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05:41 Mar-20-2008

Adam Stasuk

NDT Inspector, - -
Stasuk Testing & Inspection Ltd.,
Canada,
Joined Mar 2008
29
Rectangular vs Round Transducers

There have been several occasions found where sizing and acceptability of indications found during scanning of structural welds have been evaluated using only round transducers. These inspections were performed in accordance with the AWS/CSA UT criteria.

Specific requirements of effective crystal sizes within those AWS/CSA ultrasonic sections indicate sizing with effective width and height requirements which in principal should eliminate crystals of only diameter dimensions.

Are there conditions where a round crystal will produce a wavefront that will be equivalent to a wavefront of a rectangular crystal?

Can arguments be made that indications found by round crystal would not be equally found using rectangular or vice versa?

Would linear reflectors be more or less likely to be found than omni-directional reflectors with either transducer shape?

Are there any beam tool imaging programs that can image differences of wavefronts between the two crystal shapes?

Any responses or comments would be greatly appreciated.


 
04:11 Mar-20-2008

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
Re: Rectangular vs Round Transducers Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.

A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.

We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.


 
07:40 Mar-20-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1197
Re: Rectangular vs Round Transducers I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).

In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".

My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.

ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.

But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)


---------- Start Original Message -----------
: Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't bea whole lot of difference in response. If it's at the edges, there could be.
: We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------




 
02:01 Mar-24-2008

Adam Stasuk

NDT Inspector, - -
Stasuk Testing & Inspection Ltd.,
Canada,
Joined Mar 2008
29
Re: Rectangular vs Round Transducers Thanks Tom and Ed,
I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.

One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.

Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a larger squared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.

How do we judge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.

I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?

Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?

regards,
Adam Stasuk

----------- Start Original Message -----------
: I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
:
: ---------- Start Original Message -----------
: : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.
: : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------




 
03:38 Mar-25-2008

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1197
Re: Rectangular vs Round Transducers Adam:
What you observed is the basis for the AVG system (DGS in English) that Krautkramer described in the 1950s. The amplitude displayed is a function of the ratio of the flaw to the crystal areas. i.e. the same size flaw represents a larger area proportion for a smaller area probe. Getting all upset about a couple of dB is a bit silly. Differences can occur in spite of the same probe areas. Refracted angles can vary (and still be within tolerance) by +/-2 ° so you could have 4° variation between 2 operators with the same sized and shaped probe! A bit of skew to the beam (imposed by poor element mounting or even by the operator manually positioning the probe) can again vary the amplitude. I have measured 6 to 20dB drops from a 5° skew (depending on frequency, probe dimensions and soundpath).
It should be kept in mind that any amplitude "sorting" of indications above or below some arbitrary threshold level is statistical. Codes like AWS D1.1 (or W59) have a fair bit of conservatism built into them. This ensures that even poorly oriented flaws will provide signals exceeding the threshold. But it has no bearing on whether or not that flaw constitutes a critical condition. The AWS D1.1 accept/reject level (like most amplitude acceptance criteria) was arbitrarily set with no consideration for serviceability of the structure. They did not even verify the allowance made for attenuation! (the 2dB per inch is wrong and nobody ever questions it!)

Your question as to how to deal with this in future "if these borderline indications are in effect acceptable or rejectable without redoing the inspection", is best handled by the committee (who seem to rather sit on their hands on these matters).

You indicated the differences were "borderline" i.e. just acceptable versus "just rejectable". If assessment of a flaw by a single amplitude reading is the only option available then I suspect there are more important underlying issues in this code.

Condemning a component based on amplitude response is arbitrary and provides nothing more than a quick sorting tool. If the flaw "size" is really important then other methods of sizing it (non-amplitude-based) should be used.

As for comparing responses to element sizes and shapes, this was done 35-45 years ago. As I noted, it was the basis for the AVG system in the 1950s and then it was based on simple DSR (disc shaped reflectors) and piston generators (round elements). Ermolov extended this to other shapes (equivalent reflectors) and determined that usually the probe area was adequate for the amplitude calculations provided the length to width dimensions did not exceed 2:1 ratio. Scholarly work was carried out by Wustenburg and Mundry using these concepts to develop the Universal AVG Diagrams and I believe that Schlengermann carried out work to verify this.

