Comparison of Non Destructive Tests
X-ray radiography, gamma ray radiography, ultrasonic testing, magnetic particle testing and dye penetrant or liquid penetrant testing are commonly used non destructive tests in the marine industry. This article investigates the application, types of faults indicated, advantages and limitations or disadvantages of the above said non destructive tests.
X-ray Radiography
See: Radiography
Applications
- Air craft structures
- Structural steel works
- Ship building
- Pressure vessels and boilers
- Penstocks, etc.
Types of Faults Indicated
- Cracks
- Porosity
- Inclusions
- Lack of fusion
- Incomplete penetration
Advantages
- Provides permanent record on film
- Technique standardized
- Reference standards available
- Adjustable energy level gives high sensitivity
- Fluoroscopy techniques available
Limitations
- Trained technician needed
- Radiation hazards
- High cost of equipment
- Power source needed
Gamma-ray Radiography
See: Radiography
Applications
- Pipe work
- Penstocks
- Pressure vessels and boilers
- Structural steel works
- Ship building
Types of Faults Indicated
- Cracks
- Porosity
- Inclusions
- Lack of fusion
- Incomplete penetration
Advantages
- Provides permanent record on film
- Technique standardized
- Reference standards available
- Low initial cost
- Portable, independent of power supply
- Makes panoramic exposures
Limitations
- Trained technician needed
- Radiation hazards
- Fixed energy levels per source
- Source looses strength continuously
- Generally lower sensitivity and definition than x-ray radiography
Ultrasonic Testing
See: Ultrasonic Testing
Applications
- All types of welded work in metallic and non metallic materials
Types of Faults Indicated
- Cracks
- Porosity
- Inclusions
- Lack of fusion
- Incomplete penetration
Advantages
- Safe to use
- Fast method
- Results available immediately
- Sensitive
- Indicates presence of laminations and other plannar defects
- Indicates depth of flaw
Limitations
- Entirely dependent on operator skill
- Unsuitable for welding of complex shape or configuration
- Requires surface contact
- Surface must be clean and smooth
Magnetic Particle Testing
See: Magnetic Particle Testing
Applications
- Welds, particularly fillet welds, in all ferro magnetic materials
Types of Faults Indicated
- Cracks, Porosity, Inclusions and discontinuities at or close to the surface
Advantages
- Simple to use and interpret
- Portable and relatively inexpensive
Limitations
- Material must be ferro magnetic
- Demagnetization may be needed
- Power source required
Liquid Penetrant Testing
See Also: Dye Penetrant Testing
Applications
- All welds in ferrous and non ferrous materials and in non metallic materials
Types of Faults Indicated
- Cracks
- Blow holes
Advantages
- Simple to use and interpret
- Relatively inexpensive
- Portable and require no elaborate equipment
- Work on all materials
Limitations
- Only surface defect will be detected
- Surface must be clean and dry
- Rust or paint will mask defects