where expertise comes together - since 1996

Web's Largest Portal of Nondestructive Testing (NDT)
Open Access Database (Conference Proceedings, Articles, News), Exhibition, Forum, Network

All Forum Boards
Technical Discussions >
TOFD signals between L-L Backwall and L-Shear Backwall echo.
Career Discussions
Job Offers
Job Seeks
Classified Ads
About NDT.net
Articles & News

1865 views
05:27 Mar-03-2008

Roberto Otero

R & D, Consultant
Venezuela,
Joined Aug 2004
14
TOFD signals between L-L Backwall and L-Shear Backwall echo.

In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
Thanks in advance.
Roberto


 
03:08 Mar-03-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. Roberto:
I do not know if there is an absolute method for this. In the book by Charlesworth and Temple there is an image (Figure 5-8) that shows all the arcs for the Compression, Shear and Rayleigh modes and indicates the top and bottom signals for a single planar flaw. This image is a VERY confusing "mess" to look at.
The authors state that "...it may be necessary to make a judgement as to which are the unconverted compression wave signals from the top and bottom of the defect and then calculate the positions and curve-shapes of all possible mode converted signals."

The example they used had no backwall so it was a very thick section. It can get even more complicated on thinner sections. You may have a signal that is too weak to see in the compression mode (or lost in the lateral wave) and it may appear as a mode converted shear prior to the backwall. OR, it may provide a stronger signal from the shear headwave that may (or may not) be mode converted to compression mode.

Knowing what isin the specimen and working backwards (as done in the Figure 5-8 of the TOFD book) is fine for the mathematical assessment of the signals (although not simple!). But to see the signals without knowing all the details of their origin and try to account for what caused them is not always a straight-forward mathematic solution (and I am not sure it can be done with 100% certainty).

Ed


----------- Start Original Message -----------
: In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: Thanks in advance.
: Roberto
------------ End Original Message ------------




 
08:46 Mar-05-2008

Roberto Otero

R & D, Consultant
Venezuela,
Joined Aug 2004
14
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. ----------- Start Original Message -----------
: Roberto:
: I do not know if there is an absolute method for this. In the book by Charlesworth and Temple there is an image (Figure 5-8) that shows all the arcs for the Compression, Shear and Rayleigh modes and indicates the top and bottom signals for a single planar flaw. This image is a VERY confusing "mess" to look at.
: The authors state that "...it may be necessary to make a judgement as to which are the unconverted compression wave signals from the top and bottom of the defect and then calculate the positions and curve-shapes of all possible mode converted signals."
: The example they used had no backwall so it was a very thick section. It can get even more complicated on thinner sections. You may have a signal that is too weak to see in the compression mode (or lost in the lateral wave) and it may appear as a mode converted shear prior to the backwall. OR, it may provide a stronger signal from the shear headwave that may (or may not) be mode converted to compression mode.
: Knowing what is in the specimen and working backwards (as done in the Figure 5-8 of the TOFD book) is fine for the mathematical assessment of the signals (although not simple!). But to see the signals without knowing all the details of their origin and try to account for what caused them is not always a straight-forward mathematic solution (and I am not sure it can be done with 100% certainty).
: Ed
:
: : In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: : Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: : Thanks in advance.
: : Roberto
------------ End Original Message ------------

Hi Ed:
Thanks for your complete answer (as usual).
I was waiting for someone else to give us other point of view. I understand this is not an easy task. Perhaps it could be a field to be researched in future applications of TOFD technique.
But what is funny to me is this area in a TOFD image (between L-L and L-S Backwall echo) is larger than the "longitudinal area" ( I mean the area defined between the lateral wave and Long. backwall echo).
Thanks again.
Roberto


 
00:50 Mar-06-2008
Ryan Burns
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. ----------- Start Original Message -----------
: : Roberto:
: : I do not know if there is an absolute method for this. In the book by Charlesworth and Temple there is an image (Figure 5-8) that shows all the arcs for the Compression, Shear and Rayleigh modes and indicates the top and bottom signals for a single planar flaw. This image is a VERY confusing "mess" to look at.
: : The authors state that "...it may be necessary to make a judgement as to which are the unconverted compression wave signals from the top and bottom of the defect and then calculate the positions and curve-shapes of all possible mode converted signals."
: : The example they used had no backwall so it was a very thick section. It can get even more complicated on thinner sections. You may have a signal that is too weak to see in the compression mode (or lost in the lateral wave) and it may appear as a mode converted shear prior to the backwall. OR, it may provide a stronger signal from the shear headwave that may (ormay not) be mode converted to compression mode.
: : Knowing what is in the specimen and working backwards (as done in the Figure 5-8 of the TOFD book) is fine for the mathematical assessment of the signals (although not simple!). But to see the signals without knowing all the details of their origin and try to account for what caused them is not always a straight-forward mathematic solution (and I am not sure it can be done with 100% certainty).
: : Ed
: :
: : : In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: : : Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: : : Thanks in advance.
: : : Roberto
: Hi Ed:
: Thanks for your complete answer (as usual).
: I was waiting for someone else to give us other point of view. I understand this is not an easy task. Perhaps it could be a field to be researched in future applications of TOFD technique.
: But what is funny to me is this area in a TOFD image (between L-L and L-S Backwall echo) is larger than the "longitudinal area" ( I mean the area defined between the lateral wave and Long. backwall echo).
: Thanks again.
: Roberto
------------ End Original Message ------------

Roberto,

This is due to the nature of the technique (Time of Flight). Shear wave velocity is slower than the Longitudinal induced with the firing transducer. Keeping in mind that the Y axis represents time, it would make sense that the mode converted shear waves are "larger" in the D scan.