Until the rules are changed we are stuck with them and should be active in trying to ensure they are current with new-found knowledge. Following them like so many sheep does not help.

Ed


----------- Start Original Message -----------
: Thanks Tom and Ed,
: I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.
: One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.
: Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a largersquared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.
: How do we judge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.
: I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?
: Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?
: regards,
: Adam Stasuk
: : I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: : In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: : My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: : ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: : But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
: :
: : ---------- Start Original Message -----------
: : : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.
: : : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------




 
06:34 Mar-25-2008

John Brunk

Engineering, NDT Level III
Self employed, part-time,
USA,
Joined Oct 1999
158
Re: Rectangular vs Round Transducers I strongly suspect that rectangular transducers were adopted, and then stretched to "paintbrush" proportions, because an accountant somewhere decided that an inspector scanning a long straight weld and finding no discontinuities to evaluate could do the work faster and cheaper as the element dimension parallel to the weld was increased. Digging deeply into the myths and legends of early NDT can reveal much that is not unfoolish from the scientific standpoint.

John Brunk (doing this stuff since 1962)

----------- Start Original Message -----------
: Adam:
: What you observed is the basis for the AVG system (DGS in English) that Krautkramer described in the 1950s. The amplitude displayed is a function of the ratio of the flaw to the crystal areas. i.e. the same size flaw represents a larger area proportion for a smaller area probe. Getting all upset about a couple of dB is a bit silly. Differences can occur in spite of the same probe areas. Refracted angles can vary (and still be within tolerance) by +/-2 ° so you could have 4° variation between 2 operators with the same sized and shaped probe! A bit of skew to the beam (imposed by poor element mounting or even by the operator manually positioning the probe) can again vary the amplitude. I have measured 6 to 20dB drops from a 5° skew (depending on frequency, probe dimensions and soundpath).
: It should be kept in mind that any amplitude "sorting" of indications above or below some arbitrary threshold level is statistical. Codes like AWS D1.1 (or W59) have a fair bit of conservatism built into them. This ensures that even poorly oriented flaws will provide signals exceeding the threshold. But it has no bearing on whether or not that flaw constitutes a critical condition. The AWS D1.1 accept/reject level (like most amplitude acceptance criteria) was arbitrarily set with no consideration for serviceability of the structure. They did not even verify the allowance made for attenuation! (the 2dB per inch is wrong and nobody ever questions it!)
: Your question as to how to deal with this in future "if these borderline indications are in effect acceptable or rejectable without redoing the inspection", is best handled by the committee (who seem to rather sit on their hands on these matters).
: You indicated the differences were "borderline" i.e. just acceptable versus "just rejectable". If assessment of a flaw by a single amplitude reading is the only option available then I suspect there are more important underlying issues in this code.
: Condemning a component based on amplitude response is arbitrary and provides nothing more than a quick sorting tool. If the flaw "size" is really important then other methods of sizing it (non-amplitude-based) should be used.
:
: As for comparing responses to element sizes and shapes, this was done 35-45 years ago. As I noted, it was the basis for the AVG system in the 1950s and then it was based on simple DSR (disc shaped reflectors) and piston generators (round elements). Ermolov extended this to other shapes (equivalent reflectors) and determined that usually the probe area was adequate for the amplitude calculations provided the length to width dimensions did not exceed 2:1 ratio. Scholarly work was carried out by Wustenburg and Mundry using these concepts to develop the Universal AVG Diagrams and I believe that Schlengermann carried out work to verify this.
: Until the rules are changed we are stuck with them and should be active in trying to ensure they are current with new-found knowledge. Following them like so many sheep does not help.
: Ed
:
:
: : Thanks Tom and Ed,
: : I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.
: : One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.
: : Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a larger squared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.
: : How do wejudge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.
: : I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?
: : Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?
: : regards,
: : Adam Stasuk
: : : I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: : : In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: : : My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: : : ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: : : But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
: : :
: : : ---------- Start Original Message -----------
: : : : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : : : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. Ifit's at the edges, there could be.
: : : : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------




 
09:59 Mar-25-2008

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
512
Re: Rectangular vs Round Transducers Further to this

I did some trials a while back comparing our own ORION (10mm diameter Crystal), SAO-series (10mm square crystal) and Krautkramer MWB (8x9 crystal) transducers: Obviously there are differences but to describe them as inconclusive would be mild.

