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4915 views
06:46 Jan-03-2009

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Aggressive Radiographic Auditors Need to Take a Closer Look!

Herman Grid

I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)

Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.

This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).

The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.

Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
Ed


 
00:32 Jan-03-2009

William Blum

Consultant, Training, Level III Services
NDT Consulting Group Inc.,
USA,
Joined Nov 2000
89
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Wow, one of the most interesting posts I have seen here in a while. I have some experience with this and have made the mistake myself (the call, not the bullying!). Thanks for the tip on how to possibly prevent this mistake and I look forward to seeing other comments.

----------- Start Original Message -----------
: I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: Ed
------------ End Original Message ------------




 
03:11 Jan-03-2009

Nick Welland

Other, Quality and NDT
Aben Technical Services,
Australia,
Joined Oct 1999
42
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! ----------- Start Original Message -----------


This is an excellent post by Ed and points up the importance of mentoring and experience in radiographic interpretation. The question of optical illusions was not raised when I first studied RT some thirty years ago and it was something I had to work out for myself. I too must report, like William, falling into the same trap.
I don't know that administrative action is the most effective here; maybe an article for Materials Evaluation is in order? And certainly an alert to training schools.
Nick
: Wow, one of the most interesting posts I have seen here in a while. I have some experience with this and have made the mistake myself (the call, not the bullying!). Thanks for the tip on how to possibly prevent this mistake and I look forward to seeing other comments.
: : I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: : Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: : This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: : The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: : Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: : Ed
------------ End Original Message ------------




 
00:45 Jan-04-2009
teasers
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Excellent! But usually it all comes down to experience, a sound knowledge of the welding process and a good 20/20 vision. I still see a lot of interpreters who would disregard other discontinuities or call them something else not because it was some sort of optical illusion.
In my experience the usual cause of excessive repairs was not because of optical illusions but because of the Interpreters' lack of experience and bad vision.


----------- Start Original Message -----------
:
: This is an excellent post by Ed and points up the importance of mentoring and experience in radiographic interpretation. The question of optical illusions was not raised when I first studied RT some thirty years ago and it was something I had to work out for myself. I too must report, like William, falling into the same trap.
: I don't know that administrative action is the most effective here; maybe an article for Materials Evaluation is in order? And certainly an alert to training schools.
: Nick
: : Wow, one of the most interesting posts I have seen here in a while. I have some experience with this and have made the mistake myself (the call, not the bullying!). Thanks for the tip on how to possibly prevent this mistake and I look forward to seeing other comments.
: : : I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: : : Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: : : This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: : : The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: : : Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: : : Ed
------------ End Original Message ------------




 
03:29 Jan-04-2009

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
784
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Ed,

Excellent post and many thanks from me for sharing it. I knew about optical illusions in a general way but this is really great. I might have asked for some needless repair though not too aggressively and I confess that my team was in any case, asking far beyond the code specifications, but that was worth it considering the critical nature of the equipment and the previous accidents. Our overstrict protocols have yielded excellent results in terms of longer equipment life and less repairs once put into service (in the particular case, repair of post-service welds was very difficult).

I will alert the team about your post so that they are better aware.

Thanks.

Swamy
Retired but not tired NDT Guru!

----------- Start Original Message -----------
: I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of �perceived� lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the �Herman Grid�. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the �Springer� illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they �perceive� at the boundary between the pipe wall and the weld reinforcement (cap and root).
: The verification that it is an illusion is easily seen by covering the �whiter� region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: Ed
------------ End Original Message ------------




 
03:48 Jan-04-2009

dermot p dwyer

Consultant, level 3 aerospace
Lufthansa Technik Airmotive Ireland,
Ireland,
Joined Oct 2007
3
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! ---Hi
I have not had the experiances of the 'aggressive Auditors' but have used the technique of masking the 'lighter' areas of a radiograph and gradually moving the mask to and passed the lighter areas for many years now ( I did learn something on that Rad course in SANDT many, many years ago!!).
The technique works very well and helps with those 'questionable' areas which tend to lead to a lot of head scratching.
As for your Aggressive Auditors, we in the Aerospace industry generally do not have this problem. Our snag is auditors which are not up tp speed with how NDT operates in the workplace.
good luck!!
-------- Start Original Message -----------
: Ed,
: Excellent post and many thanks from me for sharing it. I knew about optical illusions in a general way but this is really great. I might have asked for some needless repair though not too aggressively and I confess that my team was in any case, asking far beyond the code specifications, but that was worth it considering the critical nature of the equipment and the previous accidents. Our overstrict protocols have yielded excellent results in terms of longer equipment life and less repairs once put into service (in the particular case, repair of post-service welds was very difficult).
: I will alert the team about your post so that they are better aware.
: Thanks.
: Swamy
: Retired but not tired NDT Guru!
: : I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of �perceived� lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the �Herman Grid�. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the �Springer� illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: : Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: : This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they �perceive� at the boundary between the pipe wall and the weld reinforcement (cap and root).
: : The verification that it is an illusion is easily seen by covering the �whiter� region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: : Yet failure to recognise this or to use this simple test, resultsin countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: : Ed
------------ End Original Message ------------




