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CHAPTER 7 - Radiographic Inspection - Coggle Diagram
CHAPTER 7 - Radiographic Inspection
Advantages of Radiography
It directly produce a permanent record
Capable of detecting internal flaws
Useful for NDT virtually all material & product forms
Real-time imaging is possible for some application
Disadvantages of Radiography
Radiation hazard
Sensitivity is affected by defect orientation such as fine cracks & other planar defects
Access of two sides is required
Limited by material thickness
Skill interpretation is required
Relatively slow
High capital outlay & running costs
Fluoroscopy
Advantages
Real-time imaging
Fast inspection technique
No film processing required
Can permit viewing in all direction
Disadvantages
No permanent record
Hazardous to operator
Limited to thickness
Duties Of Radiographic
Interpreter
Mask of any unwanted light from viewer
Ensure the background light is subdued
Check radiograph for correct identification
Access rad radiographic density
Calculate the radiograph sensitivity
Check the radiograph for any artefacts
Access the radiograph for any defect present
Industrial Radiography
X-Rays (Electrically generated)
Gamma Rays (Generated by the decay of unstable isotopes)
Advantages & Disadvantages of Gamma
Rays compared with X-Rays
Advantages
No water / electrical supplies needed
Equipment smaller & lighter (more portable)
Easier to perform radiography in confine areas
Equipment simple & robust
Less scatter
Less initial costs
Greater penetrating power
Better latitude which is range of thickness
Disadvantages
Reduced radiographic contrast
Exposure times generally longer
Source need replacing
Radiation cannot be switched off
Remote handling is necessary
Penetrating power cannot be adjusted
Generally inferior geometric & unsharpness
Film Artefacts
During radiography & film processing images can be formed which are not due a defect / a change in component thickness
Such image are referred to as ARTEFACTS
Type of artefacts
Crimp marks
Dirty intensifying screen
Scratched intensifying screen
Static marks
Reticulation
Solarisation
Chemical / water splashes
Diffraction mottling
Drying marks
Streakiness
Radiographic Techniques
Single Wall Single Image (SWSI)
Double Wall Single Image (DWSI)
Double Wall Double Image (DWDI)
Radiographic Quality
Density
Contrast
Definition
Image quality indicators
Radiographic Film
Density
Lack of Density
Under exposure
Developer temperature is too low
The exhausted developer
Developer is too weak
Excessive Density
Over exposure
Excessive development
Developer temperature is too high
The solution is too strong
4 Types of Cracks
Solidifications cracks
Hydrogen induced cracks
Lamellar tearing
Reheat cracks