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Technical Discussions
Marc Ferland
Marc Ferland
07:38 Jan-25-2008
Question about ASTM E2491

Hi,

My question is about the definition of "angle corrected gain" in ASTM E2491.

From the definition : "This is compensation for the variation in signal amplitudes received from fixed depth side drilled holes during S-scan calibration. The compensation is typically performed electronically at multiple depths. Note that there are technical limits to ACG, that is, beyond a certain angular range, compensation is not possible."

As I understand, ACG is used to compensate the attenuation due to beam steering. (This is why it's called _angle_ corrected gain... Am I right ?!)

The thing that is bothering me in this definition is that it stipulates that the compensation is done at multiple _depths_. Why multiple depths ? I thought TCG was applied at multiple depth (to compensate for the attenuation due to the material) and ACG at multiple angles (to compensate for beam steering). Or maybe the definition implicitly includes the TCG because the two can't live together when doing S-scan calibration.

Any clarification will be appreciated !

Thanks,

Marc Ferland



 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
00:31 Jan-26-2008
Re: Question about ASTM E2491
Marc;
Good question! I provided this definition from a list of Phased Array definitions that had been assembled with input from a variety of manufacturers and users. The wording in this definition does not seem to reflect the true intent of the function. In fact I do not think that this function even compensates for a fixed depth SDH. It is as you stated, to compensate for the effect of steering which is effectively for echo-transmittance loss with increasing angle (to some extent there is the added compensation for the slight change in wedge-path).
Using a Side Drilled Hole may not even be the best option. Instead, this would be better addressed using a radius to ensure a constant area reflecting surface.

Let me know if you have a suggestion for better wording and I can prepare the necesary changes to the document.

----------- Start Original Message -----------
: Hi,
: My question is about the definition of "angle corrected gain" in ASTM E2491.
: From the definition : "This is compensation for the variation in signal amplitudes received from fixed depth side drilled holes during S-scan calibration. The compensation is typically performed electronically at multiple depths. Note that there are technical limits to ACG, that is, beyond a certain angular range, compensation is not possible."
: As I understand, ACG is used to compensate the attenuation due to beam steering. (This is why it's called _angle_ corrected gain... Am I right ?!)
: The thing that is bothering me in this definition is that it stipulates that the compensation is done at multiple _depths_. Why multiple depths ? I thought TCG was applied at multiple depth (to compensate for the attenuation due to the material) and ACG at multiple angles (to compensate for beam steering). Or maybe the definition implicitly includes the TCG because the two can't live together when doing S-scan calibration.
: Any clarification will be appreciated !
: Thanks,
: Marc Ferland
------------ End Original Message ------------




 
 Reply 
 
Marc Ferland
Marc Ferland
06:12 Jan-28-2008
Re: Question about ASTM E2491
Ed,
Thanks a lot for your quick response. I personally would have said something like : "This is compensation for the variation in signal amplitudes caused by beam steering. The compensation is typically performed electronically at multiple angles. Note that there are technical limits to ACG, that is, beyond a certain angular range, compensation is not possible."

I've left out any reference to the SDH and/or radius because I'm not really sure what method should go in the definition (maybe calibrating on SDH is good enough for most application...)

Let me know what you think!
Marc


 
 Reply 
 
Luc Mauzeroll
Luc Mauzeroll
07:20 Apr-05-2008
Re: Question about ASTM E2491
Hello Mr. Ginzel, hello Marc,

Marc and myself have been discussing about the ACG recently, so he forwarded this topic to me.

I believe that you both are on the right track, but I would have something to add. I have made setups recently for a new job and I have fully calibrated the S-scan with ACG and TCG. I have noticed the same thing that Marc did when I calibrated using a side-drilled hole at constant depth, so I turned to the radius. But I had a hard time to calibrate from 35 to 75 degrees with the radius of the IIW block. We all know that we are losing amplitude at higher and lower angle, but I wondered why I could easily do it with a side-drilled hole at constant depth. Now the main point I want to bring to your attention is that the exit point moves from a phased-array probe. This means that if you try to calibrate from a single position, the beam will hit the radius penpendicularly at only one angle and the effect is going to be worst at higher and lower angles. It is to note that it is the same for delay calibration from a radius with a single probe position. You will end up with a distorted S-scan. Is it a possibility to still use the radius and move the probe for each angle? I doubt it.

Finally, not to show things worst than they are. As I said I used ACG and TGC recenlty, without using radius, and I have tested its quality with pretty good results. I measured amplitudes from 1.5 mm side-drilled holes at various depths, each 1/2", and at 45, 60 and 70 degrees. Most (90%) of the measures were within ±1 dB, a few would be more within ±2 dB.

Very interesting topic, I look forward to read your point of view, or from others too.

Luc Mauzeroll

----------- Start Original Message -----------
: Hi,
: My question is about the definition of "angle corrected gain" in ASTM E2491.
: From the definition : "This is compensation for the variation in signal amplitudes received from fixed depth side drilled holes during S-scan calibration. The compensation is typically performed electronically at multiple depths. Note that there are technical limits to ACG, that is, beyond a certain angular range, compensation is not possible."
: As I understand, ACG is used to compensate the attenuation due to beam steering. (This is why it's called _angle_ corrected gain... Am I right ?!)
: The thing that is bothering me in this definition is that it stipulates that the compensation is done at multiple _depths_. Why multiple depths ? I thought TCG was applied at multiple depth (to compensate for the attenuation due to the material) and ACG at multiple angles (to compensate for beam steering). Or maybe the definition implicitly includes the TCG because the two can't live together when doing S-scan calibration.
: Any clarification will be appreciated !
: Thanks,
: Marc Ferland
------------ End Original Message ------------




 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
00:42 Apr-05-2008
Re: Question about ASTM E2491
Luc
There seems to be an unfortunate potential to try to make focal laws do more than they are capable of. Just because the software can be used to enter a range of angles is perhaps misleading. But there are far too many variables for the manufacturer of probes and instruments to try to look after these limitations and in the end the verification of suitability is had by looking at the results on targets like those suggested in E-2491.