I have always used the mode converted signals as confirmation of the indication in the L wave zone. Sometimes, due to the velocity difference and separation in the signals, it is also possible to classify the defect, ie slag versus LOF, when close to your dead zones.

I hope this helps, but forgive me if I did'nt understand your question.

Ryan.


 
08:37 Mar-06-2008
Alex McLay
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. ----------- Start Original Message -----------
: : Roberto:
: : I do not know if there is an absolute method for this. In the book by Charlesworth and Temple there is an image (Figure 5-8) that shows all the arcs for the Compression, Shear and Rayleigh modes and indicates the top and bottom signals for a single planar flaw. This image is a VERY confusing "mess" to look at.
: : The authors state that "...it may be necessary to make a judgement as to which are the unconverted compression wave signals from the top and bottom of the defect and then calculate the positions and curve-shapes of all possible mode converted signals."
: : The example they used had no backwall so it was a very thick section. It can get even more complicated on thinner sections. You may have a signal that is too weak to see in the compression mode (or lost in the lateral wave) and it may appear as a mode converted shear prior to the backwall. OR, it may provide a stronger signal from the shear headwave that may (ormay not) be mode converted to compression mode.
: : Knowing what is in the specimen and working backwards (as done in the Figure 5-8 of the TOFD book) is fine for the mathematical assessment of the signals (although not simple!). But to see the signals without knowing all the details of their origin and try to account for what caused them is not always a straight-forward mathematic solution (and I am not sure it can be done with 100% certainty).
: : Ed
: :
: : : In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: : : Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: : : Thanks in advance.
: : : Roberto
: Hi Ed:
: Thanks for your complete answer (as usual).
: I was waiting for someone else to give us other point of view. I understand this is not an easy task. Perhaps it could be a field to be researched in future applications of TOFD technique.
: But what is funny to me is this area in a TOFD image (between L-L and L-S Backwall echo) is larger than the "longitudinal area" ( I mean the area defined between the lateral wave and Long. backwall echo).
: Thanks again.
: Roberto
------------ End Original Message ------------

1) Part of our training course is how to set up such that the signals become meaningful and interpret these signals to identify different types of defect
2) We are working on an analysis module in our ScanPlan software. This will allow interpretation on depth and location based upon offset/combined scanning.

I hope this helps! If you have a particular problem we can send, as a one off, a represntation showing long/long/long/shear etc.



 
07:20 Mar-11-2008
Massimo Carminati
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. ----------- Start Original Message -----------
In addition to what clearly stated, one of the benefits is detection of segregations in the plates which are sometimes not appearing in the LL area, even if they are sometimes within the LL area and close to the BW. The main problem is the "size" of the LL backwall which may vary significantly during a scan (hi-lo, cladding thickness, scanner offset etc.). Be careful because sometimes you can get continous clear indications below LL backwall which may be due to High PRF, wedges geometry and .....
: In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: Thanks in advance.
: Roberto
------------ End Original Message ------------




 
05:59 Mar-11-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: TOFD signals between L-L Backwall and L-Shear Backwall echo. Roberto:
To better clarify the potential complexities I decided to insert some images and a better description. I have posted these on my website at http://www.mri.on.ca/DoubleImaging.pdf

Even the region from the lateral wave to the backwall should not be considered in terms of JUST compression mode. There is no easy solution. Just projects for research fellows!
Ed


----------- Start Original Message -----------
: : Roberto:
: : I do not know if there is an absolute method for this. In the book by Charlesworth and Temple there is an image (Figure 5-8) that shows all the arcs for the Compression, Shear and Rayleigh modes and indicates the top and bottom signals for a single planar flaw. This image is a VERY confusing "mess" to look at.
: : The authors state that "...it may be necessary to make a judgement as to which are the unconverted compression wave signals from the top and bottom of the defect and then calculate the positions and curve-shapes of all possible mode converted signals."
: : The example they used had no backwall so it was a very thick section. It can get even more complicated on thinner sections. You may have a signal that is too weak to see in the compression mode (or lost in the lateral wave) and it may appear as a mode converted shear prior to the backwall. OR, it may provide a stronger signal from the shear headwave that may (or may not) be mode converted to compression mode.
: : Knowing what is in the specimen and working backwards (as done in the Figure 5-8 of the TOFD book) is fine for the mathematical assessment of the signals (although not simple!). But to see the signals without knowing all the details of their origin and try to account for what caused them is not always a straight-forward mathematic solution (and I am not sure it can be done with 100% certainty).
: : Ed
: :
: : : In a TOFD image it is recommended (ASME for example) a complete TOFD image including also the shear diffracted signals.
: : : Where can I find clear and practical guidelines to make decissions and to understand the signals which appears between the Long- Long backwall echo and the Long-Shear backwall echo?
: : : Thanks in advance.
: : : Roberto
: Hi Ed:
: Thanks for your complete answer (as usual).
: I was waiting for someone else to give us other point of view. I understand this is not an easy task. Perhaps it could be a field to be researched in future applications of TOFD technique.
: But what is funny to me is this area in a TOFD image (between L-L and L-S Backwall echo) is larger than the "longitudinal area" ( I mean the area defined between the lateral wave and Long. backwall echo).
: Thanks again.
: Roberto
------------ End Original Message ------------




 
07:51 Aug-16-2008
sanjeevreddy
in tofd if we introduce shar waves instead of lwaves what are the major applications . ----------- Start Original Message -----------
in tofd if we introduce shar waves instead of lwaves what are the major applications .


 


© NDT.net - The Web's Largest Portal of Nondestructive Testing (NDT) ISSN 1435-4934

Open Access Database, |Conference Proceedings| |Articles| |News| |Exhibition| |Forum| |Professional Network|