Basic Principles of Ultrasonic Testing by yre19594

VIEWS: 1,458 PAGES: 42

									Basic Principles of Ultrasonic Testing


     Basic Principles of
     Ultrasonic Testing

    Theory and Practice


             Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Examples of oscillation
ball on        pendulum                              rotating
a spring                                             earth




                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing




              Pulse
    The ball starts to oscillate as soon as it is pushed

                  Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing




                                              Oscillation




             Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Movement of the ball over time




                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing

                                                      Frequency




                                                                        Time


 From the duration of one oscillation                     One full
 T the frequency f (number of                           oscillation T
 oscillations per second) is
 calculated:    T
                   f
                1


                        Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing

                                 The actual displacement a is
                                 termed as:
                                                      nis A  a

       a
                                                                   Time
 0         90              180                       270           360
                                                                   Phase




                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Spectrum of sound
Frequency range Hz            Description                      Example


     0 - 20                  Infrasound                      Earth quake


  20 - 20.000            Audible sound                      Speech, music

   > 20.000                  Ultrasound                   Bat, Quartz crystal




                     Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Atomic structures
          gas                         liquid                         solid




• low density               • medium density                 • high density
• weak bonding forces       • medium bonding                 • strong bonding forces
                              forces                         • crystallographic
                                                               structure


                        Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Understanding wave propagation:




Ball = atom    Spring = elastic bonding force




               Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing




T

         distance travelled



             Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing


           During one oscillation T the wave
 T         front propagates by the distance :



                               Distance travelled

  From this we derive:
       T
  c
           or
                     f  c
                                             Wave equation
                 Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Sound propagation


 Longitudinal wave                   Direction of propagation
  Direction of oscillation




                             Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Sound propagation

  Transverse wave
                                     Direction of propagation
  Direction of oscillation




                             Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Wave propagation
Longitudinal waves propagate in all kind of materials.
Transverse waves only propagate in solid bodies.
Due to the different type of oscillation, transverse waves
travel at lower speeds.
Sound velocity mainly depends on the density and E-
modulus of the material.


Air            330 m/s
Water                      1480 m/s
Steel, long                                                    5920 m/s
Steel, trans
                                                    3250 m/s




                         Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Reflection and Transmission

As soon as a sound wave comes to a change in material
characteristics ,e.g. the surface of a workpiece, or an internal inclusion,
wave propagation will change too:




                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Behaviour at an interface

       Medium 1                                        Medium 2




   Incoming wave                           Transmitted wave


   Reflected wave

                           Interface


                  Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Reflection + Transmission: Perspex - Steel
                               1,87


             Incoming wave              1,0               Transmitted wave
                                        0,87




   Reflected wave


         Perspex                                         Steel

                    Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Reflection + Transmission: Steel - Perspex


           Incoming wave                               Transmitted wave
                                       1,0


                                       0,13




                                       -0,87
     Reflected wave
        Perspex                                             Steel

                  Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Amplitude of sound transmissions:



   Water - Steel           Copper - Steel                      Steel - Air


• Strong reflection   • No reflection                     • Strong reflection
• Double transmission • Single transmission                 with inverted phase
                                                          • No transmission




                     Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Piezoelectric Effect




                                                            +
                                                                Battery




    Piezoelectrical
    Crystal (Quartz)

                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Piezoelectric Effect




                                                            +



   The crystal gets thicker, due to a distortion of the crystal lattice

                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Piezoelectric Effect




                                                        +

            The effect inverses with polarity change

                   Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Piezoelectric Effect

 Sound wave
     with
 frequency f




                                                               U(f)



An alternating voltage generates crystal oscillations at the frequency f

                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Piezoelectric Effect




                                                            Short pulse
                                                            ( < 1 µs )




A short voltage pulse generates an oscillation at the crystal‘s resonant
frequency f0

                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Reception of ultrasonic waves
A sound wave hitting a piezoelectric crystal, induces crystal
vibration which then causes electrical voltages at the crystal
surfaces.

 Electrical        Piezoelectrical
                   crystal                              Ultrasonic wave
 energy




                   Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Probes

                       socket                                  Delay / protecting face
                       crystal                                 Electrical matching
                       Damping                                 Cable




 Straight beam probe               TR-probe                         Angle beam probe


                          Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
RF signal (short)




               100 ns




                    Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
RF signal (medium)




               Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Sound field


     Crystal           Focus                                      Angle of divergence
                                  Accoustical axis
                                                                            6
D0


                  N
               Near field                                 Far field




                            Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument




           0   2     4     6      8    10



                   Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument




                                                          -    +
                                                              Uh




         0   2   4       6      8     10


                     Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument




                                                         +        -
                                                             Uh




        0   2   4      6      8     10


                    Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Ultrasonic Instrument

               +
          Uv
               -


                                                            +        -
                                                                Uh




         0         2   4     6      8      10


                       Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Block diagram: Ultrasonic Instrument

         amplifier



                                 screen
                     IP                                        horizontal
                                  BE                            sweep

                                                                 clock


                                                                 pulser
 probe

                 work piece

                          Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Sound reflection at a flaw

                                 s



 Probe
                   Sound travel path
                                                     Flaw


                                     Work piece


                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Plate testing

                                                  IP

                                                                   BE



                                                           F



                delamination                  0        2       4        6   8   10
   plate
                                                       IP = Initial pulse
                                                       F = Flaw
                                                       BE = Backwall echo




                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Wall thickness measurement




  s
                                                s


       Corrosion                   0        2       4   6   8   10




               Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Through transmission testing

                                  Through transmission signal



1   T                      R                                              1


2   T                     R                                               2
                                             0       2   4   6   8   10


         Flaw


                Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Weld inspection

                                                a = s sinß
                       F
                                                 a' = a - x           ß = probe angle
          s                                                           s = sound path
                                                                      a = surface distance
                                                 d' = s cosß          a‘ = reduced surface distance
                                                                      d‘ = virtual depth
 0   20       40   60       80     100
                                                 d = 2T - t'          d = actual depth
                                                                      T = material thickness

                                                 a
                        x                        a'

                   ß                                                               d
                                                Lack of fusion
 Work piece with welding                    s


                                 Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Straight beam inspection techniques:
    Direct contact,             Direct contact,
                                                               Fixed delay
  single element probe       dual element probe




  Through transmission                              Immersion testing




                         Krautkramer NDT Ultrasonic Systems
Basic Principles of Ultrasonic Testing
Immersion testing

                            1                            2
 surface =                                                                    water delay
sound entry

  backwall                                                                     flaw


           IP                       1                 IP                      2
                        IE                                           IE

                                    BE                                        BE
                                                                          F

       0        2   4   6       8     10             0       2   4   6    8    10

                            Krautkramer NDT Ultrasonic Systems

								
To top