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00:31 Sep-08-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Phased Array sensitivity, etc.

I wish I had said that:
Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.

I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.

Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.

The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.

I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.

This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.




 
01:07 Sep-17-2004
Paul Moore
Re: Phased Array sensitivity, etc. Ed,

The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.

I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.

The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.

In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.

I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.

Cheers,

Paul

----------- Start Original Message -----------
: I wish I had said that:
: Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) wheresensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements.E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
01:00 Sep-18-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Phased Array sensitivity, etc. Paul:
Thanks for initiating a follow-up on the concerns for Phased Arrays!

Although pipeline AUT is a significant user of PA technology now, I had intended these considerations to be generic. Even in some of the boiler & pressure vessel circles there are many that want to nail down specific values and treat PA probes and techniques like the single element option. They are NOT the same and endless tolerance checks are not always necessary to provide assurance of a good inspection. Remember, sensitivity and range/delay checks are also being carried out.

There already exists a reasonable set of guidelines in setting sensitivity off known targets (FBHs or SDHs or notches) in most UT Standards. In pipeline AUT we even specify overtrace of adjacent zones (although this criterion is sometimes mistreated where a large angle or excessively small zone is used and the -6 to -14dB overtrace is still expected). Sensitivity parameters provide a “field friendly” assessment, i.e. the system is "performance based".

In spite of this practical performance-based option, there are still clients and regulatory bodies that insist on imposing rules that go beyond reasonable expectations. I have been on projects where both the equipment manufacturers and the systems users were obliged to incorporate specific values for tolerances of phased array parameters. The idea that the system performance should be adequate proof was not enough. The system manufacturers and users were obliged to develop procedures that incorporated elaborate methods to verify parameters including refracted angles, uniformity of output and numbers of active elements. Although Clients (end users of the NDT service) and regulatory bodies can certainly MAKE people do as they want, I have observed that this is often simply “importunity”. Even committee based Standards often leave the work to an individual and not all the repercussions of an omission or requirement is foreseen at the time the Standard is issued. But instead of blindly enforcing a rule that is clearly inappropriate it would be better to point it out and change it. This is easily done in a company Specification and Procedure. It may take a bit of time in a Standard or Code…but it should be addressed.

A chap I dealt with in EPRI once stated, “If you are not going to use the information you are collecting then do not collect that information”. Collecting useless information as part of a Procedure is merely a lot of extra time and paperwork that gives auditors something to fault a company on if not complied with. However, if the auditor represents the Client that required the useless bit of information, who is really to blame? The NDT company that wrote the Procedure or the Client that indicated parameter controls were mandatory?

In ASTM E-1961 we originally stipulated probe details such as refracted angle, exit point, etc. These are generally noted on the wedge for convenience of positioning of the beam relative to the geometry and placement of the wedge relative to some reference coordinate. A potential Client pointed out that since phased arrays do not have these items on the wedge then phased array systems were not to be used with E-1961. Clearly, it was never the intent to exclude ANY systems that could provide the signals required for zone discrimination. Therefore, we issued an editorial revision stating that some of these items do not apply to PA probes. That took a bit under 1 year to change! But similar requirements are found in nearly all UT codes and standards because they have not considered that PA systems could replace the traditional single element systems.

Putting silly requirements on PA probes has it parallels in single probe requirements too. Specifications such as ESI 98-2 require squint (skew) tolerance, exit point and refracted angle tolerances (to mention just a few). These are typically determined using the flat surfaces of IIW blocks. Yet, when the operators then adjust responses on the calibration blocks using carbide wear pins to adjust skewand angles….what purpose did the baseline verification have? Or, after verifying all these parameters as per requirement of the specification, the probe wedge is then curved for a pipe surface. What use was the time spent collecting the baseline data for the probe in its flat condition? The “baseline” is not longer any use!

Identifying “dead elements” in a phased array probe has been someone’s idea of an important issue. But this has an equivalent in single element probes where the wedge is removable and coupled via paste or oil. Many of us note that the wedge/probe coupling is sometimes less “ideal’ than other times. But how often is it checked? What is the effect of a 15% “poor coupling”? If it was so important to identify inactive elements in a PA probe why was there not an ongoing requirement to “quantify” probe to wedge coupling? A “pinducer” could have been used to perform a consistency test over the surface on a regular interval. But the issue was never considered important by the people that imposed the more stringent rules on PA probes. You could imagine such a test on the probe/wedge coupling condition. The pinducer would be required to be perfectly coupled to the wedge. The wedge/probe would need to be mounted in a holder that could permit movement against the pinducer that matched the wedge contour and an amplitude C-scan made. This of course should be done on a daily basis since probe/wedge coupling is a known problem…but to what end if the calibrations were within tolerance?

