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1158 views
06:16 Sep-26-2003

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1185
AUT simulator discussions

AUT simulator discussions

Due to the misreading of the forum item I posted by Mr. Rawlinson, I am posting another item where his concerns might be more appropriately addressed. Not having used the simulator indicated in his point, I cannot speak to the efficacy of the tool. If it is based on a raytracing algorithm it may provide a coarse explanation of amplitude deviation with respect to flaw orientation but to do justice to the REAL conditions EFIT modelling is required as described by Langenberg (see article online at http://www.ndt.net/article/ecndt02/195/195.htm). Unless the simulator can duplicate all the conditions of diffraction, mode conversion and echo-transmittance coefficient effects due to angle changes, it is not truly a decent simulation tool for indicating the REAL conditions of the AUT pipeline girth weld application.

The other point Mr. Rawlinson makes is his perception that coupling monitor checks are “…the most critical factor in ACC/Rej criteria”

He suggested that, “Until a company develops a system which automaticaly compensates amplitude levels to couplant loss we should be working at FBH+6DB (as the ACC/Rej level).”

Perhaps Mr. Rawlinson does not understand the technique used by most AUT companies to monitor coupling and why the allowance for variation is incorporated. This is an ideal venue to explain the situation and dispel the notion that we need auto-compensation.

In a girth weld that has been made where the weld axis is vertical (as in land-lay and S-lay projects) most AUT systems set up a pitch-catch configuration on the bottom of the pipe where, not only is the spring tension weakest but also, the crown of the weld is the highest and any extra losses due to the crown scattering portions of the beam can be compensated by adding gain to the receiver to ensure there is adequate signal received to indicate that there is couplant under BOTH the transmitting and receiving probes. This technique is configured that the zonal probe on one side transmit to the zonal probe on the opposite side of the weld. Verification that couplant is under the probe wedge is the sole reason for the couping check!

But loss of coupling signal using this technique need not only indicate loss of fluid. It is often indicated by the hi-lo (mismatch) condition, i.e. the beam is redirected or scattered by a change in geometry (not a real loss of coupling). No matter how “wet” you make the surface under such conditions you are NOT going to get an indication in the coupling monitor gate.

Coupling can also be lost when a flaw is present in the weld, i.e. the flaw interupts the through transmission. Providing this flaw is indicated as a Defect (i.e. the flaw is rejectable) this is not usually an issue because the flaw is removed in the repair. But if it is an acceptable flaw and still reduces the energy across the weld for coupling check it MIGHT cause some issues of concern for coupling.

These shortcomings of the through transmission technique can be remedied by using a separate probe for coupling checks. This option was noted in Krautkramer’s text many years ago. These were zero degree probes built into the wedge and fired separately from the angle beam. Essentially the zero degree would monitor the first backwall for significant amplitude drops. The technique doubles as a thickness monitor as well as a coupling monitor.

Another point Mr. Rawlinson has missed is that, in most AUT girth weld specifications, a requirement that EACH "probe" must have a monitoring channel. For a large multi-probe array using 20 or 30 separate wedges, that would technically be 20-30 coupling channels! Most systems have dodged the point and set up a single coupling channel for a zone and further reduce compliance by selecting only one pair of the tandems where tandem probes are used.

There is a need to monitor for coupling but Mr. Rawlinson is not correct that over-sensitivity is the only solution or that auto-coupling correction be should eventually be made by adding gain by some sort of feedback loop to the receivers. One must consider that the loss of coupling “signal” does not always mean the same as loss of “coupling fluid”.




