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- since 1996 -
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Technical Discussions
Don
Don
06:03 Jul-15-2004
Ultrasonic beam profiles for angle probes in steel

Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
I can email excel sheet if interested in calcs


    
 
 Reply 
 
Godfrey Hands
Consultant,
PRI Nadcap, United Kingdom, Joined Nov 1998, 301

Godfrey Hands

Consultant,
PRI Nadcap,
United Kingdom,
Joined Nov 1998
301
09:17 Jul-16-2004
Re: Ultrasonic beam profiles for angle probes in steel
----------- Start Original Message -----------
: Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
: 1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
: 2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
: I can email excel sheet if interested in calcs
------------ End Original Message ------------

Don,

I guess the best way is to measure the 6dB and 20dB drop points of the probes using calibration blocks with holes at different depths.
If you need accurate figures, this has to be the best way, because small differences in probe construction will mean that "identical" probes will be slightly different, and certainly different to calculated.

Hope this helps.

Regards,

Godfrey Hands.



    
 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 177

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
177
04:30 Jul-16-2004
Re: Ultrasonic beam profiles for angle probes in steel
Hello,

To rely on calculated beam profiles for angle beam probes is critical for two reasons:

1. Usually angle beam testing in metals uses transverse waves. But these transverse waves are generated by mode conversion of longitudinal waves at the interface between plastic wedge and metal. This double mode conversion (transmission-reception) couples pressure forces to shear forces and is strongly dependent on the beam angle in the wegde and on the distance between transducer and plastic/metal interface (near field).
Therefore angle beams in a two-media arrangement are not always as calculated in a one-medium solution. Additionally the beam in the metal usually is not symmetrically shaped.

2. The knowledge about the transmitted beam size is only half the solution. If the pulse-echo technique is used. The shape of the reflected beam is strongly influenced by the interaction of the transmitted beam with the reflector (size, orientation, impedance, etc.).

To define zones of coverage, it is important not only to calculate or to measure by experiment the transmitted beam size, but also to do it with a reflector which has to be detected or rejected by the ultrasonic test. The beam width measured with a point like reflector e.g. is larger than the width for a planar defect of some wavelengths (notch).

So I underline the recommendations of Godfrey Hands:
To get reliable parameters of beam size in relation to coverage of the test object, you have to do experiments on test blocks providing test reflectors with size and shape related to those which have to be accepted or rejected by the ultrasonic test.

Kind regards
Udo Schlengermann
GE Inspection Technologies Systems GmbH
Huerth, Germany
udo.schlengermann@ae.ge.com




    
 
 Reply 
 
IClampers
IClampers
01:51 Jul-20-2004
Re: Ultrasonic beam profiles for angle probes in steel
Heres how I would do it;

Use the IOW block and use 3 side drilled holes at different depths. Set the maximized signal from the first SDH (side drilled hole) at 80%. Put a mark on the side of the IOW block where the index point is. Move the probe ahead until the signal drops to 40% full screen height. Put another mark, then move the probe back until you pass the 80% keep going until the signal goes to 40% FSH. Put another mark. You now have 3 marks on the IOW block. Repeat the same process for the other two SDH's at different depths. When all 3 have been done put a beam profile overlay on the side of the IOW block. The 0 point is where the marks you made on the IOW block are for each hole. With the overlay at each point put a dot where the actual SDH lies on the overlay. When done just connect the dots. This gives an actual beam profile for 6db boundry. To do the 20 db when you maximize the first signal on each hole add in 20 db then the points will be when the signal drops back to 80% after going off screen.


