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08:25 Aug-29-2008
Nilesh Pathare
Sizing of ToFD Indications

Dear Members,
Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
Regards,
Nil


 
00:48 Aug-29-2008

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
Re: Sizing of ToFD Indications Nilesh

The proven truth is that TOFD has a much higher Probability Of Detection (POD) than other volumetric methods, e.g. RT or pulse-echo UT. It will easily detect defects which even very high quality RT may not be able to find. As the method relies only on a discontinuities presence (and not its volume or reflectivity) to produce a diffracted signal it is obviously capable of detecting flaws with very little through wall extent (TWE). However ECA derived acceptance criteria should allow for this enhanced detection capability with much greater lengths of low TWE flaws being acceptable than flaws of greater TWE. However it would be inadvisable to use the same acceptance criteria for RT and TOFD!!!

A discernible separation between upper and lower defect tip diffaction signals is needed to accurately size the flaw's TWE. A flaw of very little TWE, such as a threadlike defect or cold lap (lack of inter-run fusion orientatated parallel to the test surface), both practically undetectable by radiography, may not provide clear separation between upper and lower tip diffracted signals and therefore accurate height measurement is unlikely. Additionally, for near-surface flaws the upper tip diffracted signal may be masked by the lateral wave and the poorly-trained technician is often measuring the time duration of the wavetrain of the lower tip diffracted response.

I recommend you read Charlesworth and Temple's excellent book "Enginnering Applications of Ultrasonic TOFD" to gain an appreciation of the benefits and limitations of TOFD.

Hope this helps.

Nigel


----------- Start Original Message -----------
: Dear Members,
: Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
: If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
: Regards,
: Nil
------------ End Original Message ------------




 
09:12 Aug-30-2008
mj
Re: Sizing of ToFD Indications ----------- Start Original Message -----------
: Nilesh
: The proven truth is that TOFD has a much higher Probability Of Detection (POD) than other volumetric methods, e.g. RT or pulse-echo UT. It will easily detect defects which even very high quality RT may not be able to find. As the method relies only on a discontinuities presence (and not its volume or reflectivity) to produce a diffracted signal it is obviously capable of detecting flaws with very little through wall extent (TWE). However ECA derived acceptance criteria should allow for this enhanced detection capability with much greater lengths of low TWE flaws being acceptable than flaws of greater TWE. However it would be inadvisable to use the same acceptance criteria for RT and TOFD!!!
: A discernible separation between upper and lower defect tip diffaction signals is needed to accurately size the flaw's TWE. A flaw of very little TWE, such as a threadlike defect or cold lap (lack of inter-run fusion orientatated parallel to the testsurface), both practically undetectable by radiography, may not provide clear separation between upper and lower tip diffracted signals and therefore accurate height measurement is unlikely. Additionally, for near-surface flaws the upper tip diffracted signal may be masked by the lateral wave and the poorly-trained technician is often measuring the time duration of the wavetrain of the lower tip diffracted response.
: I recommend you read Charlesworth and Temple's excellent book "Enginnering Applications of Ultrasonic TOFD" to gain an appreciation of the benefits and limitations of TOFD.
: Hope this helps.
: Nigel
:
: : Dear Members,
: : Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
: : If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
: : Regards,
: : Nil
------------ End Original Message ------------

Dear Nigel, please don't Compare with RT and TOFD. most of the people compare with RT and TOFD its really not the actual way to interpretate TOFD. TOFD always good for your 31mm thickness weld. and diffect sizing is very important most of the tech. interpretating wrongly thats why basic TOFD qualification is very Important for TOFD interpretation. as you please note that first white phase and Last blck phase is not correct Last black phase maybe reflection of the defect.
Regards
MJ


 
02:36 Aug-31-2008

Jan Verkooijen

Director,
Sonovation,
Netherlands,
Joined Nov 1998
29
Re: Sizing of ToFD Indications Reading books on TOFD is certainly a good start for getting to grips with sizing of TOFD indications. As we have learned during nearly two decades of training TOFD operators in our accredited training school, it is something that requires the theoretical knowledge you can get form books or during structured theoretical training, but it also needs guided practice during such structured training to make the operator familiar and give him the routine to actually learn how to do it himself. I therefore agree totally with the statement that poorly trained operators may get it wrong and we as professionals should try to avoid this by making our operators truly competent in their profession by proper, structured training.

