Forum Technical Discussions      Re: Sizing of ToFD Indications Posted by: Nilesh Pathare , E-mail: Address, on September 01, 2008 at 09:26 : In Reply to: Re: Sizing of ToFD Indications posted by : Nigel Armstrong , E-mail: Address, on August 29, 2008 at 10:48 : 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 ------------ Follow Ups: Post a Followup: Name: E-Mail: Subject: Comments: ----------- Start Original Message ----------- : 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 ------------ 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