Inspection method · RT
Radiographic testing (RT)
Radiography creates an image of a component's interior, showing porosity, inclusions and lack of penetration in welds and castings.
01How it works
Radiographic testing passes X-rays or gamma rays through the component onto film or a digital detector. Differences in thickness or density, caused by voids or inclusions, appear as variations in the image. Image quality is verified with image quality indicators (IQIs), and density or signal to noise ratio requirements.
Digital radiography (computed radiography with phosphor plates, or digital detector arrays) is increasingly used and allows digital review and archiving.
02Typical industrial applications
- Butt welds in pipe and plate
- Castings, especially of valves and pumps
- Weld repairs
- Pressure equipment welds
- Assemblies for internal verification
03Benefits and what it detects
- Permanent image record
- Good detection of volumetric defects
- Direct visual interpretation
- Widely accepted by codes
04Limitations
- Radiation safety requires controlled areas
- Planar flaws parallel to the beam may be missed
- Access to both sides needed
- Less effective on thick sections and fillet welds
- Slower and more expensive than UT
05Specifying and reviewing the method
Specify technique class, image quality requirements, extent and acceptance levels. ISO 17636-1 (film) and ISO 17636-2 (digital) are common for welds, with acceptance levels in ISO 10675-1. For castings, reference radiographs such as ASTM E446 or E186 are often used.
Other references: ISO 17636-1, ISO 17636-2, ISO 10675-1, ASTM E446