NDTSupport.com - Tech Room - Radiography
Basic Test Theory
X-rays are produced by high voltage x ray machines whereas gamma rays are produced from radioactive isotopes such as Iridium 192 The x-ray or gamma rays are placed close to the material to be inspected and they pass through the material and are then captured on film This film is then processed and the image is obtained as a series of gray shades between black and white.
The choice of which type of radiation is used (x ray or gamma) depends on the type and thickness of the material to be tested and the type of defect sought. Gamma sources have the advantage of portability which makes them ideal for use in construction site working.
Benefits of the Process
Inspection of the following for internal defects:
Castings, Welds, Brazed Joints, Electronic Components, Bonds, Rubber, Composites, Munitions and Ceramics.
Can also be used for making Dimensional Measurements and for Process Control.
A test method for detecting and evaluating internal discontinuities.
Can be applied for in process inspections.
Gives indication of incorrect procedures.
Can provide a permanent record.
Disadvantages/Limitations of the Process
The process is high cost.
X-rays and gamma rays can be very hazardous.
Special precautions must be taken when performing radiography Therefore the operator will use these inside a protective enclosure or with appropriate barriers and warning signals to ensure there are no hazards to personnel.
Requires skill in making radiographic exposures, operating equipment and interpreting indications.
Requires safety precautions.
Not generally suitable for fillet weld inspection.
Radiographic Process Techniques:
Commercial X-ray or gamma unit/source .
Film and processing facilities. (for non-digital radiography)
Computer imaging system (for digital radiography)
May require robotic manipulation
Radiation safety equipment and accessories