Gamma Radiography Testing

Type of operation.
Static - development may be mechanized.

Equipment.
Radioactive isotope in storage container. Remote handling gear. Lightproof cassette. Photographic development facilities. Darkroom and illuminator for assessment.

Mode of operation.
Gamma rays, similar to X-rays but of shorter wavelength, are emitted continuously from the isotope. It cannot be ‘switched off’ so when not in use, it is kept in a heavy storage container that absorbs radiation. They pass through the work to be inspected. Parts of the work presenting less obstruction to gamma rays, such as cavities or inclusions, allow increased exposure of the film. The film is developed to form a radiograph with cavities or inclusions indicated by darker images. Section thickness increases (such as weld) appear as less dense images.

Operating parameters.
Wavelength of radiation : 0.001 - 0.015 nm
0.01 - 1 nm (1.25MeV - 80KeV)
Portability : good (except for container)
Access : good
Exposure time : 1 second - 24 hours
Thickness range : up to 250 mm
Minimum defect size : 1% of thickness

Materials.
Most weldable materials can be inspected.


Typical welding applications.
Site inspection.
Panoramic exposure for small work.

Advantages, limitations, consumables and safety as for X-ray radiograph


X-ray Radiography.

Type of operation.
Static or transportable.


Equipment.
X-ray tube. Stand and control gear. Lightproof cassette. Photographic development facilities. Dark room and illumination for assessment.


Mode of operation.
X-rays are emitted from the tube and pass through the work to be inspected. Parts of the work presenting less obstruction to X-rays, such as cavities or inclusions, allow increased exposure of the film. The film is developed to form a radiograph with cavities or inclusions indicated by darker images. Section thickness increases (such as weld under-bead) appear as less dense images.

Operating parameters.
Tube voltage : 10 - 500 kV
Tube current : 10 - 250 mA
Power consumption : 1 - 10 kW
Portability : fair
Access : fair
Exposure time : 1 sec - 10 min
Thickness range : up to 100 mm
Minimum defect size : 0.1% of thickness X 0.05 mm

Materials.
Most weldable materials may be inspected.

Typical welding applications.
Pipelines
Pressure vessels.

Overall advantages.
Accurate pictorial presentation of results.
Radiographs may be kept as a permanent record.
Not confined to welds.

Overall limitations.
Personnel must be clear of area during exposure.
Cracks parallel to film may not show up.
Film expensive.

Consumables.
Film.
Processing chemicals.
Water.
Isotope replacements - for gamma radiograph

Safety
Cumulative radiation risk to personnel requires stringent precautions.