Which two NDT methods detect surface defects?

• A. Magnetic Particle Testing (MT) and Liquid Penetrant Testing (PT)
• B. Ultrasonic Testing (UT) and Radiography (RT)
• C. Visual Inspection (VT) and Ultrasonic Testing (UT)
• D. Magnetic Particle Testing (MT) and Ultrasonic Testing (UT)

Answer: (A)

Detecting surface defects relies on methods that reveal flaws which connect to or are directly accessible from the surface. Magnetic Particle Testing magnetizes the material; a flaw that interrupts the magnetic flux causes the magnetic field to leak and the iron particles to gather along the defect, producing a visible indication on the surface. Liquid Penetrant Testing uses a penetrant fluid that seeps into surface-breaking cracks; after removing excess liquid and applying a developer, the trapped penetrant bleeds out at the defect and creates a surface-visible indication, clearly outlining the flaw.

These two are especially effective for surface defects because both are designed to show flaws that reach the surface, providing a direct surface indication. Ultrasonic Testing and Radiography are more oriented toward detecting internal or subsurface discontinuities, while Visual Testing can identify surface irregularities but may miss subsurface and can depend on lighting and cleanliness. So MT and PT together best target surface-breaking flaws.