I think the real issue is the Philosophy that says 51% indication (or whatever) is a reject and 49% is a pass and then gets upset when different operators/ transducers/ Equipment give different results. That's a much harder problem to solve

Joe


----------- Start Original Message -----------
: I strongly suspect that rectangular transducers were adopted, and then stretched to "paintbrush" proportions, because an accountant somewhere decided that an inspector scanning a long straight weld and finding no discontinuities to evaluate could do the work faster and cheaper as the element dimension parallel to the weld was increased. Digging deeply into the myths and legends of early NDT can reveal much that is not unfoolish from the scientific standpoint.
: John Brunk (doing this stuff since 1962)
: : Adam:
: : What you observed is the basis for the AVG system (DGS in English) that Krautkramer described in the 1950s. The amplitude displayed is a function of the ratio of the flaw to the crystal areas. i.e. the same size flaw represents a larger area proportion for a smaller area probe. Getting all upset about a couple of dB is a bit silly. Differences can occur in spite of the same probe areas. Refracted angles can vary (and still be within tolerance) by +/-2 ° so you could have 4° variation between 2 operators with the same sized and shaped probe! A bit of skew to the beam (imposed by poor element mounting or even by the operator manually positioning the probe) can again vary the amplitude. I have measured 6 to 20dB drops from a 5° skew (depending on frequency, probe dimensions and soundpath).
: : It should be kept in mind that any amplitude "sorting" of indications above or below some arbitrary threshold level is statistical. Codes like AWS D1.1 (or W59) have a fair bit of conservatism built into them. This ensures that even poorly oriented flaws will provide signals exceeding the threshold. But it has no bearing on whether or not that flaw constitutes a critical condition. The AWS D1.1 accept/reject level (like most amplitude acceptance criteria) was arbitrarily set with no consideration for serviceability of the structure. They did not even verify the allowance made for attenuation! (the 2dB per inch is wrong and nobody ever questions it!)
: : Your question as to how to deal with this in future "if these borderline indications are in effect acceptable or rejectable without redoing the inspection", is best handled by the committee (who seem to rather sit on their hands on these matters).
: : You indicated the differences were "borderline" i.e. just acceptable versus "just rejectable". If assessment of a flaw by a single amplitude reading is the only option available then I suspect there are more important underlying issues in this code.
: : Condemning a component based on amplitude response is arbitrary and provides nothing more than a quick sorting tool. If the flaw "size" is really important then other methods of sizing it (non-amplitude-based) should be used.
: :
: : As for comparing responses to element sizes and shapes, this was done 35-45 years ago. As I noted, it was the basis for the AVG system in the 1950s and then it was based on simple DSR (disc shaped reflectors) and piston generators (round elements). Ermolov extended this to other shapes (equivalent reflectors) and determined that usually the probe area was adequate for the amplitude calculations provided the length to width dimensions did not exceed 2:1 ratio. Scholarly work was carried out by Wustenburg and Mundry using these concepts to develop the Universal AVG Diagrams and I believe that Schlengermann carried out work to verify this.
: : Until the rules are changed we are stuck with them and should be active in trying to ensure they are current with new-found knowledge. Following them like so many sheep does not help.
: : Ed
: :
: :
: : : Thanks Tom and Ed,
: : : I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.
: : : One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.
: : : Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a larger squared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.
: : : How do we judge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.
: : : I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?
: : : Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?
: : : regards,
: : : Adam Stasuk
: : : : I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: : : : In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: : : : My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: : : : ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: : : : But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
: : : :
: : : : ---------- Start Original Message -----------
: : : : : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : : : : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.
: : : : : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------




