What is Ultrasonic Testing?
ULTRASONIC TESTING is a method for sending ultrasound into material and analyzing the returning sound waves for defect free components.
It use scanning devices called probes. After application of Couplant over the material surface probe is place over the material.
The sound travels to the end of the material and reflects back to the probe. There will be a change in acoustic property between the material and air. As a result the reflection sound is noted as back wall echo in the UT flaw detector machine screen.
How to scan for defects in Ultrasonic Inspection?
If the sound waves meet a defect in between the front walk and back wall, again there will be reflection due to acoustic property. Difference between the material and defect material, which appears between the initial sound echo and back wall echo.
Thus any defect inside the material is detected by noticing the defect echos in between the initial echo and backwall echo.
There is also possible of defect echo not appearing in the screen. The defect surface is very much inclined to the line of sound travel and the reflected sound travels in a direction away from the probe, this happens.
It is advisable to scan in different directions. Or use different angle probes, to ensure no defects are missed.
For scanning a casting normal probes (0 degree probe) are used at areas with backwall parallel to the surface, and angle probes at areas where backwall is inclined to the surface.
For Weld joints, Normal probes are used to scan Heat Affected Zone and base metals.
Angle probes are used to scan the Weld area. The scanning distance normally being 1/2 skip to 1&1/2 skip distance.
Only the location of defect can be identified by normal scanning method. To sort the size of defect, defect sizing techniques such as DAC, DGS, TCG etc are used.
To learn in detail the Ultrasonic Testing Methods and to practice Ultrasonic Scanning, reach us @ https://aqcinspection.com/.
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