----------- Start Original Message -----------
: : Nilesh
: : The proven truth is that TOFD has a much higher Probability Of Detection (POD) than other volumetric methods, e.g. RT or pulse-echo UT. It will easily detect defects which even very high quality RT may not be able to find. As the method relies only on a discontinuities presence (and not its volume or reflectivity) to produce a diffracted signal it is obviously capable of detecting flaws with very little through wall extent (TWE). However ECA derived acceptance criteria should allow for this enhanced detection capability with much greater lengths of low TWE flaws being acceptable than flaws of greater TWE. However it would be inadvisable to use the same acceptance criteria for RT and TOFD!!!
: : A discernible separation between upper and lower defect tip diffaction signals is needed to accurately size the flaw's TWE. A flaw of very little TWE, such as a threadlike defect or cold lap (lack of inter-run fusion orientatated parallel to the test surface), both practically undetectable by radiography, may not provide clear separation between upper and lower tip diffracted signals and therefore accurate height measurement is unlikely. Additionally, for near-surface flaws the upper tip diffracted signal may be masked by the lateral wave and the poorly-trained technician is often measuring the time duration of the wavetrain of the lower tip diffracted response.
: : I recommend you read Charlesworth and Temple's excellent book "Enginnering Applications of Ultrasonic TOFD" to gain an appreciation of the benefits and limitations of TOFD.
: : Hope this helps.
: : Nigel
: :
: : : Dear Members,
: : : Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
: : : If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
: : : Regards,
: : : Nil
: Dear Nigel, please don't Compare with RT and TOFD. most of the people compare with RT and TOFD its really not the actual way to interpretate TOFD. TOFD always good for your 31mm thickness weld. and diffect sizing is very important most of the tech. interpretating wrongly thats why basic TOFD qualification is very Important for TOFD interpretation. as you please note that first white phase and Last blck phase is not correct Last black phase maybe reflection of the defect.
: Regards
: MJ
------------ End Original Message ------------




 
09:26 Sep-01-2008
Nilesh Pathare
Re: Sizing of ToFD Indications Thanks Nigel.
I will go through the book which u sugessted. But Can you advice me where would I get the standard ToFD images which can explain about the type of flaw and sizing technique in more detail. I have seen few images in ASME SEC. V Article 4 and BS 7706.
But is there any one who provides the standrad Defect images for comparision with defect same like RT we have reference radiograph.

Regards,
Nilesh
----------- Start Original Message -----------
: Nilesh
: The proven truth is that TOFD has a much higher Probability Of Detection (POD) than other volumetric methods, e.g. RT or pulse-echo UT. It will easily detect defects which even very high quality RT may not be able to find. As the method relies only on a discontinuities presence (and not its volume or reflectivity) to produce a diffracted signal it is obviously capable of detecting flaws with very little through wall extent (TWE). However ECA derived acceptance criteria should allow for this enhanced detection capability with much greater lengths of low TWE flaws being acceptable than flaws of greater TWE. However it would be inadvisable to use the same acceptance criteria for RT and TOFD!!!
: A discernible separation between upper and lower defect tip diffaction signals is needed to accurately size the flaw's TWE. A flaw of very little TWE, such as a threadlike defect or cold lap (lack of inter-run fusion orientatated parallel to the test surface), both practically undetectable by radiography, may not provide clear separation between upper and lower tip diffracted signals and therefore accurate height measurement is unlikely. Additionally, for near-surface flaws the upper tip diffracted signal may be masked by the lateral wave and the poorly-trained technician is often measuring the time duration of the wavetrain of the lower tip diffracted response.
: I recommend you read Charlesworth and Temple's excellent book "Enginnering Applications of Ultrasonic TOFD" to gain an appreciation of the benefits and limitations of TOFD.
: Hope this helps.
: Nigel
:
: : Dear Members,
: : Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
: : If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
: : Regards,
: : Nil
------------ End Original Message ------------