 
04:57 Mar-26-2008

Hermann Wüstenberg

R & D
BAM Berlin,
Germany,
Joined Nov 1998
26
Re: Rectangular vs Round Transducers ----------- Start Original Message -----------
: Further to this
: I did some trials a while back comparing our own ORION (10mm diameter Crystal), SAO-series (10mm square crystal) and Krautkramer MWB (8x9 crystal) transducers: Obviously there are differences but to describe them as inconclusive would be mild.
: I think the real issue is the Philosophy that says 51% indication (or whatever) is a reject and 49% is a pass and then gets upset when different operators/ transducers/ Equipment give different results. That's a much harder problem to solve
: Joe
:
: : I strongly suspect that rectangular transducers were adopted, and then stretched to "paintbrush" proportions, because an accountant somewhere decided that an inspector scanning a long straight weld and finding no discontinuities to evaluate could do the work faster and cheaper as the element dimension parallel to the weld was increased. Digging deeply into the myths and legends of early NDT can reveal much that is not unfoolish from the scientific standpoint.
: : John Brunk (doing this stuff since 1962)
: : : Adam:
: : : What you observed is the basis for the AVG system (DGS in English) that Krautkramer described in the 1950s. The amplitude displayed is a function of the ratio of the flaw to the crystal areas. i.e. the same size flaw represents a larger area proportion for a smaller area probe. Getting all upset about a couple of dB is a bit silly. Differences can occur in spite of the same probe areas. Refracted angles can vary (and still be within tolerance) by +/-2 ° so you could have 4° variation between 2 operators with the same sized and shaped probe! A bit of skew to the beam (imposed by poor element mounting or even by the operator manually positioning the probe) can again vary the amplitude. I have measured 6 to 20dB drops from a 5° skew (depending on frequency, probe dimensions and soundpath).
: : : It should be kept in mind that any amplitude "sorting" of indications above or below some arbitrary threshold level is statistical. Codes like AWS D1.1 (or W59) have a fair bit of conservatism built into them. This ensures that even poorly oriented flaws will provide signals exceeding the threshold. But it has no bearing on whether or not that flaw constitutes a critical condition. The AWS D1.1 accept/reject level (like most amplitude acceptance criteria) was arbitrarily set with no consideration for serviceability of the structure. They did not even verify the allowance made for attenuation! (the 2dB per inch is wrong and nobody ever questions it!)
: : : Your question as to how to deal with this in future "if these borderline indications are in effect acceptable or rejectable without redoing the inspection", is best handled by the committee (who seem to rather sit on their hands on these matters).
: : : You indicated the differences were "borderline" i.e. just acceptable versus "just rejectable". If assessment of a flaw by a single amplitude reading is the only option available then I suspect there are more important underlying issues in this code.
: : : Condemning a component based on amplitude response is arbitrary and provides nothing more than a quick sorting tool. If the flaw "size" is really important then other methods of sizing it (non-amplitude-based) should be used.
: : :
: : : As for comparing responses to element sizes and shapes, this was done 35-45 years ago. As I noted, it was the basis for the AVG system in the 1950s and then it was based on simple DSR (disc shaped reflectors) and piston generators (round elements). Ermolov extended this to other shapes (equivalent reflectors) and determined that usually the probe area was adequate for the amplitude calculations provided the length to width dimensions did not exceed 2:1 ratio. Scholarly work was carried out by Wustenburg and Mundry using these concepts to develop the Universal AVG Diagrams and I believe that Schlengermann carried out work to verify this.
: : : Until the rules are changed we are stuck with themand should be active in trying to ensure they are current with new-found knowledge. Following them like so many sheep does not help.
: : : Ed
: : :
: : :
: : : : Thanks Tom and Ed,
: : : : I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.
: : : : One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.
: : : : Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a larger squared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.
: : : : How do we judge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.
: : : : I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?
: : : : Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?
: : : : regards,
: : : : Adam Stasuk
: : : : : I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: : : : : In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: : : : : My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: : : : : ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: : : : : But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
: : : : :
: : : : : ---------- Start Original Message -----------
: : : : : : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : : : : : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.
: : : : : : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
------------ End Original Message ------------