 
06:22 Jan-04-2009

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Hi all…just a word about my comment on ‘aggressive’ auditors. After university my humble start in NDT 35 years ago was as a “radiographer’s helper” under a feisty Ulsterman who taught me this method of discriminating flaw from illusion. 18 years later he hired me as an auditor on pipeline construction and made sure I instructed radiographers on his pipelines about the technique. Over the years the pipeline owner had experienced failures that resulted at through-wall repairs (typically delayed cracking). When the original film was reviewed it was seen that this illusion was often the rationale for the repair.

However, this “instructional” function of the auditor that I was given is not a common practice around the world. It is because of the authority that the “auditor” has as the company representative that his judgement can over-rule that of an experienced radiographer. If there is no reference in a Code or Standard that provides guidance on this aspect of interpretation then the most conservative evaluation will be imposed (even if it is an illusion). Codes often have instructional phrases inserted in them so I thought that perhaps those forum members on radiographic committees might be able to submit a recommendation for revision to include a small phrase to address the potential for optical illusions being called as false rejects.
Ed

----------- Start Original Message -----------
: Excellent! But usually it all comes down to experience, a sound knowledge of the welding process and a good 20/20 vision. I still see a lot of interpreters who would disregard other discontinuities or call them something else not because it was some sort of optical illusion.
: In my experience the usual cause of excessive repairs was not because of optical illusions but because of the Interpreters' lack of experience and bad vision.
:
: :
: : This is an excellent post by Ed and points up the importance of mentoring and experience in radiographic interpretation. The question of optical illusions was not raised when I first studied RT some thirty years ago and it was something I had to work out for myself. I too must report, like William, falling into the same trap.
: : I don't know that administrative action is the most effective here; maybe an article for Materials Evaluation is in order? And certainly an alert to training schools.
: : Nick
: : : Wow, one of the most interesting posts I have seen here in a while. I have some experience with this and have made the mistake myself (the call, not the bullying!). Thanks for the tip on how to possibly prevent this mistake and I look forward to seeing other comments.
: : : : I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: : : : Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: : : : This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: : : : The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: : : : Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: : : : Ed
------------ End Original Message ------------




 
08:08 Jan-04-2009

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
818
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Hi Everyone,

I totally agree with all the comments that have been made so far on this topic, yet I must say that some ''agressive auditors'' do have a mind set no matter what. I'm experiencing this situation with a third party customer regarding our UT inspection. Sometimes, we discover some small flaws in the forging that are acceptable to code and that will be removed during final machining, yet the auditor will request that the forging be repaired prior to leaving the plant. This in my opinion is totally unacessary and increses the cost of manufacturing.

I always said that there are two kind of people in the world. Those who makes mistakes because they don't know and those who knows but are too stubborn to change. You can educate the first one and solve your problem, the latter you should get rid of.

Cheerio's

Michel

----------- Start Original Message -----------
: Hi all…just a word about my comment on ‘aggressive’ auditors. After university my humble start in NDT 35 years ago was as a“radiographer’s helper” under a feisty Ulsterman who taught me this method of discriminating flaw from illusion. 18 years later he hired me as an auditor on pipeline construction and made sure I instructed radiographers on his pipelines about the technique. Over the years the pipeline owner had experienced failures that resulted at through-wall repairs (typically delayed cracking). When the original film was reviewed it was seen that this illusion was often the rationale for the repair.
: However, this “instructional” function of the auditor that I was given is not a common practice around the world. It is because of the authority that the “auditor” has as the company representative that his judgement can over-rule that of an experienced radiographer. If there is no reference in a Code or Standard that provides guidance on this aspect of interpretation then the most conservative evaluation will be imposed (even if it is an illusion). Codes often have instructional phrases inserted in them so I thought that perhaps those forum members on radiographic committees might be able to submit a recommendation for revision to include a small phrase to address the potential for optical illusions being called as false rejects.
: Ed
: : Excellent! But usually it all comes down to experience, a sound knowledge of the welding process and a good 20/20 vision. I still see a lot of interpreters who would disregard other discontinuities or call them something else not because it was some sort of optical illusion.
: : In my experience the usual cause of excessive repairs was not because of optical illusions but because of the Interpreters' lack of experience and bad vision.
: :
: : :
: : : This is an excellent post by Ed and points up the importance of mentoring and experience in radiographic interpretation. The question of optical illusions was not raised when I first studied RT some thirty years ago and it was something I had to work out for myself. I too must report, like William, falling into the same trap.
: : : I don't know that administrative action is the most effective here; maybe an article for Materials Evaluation is in order? And certainly an alert to training schools.
: : : Nick
: : : : Wow, one of the most interesting posts I have seen here in a while. I have some experience with this and have made the mistake myself (the call, not the bullying!). Thanks for the tip on how to possibly prevent this mistake and I look forward to seeing other comments.
: : : : : I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: : : : : Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: : : : : This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: : : : : The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: : : : : Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: : : : : Ed
------------ End Original Message ------------




