Unit 19: Inspection and testing
LO4: Understand how non-destructive testing
methods are used for quality assurance in a
manufacturing environment
NDT test methods – ultrasonic testing
Learner activity sheet
Activity 1
Ultrasonic testing is a non-destructive testing technique used to find faults in materials and components.
The video below demonstrates and explains ultrasonic testing. Watch the video and answer the
questions in Activity 1.
http://www.youtube.com/watch?v=UM6XKvXWVFA
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Questions
1.
What is the basic principle of operation of ultrasonic testing?
2.
What is ‘free end reflection’?
3.
What is the ‘free end’ usually called?
4.
At what speed does an ultrasonic wave travel?
5.
What are ‘pulse echo mode’ and ‘through transmission mode’?
6.
What signals are usually present in a specimen free from defects?
7.
What signals are usually present in a specimen with defects?
8.
What function does a piezo-electric disc perform?
9.
Why is a couplant gel required?
10. How can depth and not reflected signal time be plotted using an ultrasonic tester?
11. Will only abnormalities cause ultrasonic echoes?
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Activity 2
Look at the diagram below which shows a metal block with a crack. An ultrasonic probe is placed at
position A, and then at position B.
Sketch typical reflected intensity plots for the ultrasonic signal with the probe at position A and at position
B.
You can assume that the probe is making good contact with the surface of the metal, and is well
coupled.
B
Probe at A
150 mm
Crack
Time
Intensity
300 mm
A
Intensity
Ultrasonic
Probe
Probe at B
Time
1. Explain what is being shown in the plot with the probe at position A:
2. Explain what is being shown in the plot with the probe at position B:
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Activity 3
The technique for detecting cracks and defects shown in Activity 1 is not very reliable in determining the
size and position of defects. There are other techniques using ultrasonic waves that are more sensitive
and accurate, and which enable easier crack detection. These include:
1.
2.
Time-of-Flight Diffraction – TOFD
Phased array
For these two ultrasonic techniques, provide a basic description of the principle of operation.
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