Which two NDT methods are used for surface defect detection? (Reworded)

• A. Magnetic Particle Testing and Liquid Penetrant Testing
• B. Ultrasonic Testing and Visual Inspection
• C. Radiography and Ultrasonic Testing
• D. Visual Inspection and Magnetic Particle Testing

Answer: (A)

Detecting surface defects relies on techniques that give a visible indication right at or very close to the surface. Magnetic Particle Testing works by magnetizing a ferromagnetic part and applying iron particles (visible or fluorescent). Where there is a surface-breaking crack or near-surface flaw, the magnetic field leaks and the particles gather at the flaw, producing a clear indication on the surface.

Liquid Penetrant Testing involves applying a penetrant liquid to the surface, allowing it to seep into any surface-breaking defect. After cleaning the surface and applying a developer, the penetrant bleeds back out of the flaw and becomes visible, outlining the defect on the surface.

These methods are specifically chosen for surface-breaking flaws because they provide a direct, surface-visible indication of a flaw. Other NDT methods like Ultrasonic Testing or Radiography probe deeper into the material to detect internal features, and Visual Inspection alone only assesses surface condition without highlighting hidden flaws.