An Important principle of Radiography Testing procedure is
How to arrange for Radiography Testing?
Radiography is Non destructive testing method, which utilizes penetrating electromagnetic radiation for capturing the volumetric images of an object on film or digitally in a computer.
Radiography testing broadly uses any of the two types of radiation X ray or Gamma Ray for this purpose.
Gamma Ray Emitted from radio decaying isotopes. In this case radiation strength cannot be increased or decreased for purpose of inspection components of different material and different thickness. Instead only the expose time can be controlled. After calculated exposure time, the radiation emitting source is sent back in to a shielded enclosure.
X Rays are produced by a electrical system. In this case the strength of radiation can be controlled in relative to the component atomic number and thickness of material.
Here we are going to see how to make the radiographic set up and exposure ?
How to calculate the Source to Film Distance ?
How to calculate the exposure time?
Where to place the radiation source ?
Minimum Source to Film Distance calculation
Initially for calculating the SFD , first find out the maximum geometric un-sharpness allowed as per standard
Un-sharpness is the loss of definition for details in the film image as shown below
Maximum Unsharpness allowed is given in the below table as per ASME Section V Article 2
Knowing the Source size S, Object to Film Distance set and Ug Value from the given table. The unknown minimum Source to Object Distance (SOD) can be found,
The Source to film distance (SFD) = SOD + OFD
And Exposure Time can be calculated by the below formula
- Exposure time = SFD2 x EF x FF / Curie strength
- For Ex-Factor refer table, Film Factor refer table.
Knowing the calculated SFD and Film density D being used and Source type being used we can calculate the Exposure time required for Radiography shooting .
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