I would like to add some remarks to the very interesting discussion about the importance of rectangular shaped tranducers for the ultrasonic inspection. According to Dr. Josef Krautkramer, one of the main reasons to introduce rectangular membranes had been the necessity to use all resources for an improved sensitivity at probes using Quartz as a piezoelectric material. The wedges for angle beam probes offered a rectangular surface which could optimally used only by rectangular shaped transducers.
But today there are a lot of other reasons for the use of rectangular membranes. Some geometries are requiring the use of rectangular tranducers with a very specific length to width ratio to adapt to the coupling surfaces and positions or to shape the sound field according to the defect shape and situation. The linear phased array probes are allowing the application of variably sized rectangular tranducers. The transmitter-receiver probes for inclined L-waves or creeping waves are using rectangular shaped membranes with extreme length to width ratios.
This short list demonstrates that the question of soundfield and sensitivity setting for rectangular shaped tranducers is still of interest in ultrasonic inspection. Beside an old publication from 1976 (H. Wüstenberg, E. Schulz, W. Möhrle und J. Kutzner: „Zur Auswahl der Membranform bei Winkelprüfköpfen für die Ultraschallprüfung, (‚The choice of the transducer shape at angle beam probes for the Ultrasonic Inspection) “ Materialprüfung“. 18 (1976) Nr.7, July) there are two more recent works carried out at the BAM in Berlin in cooperation with IntelligeNDT Erlangen, which may be of a certain interest. They are:
Thesis of Thomas Rehfeldt (Technical University Berlin 2006), now employed at IntelligeNDT
“Theoretical and experimental verification of calculation fundamentals for sound fieldsteering in ultrasonic testing”
URL: http://opus.kobv.de/tuberlin/volltexte/2006/1279

Jens Vierke, Student work carried out at the BAM, September 2004 (Diplomarbeit) „Empfindlichkeitseinstellung und Echohöhenbewertung von Prüfköpfen mit schmalen rechteckigen Schwingern“ (Sensitivity setting and echo amplitude evaluation at probes with rectangular membranes)
28. September 2004
opus.kobv.de/tuberlin/volltexte/2006/1357/pdf/vierke_jens.pdf


H. Wüstenberg



 
08:54 Mar-26-2008

Adam Stasuk

NDT Inspector, - -
Stasuk Testing & Inspection Ltd.,
Canada,
Joined Mar 2008
29
Re: Rectangular vs Round Transducers I agree the difficult rope to walk is the 51% reject to 49% accept between different operators and equipment. The AVG/TVG/DGS methods are helpful in evaluating varied distance to gain parameters and I think most good UT technicians understand the variability of borderline calls when using any code criteria. It is sometimes more difficult to argue the point to clients and owners who only like to hear a line in the sand is drawn and there is no question to it. I appreciate all the responses and am considering requesting a ruling from AWS and CSA on the use of round transducers using their a/b/c/d calculation methods.

much appreciated discussions.

