1. Ultrasonic Testing
This technique is used for the detection of internal surface (particularly distant surface) defects in sound conducting materials. In this method high frequency sound waves are introduced into a material and they are reflected back from surface and flaws. Reflected sound energy is displayed versus time, and inspector can visualize a cross section of the specimen showing the depth of features.

2. Basic Principle of Ultrasonic Testing
A typical UT system consists of several functional units, such as the pulser/receiver, piezoelectric transducer, and display devices. A pulser/receiver is an electronic device that can produce high voltage electrical pulses. Driven by the pulser, the transducer generates high frequency ultrasonic energy. The sound energy is introduced and propagates through the materials in the form of waves. When there is a discontinuity (such as a crack) in the wave path, part of the energy will be reflected back from the flaw surface. The reflected wave signal is transformed into an electrical signal by the piezoelectrical transducer and is displayed on a screen. 2

3. Basic Principle of Ultrasonic Testing
In the figure below, the reflected signal strength is displayed versus the time from signal generation, when a echo was received. Signal travel time can be directly related to the distance. From the signal, information about the reflector location, size, orientation and other features can sometimes be gained. 2 4 6 8 10
initial
pulse
Piezoelectric Transducer
back surface
echo
crack
echo
crack
plate
Oscilloscope, or flaw detector screen

4. Piezoelectric Transducer
A transducer is a device that converts energy from one form to another. Presently, piezoelectric material is commonly used as a basic component of transducers. A piezoelectric element is a crystal which delivers a voltage when mechanical force is applied between its faces, and it deforms mechanically when voltage is applied between its faces. Because of these characteristics piezoelectric element is capable of acting as both a sensing and a transmitting element. Piezoelectric transducers have been conventionally used to convert electric signals into sound wave, or to convert sound wave into electric signals.

5. Piezoelectric Transducer
case
Signal wire
Piezoelectric element

6. Test Techniques: Normal and Angle Beam
In normal beam testing, the sound beam is introduced into the test article at 90 degree to the surface.
In angle beam testing, the sound beam is introduced into the test article at some angles other than 90.
The choice between normal and angle beam inspection usually depends on two considerations:
The orientation of the feature of interest – the sound should be directed to produce the largest reflection from the feature.
Obstructions on the surface of the part that must be worked around.

7. Couplant
A couplant is a material (usually liquid) that facilitates the transmission of ultrasonic energy from the transducer into the test specimen. Couplant is generally necessary because the acoustic impedance mismatch between air and solids (i.e. such as the test specimen) is large. The couplant displaces the air and makes it possible to get more sound energy into the test specimen so that a usable ultrasonic signal can be obtained. In contact ultrasonic testing a thin film of oil, glycerin or water is generally used between the transducer and the test surface

8. Calibration Standards
Calibration is a operation of configuring the ultrasonic test equipment to known values. This provides the inspector with a means of comparing test signals to known measurements.
Calibration standards come in a wide variety of material types, and configurations due to the diversity of inspection applications.
The following slides provide examples of specific types of standards.

9. Calibration Standards
Thickness calibration standards may be flat or curved for pipe and tubing applications, consisting of simple variations in material thickness.
ASTM Distance/Area Amplitude
Distance/Area Amplitude standards utilize flat bottom holes or side drilled holes to establish known reflector size with changes in sound path form the entry surface.
IIW
This calibration standards for use in angle beam inspections when flaws are not parallel to entry surface.

10. Advantages of Ultrasonic Testing
Thickness and lengths up to 30 ft can be tested.
Position, size and type of defect can be determined.
Instant test results.
Portable.
Capable of being fully automated.
Access to only one side necessary.

11. Limitations of Ultrasonic Testing
The operator can decide whether the test piece is defective or not while the test is in progress.
Considerable degree of skill necessary to obtain the fullest information from the test.
Very thin sections can prove difficult.