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