 
01:53 Jan-04-2009
TJ
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! I'm not so sure about applying this phenomena completely to film interpretation. My reasoning is this grid is probably the furthest thing from the varying patterns of weld metal distribution you can demonstrate.
If you are inspecting bathroom tiles I could see a problem. In most cases, with proper vision, viewing conditions and a quality radiograph the undercut (or lack of) is plain in interpretation.

TJ


 
03:28 Jan-04-2009

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! T.J. you seem to have missed the point about the perception effect. The Sprigner and Hermann grids are merely examples of the effect. Perhaps a closer related effect to our radiographic application is seen in the "Mach bands" (see a good description at http://neuro.bcm.edu/eagleman/papers/Eagleman.NatureRevNeuro.Illusions.pdf).
It is not specifically the "grid" that I was referring to but instead the contrast effect that causes the brain to form a line where none exists (hence the concern that a radiographer MAY see a dark line and interpret it as a flaw where none exists). I have seen this effect on many radiographs as have hundreds of other radiographers. The trick is to know how to verify if it is real or illusion and this is NOT always simply proper vision, viewing conditions and a quality radiograph.

If a good quality image in BMP format is available perhaps someone could upload a good image of the Mach bands...conversion to GIF tends to reduce the effect on screen

----------- Start Original Message -----------
: I'm not so sure about applying this phenomena completely to film interpretation. My reasoning is this grid is probably the furthest thing from the varying patterns of weld metal distribution you can demonstrate.
: If you are inspecting bathroom tiles I could see a problem. In most cases, with the undercut (or lack of) is plain in interpretation.
: TJ
------------ End Original Message ------------




 
00:46 Jan-05-2009

Det McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Very interesting topic guys.

Has Digital Radiography made this problem go away?


----------- Start Original Message -----------
: I wonder if there have been others with experiences of radiographic auditors bullying their opinions of so-called lack of fusion or undercut on films where most radiographers see none? The origins of “perceived” lines of so-called undercut can be attributed to a well known optical illusion known by its illustrative image the “Herman Grid”. Here a series of black squares is separated by straight white lines and the observer perceives gray blobs in the intersections of the white crosses formed by the black squares. A similar perception is had when the black squares are made smaller and the viewer perceives faint diagonal lines in the “Springer” illusion (see http://www.sapdesignguild.org/resources/optical_illusions/contrast_phenomena.html)
: Apparent brightness of a stimulus depends not only on its own luminance but also on that of the surrounding stimulation. The effect of perceiving a contrast where none exists has been documented since 1828 (Eugene Chevreul) and is generally called simultaneous contrast.
: This effect has probably be responsible for more than its fair share of unnecessary repairs due to aggressive radiographic auditors calling the fine line that they “perceive” at the boundary between the pipe wall and the weld reinforcement (cap and root).
: The verification that it is an illusion is easily seen by covering the “whiter” region (with a piece of dark paper) to reduce the contrast at the boundary. The faint grey line disappears, thereby verifying it to be an illusion and not a real flaw.
: Yet failure to recognise this or to use this simple test, results in countless unfounded weld repairs around the world. Perhaps this issue could be (should be?) addressed in the radiographic codes and standards now used.
: Ed
------------ End Original Message ------------




 
02:29 Jan-05-2009
TJ
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Ed,

After reading the .pdf I now see how this is an issue. The mach bands are of particular interest. I am surprised this was never touched on in training. It will be from now on!

Thanks,
TJ




 
04:36 Jan-05-2009

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1094
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Happy and healthy New Year to all NDT.netters.

Thanks for the links to sites showing these phenomena Ed - I've not yet explored them but I shall.

Intuitively, I had grasped the contrast problem, never really taught at NDT school though. Viewers with in-built adjustable masks are very useful for this. I assume that these effects may lead predominantly to assuming a linear indication exists, in which case the RI tech often calls in a trusted UT tech to see if a reflector exists in the area of concern. Is this a reasonable action or a display of lack-of-confidence on the part of the RI tech?


