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- since 1996 -
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Technical Discussions
Zeki Cosku Gokce
Zeki Cosku Gokce
01:34 Nov-26-2003
number of exposure

I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.

I would appriciate all the help

Regards



    
 
 Reply 
 
Juan J. Amado
Engineering, Inspection
Arco Industrial, S.A., Panama, Joined Nov 2001, 44

Juan J. Amado

Engineering, Inspection
Arco Industrial, S.A.,
Panama,
Joined Nov 2001
44
09:08 Nov-26-2003
Re: number of exposures
----------- Start Original Message -----------
: I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: I would appriciate all the help
: Regards
------------ End Original Message ------------

Zeki:

As you may infer from the formula for geometric unsharpness: Ug=Fd/D, (where Ug is geometric unsharpness, F is focal size of the source, d is the distance from the source-side of the object to the film-side of the object, and D is the distance from the source to the source-side of the object) as you reach the borders of the film in a pipe shot situation, two thing will take placesimultaneously: the thikness of the material will increase and the source to object distance will decrease. Both of these factors conspire to increase the geometric unsharpness and make the details near the border of the film blurry. Add to this the effect created by the lessened angle of incidence of the radiation beam in that same area, and distotion of the image will also come in to play.

Without getting too technical (although the formulas are straight forward, and most of the math is just geometry and algebra), I would suggest, as a general rule of thumb, to incrase the distance from the source to the surface of the pipe, and to go to a 4 shot configuration. For extreme cases, it may be necessary to segment the pipe into even more parts.


    
 
 Reply 
 
Zeki Cosku Gokce
Zeki Cosku Gokce
06:05 Nov-27-2003
Re: number of exposures
----------- Start Original Message -----------
: : I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: : I would appriciate all the help
: : Regards
: Zeki:
: As you may infer from the formula for geometric unsharpness: Ug=Fd/D, (where Ug is geometric unsharpness, F is focal size of the source, d is the distance from the source-side of the object to the film-side of the object, and D is the distance from the source to the source-side of the object) as you reach the borders of the film in a pipe shot situation, two thing will take place simultaneously: the thikness of the material will increase and the source to object distance will decrease. Both of these factors conspire to increase the geometric unsharpness and make the details near the border of the film blurry. Add to this the effect created by the lessened angle of incidence of the radiation beam in that same area, and distotion of the image will also come in to play.
: Without getting too technical (although the formulas are straight forward, and most of the math is just geometry and algebra), I would suggest, as a general rule of thumb, to incrase the distance from the source to the surface of the pipe, and to go to a 4 shot configuration. For extreme cases, it may be necessary to segment the pipe into even more parts.
------------ End Original Message ------------

Dear Juan

Thank you for your prompt response. I am trying to write some code that will do various calculations for RT personnel. In my filed it is not practical to increase the source to surface distance, and for thick schedule pipes some times it is needed for more then 4 shots. My foremen thinks that there is a formula that will tell you how many shot you need minimum (it was on his level II exam). Are you aware of any?
regards

Zeki



    
 
 Reply 
 
Radostin Kasarov
NDT Inspector
NDT Insp. lab., Bulgaria, Joined Jul 2002, 2

Radostin Kasarov

NDT Inspector
NDT Insp. lab.,
Bulgaria,
Joined Jul 2002
2
09:42 Nov-27-2003
Re: number of exposure


Next week I'll send you a sample software-calculator(Number of Exposure).
Regards
Radostin Kasarov

----------- Start Original Message -----------
: I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: I would appriciate all the help
: Regards
------------ End Original Message ------------




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

Uli Mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
02:26 Nov-27-2003
Re: number of exposure
----------- Start Original Message -----------
: I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: I would appriciate all the help
: Regards
------------ End Original Message ------------

You can find information on this subject e.g. in European Standard EN 1435, Non-destructive testing of welds - Radiographic testing of welded joints.

There are several diagrammes in that standard, where you can directly find the numbers of exposures, depending on wall thickness, outer diameter and film-focus distance. In class A (standard quality) an increase of penetrated wall thickness from film center to film end of 10 percent is accepted, in class B (special quality) 20 percent. In addition, you have to follow a second rule, concerning the maximum allowed density difference (Delta D <= 1.5 in that standard) between film end and film center. This could force you to a larger number of expositions.

Regards
Uli Mletzko
NDT group, MPA, Univerity of Stuttgart, Germany



    
 
 Reply 
 
uli mletzko
R & D, Retired
Germany, Joined Nov 1998, 89

uli mletzko

R & D, Retired
Germany,
Joined Nov 1998
89
02:30 Nov-27-2003
Re: number of exposure
----------- Start Original Message -----------
: : I am wondering if there is a formula that can be used for determining the number of exposures for a pipe that is going to be bombed with double wall single view techniqe. It seems to me that for smaller pipes and thick schedual pipes the geometrical unsharpness can be out of range at the end of the film when they are shot in 3 exposures. But is there a right hand rule, commen practice or some kind of formula to determine how man poses that is needed for shooting a pipe.
: : I would appriciate all the help
: : Regards
: You can find information on this subject e.g. in European Standard EN 1435, Non-destructive testing of welds - Radiographic testing of welded joints.
: There are several diagrammes in that standard, where you can directly find the numbers of exposures, depending on wall thickness, outer diameter and film-focus distance. In class A (standard quality) an increase of penetrated wall thickness from film center to film end of 10 percent is accepted, in class B (special quality) 20 percent. In addition, you have to follow a second rule, concerning the maximum allowed density difference (Delta D <= 1.5 in that standard) between film end and film center. This could force you to a larger number of expositions.
: Regards
: Uli Mletzko
: NDT group, MPA, Univerity of Stuttgart, Germany
------------ End Original Message ------------

Sorry, in the hurry I made an almost unexcusable typing error.
Of course Class A is 20 percent, and class B is 10 percent.

Regards
Uli Mletzko




    
 
 Reply 
 

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