 
03:00 Sep-26-2003
paul rawlinson
Re: AUT simulator discussions The research Mr Ginzle mentions is good science for Numerical Methods for the Modelling of Acoustic, Electromagnetic, Elastic and Piezoelectric Wave Propagation Problems in the Time Domain Based on the Finite Integration Technique, but can not help an inspector to grasp principles of ultrasonic testing in the real world, let alone understand AUT setups and acc/rej concepts.
The Genesis is a much simpler tool , designed not for the research student but for the NDE inspector.
The role of genesis UT simulator is not to push the envelope of acoustic science but simply to provide a simulation of the real UT world, with virtual UT equipment and virtual welds and virtual defects.
Mr Ginzle will be pleased to learn that the Genesis UT simulator takes into account probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, and Through Transmission, Hilo, root defects, porositymapping, TOF (transit)
And it simulates in the style of Krautkramer, Panametrics, RTD, RDTech, Shaw, WeldSonix, and includes multiple calibration blocks and probes.The software was developed by AUTO-Ut using experimental data and without the endorsement or support of any 3rd party company.
As far as the other points Mr Ginzle makes concerning couplant loss flagging, he has addressed well many of the concerns the industry shares.


--
This message was posted into the NDT.net Forum.
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Please do not reply to email: forum@ndt.net
For your reply to this message go to:
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----------- Start Original Message -----------
: AUT simulator discussions
: Due to the misreading of the forum item I posted by Mr. Rawlinson, I am posting another item where his concerns might be more appropriately addressed. Not having used the simulator indicated in his point, I cannot speak to the efficacy of the tool. If it is based on a raytracing algorithm it may provide a coarse explanation of amplitude deviation with respect to flaw orientation but to do justice to the REAL conditions EFIT modelling is required as described by Langenberg (see article online at http://www.ndt.net/article/ecndt02/195/195.htm). Unless the simulator can duplicate all the conditions of diffraction, mode conversion and echo-transmittance coefficient effects due to angle changes, it is not truly a decent simulation tool for indicating the REAL conditions of the AUT pipeline girth weld application.
: The other point Mr. Rawlinson makes is his perception that coupling monitor checks are “…the most critical factor in ACC/Rej criteria”
: He suggested that, “Until a company develops a system which automaticaly compensates amplitude levels to couplant loss we should be working at FBH+6DB (as the ACC/Rej level).”
: Perhaps Mr. Rawlinson does not understand the technique used by most AUT companies to monitor coupling and why the allowance for variation is incorporated. This is an ideal venue to explain the situation and dispel the notion that we need auto-compensation.
: In a girth weld that has been made where the weld axis is vertical (as in land-lay and S-lay projects) most AUT systems set up a pitch-catch configuration on the bottom of the pipe where, not only is the spring tension weakest but also, the crown of the weld is the highest and any extra losses due to the crown scattering portions of the beam can be compensated by adding gain to the receiver to ensure there is adequate signal received to indicate that there is couplant under BOTH the transmitting and receiving probes. This technique is configured that the zonal probe on one side transmit to the zonal probe on the opposite side of the weld. Verification that couplant is under the probe wedge is the sole reason for the couping check!
: But loss of coupling signal using this technique need not only indicate loss of fluid. It is often indicated by the hi-lo (mismatch) condition, i.e. the beam is redirected or scattered by a change in geometry (not a real loss of coupling). No matter how “wet” you make the surface under such conditions you are NOT going to get an indication in the coupling monitor gate.
: Coupling can also be lost when a flaw is present in the weld, i.e. the flaw interupts the through transmission. Providing this flaw is indicated as a Defect (i.e. the flaw is rejectable) this is not usually an issue because the flaw is removed in the repair. But if it is an acceptable flaw and still reduces the energy across the weld for coupling check it MIGHT cause some issues of concern for coupling.
: These shortcomings of the through transmission technique can be remedied by using a separate probe for coupling checks. This option was noted in Krautkramer’s text many years ago. These were zero degree probes built into the wedge and fired separately from the angle beam. Essentially the zero degree would monitor the first backwall for significantamplitude drops. The technique doubles as a thickness monitor as well as a coupling monitor.
: Another point Mr. Rawlinson has missed is that, in most AUT girth weld specifications, a requirement that EACH "probe" must have a monitoring channel. For a large multi-probe array using 20 or 30 separate wedges, that would technically be 20-30 coupling channels! Most systems have dodged the point and set up a single coupling channel for a zone and further reduce compliance by selecting only one pair of the tandems where tandem probes are used.
: There is a need to monitor for coupling but Mr. Rawlinson is not correct that over-sensitivity is the only solution or that auto-coupling correction be should eventually be made by adding gain by some sort of feedback loop to the receivers. One must consider that the loss of coupling “signal” does not always mean the same as loss of “coupling fluid”.
------------ End Original Message ------------