You indicated attempting to calibrate sensitivity using a range of angles from 35° to 75°! There are many reasons NOT to use this range, not the least of which there is a large component of the beam that is near the first critical angle. Just because you have entered a value of refraction that is 1° off the first critical angle (based on the centre ray of a "nominal" angle) does not mean you are clear of the beam divergence effects. In fact you are still generating some compression mode at this angle. Similarly, at the upper end of your range the divergence is causing a large portion of signal to mode convert to Rayleigh! (just look at the noise you see on a standard 70° monoelement probe!)

You have made no indication of the probe/wedge combination details. Some combinations may tolerate a bit more range and others less (but 35-75 is generally pushing thing past the limit in all cases).

Exit point migrations do occur but again, vary, depending on the probe and wedge. This could be 16mm for a long soudpath in a wedge over the range you indicated! Or it could be as small as 2-3mm on a small short wedge.

There is also a concern for focusing. Most codes do not use focusing for general weld inspection. You MAY be able to use some focusing to improve S/N ratio for some applications where the technique is not Code regulated or when working to a qualified procedure under limited tolerances of parameters. But this too (focusing) will have a significant effect on the ability to calibrate for a consistent sensitivity over a range of angles (the more you focus theless you are likely to maintain sensitivity with steering).

Regards
Ed

----------- Start Original Message -----------
: Hello Mr. Ginzel, hello Marc,
: Marc and myself have been discussing about the ACG recently, so he forwarded this topic to me.
: I believe that you both are on the right track, but I would have something to add. I have made setups recently for a new job and I have fully calibrated the S-scan with ACG and TCG. I have noticed the same thing that Marc did when I calibrated using a side-drilled hole at constant depth, so I turned to the radius. But I had a hard time to calibrate from 35 to 75 degrees with the radius of the IIW block. We all know that we are losing amplitude at higher and lower angle, but I wondered why I could easily do it with a side-drilled hole at constant depth. Now the main point I want to bring to your attention is that the exit point moves from a phased-array probe. This means that if you try to calibrate from a single position, the beam will hit the radius penpendicularly at only one angle and the effect is going to be worst at higher and lower angles. It is to note that it is the same for delay calibration from a radius with a single probe position. You will end up with a distorted S-scan. Is it a possibility to still use the radius and move the probe for each angle? I doubt it.
: Finally, not to show things worst than they are. As I said I used ACG and TGC recenlty, without using radius, and I have tested its quality with pretty good results. I measured amplitudes from 1.5 mm side-drilled holes at various depths, each 1/2", and at 45, 60 and 70 degrees. Most (90%) of the measures were within ±1 dB, a few would be more within ±2 dB.
: Very interesting topic, I look forward to read your point of view, or from others too.
: Luc Mauzeroll
: : Hi,
: : My question is about the definition of "angle corrected gain" in ASTM E2491.
: : From the definition : "This is compensation for the variation in signal amplitudes received from fixed depth side drilled holes during S-scan calibration. The compensation is typically performed electronically at multiple depths. Note that there are technical limits to ACG, that is, beyond a certain angular range, compensation is not possible."
: : As I understand, ACG is used to compensate the attenuation due to beam steering. (This is why it's called _angle_ corrected gain... Am I right ?!)
: : The thing that is bothering me in this definition is that it stipulates that the compensation is done at multiple _depths_. Why multiple depths ? I thought TCG was applied at multiple depth (to compensate for the attenuation due to the material) and ACG at multiple angles (to compensate for beam steering). Or maybe the definition implicitly includes the TCG because the two can't live together when doing S-scan calibration.
: : Any clarification will be appreciated !
: : Thanks,
: : Marc Ferland
------------ End Original Message ------------




 
 Reply 
 
Hamid
Engineering, Researcher
Ecole de technologie superieure, Canada, Joined Sep 2012, 59

Hamid

Engineering, Researcher
Ecole de technologie superieure,
Canada,
Joined Sep 2012
59
18:01 Nov-05-2014
Re: Question about ASTM E2491
In Reply to Ed Ginzel at 00:42 Apr-05-2008 .

Hi,

I am trying to make a phased-array reference block for a specific application. I went through ASTM E2491 and the discussions in the forum but I found nothing on the surface roughness of phased-array blocks.

I would please like to know if there is any restrictions on the surface roughness of a reference block for phased-array application.

Thanks,
Hamid Habibzadeh

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1303

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1303
13:37 Nov-06-2014
Re: Question about ASTM E2491
In Reply to Hamid at 18:01 Nov-05-2014 .

Hamid, your question is added to a thread on ACG. Perhaps surface finish of a block merits a new thread. E2491 gives guidance on evaluating performance of phased-array systems. The diagrams in E2491 are examples of how target patterns can be arranged to carry out some of the assessments. In the description for steering limit it is considered that the limitation is being assessed for a particular application. Typical of a practical application, E2491 states in A2.2 "Prepare a series of side drilled holes in the material to be used for the application at the distance or distances to be used in the application."
If you were making a "generic" block without concern for application it would be normal to make a "nice" surface like you see on the ISO 2400 Block #1 where the surface finish is very fine (0.8µm Ra).

 
 Reply 
 

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