Forum Technical Discussions      Re: Sizing of ToFD Indications Posted by: Jan Verkooijen    (PID_211), E-mail: Address, on August 31, 2008 at 12:36 : In Reply to: Re: Sizing of ToFD Indications posted by : mj , E-mail: Address, on August 30, 2008 at 09:12 : 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 ------------ Follow Ups: Re: Sizing of ToFD Indications Ed Ginzel 01:42 Sep-02-2008 (0) Post a Followup: Name: E-Mail: Subject: Comments: ----------- 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 ------------ Optional Link URL: Example: "http://www....html". Alternative write "http://www.ndt.net/wshop/attach/filename.htm" if you transfered a filename.htm via FTP Page Title: is important! Optional Image URL: http://www....gif Attention! Please click the button only once. This may take a moment to process Forum Technical Discussions Help