes as a reference. A longitudinal flaw is found which produces a peak in the A-scan which is 7 dB below the DAC curve.

If the length is found to be 14 mm, describe how the flaw would be reported under Acceptance Level 3 (AL3) i.e. is the weld acceptable or should it be rejected and should the flaw be recorded and/or evaluated?

Would the outcome be different if the same test was done using Acceptance level 2?

Describe how the length of the indication is measured according to ISO 11666.