![NDT test of an V2500 engine blade route](https://upload.wikimedia.org/wikipedia/commons/5/59/NDT_test_of_an_V2500_engine_blade_route.jpg)
Ultrasonic testing (UT) is a family of
non-destructive testing
Nondestructive testing (NDT) is any of a wide group of analysis techniques used in science and technology industry to evaluate the properties of a material, component or system without causing damage.
The terms nondestructive examination (NDE), n ...
techniques based on the propagation of
ultrasonic
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...
waves in the object or material tested. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are transmitted into materials to detect internal flaws or to characterize materials. A common example is
ultrasonic thickness measurement
In the field of industrial ultrasonic testing, ultrasonic thickness measurement (UTM) is a method of performing non-destructive measurement (gauging) of the local thickness of a solid element (typically made of metal, if using ultrasound testing ...
, which tests the thickness of the test object, for example, to monitor pipework
corrosion
Corrosion is a natural process that converts a refined metal into a more chemically stable oxide. It is the gradual deterioration of materials (usually a metal) by chemical or electrochemical reaction with their environment. Corrosion engine ...
.
Ultrasonic testing is often performed on steel and other
metals
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
and alloys, though it can also be used on
concrete
Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...
, wood and composites, albeit with less resolution. It is used in many industries including steel and aluminium construction, metallurgy, manufacturing,
aerospace
Aerospace is a term used to collectively refer to the atmosphere and outer space. Aerospace activity is very diverse, with a multitude of commercial, industrial and military applications. Aerospace engineering consists of aeronautics and astrona ...
,
automotive and other
transportation
Transport (in British English), or transportation (in American English), is the intentional movement of humans, animals, and goods from one location to another. Modes of transport include air, land (rail and road), water, cable, pipeline, ...
sectors.
History
The first efforts to use ultrasonic testing to detect flaws in solid material occurred in the 1930s.
[''Nondestructive Flaw Detection in Metallic Components'' Quality magazine August 2015 issue Pages 31-32 by Dan DeVries] On May 27, 1940, U.S. researcher Dr.
Floyd Firestone of the
University of Michigan
, mottoeng = "Arts, Knowledge, Truth"
, former_names = Catholepistemiad, or University of Michigania (1817–1821)
, budget = $10.3 billion (2021)
, endowment = $17 billion (2021)As o ...
applies for a U.S. invention patent for the first practical ultrasonic testing method. The patent is granted on April 21, 1942 as U.S. Patent No. 2,280,226, titled "Flaw Detecting Device and Measuring Instrument". Extracts from the first two paragraphs of the patent for this entirely new nondestructive testing method succinctly describe the basics of such ultrasonic testing. "My invention pertains to a device for detecting the presence of inhomogeneities of density or elasticity in materials. For instance if a casting has a hole or a crack within it, my device allows the presence of the flaw to be detected and its position located, even though the flaw lies entirely within the casting and no portion of it extends out to the surface. ... The general principle of my device consists of sending high frequency vibrations into the part to be inspected, and the determination of the time intervals of arrival of the direct and reflected vibrations at one or more stations on the surface of the part."
James F. McNulty (U.S. radio engineer)
Fluoroscopy () is an imaging technique that uses X-rays to obtain real-time moving images of the interior of an object. In its primary application of medical imaging, a fluoroscope () allows a physician to see the internal structure and function ...
of Automation Industries, Inc., then, in El Segundo, California, an early improver of the many foibles and limits of this and other nondestructive testing methods, teaches in further detail on ultrasonic testing in his U.S. Patent 3,260,105 (application filed December 21, 1962, granted July 12, 1966, titled “Ultrasonic Testing Apparatus and Method”) that “Basically ultrasonic testing is performed by applying to a piezoelectric crystal
transducer
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and contr ...
periodic electrical pulses of ultrasonic frequency. The crystal vibrates at the ultrasonic frequency and is mechanically coupled to the surface of the specimen to be tested. This coupling may be effected by immersion of both the transducer and the specimen in a body of liquid or by actual contact through a thin film of liquid such as oil. The ultrasonic vibrations pass through the specimen and are reflected by any discontinuities which may be encountered. The echo pulses that are reflected are received by the same or by a different transducer and are converted into electrical signals which indicate the presence of the defect.” To characterize microstructural features in the early stages of fatigue or creep damage, more advanced nonlinear ultrasonic tests should be employed. These nonlinear methods are based on the fact that an intensive ultrasonic wave is getting distorted as it faces micro damages in the material. The intensity of distortion is correlated with the level of damage. This intensity can be quantified by the acoustic nonlinearity parameter (β). β is related to first and second harmonic amplitudes. These amplitudes can be measured by harmonic decomposition of the ultrasonic signal through fast Fourier transformation or wavelet transformation.