Adam

----------- Start Original Message -----------
: : Further to this
: : I did some trials a while back comparing our own ORION (10mm diameter Crystal), SAO-series (10mm square crystal) and Krautkramer MWB (8x9 crystal) transducers: Obviously there are differences but to describe them as inconclusive would be mild.
: : I think the real issue is the Philosophy that says 51% indication (or whatever) is a reject and 49% is a pass and then gets upset when different operators/ transducers/ Equipment give different results. That's a much harder problem to solve
: : Joe
: :
: : : I strongly suspect that rectangular transducers were adopted, and then stretched to "paintbrush" proportions, because an accountant somewhere decided that an inspector scanning a long straight weld and finding no discontinuities to evaluate could do the work faster and cheaper as the element dimension parallel to the weld was increased. Digging deeply into the myths and legends of early NDT can reveal much that is not unfoolish from the scientific standpoint.
: : : John Brunk (doing this stuff since 1962)
: : : : Adam:
: : : : What you observed is the basis for the AVG system (DGS in English) that Krautkramer described in the 1950s. The amplitude displayed is a function of the ratio of the flaw to the crystal areas. i.e. the same size flaw represents a larger area proportion for a smaller area probe. Getting all upset about a couple of dB is a bit silly. Differences can occur in spite of the same probe areas. Refracted angles can vary (and still be within tolerance) by +/-2 ° so you could have 4° variation between 2 operators with the same sized and shaped probe! A bit of skew to the beam (imposed by poor element mounting or even by the operator manually positioning the probe) can again vary the amplitude. I have measured 6 to 20dB drops from a 5° skew (depending on frequency, probe dimensions and soundpath).
: : : : It should be kept in mind that any amplitude "sorting" of indications above or below some arbitrary threshold level is statistical. Codes like AWS D1.1 (or W59) have a fair bit of conservatism built into them. This ensures that even poorly oriented flaws will provide signals exceeding the threshold. But it has no bearing on whether or not that flaw constitutes a critical condition. The AWS D1.1 accept/reject level (like most amplitude acceptance criteria) was arbitrarily set with no consideration for serviceability of the structure. They did not even verify the allowance made for attenuation! (the 2dB per inch is wrong and nobody ever questions it!)
: : : : Your question as to how to deal with this in future "if these borderline indications are in effect acceptable or rejectable without redoing the inspection", is best handled by the committee (who seem to rather sit on their hands on these matters).
: : : : You indicated the differences were "borderline" i.e. just acceptable versus "just rejectable". If assessment of a flaw by a single amplitude reading is the only option available then I suspect there are more important underlying issues in this code.
: : : : Condemning a component based on amplitude response is arbitrary and provides nothing more than a quick sorting tool. If the flaw "size" is really important then other methods of sizing it (non-amplitude-based) should be used.
: : : :
: : : : As for comparing responses to element sizes and shapes, this was done 35-45 years ago. As I noted, it was the basis for the AVG system in the 1950s and then it was based on simple DSR (disc shaped reflectors) and piston generators (round elements). Ermolov extended this to other shapes (equivalent reflectors) and determined that usually the probe area was adequate for the amplitude calculations provided the length to width dimensions did not exceed 2:1 ratio. Scholarly work was carried out by Wustenburg and Mundry using these concepts to develop the Universal AVG Diagrams and I believe that Schlengermann carried out work to verify this.
: : : : Until the rules are changed we are stuck with them and should be active in trying to ensure they are current with new-found knowledge. Following them like so many sheep does not help.
: : : : Ed
: : : :
: : : :
: : : : : Thanks Tom and Ed,
: : : : : I suspected the availability of the rectangular transducers in early days was the reason that the initial requirements were set for AWS and then the copycat CSA. My conundrum is that we have audited several high profile structural projects were two inspectors were conflicting on the acceptability of indications found on the same welds. They both agree on the indications presence but could not conquer on the amplitude levels.
: : : : : One inspector found that the indications were barelly acceptable using rectangular transducers while a secondary inspector came and rejected several of the indications but was using a round transducer. Our analysis found that although they were both technically using 1/2" transducers, one was 1/2"x1/2" while the other was 1/2" dia.
: : : : : Effectively the 1/2" dia, has a smaller effective crystal area and seems be able to resolve a smaller indication with a higher amplitude response than a larger squared transducer. I was also finding that the round transducer would envoke a higher amplitude response from a rounded reflector than the square unit would under equal calibration setup. Vise-Versa the square transducer would seem find the planar / fusion type indications easier than the rounded in my attempts between the two on the same points. Thus the criteria set out in E-1065 would show a round transducer responding better than the square.