 
02:16 Sep-28-2003

Daniel H.Rice Consulting Services

Consultant, Ultrasonic Evaluation of Resistance Spot Welding
Daniel H. Rice Consulting Services,
USA,
Joined Jan 2003
10
Re: AUT simulator discussions I wanted to say something about a SIM but did not have the practical experince of performing the test.
Thankyou for your imput!!

In my experince with other SIMS, A SIM is a good place to start, a Level II inspector! Then we can let the inspector experince real world conditions, under direct supervision of a designated inspector or a level III adminisrator as your business case describes.

Follow the ASNT-TC-1A Training guidelines for "On the Job training and experince", ans you will recieve better inspectors.

----------- Start Original Message -----------
: AUT simulator discussions
: Due to the misreading of the forum item I posted by Mr. Rawlinson, I am posting another item where his concerns might be more appropriately addressed. Not having used the simulator indicated in his point, I cannot speak to the efficacy of the tool. If it is based on a raytracing algorithm it may provide a coarse explanation of amplitude deviation with respect to flaw orientation but to do justice to the REAL conditions EFIT modelling is required as described by Langenberg (see article online at http://www.ndt.net/article/ecndt02/195/195.htm). Unless the simulator can duplicate all the conditions of diffraction, mode conversion and echo-transmittance coefficient effects due to angle changes, it is not truly a decent simulation tool for indicating the REAL conditions of the AUT pipeline girth weld application.
: The other point Mr. Rawlinson makes is his perception that coupling monitor checks are “…the most critical factor in ACC/Rej criteria”
: He suggested that, “Until a company develops a system which automaticaly compensates amplitude levels to couplant loss we should be working at FBH+6DB (as the ACC/Rej level).”
: Perhaps Mr. Rawlinson does not understand the technique used by most AUT companies to monitor coupling and why the allowance for variation is incorporated. This is an ideal venue to explain the situation and dispel the notion that we need auto-compensation.
: In a girth weld that has been made where the weld axis is vertical (as in land-lay and S-lay projects) most AUT systems set up a pitch-catch configuration on the bottom of the pipe where, not only is the spring tension weakest but also, the crown of the weld is the highest and any extra losses due to the crown scattering portions of the beam can be compensated by adding gain to the receiver to ensure there is adequate signal received to indicate that there is couplant under BOTH the transmitting and receiving probes. This technique is configured that the zonal probe on one side transmit to the zonal probe on the opposite side of the weld. Verification that couplant is under the probe wedge is the sole reason for the couping check!
: But loss of coupling signal using this technique need not only indicate loss of fluid. It is often indicated by the hi-lo (mismatch) condition, i.e. the beam is redirected or scattered by a change in geometry (not a real loss of coupling). No matter how “wet” you make the surface under such conditions you are NOT going to get an indication in the coupling monitor gate.
: Coupling can also be lost when a flaw is present in the weld, i.e. the flaw interupts the through transmission. Providing this flaw is indicated as a Defect (i.e. the flaw is rejectable) this is not usually an issue because the flaw is removed in the repair. But if it is an acceptable flaw and still reduces the energy across the weld for coupling check it MIGHT cause some issues of concern for coupling.
: These shortcomings of the through transmission technique can be remedied by using a separate probe for coupling checks. This option was noted in Krautkramer’s text many years ago. These were zero degree probes built into the wedge and fired separately from the angle beam. Essentially the zero degree would monitor the first backwall for significant amplitude drops. The technique doubles as a thickness monitor as well as a coupling monitor.
: Another point Mr. Rawlinson has missed is that, in most AUT girth weld specifications, a requirement that EACH "probe" must have a monitoring channel. For a large multi-probe array using 20 or 30 separate wedges, that would technically be 20-30 coupling channels! Most systems have dodged the point and set up a single coupling channel for a zone and further reduce compliance by selecting only one pair of the tandems where tandem probes are used.
: There is a need to monitor for coupling but Mr. Rawlinson is not correct that over-sensitivity is the only solution or that auto-coupling correction be should eventually be made by adding gain by some sort of feedback loop to the receivers. One must consider that the loss of coupling “signal” does not always mean the same as loss of “coupling fluid”.
------------ End Original Message ------------




 
03:04 Sep-29-2003

Gerald King

NDT Inspector, Consultant, Trainer
Ontario Power Generation,
Canada,
Joined Apr 2003
4
Re: AUT simulator discussions Let me at the outset say that I have never had the opportunity to witness the Genesis simulator, so forgive me if my post seems uninformed. That being said, however, I do have some questions to the post by Paul Rawlinson as found below.

I don't understand how a simulator with virtual equipment, virtual welds and virtual defects can reflect the real world. You mentioned in an earlier post that the Genesis simulator shows that defects in unpredictable orientations can give a poor response - but if defects are in unpredictable orientations, how can they be simulated, given they are unpredictable?

You say that the simulator takes into account "probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, and Through Transmission, Hilo, root defects, porosity mapping, TOF (transit)" Does it also take into account such mechanical properties as the rocking of a probe due to improper carbide placement? Or lengthening of water column due to the same?

You also say it simulates " in the style ... RTD, RDTech, Shaw, WeldSonix" But "without the endorsement or support of any 3rd party company"
Does this mean that the above companies neither endorse nor support the Genesis simulator? How can you simulate the presentation of the above companies without their endorsement or support? If that is true, then how can the simulations be valid? Perhaps representative from the various companies could post on this forum to address this issue.

----------- Start Original Message -----------
: The research Mr Ginzle mentions is good science for Numerical Methods for the Modelling of Acoustic, Electromagnetic, Elastic and Piezoelectric Wave Propagation Problems in the Time Domain Based on the Finite Integration Technique, but can not help an inspector to grasp principles of ultrasonic testing in the real world, let alone understand AUT setups and acc/rej concepts.
: The Genesis is a much simpler tool , designed not for the research student but for the NDE inspector.
: The role of genesis UT simulator is not to push the envelope of acoustic science but simply to provide a simulation of the real UT world, with virtual UT equipment and virtual welds and virtual defects.
: Mr Ginzle will be pleased to learn that the Genesis UT simulator takes into account probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, and Through Transmission, Hilo, root defects, porosity mapping, TOF (transit)
: And it simulates in the style of Krautkramer, Panametrics, RTD, RDTech, Shaw, WeldSonix, and includes multiple calibration blocks and probes.The software was developed by AUTO-Ut using experimental data and without the endorsement or support of any 3rd party company.
: As far as the other points Mr Ginzle makes concerning couplant loss flagging, he has addressed well many of the concerns the industry shares.
:
: --
: This message was posted into the NDT.net Forum.
: http://www.ndt.net/wshop/forum/forum-1.htm
: Please do not reply to email: forum@ndt.net
: For your reply to this message go to:
: http://www.ndt.net/wshop/forum/messages-1/5930.html
:
: : AUT simulator discussions
: : Due to the misreading of the forum item I posted by Mr. Rawlinson, I am posting another item where his concerns might be more appropriately addressed. Not having used the simulator indicated in his point, I cannot speak to the efficacy of the tool. If it is based on a raytracing algorithm it may provide a coarse explanation of amplitude deviation with respect to flaw orientation but to do justice to the REAL conditions EFIT modelling is required as described by Langenberg (see article online at http://www.ndt.net/article/ecndt02/195/195.htm). Unless the simulator can duplicate all the conditions of diffraction, mode conversion and echo-transmittance coefficient effects due to angle changes, it is not truly a decent simulation tool for indicating the REAL conditions of the AUT pipeline girth weld application.
: : The other point Mr. Rawlinson makes is his perception that coupling monitor checks are “…the most critical factor in ACC/Rej criteria”
: : He suggested that, “Until a company develops a system which automaticaly compensates amplitude levels to couplant loss we should be working at FBH+6DB (as the ACC/Rej level).”
: : Perhaps Mr. Rawlinson does not understand the technique used by most AUT companies to monitor coupling and why the allowance for variation is incorporated. This is an ideal venue to explain the situation and dispel the notion that we need auto-compensation.
: : In a girth weld that has been made where the weld axis is vertical (as in land-lay and S-lay projects) most AUT systems set up a pitch-catch configuration on the bottom of the pipe where, not only is the spring tension weakest but also, the crown of the weld is the highest and any extra losses due to the crown scattering portions of the beam can be compensated by adding gain to the receiver to ensure there is adequate signal received to indicate that there is couplant under BOTH the transmitting and receiving probes. This technique is configured that the zonal probe on one side transmit to the zonal probe on the opposite side of the weld. Verification that couplant is under the probe wedge is the sole reason for the couping check!
: : But loss of coupling signal using this technique need not only indicate loss of fluid. It is often indicated by the hi-lo (mismatch) condition, i.e. the beam is redirected or scattered by a change in geometry (not a real loss of coupling). No matter how “wet” you make the surface under such conditions you are NOT going to get an indication in the coupling monitor gate.
: : Coupling can also be lost when a flaw is present in the weld, i.e. the flaw interupts the through transmission. Providing this flaw is indicated as a Defect (i.e. the flaw is rejectable) this is not usually an issue because the flaw is removed in the repair. But if it is an acceptable flaw and still reduces the energy across the weld for coupling check it MIGHT cause some issues of concern for coupling.
: : These shortcomings of the through transmission technique can be remedied by using a separate probe for coupling checks. This option was noted in Krautkramer’s text many years ago. These were zero degree probes built into the wedge and fired separately from the angle beam. Essentially the zero degree would monitor the first backwall for significant amplitude drops. The technique doubles as a thickness monitor as well as a coupling monitor.
: : Another point Mr. Rawlinson has missed is that, in most AUT girth weld specifications, a requirement that EACH "probe" must have a monitoring channel. For a large multi-probe array using 20 or 30 separate wedges, that would technically be 20-30 coupling channels! Most systems have dodged the point and set up a single coupling channel for a zone and further reduce compliance by selecting only one pair of the tandems where tandem probes are used.
: : There is a need to monitor for coupling but Mr. Rawlinson is not correct that over-sensitivity is the only solution or that auto-coupling correction be should eventually be made by adding gain by some sort of feedback loop to the receivers. One must consider that the loss of coupling “signal” does not always mean the same as loss of “coupling fluid”.
------------ End Original Message ------------




 
07:03 Oct-06-2003
Andrew
Re: AUT simulator discussions Q) "I don't understand how a simulator with virtual equipment, virtual welds and virtual defects can reflect the real world."

A)AS YOU SAID, WITHOUT SEEING IT, IT IS DIFFICULT TO VISUALISE. AND PERHAPS THAT IS THE WHOLE POINT OF A SIMULATOR OF ANY KIND.
THE REAL WORLD IS DIFFICULT TO DESCRIBE IN WORDS, A PICTURE TELLS A THOUSAND WORDS, A SIMULATOR TELLS A MILLION.

Q) "You mentioned in an earlier post that the Genesis simulator shows that defects in unpredictable orientations can give a poor response - but if defects are in unpredictable orientations, how can they be simulated, given they are unpredictable?"

