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- since 1996 -
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Technical Discussions
Mic
Consultant
AGM Techno consultants, India, Joined Jan 2003, 22

Mic

Consultant
AGM Techno consultants,
India,
Joined Jan 2003
22
02:39 Nov-03-2005
tofd on low thickness

Dear all,

What is the minimum thickness that can be tested with TOFD.

please give your valuable comments to mic_ndt@yahoo.com
please

some experts says 20 mm below can't be testd by TOFD???

please suggest.

Thanks
Mic




    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1268

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1268
03:13 Nov-04-2005
Re: tofd on low thickness
Mic:
TOFD is becoming a bit more popular now that it is recognised in some code documents. For practical weld inspections where the weld cap is left on there are physical was well as ultrasonic limitations. However, if used as just a forward scatter technique in isotropic media, without worries for phycyal constraints, wall thickness limitations are much reduced.
There is a paper documenting crack sizing on thin-walled tubing. The tube is 4mm wall, 100mm diameter, ZrNb alloy.
The paper is "Crack Depth Measurements in Thin-Walled Tubing", Lindenschmidt, KE and Moles, MDC., Review of Progress in Quantitative NDE, vol. 11, Plenum Press, 1992.
Error on crack depth sizing were within 0.1mm

Therefore to state a "minimum thickness" is not a simple matter. You must first define your application.

Ed

----------- Start Original Message -----------
: Dear all,
: What is the minimum thickness that can be tested with TOFD.
: please give your valuable comments to mic_ndt@yahoo.com
: please
: some experts says 20 mm below can't be testd by TOFD???
: please suggest.
: Thanks
: Mic
------------ End Original Message ------------




    
 
 Reply 
 
James Gauthier
Engineering,
ABB, Inc., USA, Joined Nov 2007, 25

James Gauthier

Engineering,
ABB, Inc.,
USA,
Joined Nov 2007
25
06:30 Nov-04-2005
Re: tofd on low thickness
Ed Ginzel could not have said it better. You must first establish the application. It seems that a lot of people have read certain articles and come away with an idea that TOFD is only good for thicknesses above 0.500 inch. The reality is that what is referenced in ASME Code Case 2235.

Weld reinforcement is crucial in determining how close together the two probes can come together for the appropriate focal depth required in the inspection. Certain weld types have little or no raised weld cap and make it easier to develope a working TOFD approach.

I would also like to summarize with the point that TOFD can be done on thicknesses below 0.500 inches. In fact in can be done on thicknesses a lot thinner, but you have to prove the application. Build the proper calibration block to represent what you are inspecting and then prove the TOFD technique to the customer. Proving the TOFD technique means you must establish detection and sizing capabilities. Keep in mind that you may have to use other techniques to compliment the other so that all aspects of detection and sizing are met.



    
 
 Reply 
 
Jim Knowles
Jim Knowles
06:41 Nov-04-2005
Re: tofd on low thickness
----------- Start Original Message -----------
: Mic:
: TOFD is becoming a bit more popular now that it is recognised in some code documents. For practical weld inspections where the weld cap is left on there are physical was well as ultrasonic limitations. However, if used as just a forward scatter technique in isotropic media, without worries for phycyal constraints, wall thickness limitations are much reduced.
: There is a paper documenting crack sizing on thin-walled tubing. The tube is 4mm wall, 100mm diameter, ZrNb alloy.
: The paper is "Crack Depth Measurements in Thin-Walled Tubing", Lindenschmidt, KE and Moles, MDC., Review of Progress in Quantitative NDE, vol. 11, Plenum Press, 1992.
: Error on crack depth sizing were within 0.1mm
: Therefore to state a "minimum thickness" is not a simple matter. You must first define your application.
: Ed
: : Dear all,
: : What is the minimum thickness that can be tested with TOFD.
: : please give your valuable comments to mic_ndt@yahoo.com
: : please
: : some experts says 20 mm below can't be testd by TOFD???
: : please suggest.
: : Thanks
: : Mic
------------ End Original Message ------------

As Ed quotes above, yes there are people using High Frequency transducers in a TOFD arrangement (25-50MHz)for use on thin sections (wrought product) what the success would be on austenitic stainless steel where the grain structure chanegs between an isotropic to an anistropic structure is an unknown unless careful attention is undertaken in the inspection qualification.
The lateral wave is a consideration but most modern TOFD equipment has the facility ofr Lateral and Back wall removal for evaluation of near suface indications.



    
 
 Reply 
 
Mic
Consultant
AGM Techno consultants, India, Joined Jan 2003, 22

Mic

Consultant
AGM Techno consultants,
India,
Joined Jan 2003
22
00:36 Nov-04-2005
Re: tofd on low thickness
Thanks to all for the valuable inputs,

My application is in service welds in hidrocarbon ind. the diameter is huge hence RT was not planned as safety precaution. I am intend to use ToFD-PE with MS 5800.

I intend to use 2mm Flat bottom holes at 1/3 from top of thickness and bottom and 1/2 of thickness. also top and bottom notch of 2 mm deep, 2mm width, and length about 25mm.

The thickness is 12.7 mm and 10 mm others are more then 20mm.

please suggest the possible design of if , the suggested calibration are not adiquate.

Mic


----------- Start Original Message -----------
: Mic:
: TOFD is becoming a bit more popular now that it is recognised in some code documents. For practical weld inspections where the weld cap is left on there are physical was well as ultrasonic limitations. However, if used as just a forward scatter technique in isotropic media, without worries for phycyal constraints, wall thickness limitations are much reduced.
: There is a paper documenting crack sizing onthin-walled tubing. The tube is 4mm wall, 100mm diameter, ZrNb alloy.
: The paper is "Crack Depth Measurements in Thin-Walled Tubing", Lindenschmidt, KE and Moles, MDC., Review of Progress in Quantitative NDE, vol. 11, Plenum Press, 1992.
: Error on crack depth sizing were within 0.1mm
: Therefore to state a "minimum thickness" is not a simple matter. You must first define your application.
: Ed
: : Dear all,
: : What is the minimum thickness that can be tested with TOFD.
: : please give your valuable comments to mic_ndt@yahoo.com
: : please
: : some experts says 20 mm below can't be testd by TOFD???
: : please suggest.
: : Thanks
: : Mic
------------ End Original Message ------------




    
 
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