This long explanation has hopefully provided the origins to the issues of Dead Elements (in pipeline AUT industry anyway) i.e. imposed as a regulatory requirement…not as a company tolerance. But no matter what the parameter tolerance, if it is useless information that serves no purpose in a performance based test, it should be deleted as a required item. A revision to the Procedure should be allowed after a sensible discussion and the Project allowed move on.

----------- Start Original Message -----------
: Ed,
: The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: Cheers,
: Paul
: : I wish I had said that:
: : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g.number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
09:07 Sep-19-2004
bill
Re: Phased Array sensitivity, etc. Who are "autsolutions"sounds suspiciously like another Rawlison brothers venture. It will undoubtedly be expert in the field of phased array of course.----------- Start Original Message -----------
: Ed,
: The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: Cheers,
: Paul
: : I wish I had said that:
: : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
01:08 Sep-19-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Phased Array sensitivity, etc. Bill:
The guys from autsolutions are some old hands-on guys that have real (not virtual) experience (in fact many years of experience).
I value their thoughts and opinions!
Ed

----------- Start Original Message -----------
: Who are "autsolutions"sounds suspiciously like another Rawlison brothers venture. It will undoubtedly be expert in the field of phased array of course.----------- Start Original Message -----------
: : Ed,
: : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : Cheers,
: : Paul
: : : I wish I had said that:
: : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot betreated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunityfor users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
05:57 Sep-25-2004
Dave Stewart
Re: Phased Array sensitivity, etc. Paul, Ed,

Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or 2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.

Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.

An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.

A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.

Thanks for bringing this subject up, I hope we can get further discussion on this matter.

Take care,
Dave


: : : Ed,
: : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : :I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : Cheers,
: : : Paul
: : : : I wish I had said that:
: : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannotexplain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
02:28 Sep-27-2004

Thomas Murphy

NDT Inspector
USA,
Joined Jul 2000
16
Re: Phased Array sensitivity, etc. Hello all,

I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.

We confirm performance of all transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.

Regards,
Tom

----------- Start Original Message -----------
: Paul, Ed,
: Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or 2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: Take care,
: Dave
:
: : : : Ed,
: : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : Cheers,
: : : : Paul
: : : : : I wish I had said that:
: : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : This discussion item is posted because I was interested to see if others have similar ordifferent experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
00:32 Sep-29-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Phased Array sensitivity, etc. The WCNDT in Montreal had a session devoted to phased array technology. It was often standing-room only in that session. One of the papers in that session was by F. Cancre on a study done on performance of phased array probes that will be worthwhile reading. NDT.net will be publishing papers from this conrference. Also, a paper was presented in 2003 at the EPRI conference on Phased Arrays. One in particular was "Development and Qualification of Procedures for Rapid Inspection of Piping Welds" by D. E. MacDonald, M. A. Dennis,J. L. Landrum and G. P. Selby. They noted that they could still maintain acceptable conditions to qualify the system/technique for the nuclear PDI if 25% of the elements in a focal law were switched off.
Regards
Ed

----------- Start Original Message -----------
: Hello all,
: I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.
: We confirm performance ofall transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.
: Regards,
: Tom
: : Paul, Ed,
: : Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: : Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: : An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: : A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: : Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: : Take care,
: : Dave
: :
: : : : : Ed,
: : : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : : Cheers,
: : : : : Paul
: : : : : : I wish I had said that:
: : : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in thesame way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) onthe basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
00:28 Sep-29-2004
Paul Moore
Re: Phased Array sensitivity, etc. I can't say that I'm completely sold on the 25% idea or + dB range. I've had a chance to have a brief look at the Cancre report. I think the underlying conclusion is that the tolerance is dependant upon the configuration. If I look at the diagrams I see changes in the characteristics of the beams. I don't see that a typical calibration piece (fbh's) will accurately reflect these changes. Wouldn't you expect different defect sizing ratios (amplitude) for a tightly focused beam and a broad beam if your calibration reflector is a small fbh? If you calibrated both a fully functional focal law and a -25% element focal law on a 2mm fbh, what would be the relative responses off a 2mm high notch of a length greater than the beam spread? It might be useful information to support the push for wider tolerances.

I try to read these types of reports with an objective eye but I can't help but let the cynic in me have a look. It would be nice to think that the vendor's motivation is the encouragement of the practical application their equipment. The cynic sees it as a patch to address a problem with the equipment. Every approach has shortcomings and you weigh the pros and cons when choosing. It would be a lot easier in this case if this particular vendor would come up with a more robust and flexible umbilical design so we wouldn't have to deal with this.

The other item that caught my eye was the manufacturers recommendation that a 9 dB signal to noise ratio be applied to the "higher" angles. This is due to the technique's difficulties with these higher angles. They may recommend it but I can't see anyone buying it.

Cheers,

Paul

----------- Start Original Message -----------
: The WCNDT in Montreal had a session devoted to phased array technology. It was often standing-room only in that session. One of the papers in that session was by F. Cancre on a study done on performance of phased array probes that will be worthwhile reading. NDT.net will be publishing papers from this conrference. Also, a paper was presented in 2003 at the EPRI conference on Phased Arrays. One in particular was "Development and Qualification of Procedures for Rapid Inspection of Piping Welds" by D. E. MacDonald, M. A. Dennis,J. L. Landrum and G. P. Selby. They noted that they could still maintain acceptable conditions to qualify the system/technique for the nuclear PDI if 25% of the elements in a focal law were switched off.
: Regards
: Ed
: : Hello all,
: : I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.
: : We confirm performance of all transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.
: : Regards,
: : Tom
: : : Paul, Ed,
: : : Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or 2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: : : Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: : : An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: : : A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: : : Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: : : Take care,
: : : Dave
: : :
: : : : : : Ed,
: : : : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : : : Cheers,
: : : : : : Paul
: : : : : : : I wish I had said that:
: : : : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
01:29 Sep-30-2004

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Phased Array sensitivity, etc. Paul:
Some of your concerns are valid and the issue at the end of the posting is a concern I have too. The statement (ANY statement) about S/N ratio is a red herring. It has nothing to do with PA configuration.

It should first be noted that the Cancre report and the EPRI report used different cables and probes from each other and those were both different from what you would have seen in your field. So this is NOT a “patch” of a manufacturer as seen by the cynic, but a field observation/concern and an effort to get a “practical” tolerance. Both reports suggest that the tolerance is dependent on the configuration. But the point is made that performance is based on function not on some number that is made up to look at only a single condition.

You state concern that the response from a FBH would not reflect changes in the beam generated by the PA probe. Yet you would be quite unaware of the same subtle changes due to coupling variation between the wedge and probe, or the un-documented changes that some companies have when angle and skew are adjusted by adjusting the carbide wear pin gaps. Do you not find it odd that Skew and Angle are required baseline recorded parameters in some Codes yet these are ignored by people as they “fiddle” with the hardware to optimise responses of FBHs? There is even one of the systems out there that has a “skew adjustment” built right into the probe pan!

If you are not going to use the information then do not require its documentation.

You state concern for the response variations for “defect sizing ratios (amplitude) for a tightly focused beam and a broad beam”. Yet in some cases (e.g. ASTM E-1961) we have set a range of acceptable overtrace that SHOULD be followed. If the spot size increases then that is reflected in the overtrace and MOST companies have policies that account for that. I have seen ONE operator (of a phased array system) actually reduce the focus to ensure that the -14 dB was achieved!

The statement you made on the SN ratio for high angle beams is also a concern for me. This has nothing to do with whether or not the probe is PA or conventional. More it is a function of the calibration block design and surface conditions. I see no reason to introduce this parameter in the probe assessment. If SN ratio is considered it should be in isolation (i.e. on an ideal target with no other boundary conditions contributing to the parameter.

In your last comment I also see that the SN ratio was in the “manufacturer’s recommendations”. Why is the manufacturer required to make recommendations on functions that are technique dependent (such as the SN ratio)? Perhaps when some twit imposes company specifications that are totally unreasonable, some users think that the manufacturer has a solution.

But when the individual imposing the rules is importunate there is no solution.
E.g. the individual making up the specification has decided that if the number of defective elements requires a focal law shift greater than 1.5° the production must stop. Is the solution to adjust the carbide wear pins?...because he sees no problem with that when it is done on a conventional system.

Hopefully we can go back to tolerance being dependant upon the configuration and performance based on function not on some number that is arbitrarily made up with no rationale.
Ed

----------- Start Original Message -----------
: I can't say that I'm completely sold on the 25% idea or + dB range. I've had a chance to have a brief look at the Cancre report. I think the underlying conclusion is that the tolerance is dependant upon the configuration. If I look at the diagrams I see changes in the characteristics of the beams. I don't see that a typical calibration piece (fbh's) will accurately reflect these changes. Wouldn't you expect different defect sizing ratios (amplitude) for a tightly focused beam and a broad beam if your calibration reflector is a small fbh? If you calibrated both a fully functional focal law and a -25% element focal law on a 2mm fbh, what would be the relative responses off a 2mm high notch of a length greater than the beam spread? It might be useful information to support the push for wider tolerances.
: I try to read these types of reports with an objective eye but I can't help but let the cynic in me have a look. It would be nice to think that the vendor's motivation is the encouragement of the practical application their equipment. The cynic sees it as a patch to address a problem with the equipment. Every approach has shortcomings and you weigh the pros and cons when choosing. It would be a lot easier in this case if this particular vendor would come up with a more robust and flexible umbilical design so we wouldn't have to deal with this.
: The other item that caught my eye was the manufacturers recommendation that a 9 dB signal to noise ratio be applied to the "higher" angles. This is due to the technique's difficulties with these higher angles. They may recommend it but I can't see anyone buying it.
: Cheers,
: Paul
: : The WCNDT in Montreal had a session devoted to phased array technology. It was often standing-room only in that session. One of the papers in that session was by F. Cancre on a study done on performance of phased array probes that will be worthwhile reading. NDT.net will be publishing papers from this conrference. Also, a paper was presented in 2003 at the EPRI conference on Phased Arrays. One in particular was "Development and Qualification of Procedures for Rapid Inspection of Piping Welds" by D. E. MacDonald, M. A. Dennis,J. L. Landrum and G. P. Selby. They noted that they could still maintain acceptable conditions to qualify the system/technique for the nuclear PDI if 25% of the elements in a focal law were switched off.
: : Regards
: : Ed
: : : Hello all,
: : : I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.
: : : We confirm performance of all transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.
: : : Regards,
: : : Tom
: : : : Paul, Ed,
: : : : Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or 2 elementsin any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: : : : Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: : : : An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: : : : A great thing about the Phased Array system is that we can monitor manydifferent parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: : : : Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: : : : Take care,
: : : : Dave
: : : :
: : : : : : : Ed,
: : : : : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recentexperiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : : : : Cheers,
: : : : : : : Paul
: : : : : : : : I wish I had said that:
: : : : : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
05:04 Oct-01-2004
Dave Stewart
Re: Phased Array sensitivity, etc. Paul, Ed,

I agree on the point made regarding the Signal to noise ratio when higher angles are utilized. If we look at the majority of inspections performed we can get a good idea on what angles are used and at what frequency. When the wedges where designed they were done so to achieve a natural 50 degree angle (refracted), this would mean that most weld profiles would be covered in a 45 to 55 degree range with little difficulty in beam steering. However this does cause more noise in the system when we work at the higher angles, the system has to work harder so to speak in order to create the higher angles resulting in the noise. The transducer design has a large role to play when we are steering the beam, the smaller the pitch used the better the steering and signal response and less noise, but with a smaller pitch we also make the transducer foot print smaller which now starts to limit us in wall thickness that can be completely covered. Another option is to increase the incident angle of the wedge in order to reduce the noise from steering the beam at the high angles; this of course would increase the footprint of the wedge.

Perhaps an increase in incident angle to 36 degrees would aid in the noise issue and only increase the footprint by 4mm.

I would agree with Ed when considering a narrow beam and a broad beam, the bottom line here is ensure the system is running to procedure and spec, which means proper overtrace values from the adjacent channels. If the system strays from the procedure/spec due to loss of elements/channels and it cannot be compensated for by increasing elements or angle change than the system would fail the calibration and corrective action taken. We want to ensure we can run the system to spec, which will give our clients a quality inspection, but at the same time we do not want to be painted into a corner due to lack or misunderstandings of the system.

