Badania_ultradzwiekowe_Krautkramer.pdf

(2403 KB) Pobierz
Nondestructive Material Testing
with Ultrasonics
Introduction to the Basic Principles
°
Contents
°
Contents
Nondestructive Material Testing with Ultrasonics
Introduction to the Basic Principles
Michael Berke
Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Why use ultrasonics for nondestructive material testing? . . . . . . . . . . . . . 5
Ultrasonic testing tasks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Detection of discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Method of testing and instrument technology . . . . . . . . . . . . . . . . . . . . . 10
The ultrasonic flaw detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Near resolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
The probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Refraction and mode conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Characteristics of angle-beam probes . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
The TR probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Locating discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibration of the instrument . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibration with a straight-beam probe . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Calibration with a TR probe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Calibration with an angel-beam probe . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Locating reflectors with an angle-beam probe . . . . . . . . . . . . . . . . . . . . 28
Evaluation of discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Scanning method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Evaluation of small discontinuities: The DGS method . . . . . . . . . . . . . . . 30
Sound attenuation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
The reference block method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Comparison of echo amplitudes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Distance amplitude curve . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
Diagnosis of indications (outlook) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
Reference list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
1.
2.
3.
4.
4.1
4.2
4.3
4.4
4.5
4.6
5.
5.1
5.1.1
5.1.2
5.1.3
5.1.4
6.
6.1
6.2
6.3
6.4
6.4.1
6.4.2
7.
8.
3
Introduction
Nondestructive material testing with
ultrasonics
is more than 40 years old.
From the very first examinations, using
ultrasonic oscillations for detection of flaws
in different materials, it has become a
classical test method based on measu-
rements with due regard to all the impor-
tant influencing factors. Today it is expec-
ted that ultrasonic testing, supported by
great advances in instrument technology,
give
reproducible test
results within narrow
tolerances. This assumes exact know-
ledge of the influencing factors and the
ability to apply these in testing technology.
Not all influences have to be seriously
regarded by the operator. In many cases
some of the influences can be neglected
without exceeding the permitted measu-
rement tolerances. Due to this, the test se-
quence is simplified and the testing time
reduced. Despite this, the future belongs
to the qualified operator who carries out
his task responsibly and who continuously
endeavours to keep his knowledge at the
latest state of the art
4
°
Contents
1.
Why use ultrasonics for
nondestructive material
testing?
At the beginning of the fifties the technician
only knew radiography (x-ray or radioac-
tive isotopes) as a method for detection of
internal flaws in addition to the methods
for nondestructive testing of material sur-
faces, e.g.
the dye penetrant and ma-
gnetic particle method.
After the Second
World War the ultrasonic method, as de-
scribed by
Sokolov
in 1935 and applied by
Firestone
in 1940, was further developed
so that very soon instruments were avail-
able for ultrasonic testing of materials.
The ultrasonic principle is based on the
fact that solid materials are good conduc-
tors of sound waves. Whereby the waves
are not only reflected at the interfaces but
also by internal flaws (material separa-
tions, inclusions etc.). The interaction ef-
fect of sound waves with the material is
stronger the smaller the wave length, this
means the higher the frequency of the
wave.
λ
=
c
f
other hand special test problems are sol-
ved, the same as before, using radiogra-
phy. In cases where the highest safety re-
quirements are demanded (e.g. nuclear
power plants, aerospace industry) both
methods are used.
2.
Ultrasonic testing tasks
Is there a primary classification of tasks
assigned to the ultrasonic operator? If we
limit ourselves to testing objects for
possible material flaws then the classifica-
tion is as follows:
1.
2.
3.
4.
Detection of reflectors
Location of reflectors
Evaluation of reflectors
Diagnosis of reflectors
(reflector type,
orientation, etc.)
c = Sound velocity [km/s]
f = Frequency [MHz]
λ
= Wave lenght [mm]
This means that ultrasonic waves must be
used in a frequency range between about
0.5 MHz and 25 MHz and that the resulting
wave length is in mm. With lower frequen-
cies, the interaction effect of the waves
with internal flaws would be so small that
detection becomes questionable. Both test
methods, radiography and ultrasonic test-
ing, are the most frequently used methods
of testing different test pieces for internal
flaws, partly covering the application
range and partly extending it.
This means that today many volume tests
are possible with the more economical and
non-risk ultrasonic test method, on the
Instead of using the word
"reflector",
the
ultrasonic operator very often uses the
term
"discontinuity".
This is defined as
being an "irregularity in the test object
which is suspected as being a flaw". In
reality, only after location, evaluation and
diagnosis has been made, can it be deter-
mined whether or not there is a flaw which
effects the purpose of the test object. The
term "discontinuity" is therefore always
used as long as it is not certain whether it
concerns a flaw which means a non-per-
missible irregularity.
°
Contents
5

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin