Ultrasonic Testing (UT) is a non-destructive testing method that makes use of short, high-frequency ultrasonic waves to recognise the defects present in a material. They commonly specialise in emitting waves into a sample material to execute the entire process. These waves are measured so that the properties and internal defects of the material can be spotted. Many ultrasonic testing devices consist of various distinct units, and these include ultrasonic transducers, display monitors and pulses & receivers. The components that are included actually depend on the type of Ultrasonic Testing in NDT being conducted by the inspector.
Now let us read about the Advanced Ultrasonic Testing Methods in NDT.
Types of Advanced Ultrasonic Testing Methods
We are all aware of the fact that because of the latest inventions in the modern world, we have gained access to various advanced technologies in different fields, one of them being NDT. Today, we are going to learn about advanced Ultrasonic Testing techniques to understand it from a broader perspective. There are different types of advanced ultrasonic testing methods that include:
- Phased Array Ultrasonic Testing
- Long Range Ultrasonic Testing
- Automated Ultrasonic Backscatter Technique
- Time of Flight Diffraction
- Internal Rotating Inspection Systems
- Dry-Coupled Ultrasonic Testing
- Rapid Ultrasonic Gridding
A) Phased Array Ultrasonic Testing - Phased Array Ultrasonic Testing is also known as PAUT. It is an Ultrasonic Testing method that employs a pack of UT probes which are made up of various small items. Each of these items in a Phased Array Ultrasonic Testing system is skilled to pulse separately. This can be achieved with the help of a computer calculated timing through a procedure which is known as phasing. This entitles the system to navigate concentrated beams through several focal distances and angles.
B) Long Range Ultrasonic Testing - Long Range Ultrasonic Testing (LRUT) is a UT method cultivated to allow the examining of large volumes of substances from a single investigation point. This method functions by fixing the rings of a transducer uniformly all around the pipe. After this step, these rings produce a sequence of low frequency guided waves, and the waves propagate symmetrically along with the axis of the pipe. This will lead to providing extensive coverage of the wall of the pipe.
C) Automated Ultrasonic Backscatter Technique - Advanced Ultrasonic Backscatter Technique (AUBT) is an Ultrasonic Testing method that is formulated for identifying the critical damages that are caused by HTHA, i.e. High-Temperature Hydrogen Attack. This method is designed for utilising it in pressure vessels and pipes. Automated Ultrasonic Backscatter Technique utilises high frequency, broadband UT probes and also a digital oscilloscope. This enables it to deliver frequency analysis and an A-Scan display.
D) Time of Flight Diffraction - Time of Flight Diffraction (TOFD) is a strategy utilised to find out for deformities existing in welds. It uses the time of flight of an ultrasonic pulse to uncover the exact whereabouts of a reflector. To find the time of flight, a set of ultrasonic transducers is used. The transmitter emits low-frequency waves that are produced at an angle. These low-frequency waves only reflect back to the receiver when they strike the imperfections.
E) Internal Rotating Inspection Systems - An Internal Rotating Inspection System (IRIS) is an ultrasonic testing method that is utilised to inspect corrosion in tubes and pipes by making use of an internally inserted probe that produces sound waves. The system operates by injecting a probe into a flooded pipe. The probe is then passed through the pipe so that the scanning can be done appropriately.
F) Dry-Coupled Ultrasonic Testing - Dry-Coupled Ultrasonic Testing (DCUT) is a great alternative and cost-effective technique that does not need to have a liquid couplant to examine metallic and nonmetallic substances. Plus, DCUT transducers are eligible to resist high voltages. Dry-Coupled Ultrasonic Testing can be conducted by using remote, wheel, contact or flexible transducers.
- Flexible transducers are generally applied on the internal or external surface of the material so that the defects are correctly identified.
- Contact transducers are typically utilised to discover deformities and to measure thickness as well.
- Wheel transducers enable the detectors to detect long piping systems in a short span of time.
- Remote transducers are beneficial and effective because they can attain thickness measurements at non-conventional angles, i.e. angles which are not 90° to the surface. This eradicates the requirement to create supports or discard elements to carry on with the inspection.
Here's an article based on different types of ultrasonic transducers.
G) Rapid Ultrasonic Gridding (RUG) - Rapid Ultrasonic Gridding (RUG) is a method of executing ultrasonic thickness in which multiple ultrasonic thickness probes are used simultaneously to quickly assemble measurements of the thickness in an already established or ad-hoc space. Like different ultrasonic testing methods, Rapid Ultrasonic Gridding catches hold of raw A-Scan data, so that it can be illustrated in B-Scan or C-Scan modes, or it can even be used to develop visual representation as 3-D models. Nevertheless, RUG is worthy enough to capture a lot of A-Scan data at a faster rate when compared to traditional techniques used for measuring thickness.
However, Ultrasonic Testing in NDT has various advantages as well as disadvantages. Ultrasonic Testing in NDT is highly useful as it is able to scan the defects present on the surface & underneath the surface of a material. It is extraordinarily accurate & precise. But, there are many materials that are not suitable for going through Ultrasonic Testing methods. Also, in order to perform Ultrasonic Testing techniques, one needs to be highly skilled & experienced.