Take care,

Dave


----------- Start Original Message -----------
: Paul:
: Some of your concernsare valid and the issue at the end of the posting is a concern I have too. The statement (ANY statement) about S/N ratio is a red herring. It has nothing to do with PA configuration.
: It should first be noted that the Cancre report and the EPRI report used different cables and probes from each other and those were both different from what you would have seen in your field. So this is NOT a “patch” of a manufacturer as seen by the cynic, but a field observation/concern and an effort to get a “practical” tolerance. Both reports suggest that the tolerance is dependent on the configuration. But the point is made that performance is based on function not on some number that is made up to look at only a single condition.
: You state concern that the response from a FBH would not reflect changes in the beam generated by the PA probe. Yet you would be quite unaware of the same subtle changes due to coupling variation between the wedge and probe, or the un-documented changes that some companies have when angle and skew are adjusted by adjusting the carbide wear pin gaps. Do you not find it odd that Skew and Angle are required baseline recorded parameters in some Codes yet these are ignored by people as they “fiddle” with the hardware to optimise responses of FBHs? There is even one of the systems out there that has a “skew adjustment” built right into the probe pan!
: If you are not going to use the information then do not require its documentation.
: You state concern for the response variations for “defect sizing ratios (amplitude) for a tightly focused beam and a broad beam”. Yet in some cases (e.g. ASTM E-1961) we have set a range of acceptable overtrace that SHOULD be followed. If the spot size increases then that is reflected in the overtrace and MOST companies have policies that account for that. I have seen ONE operator (of a phased array system) actually reduce the focus to ensure that the -14 dB was achieved!
: The statement you made on the SN ratio for high angle beams is also a concern for me. This has nothing to do with whether or not the probe is PA or conventional. More it is a function of the calibration block design and surface conditions. I see no reason to introduce this parameter in the probe assessment. If SN ratio is considered it should be in isolation (i.e. on an ideal target with no other boundary conditions contributing to the parameter.
: In your last comment I also see that the SN ratio was in the “manufacturer’s recommendations”. Why is the manufacturer required to make recommendations on functions that are technique dependent (such as the SN ratio)? Perhaps when some twit imposes company specifications that are totally unreasonable, some users think that the manufacturer has a solution.
: But when the individual imposing the rules is importunate there is no solution.
: E.g. the individual making up the specification has decided that if the number of defective elements requires a focal law shift greater than 1.5° the production must stop. Is the solution to adjust the carbide wear pins?...because he sees no problem with that when it is done on a conventional system.
: Hopefully we can go back to tolerance being dependant upon the configuration and performance based on function not on some number that is arbitrarily made up with no rationale.
: Ed
: : I can't say that I'm completely sold on the 25% idea or + dB range. I've had a chance to have a brief look at the Cancre report. I think the underlying conclusion is that the tolerance is dependant upon the configuration. If I look at the diagrams I see changes in the characteristics of the beams. I don't see that a typical calibration piece (fbh's) will accurately reflect these changes. Wouldn't you expect different defect sizing ratios (amplitude) for a tightly focused beam and a broad beam if your calibration reflector is a small fbh? If you calibrated both a fully functional focal law and a -25% element focal law on a 2mm fbh, what would be the relative responses off a 2mm high notch of a length greater than the beam spread? It might be useful information to support the push for wider tolerances.
: : I try to read these types of reports with an objective eye but I can't help but let the cynic in me have a look. It would be nice to think that the vendor's motivation is the encouragement of the practical application their equipment. The cynic sees it as a patch to address a problem with the equipment. Every approach has shortcomings and you weigh the pros and cons when choosing. It would be a lot easier in this case if this particular vendor would come up with a more robust and flexible umbilical design so we wouldn't have to deal with this.
: : The other item that caught my eye was the manufacturers recommendation that a 9 dB signal to noise ratio be applied to the "higher" angles. This is due to the technique's difficulties with these higher angles. They may recommend it but I can't see anyone buying it.
: : Cheers,
: : Paul
: : : The WCNDT in Montreal had a session devoted to phased array technology. It was often standing-room only in that session. One of the papers in that session was by F. Cancre on a study done on performance of phased array probes that will be worthwhile reading. NDT.net will be publishing papers from this conrference. Also, a paper was presented in 2003 at the EPRI conference on Phased Arrays. One in particular was "Development and Qualification of Procedures for Rapid Inspection of Piping Welds" by D. E. MacDonald, M. A. Dennis,J. L. Landrum and G. P. Selby. They noted that they could still maintain acceptable conditions to qualify the system/technique for the nuclear PDI if 25% of the elements in a focal law were switched off.
: : : Regards
: : : Ed
: : : : Hello all,
: : : : I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.
: : : : We confirm performance of all transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.
: : : : Regards,
: : : : Tom
: : : : : Paul, Ed,
: : : : : Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series, or 2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: : : : : Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: : : : : An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: : : : : A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: : : : : Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: : : : : Take care,
: : : : : Dave
: : : : :
: : : : : : : : Ed,
: : : : : : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : : : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : : : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recentexperiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : : : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : : : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : : : : : Cheers,
: : : : : : : : Paul
: : : : : : : : : I wish I had said that:
: : : : : : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : : : : : The new book is an easy read and provides not only a broad background tophased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : : : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
06:17 Oct-02-2004
Paul Moore
Re: Phased Array sensitivity, etc. The “high” angle difficulties seem easily overcome with supplemental conventional probes. The phased array contractors seem to avoid adding any additional probes to the tidy 2 probe set-up (don’t blame them). I think the pipeline phased array systems would benefit from a few extra probes (TOFD, transverse, “high” angles)

Let me just close out my interest in this particular point by going back to the non-functioning elements and lateral beam spread. As the number of non-functioning elements increases the calibration block results will represent any changes in the vertical over-tracing of 2mm flat bottom holes, but will they relate the proportional change of response from linear indications? I anticipate that as the focal spot broadens the response received from the fbh will not change in direct proportion to the response that would be received from a notch or defect with length, i.e. the change in “notch” response will be greater than the fbh. In terms of over-tracing and vertical height sizing this may be significant. I realize that in the grand scheme this is minor and is not a detection issue, but I am looking at this from a production perspective. It does not appear to be in the interest of the construction contractor to relax tolerances on non-functioning elements. More often than not these contractors are the immediate clients of the AUT contractor.

If I relate back to the original posting on this topic, there was a quote about evaluating such tolerances versus “defect parameters”. I am not sure whether or not this is what they were addressing, but let me suggest a scenario. Suppose I have an acceptance criterion that imposes a vertical height limit of 3mm. The AUT configuration is typical pipeline girth weld with inspection zones of approximately 3mm. In this situation the over-tracing calculations are critical. A few elements may be the difference between an acceptable weld and a cut-out. Forget about relating this to the performance of other systems, defect orientation/position, or any limitations of the technique in general. A relaxed tolerance allowing broad beams runs contrary to the interests of the construction contractor. Why would it be tolerated if it can be eliminated with a supply of fully functioning equipment?

I’m sure that these tolerances are just beginning to be defined and that we’ll have the opportunity to view more empirical information in the future. The industry is beginning to absorb experienced people who are comfortable with common sense and have the knowledge and confidence to make decisions. Perhaps this will allow those involved to drop the defenses a little bit and move forward.

It would be helpful if the phased array users would highlight not only the areas of irrelevance and nonsense concerning specs, but also share some of the important concerns which should be addressed in future specifications. If we could cut out some of the black magic we could get down to what this should really be all about: Service.

Cheers,

Paul


--------- Start Original Message -----------
: Paul, Ed,
: I agree on the point made regarding the Signal to noise ratio when higher angles are utilized. If we look at the majority of inspections performed we can get a good idea on what angles are used and at what frequency. When the wedges where designed they were done so to achieve a natural 50 degree angle (refracted), this would mean that most weld profiles would be covered in a 45 to 55 degree range with little difficulty in beam steering. However this does cause more noise in the system when we work at the higher angles, the system has to work harder so to speak in order to create the higher angles resulting in the noise. The transducer design has a large role to play when we are steering the beam, the smaller the pitch used the better the steering and signal response and less noise, but with a smaller pitch we also make the transducer foot print smaller which now starts to limit us in wall thickness that can be completely covered. Another option is to increase the incidentangle of the wedge in order to reduce the noise from steering the beam at the high angles; this of course would increase the footprint of the wedge.
: Perhaps an increase in incident angle to 36 degrees would aid in the noise issue and only increase the footprint by 4mm.
: I would agree with Ed when considering a narrow beam and a broad beam, the bottom line here is ensure the system is running to procedure and spec, which means proper overtrace values from the adjacent channels. If the system strays from the procedure/spec due to loss of elements/channels and it cannot be compensated for by increasing elements or angle change than the system would fail the calibration and corrective action taken. We want to ensure we can run the system to spec, which will give our clients a quality inspection, but at the same time we do not want to be painted into a corner due to lack or misunderstandings of the system.
: Take care,
: Dave
:
: : Paul:
: : Some of your concerns are valid andthe issue at the end of the posting is a concern I have too. The statement (ANY statement) about S/N ratio is a red herring. It has nothing to do with PA configuration.
: : It should first be noted that the Cancre report and the EPRI report used different cables and probes from each other and those were both different from what you would have seen in your field. So this is NOT a “patch” of a manufacturer as seen by the cynic, but a field observation/concern and an effort to get a “practical” tolerance. Both reports suggest that the tolerance is dependent on the configuration. But the point is made that performance is based on function not on some number that is made up to look at only a single condition.
: : You state concern that the response from a FBH would not reflect changes in the beam generated by the PA probe. Yet you would be quite unaware of the same subtle changes due to coupling variation between the wedge and probe, or the un-documented changes that some companies have when angleand skew are adjusted by adjusting the carbide wear pin gaps. Do you not find it odd that Skew and Angle are required baseline recorded parameters in some Codes yet these are ignored by people as they “fiddle” with the hardware to optimise responses of FBHs? There is even one of the systems out there that has a “skew adjustment” built right into the probe pan!
: : If you are not going to use the information then do not require its documentation.
: : You state concern for the response variations for “defect sizing ratios (amplitude) for a tightly focused beam and a broad beam”. Yet in some cases (e.g. ASTM E-1961) we have set a range of acceptable overtrace that SHOULD be followed. If the spot size increases then that is reflected in the overtrace and MOST companies have policies that account for that. I have seen ONE operator (of a phased array system) actually reduce the focus to ensure that the -14 dB was achieved!
