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We are committed to develop the high-tech NDT equipment. In 1980s , we researched and developed the 1st DIGITAL ultrasonic flaw detector in China, subsequently, we developed a series of first-class NDT equipment, including digital ultrasonic flaw detector, TOFD flaw detector, phased array flaw detector, ultrasonic flaw detector for rail system, ultrasonic thickness gauge, X-ray flaw detectors, videoscope and other NDT Equipment.
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Do you often wonder but never seem to get an answer about how ultrasonic flaw detectors work?
Well, we’ve all been there at some point of encountering a UT flaw detector, mostly as new users. Nonetheless, a comprehensive guide like this one will surely get you all the answers to your questions. In any case, this equipment has gone through many years of development and advancement to arrive at its present technological state. However, it remains a very reliable and easy-to-use equipment based on simple physics theory, which it uses to deliver accurate test results.
This guide gives you a complete overview of the workings and the theoretical basis for this ultrasonic flaw detection system.
So, if you are ready, let’s take a closer look.
For starters, an ultrasonic flaw detector is a piece of non-destructive testing equipment that uses the principle of sound travel and reflection to determine the presence of defects within a component.
Sound waves travel in mediums like air, solids, and liquids and, as a result, can be reflected when it encounters any barrier in their path. This is why an ultrasonic flaw detector can detect a defect in a component since defects form an obstacle in the way of the ultrasound wave generated by the UT flaw detector.
However, the specific parameters that the UT flaw detector uses are the change in speed or velocity of the ultrasound wave when it encounters a blockade caused by a fault in its path.
You might have wondered why the ultrasonic flaw detector is so prevalent as a quality assessment tool among many manufacturers. Fortunately, the reason is not far-fetched. It all boils down to the numerous benefits of this equipment and the plenteous use cases in the manufacturing industry that have made it popular.
One of such benefits is its ability to identify defects in ferrous and non-ferrous materials like plastic and wooden products with a high degree of accuracy. Also, it is very effective for identifying hidden weaknesses that might be difficult for other non-destructive testing methods like the visual inspection to identify.
While some testing methods require access to a minimum of two sides to get an accurate testing result, ultrasonic flaw detection systems only need access to one side of the test sample to get a precise result. This is another merit it has over other forms of testing, especially for products that are positioned or buried in the ground.
Finally, the fact that there is no fear of radiation hazards often associated with radiography test methods makes it highly recommendable for most quality inspections and testing.
Certain concepts are central to the characteristics of the parts or the whole of ultrasonic flaw detectors. You’ll find the essential theories and definitions you need to make sense of the UT detector below.
Ultrasonic is a type of sound wave that falls within a range of frequencies, usually outside the human hearing. While normal human hearing can pick up sound waves of up to 20,000Hz (20kHz), ultrasonic sound waves often fall within a frequency range of 500,000Hz (500kHz) to 20,000,000Hz (20MHz).
Like all waves, sound waves are also associated with vibrations which are often characterized by the number of cycles the vibrations complete in a second. This number of cycles per second is known as the wave’s frequency, and it is standardly measured in Hertz (Hz). A thousand Hertz is a Kilohertz (kHz), and a million Hertz is a MegaHertz (MHz).
Velocity is the change of distance traveled by an ultrasonic wave in a given period. Multiplying the wavelength and the frequency of the ultrasonic wave will give its velocity.
The wavelength of an ultrasonic sound wave is the distance between two consecutive peaks or lows in one complete cycle.
The three main modes of propagation for ultrasonic waves include longitudinal, shear, and surface waves. The longitudinal wave travels parallel to the medium particle, and shear waves travel perpendicular to the medium particle. In contrast, surface waves travel on the sample piece with a depth of one wavelength.
The angle of an ultrasonic wave when returning to the transducer after hitting a sample barrier is called the angle of reflection. However, when there is a change in direction away from the transducer after hitting the sample barrier, the angle made by the returning wave is known as the angle of refraction.
