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Technical Discussions
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16:55 Jan-05-2016
Unsharpness

Hi, How can we measure unsharpness from radiograph.

 
 Reply 
 
Leo
NDT Inspector,
Norway, Joined May 2008, 104

Leo

NDT Inspector,
Norway,
Joined May 2008
104
10:00 Jan-06-2016
Re: Unsharpness
In Reply to Ad at 16:55 Jan-05-2016 (Opening).

have to use duplex iqi for that.

 
 Reply 
 
Rene Stuck
Rene Stuck
13:15 Jan-06-2016
Re: Unsharpness
In Reply to Ad at 16:55 Jan-05-2016 (Opening).

Hi, what do you mean "measure unsharpness from radiograph"?
Why do you will measure that?

 
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03:29 Jan-07-2016
Re: Unsharpness
In Reply to Rene Stuck at 13:15 Jan-06-2016 .

few lines from asme secion I :
PW-51.1 When the radiographic examination method is used for a weld requiring volumetric examination by PW-11, the weld shall be examined throughout its entire
length by the X-ray or gamma-ray method in accordance with Article 2 of Section V. The requirements of T-274 are to be used as a guide but not for the rejection of
radiographs unless the geometrical unsharpness exceeds 0.07 in. (1.8 mm)

We should be able to check unsharpness from image. Otherwise how can we check the condition on unsharpness is met or not?

 
 Reply 
 
Gerald R. Reams
Gerald R. Reams
21:17 Jan-07-2016
Re: Unsharpness
In Reply to ad at 03:29 Jan-07-2016 .

ASME Section V, Article 2 has the formula for calculating Geometric Unsharpness. Each of the dimension values needed for the calculation should be included in the radiographic technique sheet or report.

 
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Malcolm Hill
United Kingdom, Joined Jun 2012, 14

Malcolm Hill

United Kingdom,
Joined Jun 2012
14
14:52 Jan-08-2016
Re: Unsharpness
In Reply to ad at 03:29 Jan-07-2016 .

Geometric Unsharpness Calculations
When performing an X-ray inspection, the geometric unsharpness of the inspection setup needs to be taken into consideration, especially when using geometric magnafication. The size of the X-ray tube focal-spot and the magnification factors, namely the source-to-specimen and specimen-to-detector distances, are used to calculate the geometric unsharpness of the inspection setup. The allowable amount of unsharpness is controlled by specification being followed. In general, the allowable amount is 1/100 of the material thickness up to a maximum of 1mm (0.040 inch).


Geometric unsharpness or the size of the penumbra (Ug) can be calculated using the following equation:
Ug = f * b/a
Where: f = X-ray generator focal-spot size.
a = distance from x-ray source to front surface of material/object
b = distance from the material/object to the detector

 
 Reply 
 
Dr. Uwe Zscherpel
Director,
BAM Berlin, Germany, Joined Jan 2010, 83

Dr. Uwe Zscherpel

Director,
BAM Berlin,
Germany,
Joined Jan 2010
83
09:17 Jan-11-2016
Re: Unsharpness
In Reply to Malcolm Hill at 14:52 Jan-08-2016 .

Dear all,
please be aware that the total image unsharpness of a radiograph has contributions from geometrical unsharpness caused by the extension of the focal spot and the magfnification factor as well as a contribution from the detector unsharpness. The latter is neglected for NDT films, but becomes more important with digital detector having pixels of discrete size. Please see ISO 17636-2 for a more general consideration. The image unsharpness is measured accorsing to ASTM E 2002 or ISO 19232-5 with a platimium duplex wire gauge.
Best regards
Uwe Z.

 
 Reply 
 

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