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Everything you Want to Know About Ultrasonic Testing

In this blog post, you’ll read:This ultimate guide answers all your ultrasonic testing questions to help you further understand this beneficial non-destructive testing method.

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Have you always had questions about ultrasonic testing that you wished someone would clarify for you?

While ultrasonic testing has enjoyed various applications across many industries, and after numerous benefits, many individuals that sometimes include non-destructive testing professionals still have unanswered questions about ultrasonic testing. The benefits of ultrasonic testing as a non-destructive testing method are numerous but understanding its working principles and unique applications is also very advantageous. This ultimate guide answers all your ultrasonic testing questions to help you further understand this beneficial non-destructive testing method.

So, if you are ready, let’s dive in together. 


⒈ What is ultrasonic testing? 


what is ultrasonic testing


Ultrasonic testing, abbreviated as UT, is a method for evaluating a test component’s thickness or its internal structure by employing high-frequency sound waves. The frequencies, or pitch, utilized for ultrasonic testing are several orders of magnitude higher than the limit of human hearing, often ranging from 500 kHz to 20 MHz.

Ultrasonic testing, a non-destructive testing method, is perfect for detecting flaws, defects, and welded seams when destroying the target sample is not an option.

Aside from discovering flaws in production samples, frequent UT inspections are ideal for monitoring for corrosion in existing equipment, such as pipelines, and are an essential component of any predictive maintenance program. Many ultrasonic flaw detectors contain a trigonometric function that enables rapid and precise location detection of flaws when doing shear wave inspections. Furthermore, certain ultrasonic testing devices may adjust the measurement depending on the material’s surface conditions


➤ Related Article: Phased Array Ultrasonic Testing



⒉ How does it work?


High-frequency sound waves are mainly directed, and they will travel through a material (such as steel or plastic) until they come into contact with another medium (such as air). At that point, they will reflect on their source. Studying these reflections makes it possible to determine the thickness of a test piece or detect evidence of faults or other hidden internal flaws.

An ultrasound transducer linked to a piece of diagnostic equipment is passed over the item being examined during ultrasonic testing. In most cases, a couplant (such as oil) or water separates the transducer from the test item, as in immersion testing.

Interestingly, the ultrasound waveform may be received in reflection and attenuation.

In reflection (or pulse-echo) mode, the transducer sends and receives pulsed waves as the “sound” is reflected in the instrument. Reflected ultrasound is caused by an interface, such as the item’s back wall or a flaw inside the object. The diagnostic machine shows these data in the form of a signal with an amplitude reflecting the strength of the reflection and a distance representing the arrival time of the reflection.

A transmitter delivers ultrasound via one surface in attenuation (or through-transmission) mode. At the same time, a separate receiver measures the quantity that has reached it on another surface after traveling through the medium. Imperfections or other variables in the area between the transmitter and receiver decrease the volume of sound transmitted, exposing their existence. Using the couplant improves the process’s efficiency by lowering ultrasonic wave energy losses caused by surface separation



⒊ Why is it used?


Ultrasonic testing, a non-destructive testing method, is perfect for finding flaws and defects without causing damage to the item or substance being examined. Periodic ultrasonic inspections may also check for corrosion or the progression of recognized flaws, possibly preventing a part, component, or complete asset from failing. It is employed in various sectors such as aerospace, automotive, construction, medical, metallurgy, and manufacturing. 



⒋ What types of materials can be tested?


Ultrasonic testing is frequently utilized in industrial applications on metals, polymers, composites, and ceramics. Wood and paper products are the only typical technical materials that are inappropriate for ultrasonic testing with traditional equipment. Ultrasonic technology is also commonly employed in diagnostic imaging and medical research in the biomedical area. Many rough-textured and smooth materials are subjected to ultrasonic testing to guarantee that they fulfill quality production standards. There are still unique ultrasonic testing and inspection devices designed for particular and unique testing situations.



⒌ What are the advantages of ultrasonic testing?


Ultrasonic testing has many benefits.

