Ultrasonic testing can be an invaluable part of a predictive maintenance program. And it is important to understand the basics of the ultrasonic testing and how it can benefit you and the facility you are responsible for.
What is Ultrasonic Testing
Ultrasonic testing (UT) is a non-destructive testing method that utilizes sound waves above the range of human hearing to gather critical data about material defects, cracks, and thickness. In particular, ultrasonic testing can perform measurements (such as wall thickness) and detect internal flaws in materials that cannot be seen by the human eye without destroying the object being tested.
However, ultrasonics can be used for other purposes as well. These include leak detection in pneumatic and steam-driven processes, steam condensate trap surveys, and bearing lubrication (including both preventative and corrective).
What Kinds of Materials Can Ultrasonic Testing be Used With?
Ultrasonic testing works best with metals such as steel and aluminum, as well as other metal alloys. It does not, however, work well with large-grained metals. In addition to metal, ultrasonic testing can also be used with concrete as well as various composites and even some polymers.
How is Ultrasonic Testing Used?
Ultrasonic testing is used in a variety of industries, including metallurgy, aerospace, manufacturing, construction, and automotive. It finds uses wherever there is a need to detect defects beneath the surface of a material or to make thickness/wall measurements that cannot be obtained without destroying the object. In addition, it can detect the presence of high-pressure leaks and be used for conducting surveys on steam condensate traps.
How Ultrasonic Testing Works
When ultrasonic waves pass through materials like steel and aluminum, they will be reflected back with almost the same energy if no anomalies are present. If they encounter a defect like a crack, the energy and frequency will not be reflected back in the same manner.
Using this principle, ultrasonic technicians can study the waveform that is reflected back and use diagnostic tools to determine what type of defect is present and approximately where it is located. They can also use the same principles to determine the thickness of a pipe to determine the effects of corrosion upon it.
More specifically, a probe sends ultrasonic sound wave energy into an object. The probe may be separated from that object by a couplant whose purpose is to increase the efficiency with which the sound wave is transmitted. Typical couplants include water, oil, and gel.
From there, one of two basic types of ultrasonic testing will take place: pulse-echo or through-transmission. In a pulse-echo, or reflection test, the same probe is used to emit energy into the object and receive the reflected energy back. The through-transmission test, also called the attenuation test, uses an emitter and a separate receiver. The receiver will accept the sound energy that has passed through the opposite side of the object. Both methods use information about the sound energy that has either been reflected back or transmitted through in order to look for defects and determine the thickness of the material.
When used for leak detection, the ultrasound probe is used to pick up on sounds that cannot be heard by the human ear. These sounds are conditioned and heard by a technician using a headset. Trained technicians can recognize the tell-tale sounds of leaks (e.g., rushing sounds) that are produced by turbulence as the gas exits the leak. The location and direction can then be determined by the intensity of the sound. Technicians can also perform effective inspections of steam traps and valves, as well as assess the state of bearing lubrication.
The Difference That a Certified Ultrasonic Technician Makes
Depending on the material and sensitivity of the equipment, ultrasonic testing can not only determine the presence of flaws, but NDT-certified technicians can use the data to estimate their location, size, shape, and orientation as well as the nature of the defect. Skilled technicians are also needed to develop truly beneficial inspection procedures, whether used for finding object faults or leaks.
In addition, results from testing can include not just major faults and defects within the part but can also include noise and data from the normal aspects of the object. An NDT-certified technician is needed to differentiate between these three different types of results and to determine if additional non-destructive testing may also be needed. These skills also mean that the information a technician extracts from the results is highly reliable.
Benefits to Using Ultrasonic Testing
Let’s discuss the various benefits associated with the use of ultrasonic testing. First, it is a non-destructive test that doesn’t change the object in any way. It is also non-hazardous to nearby personnel as well as nearby equipment, processes, and materials.
Ultrasonic testing is also more accurate and consistent than other non-destructive testing methods in (a) determining the thickness of parts with parallel surfaces and (b) determining the depth of flaws. Because it is highly sensitive, it can detect extremely small flaws. In addition, the high penetrating power of ultrasound allows it to detect the presence of flaws that are deep within a part. And, in most cases, only one surface needs to be accessible for testing to take place.
Ultrasonic testing is highly reliable and far safer than other leak detection methods, as well. Regular leak detection testing can reduce the cost associated with gaseous losses and enable equipment to perform much more efficiently. It is also highly reliable as part of steam trap and valve inspection.
Finally, quick decisions can be made based on the data because the results of ultrasonic testing are immediate.
Limitations to Ultrasonic Testing
There are, however, some limitations and disadvantages to ultrasonic testing. As discussed earlier, it takes a very experienced technician to correctly interpret the data and develop robust ultrasonic inspection procedures. In addition, the cost of equipment and training is more expensive compared to other testing options.
Other limitations are related to the part to be tested. For example, parts that are very small or thin, irregular in shape, non-homogenous, or rough will be more challenging to inspect. Thick parts may take more time to be tested. And the surface of the part must be cleaned before testing, which includes removing any loose paint or scaling.
Why You Should Use Ultrasonic Testing
When used as part of periodic inspections, ultrasonic testing can be used to check for the development of new flaws, the growth of known flaws, and the presence of corrosion. It is also key to safely detecting high-pressure leaks and for inspecting valves and steam traps. When used regularly, the results of testing by an NDT-certified technician can help prevent catastrophic failures.
