Ultrasonic testing (UT) comprises a range of non-destructive testing (NDT) techniques that send ultrasonic waves through an object or material. These high-frequency sound waves are transmitted into materials to characterise the material or for flaw detection.
Most UT inspection applications use short pulse waves with frequencies ranging from 0.1-15 MHz, although frequencies up to 50 MHz can be used. One common application for this test method is ultrasonic thickness measurement, which is used to ascertain the thickness of an object such as when assessing pipework corrosion.
Ultrasonic Testing comprises a few methods that are used to determine any flaw or irregularities in any material. Check them out.
1) Phased Array Ultrasonic Testing (PAUT):
Phased Array Ultrasonic scanning unit involves many crystals arranged in a manner that sends sound waves in different directions inside the material. The sound from different crystals are timed by the computer at different phases – hence the name Phased Array (Timed elements & Arrangement of elements)
The Major Advantage of the technology are:
→ Inspection is quick since the manual to and fro movement by the user is not required.
More possibility of finding defects without using different angle probes, since a single probe scans in a different direction.
→ PAUT gives multiple views of the defects through advanced presentation views such as B-Scan (depth of defect) view, C-Scan View(Top view), S-Scan view (sectorial view) and conventional A-scan view (echo pattern).
Complete scanning can be recorded and interpretation can be made later by many people. So the technology is believed to be a reliable process for inspection.
2) Introduction to Time Of Flight Diffraction UT (TOFD):
The technology is used for Crack detection at a rapid rate. The method involves two Ultrasonic probes; a “transmitter’ and a “receiver” attached to a fixture. The fixture can be operated manually or robotic. The technology finds defects by analyzing the time of sound travel and sound diffracted from the crack tips, hence the name “ Time of Flight Diffraction”.
The TOFD methods give a visual representation of the defects as shown here. The technology exactly locates the defect and measures the size of the defect.
3) Introduction to Long Range Ultrasonic Testing / Guided Wave Testing:
The technology is used to scan a complete length of pipe for internal corrosion, cracks or damages.
Long Range UT involves multiple Probes fixed around the circumference of the pipe. The sound is sent in a manner it travels through the wall of the pipe up to the end (Flange ) of the pipe and returns back. The low-frequency sound waves are sent to avoid loss of sound due to scattering.
The sound reflected from the obstructions is shown on the screen. The A-symmetrical sound echoes are identified as defects and locations of the defect is shown in the sweep range of the screen.
The size of the defects is also can be interpreted by using Distance Amplitude Curve.
The major advantages of Guided Wave testing or Long Range UT are:
→ It is a speedy testing method, a long length of pipe can be scanned quickly
→ Full access to the pipe length is not required
→ Even Insulated or underground pipes can be scanned without excavation the whole pipe length.
Besides Ultrasonic Testing, there are many different methods of NDT available. You can read about them here.
Conclusion:
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