A) YES, PREDICTING THE UNPREDICTABLE IS A POOR USE OF ENGLISH. HOWEVER THE CORRECT ENGLISH WOULD BE;-
"" the Genesis simulator shows that defects in UNEXPECTED orientations can give a poor response ""


Q) "You say that the simulator takes into account "probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, and Through Transmission, Hilo, root defects, porosity mapping, TOF (transit)" Does it also take into account such mechanical properties as the rocking of a probe due to improper carbide placement? Or lengthening of water column due to the same? "

A) IMPROPER CARBIDE PLACEMENT HAS NOT BEEN ADDRESSED IN THE CURRENT VERSION OF GENESIS AUTO-UT SIMULATOR.
HOWEVER YOU COMMENTS ARE IMPORTANT AND FUTURE VERSIONS MAY WELL ADDRESS THIS PROBLEM.

CONSTRUCTIVE OBSERVATIONS SUCH AS THIS , FROM HANDS ON AUT PROFESSIONALS, HAVE BEEN THE DRIVING FORCE BEHIND THE CONTINUING EVOLUTION OF GENESIS AUTO-UT SIMULATOR.

Q) "You also say it simulates " in the style ... RTD, RDTech, Shaw, WeldSonix" But "without the endorsement or support of any 3rd party company" Does this mean that the above companies neither endorse nor support the Genesis simulator? How can you simulate the presentation of the above companies without their endorsement or support? If that is true, then how can the simulations be valid? Perhaps representative from the various companies could post on this forum to address this issue. "

A) WITHOUT THE SUPPORT OF.... THIS MEANS THEY DID NOT HELP OR ENCOURAGE AUTO-UT LTD IN ANY WAY DURING THE YEARS OF RESEACH AND DEVELOPMENT. SIMILAR TO THE ORIGINAL AIRFORCE FLIGHT SIMULATOR , IT HAS BEEN INSPIRED BY THE GUYS IN THE EJECTOR SEAT AND NOT THE NASA SCIENTISTS.