----------- Start Original Message -----------
: Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
: 1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
: 2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
: I can email excel sheet if interested in calcs
------------ End Original Message ------------




    
 
 Reply 
 
Ed T.
Ed T.
05:58 Jul-20-2004
Re: Ultrasonic beam profiles for angle probes in steel
----------- Start Original Message -----------
: Heres how I would do it;
: Use the IOW block and use 3 side drilled holes at different depths. Set the maximized signal from the first SDH (side drilled hole) at 80%. Put a mark on the side of the IOW block where the index point is. Move the probe ahead until the signal drops to 40% full screen height. Put another mark, then move the probe back until you pass the 80% keep going until the signal goes to 40% FSH. Put another mark. You now have 3 marks on the IOW block. Repeat the same process for the other two SDH's at different depths. When all 3 have been done put a beam profile overlay on the side of the IOW block. The 0 point is where the marks you made on the IOW block are for each hole. With the overlay at each point put a dot where the actual SDH lies on the overlay. When done just connect the dots. This gives an actual beam profile for 6db boundry. To do the 20 db when you maximize the first signal on each hole add in 20 db then the points will be when the signal drops back to 80% after going off screen.
:
: : Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
: : 1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
: : 2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
: : I can email excel sheet if interested in calcs
------------ End Original Message ------------

Please keep in mind the beam spread will vary from material to material and from probe/wedge combination to probe/wedge combination. I think the best way is to use the reflectors from hemispherical bottoms of round bottomed holes drilled in a block at varying depths. This allows you can find both the horizontal and vertical beam spread measurements.
This is detailed in ASME Section V, Article 4, Nonmandatory Appendix B-466and Figure B-466.



    
 
 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
09:18 Jul-20-2004
Re: Ultrasonic beam profiles for angle probes in steel
Concerning beam profiles
I would like to add to the excellent comments by my associates Schlengermann and Hands. The "calculated" divergence of beams is perhaps optimistic when dealing with assessment of the vertical extent of the beam (which seems to be the most prevalent assessment used). In an article by myself and Hotchkiss (http://www.ndt.net/article/ginzel/hotchkis/hotchkis.htm) we used a somewhat more rigorous method whereby modelled beams were analysed using a mock-up of the "traditional" techniques described using the IOW blocks. These may provide a rough estimate of divergence but another aspect not often considered is the fact that some of the beam is still forming its wavefront in an interference pattern within the wedge of an angle beam. The portion of the beam in the wedge and the fact that the near field may be in the wedge or may be formed beyond the wedge and inside steel being tested, will also have an effect on the assessed pressure distributions and hence the profile.

With theadvent of phased array probes and electronic raster scans this is an important consideration when the focal spot is intended to occur at a specific location. If the number of elements is just adequate for a focal spot to occur in the steel at the back of the wedge (thinest portion) there may not be enough elements in the focal law to focus in steel when using a longer soundpath in the wedge.

This highlights the general problem of assessing internally focused probes. The simple divergence equations applied from an unfocused probe are totally unsuitable when dealing with angled contact focused beams in steel.

Lateral beam size assessments are also required. This would be done to reduce the oversizing of flaw length. One technique used is described in ASME Section V Article 4 Figure B-466 (Nonmandatory Appendix B). But to carry out such an assessment by manual movement is, in reality, very difficult. Mechanised and encoded motion would be better to use with this technique.

Regards
Ed
----------- Start Original Message -----------
: Hello,
: To rely on calculated beam profiles for angle beam probes is critical for two reasons:
: 1. Usually angle beam testing in metals uses transverse waves. But these transverse waves are generated by mode conversion of longitudinal waves at the interface between plastic wedge and metal. This double mode conversion (transmission-reception) couples pressure forces to shear forces and is strongly dependent on the beam angle in the wegde and on the distance between transducer and plastic/metal interface (near field).
: Therefore angle beams in a two-media arrangement are not always as calculated in a one-medium solution. Additionally the beam in the metal usually is not symmetrically shaped.
: 2. The knowledge about the transmitted beam size is only half the solution. If the pulse-echo technique is used. The shape of the reflected beam is strongly influenced by the interaction of the transmitted beam with the reflector (size, orientation, impedance, etc.).
: To define zones of coverage, it is important not only to calculate or to measure by experiment the transmitted beam size, but also to do it with a reflector which has to be detected or rejected by the ultrasonic test. The beam width measured with a point like reflector e.g. is larger than the width for a planar defect of some wavelengths (notch).
: So I underline the recommendations of Godfrey Hands:
: To get reliable parameters of beam size in relation to coverage of the test object, you have to do experiments on test blocks providing test reflectors with size and shape related to those which have to be accepted or rejected by the ultrasonic test.
: Kind regards
: Udo Schlengermann
: GE Inspection Technologies Systems GmbH
: Huerth, Germany
: udo.schlengermann@ae.ge.com
------------ End Original Message ------------




