 
1260 views  Technical Discussions   Zeki Cosku Gokce
 Zeki Cosku Gokce
 01:34 Nov262003 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
 
   Juan J. Amado Engineering, Inspection Arco Industrial, S.A., Panama, Joined Nov 2001, ^{44}   09:08 Nov262003 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 sourceside of the object to the filmside of the object, and D is the distance from the source to the sourceside 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.
 
   Zeki Cosku Gokce
 Zeki Cosku Gokce
 06:05 Nov272003 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 sourceside of the object to the filmside of the object, and D is the distance from the source to the sourceside 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
 
   Radostin Kasarov NDT Inspector NDT Insp. lab., Bulgaria, Joined Jul 2002, ^{2}   09:42 Nov272003 Re: number of exposure Next week I'll send you a sample softwarecalculator(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 
 
   Uli Mletzko R & D, Retired Germany, Joined Nov 1998, ^{89}   02:26 Nov272003 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, Nondestructive 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 filmfocus 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
 
   uli mletzko R & D, Retired Germany, Joined Nov 1998, ^{89}   02:30 Nov272003 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, Nondestructive 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 filmfocus 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
 
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