Non-destructive testing, or NDT, involves observing or measuring objects without damaging them. NDT techniques rely on principles like fluorescence and reflectivity to look inside an object without tearing it apart.
Some of the most common NDT techniques are A-scan, B-scan, and C-scan, which use sound waves to examine different parts of an object’s interior. Professionals have used these methods in fields like engineering and construction for decades. However, they are still often misunderstood by those who do not know much about them.
I. A-Scan Ultrasonic Testing
1. What is A-Scan in Ultrasonic Testing?
An ultrasound scan (also called an A-scan) is a test that uses high-frequency sound waves to generate a picture of a weldment’s interior. The image produced by ultrasound scanning is similar to that produced by computed tomography (CT). A-scan can be used to locate flaws that may not be visible through visual inspection.
However, while these scans provide highly detailed images of materials’ internal structure, A-scans provide less detailed images because they can only scan objects within their cross-section rather than across multiple cross-sections as CT scans do. Although not as detailed as CT scans, A-scans can still detect flaws in most metals and some nonmetals like wood.
You can use A-scan for several field applications. One important application of the A-scan in NDT is that it gives engineers an efficient way to assess pipe flaws in underwater pipelines.
In addition to underwater applications, A-scan testing has proven useful in making sure metallic pipes are safe for drinking water transmission and other fluid transmissions.
For example, tests have shown that A-scan can detect anomalies in steel pipes because of corrosion or faulty welds.
Simply put, without a baseline scan, you do not know what normal looks like. It is important to have a baseline for whatever purpose you need it. Whether you are improving your manufacturing process or trying to find surface defects in your products, A-scan testing can provide those answers.
For example: If you wanted to see if there was any change in dimensional tolerances of your product over time (maybe as part of a cost-containment initiative) but did not have any previous data – well, now you do.
II. B-Scan Ultrasonic Testing
1. What is B-Scan in Ultrasonic Testing?
B-scans bounce sound waves off metal or other solid surfaces to make pictures of what is inside. They are used to find flaws in metals or other solids. The metal part being tested is called a test object, and it is mounted on a machine called an ultrasonic test unit.
As it moves along on its rails, an arm with a tiny probe sends sound waves into its surface. A computer collects those waves as they echo back from inside the part. With that information, the software makes a picture of what is inside.
What you see when you look at your smartphone is not different—except that the smartphone has far better resolution. That makes some ultrasound images clearer than others!
One application of a B-scan machine is to inspect surfaces of metals where there can be cavities or defects in them.
For example, buried cracks within aluminum engine blocks or even hard-to-reach areas inside engines would be difficult for non-destructive techniques. Another application that uses B-scan machines is inspecting welds or cracks in a vessel under pressure, such as a boiler.
The other main application that uses these machines is inspections on aircraft wings or fuselages.
These three applications (and many others) use B scan radiography due to its ability to produce high-quality images at high speeds and with great accuracy, making it superior to most other inspection methods.
B-Scan is important in NDT for one simple reason: B-Scan takes cross-sectional images of a part instead of surface defect images like A-Scan. Doing this allows inspectors to understand better how serious defects are in part.
Without using B-Scan, parts will look clean when major problems cannot be seen with an A-Scan inspection. People often create defective parts without even knowing it because they are not viewing defects at a microscopic level.
B-scan is extremely important for detecting surface and subsurface defects without expensive XRD or CT scanning tools.
III. C-Scan Ultrasonic Testing
1. What is C-Scan in Ultrasonic Testing?
An ultrasound scan is a safe way to examine hidden or hard-to-access metals. C-scan technology is designed for examining industrial parts without having to dismantle them. C-scans typically deliver clear, high-quality images in real-time.
With ultrasound, you do not need special equipment (like X-rays) or chemicals to see inside your part. You can use ultrasound at various stages of production—right from initial inspection through final quality control checks before shipping.
This ensures that every batch of manufactured products meets your standards and expectations.
The main application of a C-scan or XRD scan in an NDT process is to analyze cracks that are not visible to the naked eye. It finds cracks on welds and can also locate them inside components such as engine blocks, cylinder heads, valves, etc.
Additionally, it finds flaws like inclusions or porosity in castings made by sand molds which are generally very difficult to detect with conventional radiography techniques.
For instance, they may be found on high nickel alloys that have been subjected to solution heat treatment (quenching), resulting in solidification cracking caused by cooling rate fluctuations.
When performing any test on a manufactured component or end product, non-destructive testing may be performed to determine if all critical manufacturing parameters were achieved.
Doing this ensures no major issues with your parts or products at the final assembly. For example, when making parts for aerospace components, testing needs to be done to assure materials meet specifications for strength and can withstand harsh weather conditions.
The C in C-scan stands for composition, referring to what elements make up a particular material.
Ultimately, this can help determine if correct metals were used or added something that should not have been (such as paint). This type of scanning is usually done on metallic parts but can also be done on nonmetallic items such as glass samples.
➤ Related Article: What is Angle Beam Testing?
➤ Related Article: What is Pulse-echo Ultrasonic Measurement?
Now that you know what each of these scanning methods is used for in non-destructive testing and learn how it works. Understanding how it does is crucial to understand what it does.
Understanding each of these will give you a strong base of knowledge to form opinions on when they should be used and when they should not.
At the very least, brush up on your general knowledge of these methods in non-destructive testing; it never hurts to have more information at your disposal. When looking deeper at these NDT methods, you need to know their similarities, differences, applications, and overall importance.