Chapter 4

Question 1

Explain how ultrasound is generated and give two examples of the crystals used to generate ultrasound.

Answer 1

Ultrasound is generated by means of piezo-electric materials that
convert electrical energy to mechanical energy and vice-versa.
Two examples of crystals: Quartz crystals, Barium titanate or Lithium
Sulphate

Question 2

state the two techniques of ultrasound testing and briefly describe two differences

Answer 2

Pulse-echo Technique / Through Transmission Technique
1. Uses only one probe / uses two probes
2. The same probe acts as both the transmitter and receiver / one probe act as
transmitter and the other as receiver
3. Measurement of thickness of plate is possible / cannot measure thickness of plate

Question 3

list four advantages of dye penetrant testing for the detection of surface discontinuities.

Answer 3

1. Suitable on all homogeneous
2. Not affected by defect orientation
3. Minimum skill required to perform
4. Defects must be open to surface detects
5. May be applied without sophisticated equipment

Question 4

what are the two basic groups of the penetrant process? briefly describe their main differences.

Answer 4

Penetrants processes are usually separated into two basic groups, visible and
fluorescent.
Visible penetrants are those which contain a very bright dye, usually red, that is
viewed under bright white light.
Fluorescent penetrants contain a dye which fluoresces (glows) brilliantly under
filtered ultra-violet light (often called black light).

Question 5

what are the two types of magnetic particles that are commonly used in the magnetic particle test?

Answer 5

There are two types of magnetic particles for use in the magnetic inspection, the wet
particles and dry particles

Question 6

magnetic particle testing can result in residual magnetism in the specimen. give two reasons where residual magnetism is undesirable.

Answer 6

(a) Adverse effects on instruments, eg. aircraft compass.
(b) Interference with future machining operations by causing chips to adhere to
cutting tools.
(c) Adherence of magnetic particles to moving parts thereby accelerating wear.
(d) Induction of stray voltages in adjacent circuits.

Question 7

what type of magnetic field is generated with Prod Contacts in magnetic particle testing?

Answer 7

Circular magnetic field

Question 8

The type of defect easily detected by magnetic particle inspection is?

Answer 8

surface discontinuity at 90 degrees to the magnetic field