----------- Start Original Message -----------
: Let me at the outset say that I have never had the opportunity to witness the Genesis simulator, so forgive me if my post seems uninformed. That being said, however, I do have some questions to the post by Paul Rawlinson as found below.
: I don't understand how a simulator with virtual equipment, virtual welds and virtual defects can reflect the real world. You mentioned in an earlier post that the Genesis simulator shows that defects in unpredictable orientations can give a poor response - but if defects are in unpredictable orientations, how can they be simulated, given they are unpredictable?
: You say that the simulator takes into account "probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, and Through Transmission, Hilo, root defects, porosity mapping, TOF (transit)" Does it also take into account such mechanical properties as the rocking of a probe due to improper carbide placement? Or lengthening of water column due to the same?
: You also say it simulates " in the style ... RTD, RDTech, Shaw, WeldSonix" But "without the endorsement or support of any 3rd party company"
: Does this mean that the above companies neither endorse nor support the Genesis simulator? How can you simulate the presentation of the above companies without their endorsement or support? If that is true, then how can the simulations be valid? Perhaps representative from the various companies could post on this forum to address this issue.
: : The research Mr Ginzle mentions is good science for Numerical Methods for the Modelling of Acoustic, Electromagnetic, Elastic and Piezoelectric Wave Propagation Problems in the Time Domain Based on the Finite Integration Technique, but can not help an inspector to grasp principles of ultrasonic testing in the real world, let alone understand AUT setups and acc/rej concepts.
: : The Genesis is a much simpler tool , designed not for the research student but for the NDE inspector.
: : The role of genesis UT simulator is not to push the envelope of acoustic science but simply to provide a simulation of the real UT world, with virtual UT equipment and virtual welds and virtual defects.
: : Mr Ginzle will be pleased to learn that the Genesis UT simulator takes into account probe angles, refraction, reflection, orientation of reflectors, texture of reflectors , attenuation, and algorithms of UT propagation, as well as simulation of AUT, TOFD, Pulse Echo, Tandem, andThrough Transmission, Hilo, root defects, porosity mapping, TOF (transit)
: : And it simulates in the style of Krautkramer, Panametrics, RTD, RDTech, Shaw, WeldSonix, and includes multiple calibration blocks and probes.The software was developed by AUTO-Ut using experimental data and without the endorsement or support of any 3rd party company.
: : As far as the other points Mr Ginzle makes concerning couplant loss flagging, he has addressed well many of the concerns the industry shares.
: :
: : --
: : This message was posted into the NDT.net Forum.
: : http://www.ndt.net/wshop/forum/forum-1.htm
: : Please do not reply to email: forum@ndt.net
: : For your reply to this message go to:
: : http://www.ndt.net/wshop/forum/messages-1/5930.html
: :
: : : AUT simulator discussions
: : : Due to the misreading of the forum item I posted by Mr. Rawlinson, I am posting another item where his concerns might be more appropriately addressed. Not having used the simulator indicated in his point, I cannot speak to the efficacy of the tool. If it is based on a raytracing algorithm it may provide a coarse explanation of amplitude deviation with respect to flaw orientation but to do justice to the REAL conditions EFIT modelling is required as described by Langenberg (see article online at http://www.ndt.net/article/ecndt02/195/195.htm). Unless the simulator can duplicate all the conditions of diffraction, mode conversion and echo-transmittance coefficient effects due to angle changes, it is not truly a decent simulation tool for indicating the REAL conditions of the AUT pipeline girth weld application.
: : : The other point Mr. Rawlinson makes is his perception that coupling monitor checks are “…the most critical factor in ACC/Rej criteria”
: : : He suggested that, “Until a company develops a system which automaticaly compensates amplitude levels to couplant loss we should be working at FBH+6DB (as the ACC/Rej level).”
: : : Perhaps Mr. Rawlinson does not understand the technique used by most AUT companies to monitor coupling and why the allowance for variation is incorporated. This is an ideal venue to explain the situation and dispel the notion that we need auto-compensation.
: : : In a girth weld that has been made where the weld axis is vertical (as in land-lay and S-lay projects) most AUT systems set up a pitch-catch configuration on the bottom of the pipe where, not only is the spring tension weakest but also, the crown of the weld is the highest and any extra losses due to the crown scattering portions of the beam can be compensated by adding gain to the receiver to ensure there is adequate signal received to indicate that there is couplant under BOTH the transmitting and receiving probes. This technique is configured that the zonal probe on one side transmit to the zonal probe on the opposite side of the weld. Verification that couplant is under the probe wedge is the sole reason for the couping check!
: : : But loss of coupling signal using this technique need not only indicate loss of fluid. It is often indicated by the hi-lo (mismatch) condition, i.e. the beam is redirected or scattered by a change in geometry (not a real loss of coupling). No matter how “wet” you make the surface under such conditions you are NOT going to get an indication in the coupling monitor gate.
: : : Coupling can also be lost when a flaw is present in the weld, i.e. the flaw interupts the through transmission. Providing this flaw is indicated as a Defect (i.e. the flaw is rejectable) this is not usually an issue because the flaw is removed in the repair. But if it is an acceptable flaw and still reduces the energy across the weld for coupling check it MIGHT cause some issues of concern for coupling.
: : : These shortcomings of the through transmission technique can be remedied by using a separate probe for coupling checks. This option was noted in Krautkramer’s text many years ago. These were zero degree probes built into the wedge and fired separately from the angle beam. Essentially the zero degree would monitor the first backwall for significant amplitude drops. The technique doubles as a thickness monitor as well as a coupling monitor.
: : : Another point Mr. Rawlinson has missed is that, in most AUT girth weld specifications, a requirement that EACH "probe" must have a monitoring channel. For a large multi-probe array using 20 or 30 separate wedges, that would technically be 20-30 coupling channels! Most systems have dodged the point and set up a single coupling channel for a zone and further reduce compliance by selecting only one pair of the tandems where tandem probes are used.
: : : There is a need to monitor for coupling but Mr. Rawlinson is not correct that over-sensitivity is the only solution or that auto-coupling correction be should eventually be made by adding gain by some sort of feedback loop to the receivers. One must consider that the loss of coupling “signal” does not always mean the same as loss of “coupling fluid”.
------------ End Original Message ------------




 
02:40 Jan-28-2006
etshoys
etshoys test. ignore it. (kudatdyt)


 


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