Non-destructive testing, otherwise referred to as NDT, is simple in concept: find flaws before the time they become problems. Engineers and inspectors across all industries employ it to keep things strong, safe, and functional. To find internal flaws you can’t find on the surface there is one technique that reigns supreme: ultrasonic testing.
Ultrasonic testing involves putting sound into something and listening to how it responds. It is precise, quick, and does not leave a mark. From Checking the weld on a pipe to checking an aircraft wing, ultrasonic testing can tell you what is happening inside without opening it up and without having to cut anything open.
Let us take a look at what it can accomplish, why it is valuable, and how it fits into the grand scheme of non-destructive testing.
What Is Ultrasonic Testing?
Ultrasonic testing is in essence high-frequency sound waves, usually above the range that humans can hear. A portable probe emits the sound into the item. Upon reaching an irregular object, such as void space or crack, part of the sound is reflected. A technician looks for the return sound on the screen and interprets the size, shape, and location of the flaw.
The same concept by which bats can fly, or submarines can employ sonar. The device emits a pulse, then listens for the return. Except in this case, the target is thick metal, plastic, or composite. And the purpose is to ensure it resists stress.
Why Use Ultrasonic Testing?
Ultrasonic testing has a few considerable advantages to offer:
- It works well on thick substances. Where other NDT methods struggle to penetrate deeply into metal, ultrasonic waves can penetrate several inches into steel.
- It detects internal defects. As opposed to other tests like dye penetrant testing or magnetic particle testing, which inspect the surface, this one goes inside.
- It provides precise measurements. Just as the flaw can be revealed by the technician, they can measure the size and depth to precision.
- It does not damage the material. The part is still functional and intact, and it saves time and money.
In summary, ultrasonic testing is when you’d prefer to have an in-depth examination without having to disassemble things.
Where It’s Used?
You’ll find ultrasonic testing NDT being used in more places than you might imagine. It is an important part of:
Aerospace
Airplanes employ close tolerance and fatigue resistance. They employ ultrasonic inspection to test wings, fuselage, engine components, and landing gear components. A major threat is created by having such a crack allowed to form undetected. That is something this method can prevent.
Oil and Gas
Pipes travel for miles over rough ground. They experience pressure, corrosion, and mechanical stress. Ultrasonic testing checks welds, storage vessels, and valves. It finds the onset of weakness in time, before it leads to rupture.
Power generation
Nuclear and fossil fuel systems are both operated under high temperature and high pressure. Pressure vessels and boilers must be sound. Their safe condition is assured by ultrasonic testing.
Manufacturing
Ultrasonic testing helps to locate defects in the material early on. They can test vehicle axles, train wheels, or steel beams. Fewer defects in initial stages mean fewer repairs down the line.
Construction
Ultrasonic inspection is also useful to civil structures. Consider bridges, cranes, and water towers, for instance. As they get older, inspectors need to have some method of determining what is happening within the steel.
What it can measure?
Ultrasonic testing can reveal an array of types of flaws, including:
- Surface-breaking and subsurface (buried) cracks
- Porosity, or air entrapment
- Inclusions (foreign matter in the structure)
- Wall thinning and pipe thinning by corrosion
- Insufficient fusion, or failure to penetrate welds
And because the equipment can measure wall thickness, it’s also perfect for tracking wear and tear over time.
How it operates in practice
A coupling gel is placed on the part by a technician (somewhat similar to medical imaging via ultrasound) and the probe is placed over it. Sound pulses are transmitted by the instrument through the part and read by the reflected echoes.
If there is no defect, the wave passes through and returns clean. If there is an empty space, or crack, then a portion of the signal bounces back early. There is a spike registered by the screen, and the technician can investigate further.
In more sophisticated systems, this is done automatically. Bots can scan large areas or pipes and read thousands per hour. A 3D image of the inside of the part is created using the scan information inputted into software.
What are the limitations?
Although it is effective, ultrasonic testing is not perfect. It is not well suited to test complex geometries or rough surfaces. And it works best where it can get good access to surface.
It also takes skill — the test is only as good as the training and focus of the technician. For this reason, ultrasonic testing is typically most effective as part of an overall more comprehensive NDT methodology. You can start using visual inspection, proceed to ultrasonic, and then confirm by using another technique.
Seeing what’s going on inside a part without cutting it open isn’t science fiction — it’s part of everyday work in many industries. And ultrasonic testing is one of the tools that makes it possible. It reinforces faith in projects where failure is not an option. It provides safety, saves money, and helps to extend the life of crucial equipment. It does not make it to the headlines but quietly keeps industry wheels turning –echo by echo.