Radiographic Testing (RT) is an NDT method that sends X-rays or gamma rays through a part onto film or a detector. The result is a radiograph: a shadow picture of the inside of the part, kept as a permanent record that a client, auditor or Level III can review years later. RT works on almost any material, from welds and large castings to electronic components.
How it works: a shadow picture
Radiation passing through a part is weakened according to the thickness, density and atomic number of the material. Thinner or less dense areas let more radiation through, so the film turns darker. A gas bubble in a steel casting, for example, shows as a dark spot. Tungsten inclusions or excess weld metal show lighter.
Geometry controls sharpness. Geometric unsharpness (Ug) grows when the source is large, too close to the part, or when the film is far from the part. The recipe for a sharp shadow: small source, distant source, film close to the part, beam square to it. Every exposure includes an IQI (Image Quality Indicator) to prove the technique is sensitive enough.
X-rays and gamma rays
| X-rays | Gamma rays | |
|---|---|---|
| Origin | Fast electrons hitting a target in a tube | Decay of a radioactive isotope |
| Energy | Adjustable through kV and mA | Fixed by the isotope |
| Switching off | Stops when the machine is off | Cannot be switched off; must always be shielded |
| Power | Needs electricity | No electricity needed; suited to pipelines and remote sites |
| Examples | Portable tank-type units of about 100–300 kV | Ir-192 (half-life 73.8 days), Se-75 (120 days), Co-60 (5.27 years) |
Basic RT steps
- Choose the lowest-energy source that still penetrates the part in a reasonable time, since lower energy gives better contrast.
- Set the geometry and technique; for pipe there are SWSI, DWSI and DWDI depending on diameter and access.
- Place the film, location markers and IQI (usually on the source side).
- Work out the exposure from an exposure chart and the inverse square law, then expose.
- Survey with a survey meter after every exposure.
- Process the film: develop, stop, fix, wash and dry (or read the imaging plate for digital radiography).
- Interpret the film: check validity (identification, density, IQI, artefacts), then detect, identify and evaluate indications against the code’s acceptance criteria.
- Write the report with the technique, results, interpreter’s name, certification level and signature.
Flaws RT finds
In welds, RT finds porosity, slag inclusions, incomplete penetration, lack of fusion, cracks, undercut, tungsten inclusions, burn-through and root concavity. In castings it finds gas porosity, shrinkage, hot tears, sand inclusions and cold shuts. RT is strongest on volumetric flaws. A tight crack lying across the beam can be invisible, so codes often call for UT or extra RT angles.
Radiation safety
X-rays and gamma rays cannot be seen or felt. The protection principles are time, distance and shielding: doubling the distance cuts the dose rate to a quarter. Never enter a radiation area without a calibrated survey meter and a personal dosimeter. In Indonesia, licensing, the Radiation Protection Officer (PPR) and operator qualifications are regulated by BAPETEN.
Advantages and limitations
| Advantages | Limitations |
|---|---|
| Permanent image record | Radiation hazard; needs a licence and a controlled area |
| Almost any material | Needs access to two sides (source and film) |
| Excellent for volumetric flaws and internal shape | Planar cracks depend on the beam angle |
| Results can be reviewed at any time | Flaw depth is not shown directly; slow for thick parts |
Learn RT from scratch
In the Radiographic Testing (RT) Level II course you learn radiation sources, shadow geometry, IQIs and radiograph interpretation through interactive animations, then practise on an X-ray and gamma camera exposure simulator. Start with free Lesson 1: The radiographic process & radiation.
Fact source: RT Level II workbook, pp. 8–43, 48, 90–96, 111, 152–170.
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