Ultrasonic Test

Question 1

What is Ultrasound?

Answer 1

Ultrasound is sound wave above the audio frequency of 20 kHz and is used in detecting
defects. ‘This method of testing is known as ultrasonic flaw detection.

Almost all the ultrasonic energy is reflected at a boundary surface.

Question 2

How does Ultrasound differ from X-rays in Intensity?

Answer 2

Ultrasound waves differ from X-rays in that its intensity is practically undiminished after
travelling several meters of material.

Ultrasonic energy cannot pass from metal to air but X-rays pass from metal to air without any
loss of energy.

Question 3

How is Ultrasound generated?

Answer 3

The ultrasound used in flaw detection is normally generated by means of piezo-electric
materials.

A piezo-electric material is one that converts electrical energy to mechanical energy and vice-versa.

Piezo-electric materials commonly used in ultrasonic flaw detection are Quartz Crystal, Barium
Titanate and Lithium Sulphate.

Question 4

State 4 Applications for Ultrasound

Answer 4

Aerospace precision

Maintaining quality control

Ensuring structural integrity

Thickness Measurement

Question 5

Describe the Pulse-Echo Technique

Answer 5

A pulse of ultrasound travels through the specimen until it is reflected back to the
transducer (probe) from an interface, which can be a defect or the back wall.

The reflected sound will produce an amplitude (y-axis) which is displayed on the cathode
ray oscilloscope.

Since the velocity of the ultrasound is known, the time in terms of distance travelled can be
registered along the x-axis.

Question 6

Describe the Through Transmission Technique

Answer 6

Same basic equipment as pulse-echo but uses two separate transducers for the transmitting
and receiving functions so that they may be positioned on opposite sides of the specimen.

Receiver is used to measure variations in the amplitude of the ultrasound, transmitted
through the specimen.

Discontinuity of the specimen structure will produce areas of reduced amplitude.

Question 7

List 4 Advantages of Ultrasound

Answer 7

Results are immediate

High penetrating power

Non-hazardous to nearby personnel or material

Greater accuracy compared to other NDTs

Question 8

List 4 Disadvantages of Ultrasound

Answer 8

Parts that are rough or uneven may be difficult to inspect

Lubricant (or couplant) is required

Material should be water resistant if water is used as the lubricant / couplant

Careful attention should be given to when doing the ultrasonic test