: : The statement you made on the SN ratio for high angle beams is also a concern for me. This has nothing to do with whether or not the probe is PA or conventional. More it is a function of the calibration block design and surface conditions. I see no reason to introduce this parameter in the probe assessment. If SN ratio is considered it should be in isolation (i.e. on an ideal target with no other boundary conditions contributing to the parameter.
: : In your last comment I also see that the SN ratio was in the “manufacturer’s recommendations”. Why is the manufacturer required to make recommendations on functions that are technique dependent (such as the SN ratio)? Perhaps when some twit imposes company specifications that are totally unreasonable, some users think that the manufacturer has a solution.
: : But when the individual imposing the rules is importunate there is no solution.
: : E.g. the individual making up the specification has decided that if the number of defective elements requires a focal law shift greater than 1.5° the production must stop. Is the solution to adjust the carbide wear pins?...because he sees no problem with that when it is done on a conventional system.
: : Hopefully we can go back to tolerance being dependant upon the configuration and performance based on function not on some number that is arbitrarily made up with no rationale.
: : Ed
: : : I can't say that I'm completely sold on the 25% idea or + dB range. I've had a chance to have a brief look at the Cancre report. I think the underlying conclusion is that the tolerance is dependant upon the configuration. If I look at the diagrams I see changes in the characteristics of the beams. I don't see that a typical calibration piece (fbh's) will accurately reflect these changes. Wouldn't you expect different defect sizing ratios (amplitude) for a tightly focused beam and a broad beam if your calibration reflector is a small fbh? If you calibrated both a fully functional focal law and a -25% element focal law on a 2mm fbh, what would be the relative responses off a 2mm high notch of a length greater than the beam spread? It might be useful information to support the push for wider tolerances.
: : : I try to read these types of reports with an objective eye but I can't help but let the cynic in me have a look. It would be nice to think that the vendor's motivation is the encouragement of the practical application their equipment. The cynic sees it as a patch to address a problem with the equipment. Every approach has shortcomings and you weigh the pros and cons when choosing. It would be a lot easier in this case if this particular vendor would come up with a more robust and flexible umbilical design so we wouldn't have to deal with this.
: : : The other item that caught my eye was the manufacturers recommendation that a 9 dB signal to noise ratio be applied to the "higher" angles. This is due to the technique's difficulties with these higher angles. They may recommend it but I can't see anyone buying it.
: : : Cheers,
: : : Paul
: : : : The WCNDT in Montreal had a session devoted to phased array technology. It was often standing-room only in that session. One of the papers in that session was by F. Cancre on a study done on performance of phased array probes that will be worthwhile reading. NDT.net will be publishing papers from this conrference. Also, a paper was presented in 2003 at the EPRI conference on Phased Arrays. One in particular was "Development and Qualification of Procedures for Rapid Inspection of Piping Welds" by D. E. MacDonald, M. A. Dennis,J. L. Landrum and G. P. Selby. They noted that they could still maintain acceptable conditions to qualify the system/technique for the nuclear PDI if 25% of the elements in a focal law were switched off.
: : : : Regards
: : : : Ed
: : : : : Hello all,
: : : : : I have been following this post. We have been doing phased array inspections since 1998. I thought I would communicate what we do for phased array inspection.
: : : : : We confirm performance of all transducers prior to each inspection based on special blocks for that application. These measure angular and focus accuracy. General transducer characteristics such as center frequency, dampening, etc. are confirmed annually. In addition we have requirements as to the number of "dead" elements. Adjacent "dead" elements are considered more detrimental than separate elements within this qualification. IMHO PA transducer calibration requirements are no less important than single element transducers. They are just more difficult.
: : : : : Regards,
: : : : : Tom
: : : : : : Paul, Ed,
: : : : : : Been quite busy lately and did not get to the forum of late. Sorry I missed the original discussion but perhaps a few points of my own my help. I agree some of the original limitations put on dead elements/channels in a phased array system were very limiting, such that in some instances these limitations would make it impossible to do the job. Some of these limitations have been a maximum of 2 elements/channels in series,or 2 elements in any focal law is unacceptable. Most of these limitations have come about due to lack of experience with the systems and situations where dead elements/channels are present.
: : : : : : Of late we have adopted an element verification procedure where regardless of the number of elements/channels that are defective the system is to be judged on performance as it is with other systems. In short if the system is producing repeatable acceptable calibrations, the signal overtrace from adjacent channels is as per procedure (ensuring no excessive beam skewing) and the signal to noise ratio is as per procedure then the system is considered to be performing at an acceptable level.
