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Technical Discussions
Robert Oakley
Robert Oakley
09:39 Sep-16-2002
Probability of detection within a specific NDT method as a function of flaw size

I am a student engineer for a company called Miltec, and I am searching for information concerning the probability of detection by any and all methods of NDT as a function of flaw size. In addition I require figures on the probability of false detection by any and all NDT methods as a function of flaw size. Any help whatsoever as to references and sources for this material would be greatly appreciated.


    
 
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Terry Oldberg
Engineering, Mechanical Electrical Nuclear Software
Consultant, USA, Joined Oct 1999, 42

Terry Oldberg

Engineering, Mechanical Electrical Nuclear Software
Consultant,
USA,
Joined Oct 1999
42
08:10 Oct-11-2002
Re: Probability of detection within a specific NDT method as a function of flaw size
Your requirements cannot be met, for past and current methods of flaw detection violate the axiom of probability theory that is known as Unit Measure. It follows that at least one of the two probabilities that you desire is not defined. (See my paper at http://www.ndt.net/article/v04n05/oldberg/oldberg.htm plus my postings in this forum on the topic of "Unit Measure violations" for details.)

By the way, when you say that you require a probability of false call as a function of flaw size, you seem to be making a mistake, for the statistical population underlying a probability of false call would be comprised of non-flaws.




    
 
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David Forsyth
R & D
TRI/Austin, USA, Joined Nov 2001, 41

David Forsyth

R & D
TRI/Austin,
USA,
Joined Nov 2001
41
07:54 Oct-15-2002
Re: Probability of detection within a specific NDT method as a function of flaw size
>I am a student engineer for a company called Miltec, and I am searching for information concerning the probability of detection by any and all methods of NDT as a function of flaw size.

There are collections of POD curves publicly available from NTIAC (see http://www.ntiac.com), but these curves should only be used for qualitative purposes, unless you have exactly the same specimen, flaw type, and inspection equipment and procedure you can not use these quantitatively.

>In addition I require figures on the probability of false detection by any and all NDT methods as a function of flaw size. Any help whatsoever as to references and sources for this material would be greatly appreciated.
.

P(false call) is not related to flaw size, NTIAC document also shows P(false call) information. P(false call) is P(noise > threshold level). noise can be measured and threshold can be

Not everyone agrees with Oldberg or the conclusions in his paper.

Dave.


    
 
 Reply 
 
rodney fordham
Consultant
United Kingdom, Joined Feb 2002, 12

rodney fordham

Consultant
United Kingdom,
Joined Feb 2002
12
01:09 Oct-15-2002
Re: Probability of detection within a specific NDT method as a function of flaw size
: >I am a student engineer for a company called Miltec, and I am searching for information concerning the probability of detection by any and all methods of NDT as a function of flaw size.
.
: There are collections of POD curves publicly available from NTIAC (see http://www.ntiac.com), but these curves should only be used for qualitative purposes, unless you have exactly the same specimen, flaw type, and inspection equipment and procedure you can not use these quantitatively.
.
: >In addition I require figures on the probability of false detection by any and all NDT methods as a function of flaw size. Any help whatsoever as to references and sources for this material would be greatly appreciated.
: .
.
: P(false call) is not related to flaw size, NTIAC document also shows P(false call) information. P(false call) is P(noise > threshold level). noise can be measured and threshold can be
.
: Not everyone agrees with Oldberg or the conclusions in his paper.
.
: Dave.
.
but those who disagree owe it to all of us out here to explain in clear logical arguments exactly why they disagree.

In my experience, especially in the most important cases, Terry Oldberg is absolutely right.



    
 
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