----------- Start Original Message -----------
: Ed,
: After reading the .pdf I now see how this is an issue. The mach bands are of particular interest. I am surprised this was never touched on in training. It will be from now on!
: Thanks,
: TJ
------------ End Original Message ------------




 
08:00 Jan-05-2009

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1208
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! Nigel:
I think that a radiographer should be able to address this independently (which is why I was hoping to get the technique of using a mask incorporated into Standards to eliminate the false calls and to ensure a simple arbitration method with auditors).
Dent's question about this phenomenon occurring on digital radiographs is probably one he could answer better than I. The effect is NOT actually equipment dependent as it is the brain's reaction to a chemical stimulous in the eyes. If we can see this effect on our computer monitors from the examples of optical illustions then I suspect that there is a potential that the human viewer will also see the effect on a digital version of a radiograph.

----------- Start Original Message -----------
: Happy and healthy New Year to all NDT.netters.
: Thanks for the links to sites showing these phenomena Ed - I've not yet explored them but I shall.
: Intuitively, I had grasped the contrast problem, never really taught at NDT school though. Viewers with in-built adjustable masks are very useful for this. I assume that these effects may lead predominantly to assuming a linear indication exists, in which case the RI tech often calls in a trusted UT tech to see if a reflector exists in the area of concern. Is this a reasonable action or a display of lack-of-confidence on the part of the RI tech?
:
: : Ed,
: : After reading the .pdf I now see how this is an issue. The mach bands are of particular interest. I am surprised this was never touched on in training. It will be from now on!
: : Thanks,
: : TJ
------------ End Original Message ------------




 
05:27 Jan-06-2009

Dent McIntyre

Consultant, NDE Manager NDELevel III/3
NDT Consultant,
Canada,
Joined Nov 1998
247
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! I suspect that with digital RT that this is not a problem. The fact that you can adjust density, zoom, mask, crop, etc gives the radiographer far more tools and information to make better judgements.

Does anyone out there have any digital RT experience with this issue?


----------- Start Original Message -----------
: Nigel:
: I think that a radiographer should be able to address this independently (which is why I was hoping to get the technique of using a mask incorporated into Standards to eliminate the false calls and to ensure a simple arbitration method with auditors).
: Dent's question about this phenomenon occurring on digital radiographs is probably one he could answer better than I. The effect is NOT actually equipment dependent as it is the brain's reaction to a chemical stimulous in the eyes. If we can see this effect on our computer monitors from the examples of optical illustions then I suspect that there is a potential that the human viewer will also see the effect on a digital version of a radiograph.
: : Happy and healthy New Year to all NDT.netters.
: : Thanks for the links to sites showing these phenomena Ed - I've not yet explored them but I shall.
: : Intuitively, I had grasped the contrast problem, never really taught at NDT school though. Viewers with in-built adjustable masks are very useful for this. I assume that these effects may lead predominantly to assuming a linear indication exists, in which case the RI tech often calls in a trusted UT tech to see if a reflector exists in the area of concern. Is this a reasonable action or a display of lack-of-confidence on the part of the RI tech?
: :
: : : Ed,
: : : After reading the .pdf I now see how this is an issue. The mach bands are of particular interest. I am surprised this was never touched on in training. It will be from now on!
: : : Thanks,
: : : TJ
------------ End Original Message ------------




 
08:06 Jan-06-2009

chris s

Consultant, qc manager
USA,
Joined Apr 2007
9
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! ----------- Start Original Message -----------
I assume that these effects may lead predominantly to assuming a linear indication exists, in which case the RI tech often cal Is this a reasonable action or a display of lack-of-confidence on the part of the RI tech?
------------ End Original Message ------------

For an individual not to use all assets available, that would be a disservice.




 
17:18 Jan-12-2009

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! In Reply to TJ at 02:29 Jan-05-2009 .

In 1970 as a newcomer to NDT I had to assist to NDT RT courses, performed by MPA (Univ. Stuttgart) on behalf of the german society for NDT (DGZfP, Berlin). At that time the MACH effect was described in the RT course documents, originating from the 1960th (written or edited by Prof. Vaupel, BAM, Berlin), and the effect is discussed in the DGZfP RT courses until today.

 
19:25 Jan-12-2009
TJ Franchuk
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! In Reply to Uli Mletzko at 17:18 Jan-12-2009 .

Can you recall if the training asked the viewer to just be aware of the illusion or a technique to reveal it?

Thanks, TJ

 
12:09 Aug-12-2013

George Shields

NDT Inspector, NDT Level 3
United Kingdom,
Joined Oct 2012
30
Re: Aggressive Radiographic Auditors Need to Take a Closer Look! In Reply to Ed Ginzel at 06:46 Jan-03-2009 (Opening).

Just stumbled on to this post.
Great Post Ed.
Many Thanks

 


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