How it works
![Ultrasonic pipeline test](https://upload.wikimedia.org/wikipedia/commons/9/95/Ultrasonic_pipeline_test.jpg)
In ultrasonic testing, an ultrasound
transducer
A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another.
Transducers are often employed at the boundaries of automation, measurement, and contr ...
connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant
[https://www.nde-ed.org/EducationResources/CommunityCollege/Ultrasonics/EquipmentTrans/Couplant.htm ''Couplant'' Iowa State University - Center for Non-Destructive Evaluation retrieved 8//1/2021] such as a gel, oil or water,
[ as in immersion testing. However, when ultrasonic testing is conducted with an Electromagnetic Acoustic Transducer (EMAT) the use of couplant is not required.
There are two methods of receiving the ultrasound waveform: reflection and ]attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable att ...
. In reflection (or pulse-echo) mode, the transducer performs both the sending and the receiving of the pulsed waves as the "sound" is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the object or from an imperfection within the object. The diagnostic machine displays these results in the form of a signal with an amplitude
The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of amplit ...
representing the intensity of the reflection and the distance, representing the arrival time Time of arrival (TOA or ToA) is the absolute time instant when a radio signal emanating from a transmitter reaches a remote receiver.
The time span elapsed since the time of transmission (TOT or ToT) is the ''time of flight'' (TOF or ToF).
Time diff ...
of the reflection. In attenuation (or through-transmission) mode, a transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of sound transmitted, thus revealing their presence. Using the couplant increases the efficiency of the process
by reducing the losses in the ultrasonic wave energy due to separation between the surfaces.
Features
Advantages
#High penetrating power, which allows the detection of flaws deep in the part.[
#High sensitivity, permitting the detection of extremely small flaws.][
#Greater accuracy than other nondestructive methods in determining the depth of internal flaws and the thickness of parts with parallel surfaces.
#Some capability of estimating the size, orientation, shape and nature of defects.
#Some capability of estimating the structure of alloys of components with different acoustic properties
# Non-hazardous to operations or to nearby personnel and has no effect on equipment and materials in the vicinity.
#Capable of portable or highly automated operation.
#Results are immediate. Hence on the spot decisions can be made.][
#It needs to access only one surface of the product that is being inspected.][
]
Disadvantages
#Manual operation requires careful attention by experienced technicians. The transducers alert to both normal structure of some materials, tolerable anomalies of other specimens (both termed “noise”) and to faults therein severe enough to compromise specimen integrity. These signals must be distinguished by a skilled technician, possibly requiring follow up with other nondestructive testing methods.[U.S. Patent 3,260,105 for Ultrasonic Testing Apparatus and Method to James F. McNulty at lines 37-48 and 60-72 of Column 1 and lines 1-4 of Column 2.]
#Extensive technical knowledge is required for the development of inspection procedures.[
#Parts that are rough, irregular in shape, very small or thin, or not homogeneous are difficult to inspect.
#Surface must be prepared by cleaning and removing loose scale, paint, etc., although paint that is properly bonded to a surface need not be removed.
#Couplants are needed to provide effective transfer of ultrasonic wave energy between transducers and parts being inspected][ unless a non-contact technique is used. Non-contact techniques include Laser and Electro Magnetic Acoustic Transducers (]EMAT
Electromagnetic acoustic transducer (EMAT) is a transducer for non-contact acoustic wave generation and reception in conducting materials. Its effect is based on electromagnetic mechanisms, which do not need direct coupling with the surface of th ...
).
#Equipment can be expensive [
#Requires reference standards and calibration][
]
Standards
;International Organization for Standardization
The International Organization for Standardization (ISO ) is an international standard development organization composed of representatives from the national standards organizations of member countries. Membership requirements are given in Ar ...