  • It is non-destructive. Thus, samples are retained.
  • The test piece does not need to be cut, sectioned, or subjected to potentially harmful chemicals.
  • Unlike mechanical thickness instruments such as calipers and micrometers, access to just one side is necessary.
  • Unlike radiography, there are no known health risks connected with ultrasonic testing.
  • The findings are extremely reproducible and dependable when a test is set up correctly.
  • High penetration power allows for defect identification deep into a component. 
  • High sensitivity, which allows for the detection of minor flaws
  • Greater accuracy in determining the depth of internal flaws and the thickness of parts with parallel surfaces when compared to other non-destructive testing methods 
  • Capable of estimating size, shape, orientation, and nature of defects 
  • Capable of evaluating alloy structures of components with differing acoustic properties
  • Immediate findings may be received, allowing for quick choices


➤ Related Article: What’s the Advantage and Limitation of Ultrasonic Testing?



⒍ What are some limitations of ultrasonic testing?


However, there are a few limits to ultrasonic testing, which are as follows:

  • Ultrasonic fault detection necessitates a qualified operator who can set up a test using suitable reference standards and accurately interpret the findings.
  • Inspection of certain complicated geometries may be difficult.
  • Ultrasonic thickness gauges must be calibrated in relation to the material under consideration.
  • Multiple setups may be required for applications needing a broad range of thickness measurement or measurement of acoustically varied materials.


Ultrasonic thickness gauges are more costly than mechanical thickness gauges.

  • Inspection and data interpretation needs the use of skilled technicians.
  • False-positive findings, also known as false signals, may occur as a consequence of acceptable irregularities and the component geometry itself. 
  • Rough, irregularly shaped, extremely tiny or thin, or not homogenous objects are challenging to analyze.
  • Loose scaling or paint must be removed before testing may begin, but clean, well-bonded paint can be left in place.
  • Complaints are necessary for standard UT testing.
  • UT may be less sensitive than radiographic testing for volumetric flaws, especially metal inclusions testing.



⒎ What are some applications of ultrasonic testing?


What are the applications of ultrasonic testing


Ultrasonic testing offers various uses in several sectors, including testing the material or component’s integrity. This may entail testing welds to see whether there are any discontinuities and determining the specific location of a discontinuity in a weld. Its performance is suitable for ferrous and non-ferrous materials, as well as thicker parts and those accessible only from one side. UT can also identify finer imperfections and planar flaws that radiography testing may not be able to detect as easily.

Furthermore, ultrasonic testing has a wide range of applications in aerospace, automotive, construction, rail, medical, and oil & gas. This testing method may need a high degree of operator training and competence, and it is reliant on the development and implementation of appropriate testing protocols. 



⒏ What is an ultrasonic transducer?


Any device that transfers one kind of energy into another is a transducer. Electrical power is converted into mechanical vibrations (sound waves) using an ultrasonic transducer, and sound waves are converted back into electrical energy. They are typically compact, portable assemblies that come in various frequencies and designs to meet particular test requirements. However, their most outstanding value is in their capacity to broadcast and receive ultrasonic signals, which is required for any ultrasonic defect detector to work. They may exist as single-element transducers or multi-element transducers inside a fault detector. The critical point is that they are unique in defect detecting precision and agility. 



⒐ What is an ultrasonic flaw detector?


Sound waves flowing through a material will reflect flaws such as fractures and vacancies in predictable patterns. An ultrasonic flaw detector is a device that produces and analyzes ultrasonic signals to provide a waveform display that a trained operator may use to discover hidden flaws in a test item. The operator recognizes a good part’s typical reflection pattern and then searches for alterations in that pattern that may reveal flaws.



⒑ What defects can you find with an ultrasonic detector?


What defects can you find with an ultrasonic detector


Ultrasonic defect detectors can discover and quantify a broad range of fractures, voids, dis-bonds, inclusions, and other structural integrity issues. The smallest detectable defect size in a specific application is determined by the material being evaluated and the kind of problem under consideration. However, various businesses choose the sort of flaws they attempt to uncover depending on the material and its industrial demands. Metals, for example, are used because of their capacity to bear the stress, and the kind and thickness of metal define the amount of stress resistance it can provide. As a result, flaws like fractures and corrosion might restrict certain metallic qualities. Importantly, for welded joints where anomalies and flaws may reduce joint strength, defects such as porosity, inclusions, and fractures become the crucial defect under investigation utilizing an ultrasonic flaw detector. 



⒒ What is an ultrasonic thickness gauge?


