Ultrasonics

Last update: Jan 13, 2017

Ultrasonic Testing (UT) is a group of nondestructive examination (NDE) techniques that use short, high-frequency ultrasonic waves to identify flaws in a material. They generally work by emitting waves into a material. By measuring these waves, the properties of the material and internal flaws can be identified. Most UT devices consist of many separate units. These can include pulsers and receivers, transducers, and display monitors. The components included depend on the type of UT that the inspector is performing.

There are several different types of ultrasonic testing. These include methods such as Automated Ultrasonic Backscatter Technique (AUBT), Phased Array Ultrasonic Testing (PAUT), Long Range Ultrasonic Testing (LRUT), Internal Rotating Inspection Systems (IRIS), and Time of Flight Diffraction (TOFD).

Automated Ultrasonic Backscatter Technique (AUBT) is a UT technique developed for detecting damage from High-Temperature Hydrogen Attack (HTHA). The technique is for use in pressure vessels and piping. The technique makes use of high frequency, broadband UT probes and a digital oscilloscope. These allow it to provide both an A-Scan display and frequency analysis.

Phased Array Ultrasonic Testing (PAUT) is a UT technique that utilizes a set of UT probes made up of numerous (anywhere from 16 to over 250) small elements. Each of the elements in a PAUT system is able to pulse individually. This is done with computer calculated timing, through a process known as phasing. This allows the system to steer focused beam through various angles and focal distances.

Long Range Ultrasonic Testing (LRUT) is a UT method developed to allow for testing large volumes of material from a single test point. This method works by fixing transducer rings uniformly around a pipe. These rings then generate a series of low frequency guided waves. The  waves can then propagate symmetrically along the pipe axis. This provides complete coverage of the pipe wall.

An Internal Rotating Inspection System (IRIS) is an ultrasonic technique used to detect corrosion in piping and tubing. using an internally inserted probe that generates sound waves. The system works by  inserting a probe into a flooded pipe. The probe them move through the pipe, scanning as it goes.

Time of Flight Diffraction (TOFD) is a method used to look for flaws in welds. It uses the time of flight of an ultrasonic pulse to find the location of a reflector. To find the TOF, the method uses a pair of ultrasonic transducers. The transmitter emits low frequency waves that propagate at an angle. They only diffract back to the receiver if they hit a defect.

In general, UT has several advantages and disadvantages. It’s useful because it can scan for flaws both on and underneath the surface. It is also useful for it's incredible accuracy. On the other hand, not all materials are receptive to ultrasonic testing. It also has the disadvantage that it requires a good deal of skill and training to perform.

 

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