As previously mentioned, ultrasonic flaw detectors have seen a series of advancements over the years with numerous modifications to improve their efficiency. Nonetheless, the essential working parts for a contemporary ultrasonic flaw detector consist of the following parts highlighted below.
One interesting thing about ultrasonic flaw detectors is their ability to inspect both ferrous and non-ferrous material. This characteristic is an advantage that endears this NDT tool to quality inspectors and manufacturers. So, let’s take a look at some of its material applications.
There are three types of ultrasonic flaw detector types available in the market today, and each is selected based on the nature of the test sample under examination.
This technique is often used when identifying defects like delamination, voids, cracks, and porosity that occur parallel to the test sample’s surface. While any transducers including contact, delay line, immersion, or dual element can be used, it is essential to know that they all launch longitudinal waves in straight lines with the test sample. Nonetheless, they are very suitable for testing forgings, pins, and bolts that can crack parallel to an accessible surface of the sample.
This is the most effective technique for welds and joins, which do not have parallel discontinuities with the test sample’s surface. Typical factors like weld geometry, weld crown, and flaw orientation with this type of inspection become critical. Likewise, the angle of the generated beam is also critical as the welds need to be inspected from the sides. This technique forms the most used method for ultrasonic flaw detectors.
For this technique, an array of numerous transducers is located at various points to surround the test sample and work in sync to produce an accurate test image. Particularly, it allows for easy assessment of cracks, discontinuities, and porosity with clear images. But more importantly, it is intuitive with a user-friendly interface and colorful graphics for easy interpretation. Perhaps this type of ultrasonic testing is the best as it is by far the most versatile, fast, and offers image magnification for an enhanced image resolution.
Calibration often involves using a known standard to set the precision and accuracy of the ultrasonic flaw detector. While there are several methods and ways to go about this, we will only look at the three calibration methods associated with the ultrasonic flaw detectors.
In most contemporary ultrasonic flaw detectors, reflectors are critical to the accuracy of the result you get. However, sizing this reflector can pose a challenge to your testing and hinder the accuracy of your result. Hence, the need to apply a suitable sizing technique for your reflector. Here are the most common techniques highlighted below.
While these two techniques are two sides of the same coin yet, they have different case uses specific to each technique.
DAC, which stands for Distance Amplitude Correction curve, is employed to plot the variable amplitude for reflectors of the same but with differing distances from the transducers. The reflectors, in this case, often produce echoes with a decreasing amplitude as the distance to the transducer also decreases.
TVG, on the other hand, stands for Time Varied Gain and typically increases the gain by 80% based on the function of time, which helps to bring all the reference echoes to the same height. This gain is often noticeable across the screen through the single value gain presented. But while it is important to note that TVG compensates for the acoustic factors, it is equally critical to observe that the reference reflector peaks downwards rather than drawing a curve on the screen like for DAC.
Distance/Gain/Size (DGS) technique is a form of equivalent reflector size method where the amplitude of the echo from the reflector is related to the flat bottom hold of the same distance. While this technique traditionally involves comparing the echo with printed curves, the contemporary digital detector available today can automatically calculate the equivalent reflector size for a gated peak while using a calibration routine to draw the curve. Moreover, DGS is also known as Abstand Verstarkung Grosse (AVG) from its German name.
In a nutshell, ultrasonic flaw detectors are a very reliable, fast, and accurate quality inspection tool that has undergone various advancements over the years and is now very popular in the manufacturing industry. However, understanding certain properties such as frequency, velocity, wavelength, and angle of reflection and refraction are critical to understanding the operations of the UT detector.
Nevertheless, it is very advantageous as it can identify internal and external flaws for various materials, including ferrous and non-ferrous materials like plastic, ceramics, and fiberglass.
Hopefully, this guide has helped figure out the workings of ultrasonic flaw detectors because that’s all that matters.
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Send us an inquiry, we will feedback to you ASAP!
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