AMT501 MATERIALS AND PROCESSES NDI, U LTRASONIC I NSPECTION
Doc. AMT501, MW2011-12, Rev. O In this lesson we are going to…?Discuss Non Destructive Inspection…
?Describe Ultrasonic Inspection
?Explain Ultrasonic Inspection Procedures
?Explain Ultrasonic Inspection Procedures
?Advantages and Disadvantages
References
AC43.13-1B
Chapter 5
pages5-41through5-50 pages 5-41 through 5-50
General Textbook Chapter 11
Pages 11-18 through 11-20Ultrasonic Inspection Ultrasonic Inspection can be used on:?Plastics
?Ceramics
?Most metals
?And even babies…
Ultrasonic Inspection
?This NDT method uses high frequency sound in the range of 200 KHz to 25 MHz to detect internal defects in the part under test.
H dibl t20000H
?Humans audible range up to 20 000 Hz
?Rodents audible range up to 100 000 Hz
?Bats, whales, dolphins up to 150 000 Hz
?NDT –200 000 to 25 000 000 Hz
?Note: Hertz is a unit of frequency equal to one cycle per second Ultrasonic Inspection ?Ultrasonics is based upon the principle that a change in acoustic impedance in a material will cause a reflection of some or all of the sound beam
h lik h
?much like an echo
?Acoustic impedance is the resistance of a given medium to the passage of sound
Ultrasonic Inspection Ultrasonic Equipment Ultrasonic Inspection Ultrasonic Equipment
Inside the transducer…
Ultrasonic Inspection
How it works…
?Ultrasonic testing equipment is based on an electronic oscillator that produces AC current
ith the proper freq enc
?with the proper frequency,
?which is amplified to the proper strength,
?and sent to a transducer placed on the test material ?The transducer causes the test material to vibrate at the oscillators frequency.
?When the vibrations reach the other side of the material they bounce back and create an electrical impulse at the transducer that is displayed on the CRT Ultrasonic Inspection
The Piezoelectric Crystal
?High frequency sound is transmitted into the material by a piezoelectric crystal and changes electrical energy into mechanical energ and ise ersa
mechanical energy and vise-versa.
?The “echo” is received
?converted from sound back into electrical
?displayed on display unit (CRT or LCD)
Ultrasonic Inspection Frequencies
?Each transducer is designed to operate at a certain frequency which is shown on the transducer
?A change in frequency will change the wavelength only and not the speed of sound.
?Low frequencies will penetrate deeper than higher frequencies due to their longer wavelength
?High frequencies will detect smaller defects that may be missed by low frequencies Ultrasonic Inspection
Using Ultrasound
?There are three ways in which ultrasonic energy is induced into the test specimen.
1. (a) Pulse Echo -Direct contact on one side of the
material only
(b) Pulse Echo (Angled) -Wedge is used to angle
the transmitter
2. Through Transmission -Transmitter on one side and
receiver on the other
Ultrasonic Inspection
Using Ultrasound
?There are three ways in which ultrasonic energy is induced into the test specimen.
3. Immersion -Test piece is immersed in water to
insure good coupling between the parts surface and the transducer Ultrasonic Inspection Using Ultrasound
Ultrasonic Inspection Using Ultrasound Ultrasonic Inspection Using Ultrasound
Ultrasonic Inspection
Calibration of Equipment
?Note: No matter which method is used, a calibration must be performed before any ultrasonic inspection has validity.Ultrasonic Inspection
?The type of sound wave directed at a material is determined by the orientation of the transducer to the materials surface.
?The desired orientation can be achieved through the
g
use of acrylic wedges inserted between the transducer and the materials surface.
?When this is done a film of water or oil (couplant) should be used between the transducer and the wedge, and the wedge and the material’s surface to ensure a better contact.
Ultrasonic Inspection
The Wave
?Waves can go straight through a piece
?Longitudinal wave
?Longitudinal wave
?Waves can be angulated to travel along the surface ?Rayleigh wave or surface wave
?The wave must hit the defect near 90o for the wave to reflect back Ultrasonic Inspection Longitudinal Wave
?Sheer waves also travel out perpendicular to the longitudinal wave
Ultrasonic Inspection
Surface or Rayleigh Wave
Ultrasonic Inspection
?There are two basic systems used in ultrasonic
inspection:
?Pulse-echo System
y
?Resonance System
Ultrasonic Inspection
?Pulse-Echo
?With the pulse-echo system a cathode ray
oscilloscope or LCD is used as a fault indicator. ?A time-based signal produces a straight-line across the CRT screen
?When a pulse of energy is sent into the material, a peak occurs on this base line.
?When it echoes back another peak occurs showing the back wall Ultrasonic Inspection
?Pulse-Echo
?There is a definite relationship between the physical distance of the front and back surface of the test
i d th di t b t th k th
piece and the distance between the peaks on the
base line.
?If a fault or a crack exists between the two surfaces a portion of the sound wave will be reflected back
ahead of the original wave.
?The crack will show as a smaller peak between the
front and rear peaks.
Ultrasonic Inspection
?Pulse-Echo
?The CRT has a calibrated grid that is adjustable so the front and back surface peaks can be set on a
calibration line.
?Once the peaks have been set than any change in thickness is going to show as a change in the
distance between the peaks.
?Could be corrosion Ultrasonic Inspection Interpretation of Indications
?Front and back indications
Ultrasonic Inspection
?Resonance
?Resonance is used to measure thickness of a
material having a constant thickness and smooth f
surfaces.
?The oscillator's frequency is matched to the
resonance point of the material being tested.
?This method of inspection is effective in locating wear or corrosion.
?It is also used to ensure that plexiglass windows that have been polished to remove surface defects
maintain their minimum thickness.Ultrasonic Inspection Advantages
?Suitable for surface and subsurface defects ?Sensitive to small defects
?Immediate test results
?Little part preparation
?Wide range of material thickness can be inspected
Ultrasonic Inspection Disadvantages
?Surface to be inspected must be accessible to sonic probe
?Rough surfaces interfere with test results
Rough surfaces interfere with test results
?No permanent test record
?Test method is directional dependent on sound beam -defect orientation
?High degree of skill and experience required to set up and interpret results for varied test conditions. Ultrasonic Inspection Review
?What are two types of waves?
?Longitudinal and Surface
?Which frequency will penetrate deeper?
?Low frequency goes deeper ?Changing the frequency will change what?
?Wavelength not speed
?What types of materials can be inspected?
?Plastic, ceramics and most metals
Ultrasonic Inspection
Review
?At what angle do the waves need to hit the defect if they are going to show?
Cl t90
?Close to 90
?What will ultrasonic testing detect?
?Surface and subsurface defects plus material
thinning and thicknesses
?What are the two methods of inspection?
?Pulse-Echo and Resonance