: : : : : : An element verification check is performed on regular intervals in order to monitor element/channel status, the results of the verification are then recorded. The bottom line is that we are proving the system with the calibrations.
: : : : : : A great thing about the Phased Array system is that we can monitor many different parameters and when we experience instances where defective elements/channels are causing problems we can compensate for these by changing focal law parameters and therefore keeping the system within procedure.
: : : : : : Thanks for bringing this subject up, I hope we can get further discussion on this matter.
: : : : : : Take care,
: : : : : : Dave
: : : : : :
: : : : : : : : : Ed,
: : : : : : : : : The issue of non-functioning elements etc. is an issue that I have recently had to try to nail down. Unfortunately the AUT contractor themselves submitted tolerances based on company literature which became unachievable.
: : : : : : : : : I am very interested in any literature out there and will search out this document. What is unfortunate is that with the advent of "off the shelf" AUT equipment the companies that purchase such equipment can not buy experience.
: : : : : : : : : The client need not answer why such limits must be imposed. The contractor must explain why they may be irrelevant. My recent experiences with phased array have been very positive and I have recognized many of these inappropriate specification details. Until phased array becomes the norm it is up to the AUT contractors using this technology to supply comprehensive documentation supporting variations from the specs currently in place. There must be some controls in place and they should be relevant to the technology. I have seen it go very poor when tolerances were not imposed.
: : : : : : : : : In the end it comes down to service. Buying a system and supplying personnel is not enough. An AUT contractor should be able to answer the concerns of their clients regardless of the validity of such concerns.
: : : : : : : : : I am a huge fan of phased array technology and I will be eager to participate in any discussions regarding it. I hope this thread may lead to a discussion of what are relevant concerns and what should be put to rest.
: : : : : : : : : Cheers,
: : :: : : : : : Paul
: : : : : : : : : : I wish I had said that:
: : : : : : : : : : Have you every read something on a familiar topic, that, having seen it laid out in print in front of you, you see that the wording is a clear and precise expression of the obvious that others seemed to be missing? When I read such a phrase I wish I had said it.
: : : : : : : : : : I have just read the new book released by RD Tech, “Introduction to Phased Array Ultrasonic Technology Applications” and found a few such items. One in particular comes to mind (Section 3.16.2) where sensitivity tolerance is discussed for phased array probes. “Once the phased array probe and system are calibrated for a specific task (reflector type, ultrasonic path range, amplitude threshold, SNR level, reporting level, sizing method) the reproducibility of results must be evaluated versus the defect parameters, not from probe to probe or from inspection to inspection.” This is an excellent and practical observation.
: : : : : : : : : : Too often I have seen people imposing stringent rules to monitor a UT system and they ignore the fact that phased array probes cannot be treated in the same way as the traditional single element probes. I have even personally been obliged to incorporate requirements for phased array performance in procedures so as to conform to specifications knowing full well that the specification was out of touch with the function of the test. Elaborate “rules” have been made for a variety of aspects relating to phased array probes that have little or no bearing on the application requirements. E.g. number of inactive elements or connectors has been brought up as a putative concern by several “policy makers” and “specification writers”. They want limits placed on the numbers allowed inactive. But they cannot explain WHY such limits must be in place. When sensitivity calibration is determined by the amplitude response from a specified target there can be several options to achieve that goal.
: : : : : : : : : : The new book is an easy read and provides not only a broad background to phased array applications and probe aspects, it also has a good section (Section 2) on the basic formulae and ultrasonic reference data. There the material is presented with tables and colour illustrations using simple terms, avoiding getting lost in the esoterica of the background academics.
: : : : : : : : : : I suppose regulating performance is desirable for some stages of UT (such as at the manufacturing stage). However, extreme tolerance requirements imposed on equipment need not necessarily ensure improvement in defect detection and sizing. As well, many of the baseline tests run at the manufacturer cannot be repeated in the field (e.g. as a result of different test equipment, wear, shaping of wedges, etc). Therefore many of the imposed specification requirements cannot be practically met.
: : : : : : : : : : This discussion item is posted because I was interested to see if others have similar or different experiences concerning phased array versus single element specifications. With the new publication “Introduction to Phased Array Ultrasonic Technology Applications” it may be an opportunity for users to become better acquainted with phased array technology and its differences (and similarities) to traditional single element UT.
------------ End Original Message ------------




 
04:25 Sep-04-2006
Raheem
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