    
 
 Reply 
 
Ed T.
Ed T.
01:39 Jul-20-2004
Re: Ultrasonic beam profiles for angle probes in steel
----------- Start Original Message -----------
: Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
: 1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
: 2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
: I can email excel sheet if interested in calcs
------------ End Original Message ------------

Gentlemen,
I believe we are deviating from the original question here.
If I’m not mistaken, Don originally, asked, "Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes?"
It was a simple question deserving of a simple answer. There was nothing mentioned of zones of coverage, focal spots or phased array. Only advice on the best way to estimate 6db and 20dB beam edges for angle probes.
Don is asking for help, so let's help him.
We all appreciate the input of knowledgeable, educated and experienced persons, and this is a forum for just that, but I think we need to address a question directly when a question is asked directly. Let's not complicate things that don't require complicating.
If he is using conventional UT with manual probes, we all know the best way to determine beam spread is to use the technique delineated in ASME V, Article 4, Nonmandatory Appendices, B466.
If he needs additional information, he can ask.
I sincerely apologize if I have offended anyone, but if I were to ask for help regarding NDT issues, I would appreciate a straight answer, as I'm sure all of you would as well.





    
 
 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
03:00 Jul-20-2004
Re: Ultrasonic beam profiles for angle probes in steel
Ed:
You are correct in assessing our apparent digression. However, I got the impression that Don was trying to CALCULATE the beam edges. In our very wordy explanations we seem to be agreeing that calculations are probably not the best option and can only give gross approximations at best. What all seem to agree on is that placing the probe on a block with small targets and performing a probe-specific amplitude drop assessment is the most reliable way of accomodating all the variables that might exist. (and even then the variable of constant coupling is to be overcome).

Perhaps a better knowledge of Don's requirement is required. Is this for a pressure vessel flaw size correction exercise or simply to order the probe that is most likely to have desired charateristics?
Ed

----------- Start Original Message -----------
: : Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes. I have tried 2 different methods, and do not know which is best.
: : 1)calculate divergence angles in wedge material, and then using snells law calculate new refracted angles in steel test material
: : 2)calculate "equivalent crystal size" and use this to calculate divergence angles in steel test material.
: : I can email excel sheet if interested in calcs
: Gentlemen,
: I believe we are deviating from the original question here.
: If I’m not mistaken, Don originally, asked, "Does anybody know the best way to estimate 6db and 20dB beam edges for angle probes?"
: It was a simple question deserving of a simple answer. There was nothing mentioned of zones of coverage, focal spots or phased array. Only advice on the best way to estimate 6db and 20dB beam edges for angle probes.
: Don is asking for help, so let's help him.
: We all appreciate the input of knowledgeable, educated and experienced persons, and this is a forum for just that, but I think we need to address a question directly when a question is asked directly. Let's not complicate things that don't require complicating.
: If he is using conventional UT with manual probes, we all know the best way to determine beam spread is to use the technique delineated in ASME V, Article 4, Nonmandatory Appendices, B466.
: If he needs additional information, he can ask.
: I sincerely apologize if I have offended anyone, but if I were to ask for help regarding NDT issues, I would appreciate a straight answer, as I'm sure all of you would as well.
------------ End Original Message ------------




    
 
 Reply 
 

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