 
01:42 Sep-02-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Sizing of ToFD Indications Nilesh:
I would like to first commend my associates for their correct assessments of the situation. Nigel pointed out that your issues with DETECTING flaws with TOFD reflects on the superior capability of TOFD compared to RT (and often other AUT options)...and it is a fair comparison when dealing with POD (contrary to MJ's concerns).
Jan's concerns for training correctly indicates how poorly some people reading it understood some of the excellent literature. For most users of TOFD the details of analysis can only be achieved with hands-on instruction. The explanation you gave of your sizing suggests that you are not using the correct signals when simply identifying the "first white phase and last black".

Structured training is now available from reputable facilities such as Lavender, TWI and Sonovation...and others. Before making assumptions about TOFD and its capabilities it would be advisable to be more technically aware of how the process works and its limitations.

As for a "standard" set of TOFD charts as you might see in RT...this is not very practical (and they are not available as a standard). The nice images I see in descriptions of what to look for to identify flaws using TOFD are generally made using specially fabricated test plates. The examples selected are IDEAL and not really representative of real-world welding conditions. The general descriptions of the 3 flaw types as noted in BS7706 are about as good as it gets...point-like, thread-like and planar.
Regards
Ed


----------- Start Original Message -----------
: Reading books on TOFD is certainly a good start for getting to grips with sizing of TOFD indications. As we have learned during nearly two decades of training TOFD operators in our accredited training school, it is something that requires the theoretical knowledge you can get form books or during structured theoretical training, but it also needs guided practice during such structured training to make the operator familiar and give him the routine to actually learn how to do it himself. I therefore agree totally with the statement that poorly trained operators may get it wrong and we as professionals should try to avoid this by making our operators truly competent in their profession by proper, structured training.
: : : Nilesh
: : : The proven truth is that TOFD has a much higher Probability Of Detection (POD) than other volumetric methods, e.g. RT or pulse-echo UT. It will easily detect defects which even very high quality RT may not be able to find. As the method relies only on a discontinuities presence (and not its volume or reflectivity) to produce a diffracted signal it is obviously capable of detecting flaws with very little through wall extent (TWE). However ECA derived acceptance criteria should allow for this enhanced detection capability with much greater lengths of low TWE flaws being acceptable than flaws of greater TWE. However it would be inadvisable to use the same acceptance criteria for RT and TOFD!!!
: : : A discernible separation between upper and lower defect tip diffaction signals is needed to accurately size the flaw's TWE. A flaw of very little TWE, such as a threadlike defect or cold lap (lack of inter-run fusion orientatated parallel to the test surface), both practically undetectable by radiography, may not provide clear separation between upper and lower tip diffracted signals and therefore accurate height measurement is unlikely. Additionally, for near-surface flaws the upper tip diffracted signal may be masked by the lateral wave and the poorly-trained technician is often measuring the time duration of the wavetrain of the lower tip diffracted response.
: : : I recommend you read Charlesworth and Temple's excellent book "Enginnering Applications of Ultrasonic TOFD" to gain an appreciation of the benefits and limitations of TOFD.
: : : Hope this helps.
: : : Nigel
: : :
: : : : Dear Members,
: : : : Sizing of Indications found by AUT ToFD is challenging since we are replacing RT with this AUT. In my experience I observed many recordable indications in ToFD images and No indications in RT films for the same location. Thickness of job is 31mm and DWSI shot for RT.
: : : : If we make sizing of defects by taking first white phase and last black phase of ToFd indication it gives more height than actual. So can anyone highlight me with his previous experience regarding the sizing technique.
: : : : Regards,
: : : : Nil
: : Dear Nigel, please don't Compare with RT and TOFD. most of the people compare with RT and TOFD its really not the actual way to interpretate TOFD. TOFD always good for your 31mm thickness weld. and diffect sizing is very important most of the tech. interpretating wrongly thats why basic TOFD qualification is very Important for TOFD interpretation. as you please note that first white phase and Last blck phase is not correct Last black phase maybe reflection of the defect.
: : Regards
: : MJ
------------ End Original Message ------------




 


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