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- since 1996 -

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Technical Discussions
John Wiliams
John Wiliams
07:22 May-09-2000
Double wall double image

What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120


 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
08:18 May-09-2000
Re: Double wall double image
: What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120

If your term 'double image' is referring to the situation, where you have a 'small' diameter of the tube (> 100 mm) and a 'large' source distance (some 100 mm away from the tube), there is no difference. Either 0/60/120 or 0/120/240 deg. interleave are possible (and allowed due to the European or former German standards).

Only in the situation of 'Double wall single image' (large tube diameter, source near the outer surface of the tube), only 0/120/240 deg are possible, of course.

OK ?

Best regards
Uli Mletzko, NDT Group,
State Materials Testing Institute (MPA),
University of Stuttgart, Germany




 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
08:24 May-09-2000
Re: Double wall double image

: diameter of the tube (> 100 mm)

Sorry for my mistyping. Of course it should be

diameter of the tube (< 100 mm) (less than 100 mm)

Best regards
Uli Mletzko, NDT Group,
State Materials Testing Institute (MPA),
University of Stuttgart, Germany




 
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Jacques Parent
Jacques Parent
08:49 May-09-2000
Re: Double wall double image
: What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120

Double wall exposure and superimposed double wall viewing only
0-120-240
or
0-60-120

The 240 and 60 shots provide the same coverage with opposite top and bottom walls.

I believe the 60 shot is prefered because it is easier to set up from a shooting point of view. All three shots are taken from the same quadrant.

Regards
jp




 
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Nick Welland
Nick Welland
01:12 May-11-2000
Re: Double wall double image
: : What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120

: Double wall exposure and superimposed double wall viewing only
: 0-120-240
: or
: 0-60-120

: The 240 and 60 shots provide the same coverage with opposite top and bottom walls.

: I believe the 60 shot is prefered because it is easier to set up from a shooting point of view. All three shots are taken from the same quadrant.

: Regards
: jp

I agree that on site the 0, 60, 120 is usually easier to set up and provides the same coverage. But when considering the loss of sensitivity with double-wall viewing, especially superimposed, the 0-120-240 scheme would seem to ensure the favourable near-film location is available in all quadrants.
Nick


 
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Jacques Parent
Jacques Parent
04:51 May-11-2000
Re: Double wall double image
M. Welland;

I know what you are saying and I do not disagree.
But:
1) 0, 120, 240 shooting on small diameter (<100mm) does not ensure complete coverage on the film side. One still need to evaluate the source side image.

2) Source side IQI's (as required by Code) ensure equivalent and acceptable sensitivity.

In my opinion both techniques are acceptable and the choice should be left to the "shooter"

Regards
jp




 
 Reply 
 
Nick Welland
Nick Welland
02:11 May-12-2000
Re: Double wall double image
: M. Welland;

: I know what you are saying and I do not disagree.
: But:
: 1) 0, 120, 240 shooting on small diameter (<100mm) does not ensure complete coverage on the film side. One still need to evaluate the source side image.

: 2) Source side IQI's (as required by Code) ensure equivalent and acceptable sensitivity.

: In my opinion both techniques are acceptable and the choice should be left to the "shooter"

: Regards
: jp

OK Jacques, c'est entendu, either technique is acceptable. I was trying to see whether there would in fact be any justification for preferring 0-120-240.

Regards
Nick Welland



 
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john williams
john williams
04:17 May-18-2000
Re: Double wall double image
: What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120
What is the best method to x-ray two plates of different thicknesses (12mm to 40mm). Also is it true that if you increase the kv by 20 your exposure time is reduced by 50%.





 
 Reply 
 
Uli Mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
07:07 May-19-2000
Re: Double wall double image
: : What is the reasoning behind when taking 3 shots at 120 degrees to each other rather than 0deg,60 & 120

Unfortunately you have posted your question as follow-up to a wrong subject. Posting of answers therefore may be difficult.

: What is the best method to x-ray two plates of different thicknesses (12mm to 40mm).

You have to know the exposure chart of the x-ray tube (milliamps depending on wall thickness, with voltage as parameter, for a certain film) and the exposure chart (with gamma information) of that film. Then you have the choice for the maximum density (thin wall) and the minimum density (thick wall). The output should be one single voltage, where the task could be solved.
To have a wallthickness difference of 22 mm within a density range of 2 (2.0 to 4.0), you will need high energy like Cobalt 60 or a linear accelerator. The task can't be solved with standard x-ray tubes (you need a flat inclination of exposure chart line).

: Also is it true that if you increase the kv by 20 your exposure time is reduced by 50%.

This is depending not only from the increase, but also from the voltage itself. The output (intensity) of a x-ray tube is depending roughly from the square of the actual peak voltage (integral of or area below the spectral intensity curve). The exposure is depending roughly on the inverse of the intensity.

Regards
Uli Mletzko
MPA, University of Stuttgart, Germany



 
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saeed payam
NDT Inspector
Iran, Joined May 2002, 1

saeed payam

NDT Inspector
Iran,
Joined May 2002
1
04:39 May-22-2002
Re:film
can you lead me to a site wich it able to show by,online,any welds defect on radiographic film or send it by e-mail to me please.


 
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