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Radiography - Coggle Diagram
Radiography
Principles
transmission of ionising radiation through a material
film or fluorescent screens
photographic emulsion
to detect changes in density and thickness
internal and surface breaking defects.
types of radiation
gamma
X
Discontinuities
absorbs less radiation than the parent material
image appears black
Applications
Pipeline weld inspections - internal - using X or gamma-ray crawlers.
Pipe weld inspections - external - using X and gamma-ray.
Welders' test pieces - permanent record.
Last castings - for void and segregation content.
Pipework corrosion surveys - using double-wall double-image shots with gamma radiation.
Submarine or surface ship insert welds.
Equipment
Gamma radiography
decay of unstable radioactive isotopes
Cobalt-60
Half life -5-26 years
Energy level - 1,170-1,330keV
Ytterbium-169
Half life - 32 days
Energy level - 50-300keV
Iridium-192
Half life - 74 days
Energy level - 300-600keV
Isotope container
lead lined container
Wind-out
X-radiography
cathode
incandescent filament
supplies electrons
milliamperage controls the quantity of radiation
anode
tungsten target
Benson Line focus
beryllium window
kilovoltage
controls the energy level / penetrating power
Image quality indicators (IQIs)
assess the contrast and definition of the radiographic image
Step-hole type
placed on shims
wire type
across the object
Sensitivity
Radiograph sensitivity = Diameter of smallest visible wire / Thickness of test object x 100%
In weld radiography a sensitivity of 2% or better is aimed for.
Step-hole type = Diameter of smallest visible hole / Thickness of test object x 100%
Advantages/disadvantages
Disadvantages
Ionising radiation is a serious health hazard.
A time consuming process when film development is taken into account.
Expensive both in capital costs and in providing radiographic film.
Two sides of test piece have to be accessible.
Interpretation of radiographs requires skill.
Can be sensitive to defect orientation and so can miss planar flaws.
Advantages
A permanent record is produced.
Good for measuring volumetric defects (porosity, inclusions).
Can be used on a wide variety of materials.
The method makes it possible to inspect in accessible structures and assemblies.