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- since 1996 -
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Technical Discussions
Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 138

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
09:49 Sep-07-2003
TOFD versus Phased Array

Interested on comments regarding TOFD versus Phased Array? I have asked a few manufacturers which system gives the best results on duplex stainless steels and never get any detailed responses.

1. I have heard Phased Array is better on Duplex stainless steels.

2. I have heard TOFD is no good on Duplex stainless steels

3. I have heard TOFD can be used on Duplex stainless steels (no mention of if it works or not, depends on who s selling it).

Curious to hear from hands on people of what works and what doesnt.

Kind Regards

Mike Trinidad


    
 
 Reply 
 
Steven Johnson
Consultant
USA, Joined Mar 2004, 16

Steven Johnson

Consultant
USA,
Joined Mar 2004
16
01:14 Sep-08-2003
Re: TOFD versus Phased Array
TOFD has problems in Stainless steel welds due to the large grain structure. Phased array works good on Stainless, but has been having problems with the dissimular material welds.


    
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1266

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1266
07:21 Sep-08-2003
Re: TOFD versus Phased Array
Michael:
I find it interesting that people are telling you that you should even be COMPARING TOFD to Phased Array.

As for the concerns of Duplex stainless I would think that the difficulties experienced are based on the relatively coarse grain structure, and solutions are being sought for ultrasonic applications that attempt to provide a reduction of the grain boundary scattering of ANY beam, no matter its origin. TOFD is merely a forward scatter technique and USUALLY (but not always) uses compression mode wave. The longer wavelength in a compression mode is less scattered for the same frequency using shear mode. Similar efforts have been made using backscatter techniques using the compression mode. But all angled compression beams induced in a material, using refraction from the probe, will also suffer from the mode conversion effects when used under the first critical angle.

But back to the first point, i.e. that being TOFD versus Phased Array. I do not see this as a "comparison"!! TOFD is a forward scatter application of a wavefront, i.e. it is a UT technique. But Phased array is simply a convenient method of forming a wavefront, i.e. it is a hardware apparatus. There is no real difference between a 5MHz compression planewave generated by a single element probe and that produced by a phased array probe of similar dimensions (the basic concept of Huygens' point construction of a wavefront).

Advantages of phased array over single element probes may be discussed but it would not be correct to compare TOFD to phased array, in fact, I have used phased array probes in TOFD configurations. In fact, many of the basic concepts we learn in Level 1 UT courses, such as Near Zone lengths, Beam Diameter calculations, beam diveregence, etc. can all be used with the beam analyses on phased array generated pulses.

Ed


----------- Start Original Message -----------
: Interested on comments regarding TOFD versus Phased Array? I have asked a few manufacturers which system gives the best results on duplex stainless steels and never get any detailed responses.
: 1. I have heard Phased Array is better on Duplex stainless steels.
: 2. I have heard TOFD is no good on Duplex stainless steels
: 3. I have heard TOFD can be used on Duplex stainless steels (no mention of if it works or not, depends on who s selling it).
: Curious to hear from hands on people of what works and what doesnt.
: Kind Regards
: Mike Trinidad
------------ End Original Message ------------





    
 
 Reply 
 
Jamie Gauthier
Jamie Gauthier
09:18 Sep-08-2003
Re: TOFD versus Phased Array
I definitely have to agree with Ed Ginzels comment on this. You cannot compare TOFD with Phased Array! Now to get back to TOFD on stainless materials it is a matter of trying it out on a test piece. Depending on the grain structure, some materials can be tested with the TOFD technique. A sample piece made out of the same material can be used to determine if you have good enough sensitivity to detect welding defects. Of course you still need to use shearwave to inspect the root and cap of the weld. It may not work with some stainless steel alloys. Having a wide variety of transducers to test with also helps.





    
 
 Reply 
 
Mike Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 138

Mike Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
08:34 Oct-04-2003
Re: TOFD versus Phased Array
Ed and Jamie

Thanks for the interesting comments which are much food for thought.

Actually good to get some straight answers.

Regards

Mike Trinidad
----------- Start Original Message -----------
: I definitely have to agree with Ed Ginzels comment on this. You cannot compare TOFD with Phased Array! Now to get back to TOFD on stainless materials it is a matter of trying it out on a test piece. Depending on the grain structure, some materials can be tested with the TOFD technique. A sample piece made out of the same material can be used to determine if you have good enough sensitivity to detect welding defects. Of course you still need to use shearwave to inspect the root and cap of the weld. It may not work with some stainless steel alloys. Having a wide variety of transducers to test with also helps.
------------ End Original Message ------------




    
 
 Reply 
 
mojtaba
mojtaba
07:29 Dec-19-2004
Re: TOFD versus Phased Array
hi


    
 
 Reply 
 

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