An ultrasonic thickness gauge is an instrument that generates sound pulses in a test piece and waits for the time interval till the echoes are heard and carefully measured. The gauge, which has been programmed with the speed of sound in the test material, uses the sound velocity information and the observed time interval to compute thickness using the simple equation [distance] = [velocity] multiplied by [time]. The use of an ultrasonic thickness gauge has multiple advantages. It operates in various sectors, including the quick assessment of material thickness in aviation, petrochemical, oil and gas, and the automobile industry.  



⒓ How accurate are ultrasonic thickness gauges?


Commercial ultrasonic gauges can attain a degree of precision as high as 0.001 mm (0.00004 in.) and 0.025 mm (0.001 in.) or higher in most common engineering materials under ideal circumstances. The homogeneity of sound velocity in the test material, the degree of sound scattering or absorption, the surface quality, and the precision and care with which the instrument has been calibrated for the application at hand are factors influencing accuracy. These considerations may also impact the ultrasonic thickness gauge used for a specific thickness measuring procedure. Furthermore, the degree of precision of an ultrasonic thickness gauge often influences the cost of the ultrasonic thickness gauge with greater accuracy, generally costing more than an ultrasonic thickness gauge with lower accuracy. More automation may also improve the accuracy and cost of an ultrasonic thickness gauge by removing the human error that is often brought into a manual instrument.



⒔ What is an ultrasonic scanner?


An ultrasonic scanner is a non-destructive testing instrument that uses ultrasound principles to find flaws in industrial components and products, particularly those with limited access. Ultrasonic scanners work by projecting and receiving ultrasonic waves, and analyzing the returned signal helps identify the nature of the substance under investigation. All procedures use one of three types of inspection inclusion: transmissions, pulse-echo, and resonance. They only need access to one side of the sample material under investigation to make their observations. Furthermore, ultrasonic scanners are often fitted with a screen to monitor the received pulse signals and make a rapid judgment of the type of imperfection existing in the material under investigation. For the most part, ultrasonic scanners use a complete collection of software modules to carry out their operations and aid in analysis in both industrial and laboratory settings. 



⒕ Why should you use an ultrasonic scanner for NDT inspection?


There are various reasons you should use an ultrasonic scanner for NDT inspections. Still, all of them are related to the advantages that ultrasonic scanners provide when used for NDT inspection. The first of these advantages is its precision since ultrasonic scanners can detect minor and major flaws in an item. Ultrasonic scanners may help save production costs since the sample under evaluation is never damaged during the examination. Similarly, the constraint of just employing visual inspection is solved using ultrasonic scanners. But that isn’t all. The ultrasonic scanner also provides operator safety since it does not offer any risk to persons, such as radioactive injury. Furthermore, ultrasonic can discover flaws deeper than other NDT techniques and instruments because it can locate defects in difficult-to-reach regions. 



⒖ What are other types of ultrasound instruments available? 


In addition to the ultrasonic scanner used for NDT inspection, there is a variety of additional ultrasonic-based equipment. Ultrasonic imaging systems, for example, are used to create highly detailed images akin to X-rays by mapping the interior structure of a component using sound waves. In industrial settings, phased array technology, initially designed for medical diagnostic imaging, is utilized to make cross-sectional images. The aerospace industry and metalworking suppliers use large scanning equipment to detect hidden flaws in raw materials and final items. Ultrasonic pulses and receivers, and signal analyzers are employed in a wide range of materials research applications. Ultrasonic thickness gauges use the ultrasound principle to assess the thickness of different objects and components to determine whether they fit their design parameters. On the other hand, coating thickness gauges validate the consistency of protective coatings on equipment and parts to guarantee that they fulfill specifications or establish their actual value. Other ultrasound-based equipment includes flawed specimens, calibration blocks, and ultrasonic flaw detectors. 




In conclusion, understanding and knowledge of ultrasonic testing are very important. It helps you carry out non-destructive inspections using ultrasonic devices and employing the right tool for the job. Consequently, knowing the critical settings for ultrasonic equipment and essential factors that affect the accuracy of the ultrasonic testing result will prove vital for an efficient quality assessment procedure. 

Ultimately, the budget, level of accuracy required for the ultrasonic test, and the manufacturer all have their part in the eventual result. Now that you are equipped with all this information, what is your next move? 

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