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Ultrasonic testing

Ultrasonic testing is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Ultrasonic testing rather than just read about it. In short: Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse waves with centre frequencies ranging from 0.1-15MHz and occasionally up to 50MHz, are transmitted into materials to detect internal flaws or to characterize materials.

Ultrasonic testing — main illustration
Ultrasonic testing — illustration

Key takeaways

  • Ultrasonic testing belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Ultrasonic testing to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Ultrasonic testing from memory before moving on to harder problems.

Reference excerpt

Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse waves with centre frequencies ranging from 0.1-15MHz and occasionally up to 50MHz, are transmitted into materials to detect internal flaws or to characterize materials. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion and erosion. Ultrasonic testing is extensively used to detect flaws in welds. Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is used in many industries including steel and aluminum construction, metallurgy, manufacturing, aerospace, automotive and other transportation sectors.

History The first efforts to use ultrasonic testing to detect flaws in solid material occurred in the 1930s. On May 27, 1940, U.S. researcher Dr. Floyd Firestone of the University of Michigan 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 the 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) 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 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 affected 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

In ultrasonic testing, an ultrasound transducer connected to a diagnostic machine is passed over the object being inspected. The transducer is typically separated from the test object by a couplant 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 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 representing the intensity of the reflection and the distance, representing the arrival time 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 travelling 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.

Examples Sources: One of the examples that utilize ultrasound for proving material property is the measurement of grain size of specific material. Unlike destructive measurement, ultrasound offers methods to measure grain size in non-destructive way with even higher detection efficiency. Measurement of grain size using ultrasound can be accomplished through evaluating ultrasonic velocities, attenunations, and backscatter feature. Theoretical foundation for scattering attenunation model was developed by Stanke, Kino, and Weaver. With constant frequency, the scattering attenuation coefficient depends mainly on the grain size; Zeng et al, figured out that in pure Niobium, attenuation is linearly correlated with grain size through grain boundary scattering. This concepts of ultrasonic proving can be used to inversely resolve the grain size in the time domain when the scattering attenuation coefficient is measured from testing data, providing the non-destructive way to predict material's property with rather simple instruments.

Features

… excerpt ends here. Continue reading the full article.

Illustrations

Ultrasonic testing: An example of Ultrasonic Testing (UT) on blade roots of a V2500 IAE aircraft engine. Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special borescope tool (video probe). Step 2: Instrument settings are input. Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.
An example of Ultrasonic Testing (UT) on blade roots of a V2500 IAE aircraft engine. Step 1: The UT probe is placed on the root of the blades to be inspected with the help of a special borescope tool (video probe). Step 2: Instrument settings are input. Step 3: The probe is scanned over the blade root. In this case, an indication (peak in the data) through the red line (or gate) indicates a good blade; an indication to the left of that range indicates a crack.
Ultrasonic testing: Principle of ultrasonic testing. LEFT: A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo. RIGHT: A defect creates the third indication and simultaneously reduces the amplitude of the back wall indication. The depth of the defect is determined by the ratio D/Ep.
Principle of ultrasonic testing. LEFT: A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe, and the second due to the back wall echo. RIGHT: A defect creates the third indication and simultaneously reduces the amplitude of the back wall indication. The depth of the defect is determined by the ratio D/Ep.
Ultrasonic testing: At a construction site, a technician tests a pipeline weld for defects using an ultrasonic phased array instrument. The scanner, which consists of a frame with magnetic wheels, holds the probe in contact with the pipe by a spring. The wet area is the ultrasonic couplant that allows the sound to pass into the pipe wall.
At a construction site, a technician tests a pipeline weld for defects using an ultrasonic phased array instrument. The scanner, which consists of a frame with magnetic wheels, holds the probe in contact with the pipe by a spring. The wet area is the ultrasonic couplant that allows the sound to pass into the pipe wall.
Ultrasonic testing: Non-destructive testing of a swing shaft showing spline cracking
Non-destructive testing of a swing shaft showing spline cracking

Worked examples

Example 1 — a first encounter with Ultrasonic testing

Start with the simplest possible case. Write down what Ultrasonic testing claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Ultrasonic testing before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Ultrasonic testing ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Ultrasonic testing

In research
Ultrasonic testing appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Ultrasonic testing in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Ultrasonic testing is common in secondary-school and first-year university syllabi. It links to neighbouring topics Nondestructive testing, Ultrasound, Welding, so understanding it makes those chapters shorter.
In everyday life
Look for Ultrasonic testing outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.
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How to study Ultrasonic testing in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Ultrasonic testing means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Ultrasonic testing out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ultrasonic testing in simple terms?

Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse waves with centre frequencies ranging from 0.1-15MHz and occasionally up to 50MHz, are…

Why does Ultrasonic testing matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Ultrasonic testing?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Ultrasonic testing.

Tags

  • Nondestructive testing
  • Ultrasound
  • Welding

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