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Technical Discussions
suresh
suresh
01:44 Jan-05-2007
crack sizing using TOFD

TOFD gives a exact length or a projected length?


    
 
 Reply 
 
Jan Verkooijen
Director,
Sonovation, Netherlands, Joined Nov 1998, 29

Jan Verkooijen

Director,
Sonovation,
Netherlands,
Joined Nov 1998
29
08:45 Jan-08-2007
Re: crack sizing using TOFD
----------- Start Original Message -----------
: TOFD gives a exact length or a projected length?
------------ End Original Message ------------

As with any NDT technique, we are looking at signals which are representing the anomaly, not the anomaly itself. Therefore, by default we do not measure the exact length (by the way: is any measurement in life exact?). However, over the last 20 years, TOFD has probably been used more in validations, round robin trials et cetera than any other NDT technique. From this, we have established that TOFD is probably the most accurate sizing technique for embedded defects presently available to the world. A recent test for a major oil company we did on some 30 rootcracks in thin walled material, which were compared to physical measurements after destructive testing showed a mean error on height sizing for TOFD of 0.27 mm with a standard deviation of 0.7 mm. The X-Ray results obviously did not give any height measurement. On the length measurement the accuracy of TOFD was 2.6 mm, with a standard deviation of 4.5 mm. For X-Ray the accuracy of the length measurement was -19 mm (undersized) with a standard deviation of 43.5 mm. By the way, X-Ray only revealed 55% of the cracks, whereas TOFD found 97%.

I hope this answers your qquestion


    
 
 Reply 
 
suresh
suresh
09:20 Jan-10-2007
Re: crack sizing using TOFD
Hi

Thank u Mr.Jan

Have no doudts about capabilities of techniques.

But like to know whether TOFD responds to the crack profile.

What if a situation, where a flaw grows into a defect, yet gives a same time lag in diffracted signal( may be hypothtical, have no idea of in-service inspection procedures)

Thank u

----------- Start Original Message -----------
: : TOFD gives a exact length or a projected length?
: As with any NDT technique, we are looking at signals which are representing the anomaly, not the anomaly itself. Therefore, by default we do not measure the exact length (by the way: is any measurement in life exact?). However, over the last 20 years, TOFD has probably been used more in validations, round robin trials et cetera than any other NDT technique. From this, we have established that TOFD is probably the most accurate sizing technique for embedded defects presently available to the world. A recent test for a major oil company we did on some 30 rootcracks in thin walled material, which were compared to physical measurements after destructive testing showed a mean error on height sizing for TOFD of 0.27 mm with a standard deviation of 0.7 mm. The X-Ray results obviously did not give any height measurement. On the length measurement the accuracy of TOFD was 2.6 mm, with a standard deviation of 4.5 mm. For X-Ray the accuracy of the length measurement was -19 mm (undersized) with a standard deviation of 43.5 mm. By the way, X-Ray only revealed 55% of the cracks, whereas TOFD found 97%.
: I hope this answers your qquestion
------------ End Original Message ------------




    
 
 Reply 
 
Jan Verkooijen
Director,
Sonovation, Netherlands, Joined Nov 1998, 29

Jan Verkooijen

Director,
Sonovation,
Netherlands,
Joined Nov 1998
29
08:43 Jan-11-2007
Re: crack sizing using TOFD
I have no idea what you mean exactly, but yes, TOFD diffracted signals combined into a TOFD scan do follow the crack profile quite well in most cases.

We do have an accredited training school which can supply answers to most of your questions during regular or client specific training courses!

Unfortunately the course for next week is overbooked allready, but we do have some capacity on the March course (in German) and on the April/May course in English.

Best regards,

Jan Verkooijen

----------- Start Original Message -----------
: Hi
: Thank u Mr.Jan
: Have no doudts about capabilities of techniques.
: But like to know whether TOFD responds to the crack profile.
: What if a situation, where a flaw grows into a defect, yet gives a same time lag in diffracted signal( may be hypothtical, have no idea of in-service inspection procedures)
: Thank u
: : : TOFD gives a exact length or a projected length?
: : As with any NDT technique, we are looking at signals which are representing the anomaly, not the anomaly itself. Therefore, by default we do not measure the exact length (by the way: is any measurement in life exact?). However, over the last 20 years, TOFD has probably been used more in validations, round robin trials et cetera than any other NDT technique. From this, we have established that TOFD is probably the most accurate sizing technique for embedded defects presently available to the world. A recent test for a major oil company we did on some 30 rootcracks in thin walled material, which were compared to physical measurements after destructive testing showed a mean error on height sizing for TOFD of 0.27 mm with a standard deviation of 0.7 mm. The X-Ray results obviously did not give any height measurement. On the length measurement the accuracy of TOFD was 2.6 mm, with a standard deviation of 4.5 mm. For X-Ray the accuracy of the length measurement was -19 mm (undersized) with a standard deviation of 43.5 mm. By the way, X-Ray only revealed 55% of the cracks, whereas TOFD found 97%.
: : I hope this answers your qquestion
------------ End Original Message ------------




    
 
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