(ISO)
* ISO 2400: ''Non-destructive testing - Ultrasonic testing - Specification for calibration block No. 1'' (2012)
* ISO 7963: ''Non-destructive testing — Ultrasonic testing — Specification for calibration block No. 2'' (2006)
* ISO 10863: ''Non-destructive testing of welds -- Ultrasonic testing -- Use of time-of-flight diffraction technique (TOFD)'' (2011)
* ISO 11666: ''Non-destructive testing of welds — Ultrasonic testing — Acceptance levels'' (2010)
* ISO 16809: ''Non-destructive testing -- Ultrasonic thickness measurement'' (2012)
* ISO 16831: ''Non-destructive testing -- Ultrasonic testing -- Characterization and verification of ultrasonic thickness measuring equipment'' (2012)
* ISO 17640: ''Non-destructive testing of welds - Ultrasonic testing - Techniques, testing levels, and assessment'' (2010)
* ISO 22825, ''Non-destructive testing of welds - Ultrasonic testing - Testing of welds in austenitic steels and nickel-based alloys'' (2012)
* ISO 5577: ''Non-destructive testing -- Ultrasonic inspection -- Vocabulary'' (2000)
;European Committee for Standardization
The European Committee for Standardization (CEN, french: Comité Européen de Normalisation) is a public standards organization whose mission is to foster the economy of the European Single Market and the wider European continent in global tr ...
(CEN)
*EN 583, ''Non-destructive testing - Ultrasonic examination''
*EN 1330-4, ''Non destructive testing - Terminology - Part 4: Terms used in ultrasonic testing''
*EN 12668-1, ''Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 1: Instruments''
*EN 12668-2, ''Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 2: Probes''
*EN 12668-3, ''Non-destructive testing - Characterization and verification of ultrasonic examination equipment - Part 3: Combined equipment''
*EN 12680, ''Founding - Ultrasonic examination''
*EN 14127, ''Non-destructive testing - Ultrasonic thickness measurement''
(Note: Part of CEN standards in Germany accepted as DIN EN, in Czech Republic as CSN EN.)
See also
* Non-Contact Ultrasound
*Phased array ultrasonics
Phased array ultrasonics (PA) is an advanced method of ultrasonic testing that has applications in medical imaging and industrial nondestructive testing. Common applications are to noninvasively examine the heart or to find flaws in manufac ...
*Time-of-flight diffraction ultrasonics
Time-of-flight diffraction (TOFD) method of ultrasonic testing is a sensitive and accurate method for the nondestructive testing of welds for defects. TOFD originated from tip diffraction techniques which were first published by Silk and Liddin ...
(TOFD)
* (TOF)
*Internal rotary inspection system
Internal rotary inspection system (IRIS) is an ultrasonic method for the nondestructive testing of pipes and tubes. The IRIS probe is inserted into a tube that is flooded with water, and the probe is pulled out slowly as the data is displayed and ...
(IRIS) ultrasonics for tubes
* EMAT Electromagnetic Acoustic Transducer
*ART (Acoustic Resonance Technology)
Acoustic resonance technology (ART) is an acoustic inspection technology developed by Det Norske Veritas over the past 20 years. ART exploits the phenomenon of half-wave resonance, whereby a suitably excited resonant target (such as a pipeline wa ...
References
Further reading
* Albert S. Birks, Robert E. Green, Jr., technical editors ; Paul McIntire, editor. ''Ultrasonic testing'', 2nd ed. Columbus, OH : American Society for Nondestructive Testing
The American Society for Nondestructive Testing, Inc. or ASNT is a technical society for nondestructive testing (NDT) professionals. ASNT evolved from ''The American Industrial Radium and X-ray Society'' which was founded in 1941. Its headquarters ...
, 1991. .
* Josef Krautkrämer, Herbert Krautkrämer. ''Ultrasonic testing of materials'', 4th fully rev. ed. Berlin; New York: Springer-Verlag, 1990. .
* J.C. Drury. ''Ultrasonic Flaw Detection for Technicians'', 3rd ed., UK: Silverwing Ltd. 2004. (Se
Chapter 1
online (PDF, 61 kB)).
* Nondestructive Testing Handbook, Third ed.: Volume 7, Ultrasonic Testing. Columbus, OH: American Society for Nondestructive Testing.
* Detection and location of defects in electronic devices by means of scanning ultrasonic microscopy and the wavelet transform measurement, Volume 31, Issue 2, March 2002, Pages 77–91, L. Angrisani, L. Bechou, D. Dallet, P. Daponte, Y. Ousten
*
{{Authority control
Nondestructive testing
Ultrasound
Welding