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Participant

Join Date: Nov 2015
Posts: 4

Non-Destructive Testing By UT

03/02/2016 7:07 AM

when we are checking defect invisible in welding carbon steel specimen, is the law below correct or not ? please inform me by physical or mechanical evidence,

defect = 1/2 wavelength

Defect = 1/2 λ

thanks

Mostafa jassim mohammed

QA/QC- Engineer

Bawabat Al Fayhaa Company

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Guru
Technical Fields - Project Managers & Project Engineers - New Member

Join Date: Oct 2013
Location: Texas.Baytown
Posts: 697
Good Answers: 26
#1

Re: Non-destructive testing by UT

03/02/2016 7:12 AM

Actually you need several wavelengths to be easily detectable. I do not know what "defect invisibility" is. Sometimes its not a defect but just different medium the wave reflects from. Remember a wave reflects according to acoustic impedance mismatch.

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Guru

Join Date: Jun 2007
Posts: 1047
Good Answers: 40
#2

Re: Non-Destructive Testing By UT

03/02/2016 10:51 PM

Re: "is the law below correct"... It is not a law, but rather, a formula / guideline that we adhere to. It reminds us that the maximum wavelength that we should use for any given interrogation, should be no longer than two times the diameter of the critical flaw.

Thus, knowing what the smallest flaw that you must detect is, allows you to determine the optimum frequency to use, for any given material, in order to assure detectability, while avoiding too much "grass", or "trash" on the CRT screen (or other type of display), which will result from using too high of a frequency, and thus seeing echoes from itty-bitty tiny stuff with which you are not concerned.

Velocity = Frequency X Wavelength, so

Wavelength = Velocity / Frequency, and

Frequency = Velocity / Wavelength

These things, above, irrespective of any defects.

Once (either) Code or Specification gives you a critical defect size, THEN you employ the other formula, to determine your optimal frequency for that interrogation.

Hope that "clarifies things".

Cheers, and Best Wishes for your success!

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