Radiographic Testing (RT) is a non-destructive testing (NDT) method that uses X-rays or Gamma rays to examine the internal structure of materials and detect hidden defects. It is widely used in industries where internal integrity is critical.
Table of Contents
1. Principle of Radiographic Testing
🔹 Working Principle:
- High-energy X-rays or Gamma rays are directed toward the test specimen.
- As radiation passes through the material, it is absorbed differently depending on thickness and density.
- The transmitted radiation falls on a film or digital detector.
- Variations in absorption create an image showing:
- Internal defects
- Density changes
- Structural inconsistencies
🔹 Key Concept:
- Based on differential absorption of radiation
- Denser regions absorb more radiation → lighter image
- Defects (voids, cracks) appear darker
2. Types of Radiation Used
🔹 (a) X-Rays
- Produced by X-ray tubes
- Suitable for thin to medium thickness materials
- Easily controlled
🔹 (b) Gamma Rays
- Produced by radioactive isotopes like:
- Cobalt-60
- Iridium-192
- Suitable for thicker materials
- Portable but harder to control
3. Basic Components of RT Setup
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🔹 Main Components:
- Radiation Source – X-ray tube or gamma source
- Specimen (Test Object)
- Film or Digital Detector – Captures image
- Film Cassette & Intensifying Screens
- Control Unit – Regulates exposure
- Protective Shielding – Ensures safety
4. Types of Radiographic Testing
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🔹 (a) Film Radiography
- Uses photographic film
- High image quality
- Time-consuming processing
🔹 (b) Digital Radiography (DR)
- Uses digital detectors
- Instant results
- Easy storage and analysis
🔹 (c) Computed Radiography (CR)
- Uses imaging plates scanned digitally
- Intermediate between film and DR
🔹 (d) Real-Time Radiography
- Continuous imaging
- Used for dynamic inspection
5. Types of Defects Detected
- Cracks
- Porosity
- Voids
- Inclusions
- Lack of fusion in welds
- Thickness variations
6. Advantages of Radiographic Testing
✔ Detects internal defects clearly
✔ Provides permanent record (film/image)
✔ Suitable for complex shapes
✔ High accuracy for volumetric defects
✔ Minimal surface preparation required
7. Limitations of Radiographic Testing
❌ Radiation hazard (strict safety required)
❌ High cost
❌ Time-consuming (especially film)
❌ Less effective for planar defects (like tight cracks)
❌ Requires access to both sides of specimen
8. Safety Precautions
⚠ Use proper shielding (lead barriers)
⚠ Maintain safe distance
⚠ Use personal dosimeters
⚠ Follow radiation safety regulations
⚠ Only trained personnel should operate
9. Applications of Radiographic Testing
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🔹 Industrial Applications:
- Weld inspection (pipelines, pressure vessels)
- Casting inspection
- Aerospace components
- Nuclear industry
- Shipbuilding
- Structural components
10. Comparison with Ultrasonic Testing (UT)
| Feature | Radiographic Testing | Ultrasonic Testing |
|---|---|---|
| Principle | Radiation absorption | Sound wave reflection |
| Defect detection | Volumetric defects | Internal & planar defects |
| Safety | Hazardous | Safe |
| Record | Permanent image | No permanent record (unless stored digitally) |
| Thickness measurement | Limited | Excellent |
🔷 11. Important Terms
- Radiographic Density – Degree of film blackening
- Contrast – Difference between light and dark areas
- Exposure Time – Duration of radiation
- Penetrameter (IQI) – Image quality indicator
- Scatter Radiation – Unwanted radiation affecting image