: : : : : How do we judge in future if these borderline indications are in effect acceptable or rejectable without redoing the inspection? If we simply dictate a code requirement than the results of the square transducer should be the only one to be acceptable. However, a majority of the inspection personnel I find seem to be using the rounded for all applications including AWS without a pre-approved annex K. I typically prefer the the rounded transducer for ease of orbiting around any specific indications with an equal beam shape but cannot commit personnal preference over the code requirements.
: : : : : I am curious if the Olympus NDT group has evaluated the difference in signal response from a rounded or flat reflector using the two transducer shapes?
: : : : : Additionally out of curiousity, would round crystals in a PA system effect beam stearing differently than using the square ones?
: : : : : regards,
: : : : : Adam Stasuk
: : : : : : I suspect Tom is correct in the way this got codified and then we are stuck with it until someone sees the problems and actually does something about it (like any Code).
: : : : : : In its defence, AWS D1.1 (but not its outdated clone CSA W-59) has an informative Annex. Annex K in Section K4 states you may use "any other shape" provided they are included in the procedure and properly qualified".
: : : : : : My personal experience with rectangular elements is the tendency to have pronounced lobes off the corners. Probably a result of being more difficult to ensure mechanical clamping and therefore higher vibrational displacements.
: : : : : : ASTM E-1065 provides instruction on how to assess sound fields using either pulse-echo techniques and a ball reflector or a hydrophone.
: : : : : : But for a really interesting display there is a visualisation system using the principles of acoustography (see http://www.santecsystems.com/acoustography)
: : : : : :
: : : : : : ---------- Start Original Message -----------
: : : : : : : Interesting question. Square or rectangular elements are used in AWS code inspections, but circular elements are used in almost all other flaw detection and thickness gaging applications involving single-element transducers. I suspect that like a lot of other things in the industry, this got codified decades ago and now it's just the way things are.
: : : : : : : A rectangular element and a round element of the same frequency and diameter/major axis will always generate different beam profiles, with a symmetrical cylinder expanding into a cone in the far field for a round element, a squarish profile with rounded corners for a non-round element. Additionally, for a rectangular element the near field length and resulting pressure profiles will be different across the x and y dimensions, creating a rather complex beam profile. Of course the sound energy level out at the edges of the beam is much lower than at the center, so in practical terms this is less of an issue than it might seem. If your reference hole or flaw is near the center of the beam, there won't be a whole lot of difference in response. If it's at the edges, there could be.
: : : : : : : We (the Panametrics-NDT group of Olympus NDT) have used standard C-scan systems to generate very nice color beam profile images from various types of transducers by scanning across a small ball target while varying the water path. If you have access to an immersion C-scan system it's usually an easy thing to set up. No special software other than the basic C-scan package is required.
: I would like to add some remarks to the very interesting discussion about the importance of rectangular shaped tranducers for the ultrasonic inspection. According to Dr. Josef Krautkramer, oneof the main reasons to introduce rectangular membranes had been the necessity to use all resources for an improved sensitivity at probes using Quartz as a piezoelectric material. The wedges for angle beam probes offered a rectangular surface which could optimally used only by rectangular shaped transducers.
: But today there are a lot of other reasons for the use of rectangular membranes. Some geometries are requiring the use of rectangular tranducers with a very specific length to width ratio to adapt to the coupling surfaces and positions or to shape the sound field according to the defect shape and situation. The linear phased array probes are allowing the application of variably sized rectangular tranducers. The transmitter-receiver probes for inclined L-waves or creeping waves are using rectangular shaped membranes with extreme length to width ratios.
: This short list demonstrates that the question of soundfield and sensitivity setting for rectangular shaped tranducers is still of interest in ultrasonic inspection. Beside an old publication from 1976 (H. Wüstenberg, E. Schulz, W. Möhrle und J. Kutzner: „Zur Auswahl der Membranform bei Winkelprüfköpfen für die Ultraschallprüfung, (‚The choice of the transducer shape at angle beam probes for the Ultrasonic Inspection) “ Materialprüfung“. 18 (1976) Nr.7, July) there are two more recent works carried out at the BAM in Berlin in cooperation with IntelligeNDT Erlangen, which may be of a certain interest. They are:
: Thesis of Thomas Rehfeldt (Technical University Berlin 2006), now employed at IntelligeNDT
: “Theoretical and experimental verification of calculation fundamentals for sound field steering in ultrasonic testing”
: URL: http://opus.kobv.de/tuberlin/volltexte/2006/1279
:
: Jens Vierke, Student work carried out at the BAM, September 2004 (Diplomarbeit) „Empfindlichkeitseinstellung und Echohöhenbewertung von Prüfköpfen mit schmalen rechteckigen Schwingern“ (Sensitivity setting and echo amplitude evaluation at probes with rectangular membranes)
: 28. September 2004
: opus.kobv.de/tuberlin/volltexte/2006/1357/pdf/vierke_jens.pdf
:
: H. Wüstenberg
------------ End Original Message ------------




 


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