Ultrasound Testing
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Ultrasound testing
History of ultrasound
Flaw detection based on ultrasound is one of the oldest non-destructive testing methods alongside X-ray gross structure analysis. Following the discovery of the piezoelectric effect (1880–1881) by the Curie brothers for measuring and generating non-stationary pressures and vibrations, the beginnings of the technical utilisation of ultrasound can be dated to around 1940. It was recognised that ultrasound interacts with the workpiece to be tested and reacts with a change in intensity and transit time. In 1942, the technical foundations were laid for time-of-flight measurement with separate transmitter and receiver sensors in through-transmission mode (Trostzange) and later for pulse-echo technology. In the years 1949–1950, Krautkrämer, Hürth, developed the first analogue ultrasonic testing device for non-destructive fault detection using pulse-echo ultrasonic technique. In 1973, Karl Deutsch released the first device with a digital display and in 1982 the Echograph with an integrated microprocessor.
Following the development of angle beam sensors (approx. 1952) and transmitter-receiver sensors (approx. 1957), welded joints and thin components could be analysed for specific manufacturing or processing-related defects. The development of ultrasonic immersion bath technology using imaging ultrasound can be dated to around 1970 and squirter technology and air-ultrasound to around 1980 [1, 2]. More recent developments in digital testing technology, phased array technology, the TOFD testing and evaluation method (Time of Flight Diffraction Technique) or guided waves prove that the physical limits of ultrasonic testing technology are far from exhausted.
Ultrasonic testing technology
Ultrasonic testing is an active acoustic testing method in which ultrasonic waves (longitudinal or transverse waves) are transmitted into a test piece using one or more sensors (sensor field) to detect internal defects (imperfections) or determine geometric dimensions (wall thickness). Using a second sensor (receiver in through-transmission technology) or after switching the transmitter to receive (pulse-echo technology), the sound waves, which have changed in transit time, frequency and intensity, are received and further processed for display purposes, utilising the inverse piezoelectric effect.
Ultrasonic testing, known in medicine as sonography, is based on the use of ultrasonic waves with a frequency > 20 kHz, whereby technical applications use the frequency range from approx. 100 kHz to 100 MHz. As the sound waves propagate in different media at different ultrasound velocities (see: ultrasonic runtime measurement) and are reflected, shadowed, refracted or scattered and weakened at media interfaces with different sound impedance (air, water, metal), these physical effects can be used to detect defects or imperfections (blowholes, inclusions), whereby generally only defects that are greater than half the wavelength (λ/2) are recognisable. These methods can be used to determine the type and size of defects based on known target values and the depth of the discontinuity in the test piece can be determined using time-of-flight measurement. However, due to different acoustic impedances at external interfaces, coupling agents (oil, water) are usually required to introduce the ultrasound into the test piece, which minimise the reflection of the ultrasound at the surface [3−6] or improve the transmission of sound waves into the solid.
Ultrasonic sensors
Depending on the application and type of wave, different ultrasonic sensors are used in practice:
- Standard sensors
- Angle sensors
- Transmitter (S)-receiver (E) sensors
- Composite sensors
- Shock wave sensors
- Immersion bath sensors
- Phased array sensors
Imaging visualisation
The simplest display method in ultrasonic testing is the A-scan, which represents the square of the HF-scan. Scanning imaging test methods ( immersion bath, phased array technology or air ultrasound) can be used to generate the B-, C- and D-scan or the F-scan with significantly improved informative value through frequency-related evaluation. Special inspection and evaluation techniques such as TOFD (time-of-flight diffraction technique) or SAFT (Synthetic Aperture Focusing Technique) are also available.
In principle, ultrasonic testing is standardised in ISO 16810 and the terminology used is standardised in DIN EN 1330-4, whereby special standards apply for the various applications on welded joints, forgings or wall thickness measurement, although mostly only for metallic materials [7, 8]. There are currently no binding standards for ultrasonic testing of plastics.
Qualification of ultrasonic inspectors
A personnel certification (DPZ certificate), usually from the German Society for Non-Destructive Testing – DGZfP, is required to carry out ultrasonic testing and is valid for 5 years for a specific testing method [9]. There are 3 qualification levels 1 to 3 (Level) for ultrasonic testing UT, which are also adapted to the various areas of application (e.g. aerospace industry, welding technology or cast part and pipe production).
See also
- Non-destructive polymer testing
- Acoustic properties
- Ultrasound – Elastic parameters
- Air-ultrasound
- Ultrasound runtime measurement
References
| [1] | Husarek, V., Castel, J. G.: Beitrag zur Geschichte der Ultraschallprüfung in Deutschland und Frankreich. DGZfP-Jahrestagung „Zerstörungsfreie Werkstoffprüfung“ 2001, Sofranell, Frankreich, Proceedings 75-CD |
| [2] | Guicking, D.: Erwin Meyer – Ein bedeutender deutscher Akustiker – Biographische Notizen. Universitätsdrucke, Universitätsverlag, Göttingen (2012), (http://www.guicking.de/dieter/Erwin-Meyer.pdf) (accessed on 26/05/2025) |
| [3] | Krautkrämer, J., Krautkrämer H.: Werkstoffprüfung mit Ultraschall. Springer, Berlin (1986), (ISBN 978-3-662-10909-0) |
| [4] | Deutsch, V., Platte, M., Vogt, M.: Ultraschallprüfung – Grundlagen und industrielle Anwendungen. Springer, Berlin (1997), (ISBN 3-540-62072-9; see AMK-Library under M 45) |
| [5] | Matthies, K. u. a.: Dickenmessung mit Ultraschall. DVS-Verlag GmbH, 2nd Edition, Berlin (1998), (ISBN 3-87155-940-7; see AMK-Library under M 44) |
| [6] | Schiebold, K.: Zerstörungsfreie Werkstoffprüfung – Ultraschallprüfung. Springer, Berlin (2014), (ISBN 978-3-662-44699-7) |
| [7] | ISO 16810 (2024-10): Non-destructive Testing – Ultrasonic Testing – General Principles |
| [8] | DIN EN 1330-4 (2010-05): Non-destructive Testing – Terminology – Part 4: Terms Used in Ultrasonic Testing (withdrawn; replaced by ISO/DIS 5577 (2024-09-Draft) |
| [9] | ISO 9712 (2021-12): Non-destructive Testing – Qualification and Certification of NDT Personnel |