A company is performing a repair weld on a thick-walled, critical pressure component made of a ferromagnetic alloy. The repair involves complex geometry. Following the weld, the inspector needs to perform a surface NDT that can detect very fine surface-breaking cracks and shallow subsurface flaws, even through a thin layer of mill scale or paint. Which NDT method would provide the most sensitive and reliable results under these conditions?

Question: A company is performing a repair weld on a thick-walled, critical pressure component made of a ferromagnetic alloy. The repair involves complex geometry. Following the weld, the inspector needs to perform a surface NDT that can detect very fine surface-breaking cracks and shallow subsurface flaws, even through a thin layer of mill scale or paint. Which NDT method would provide the most sensitive and reliable results under these conditions?

Answer options:

• Eddy Current Testing (ECT) ✅ Magnetic Particle Testing (MT) with a fluorescent wet method
• Liquid Penetrant Testing (PT) with a fluorescent post-emulsifiable method
• Ultrasonic Testing (UT) with phased array transducers

Correct answer: Magnetic Particle Testing (MT) with a fluorescent wet method

Explanation: For ferromagnetic materials, Magnetic Particle Testing (MT), especially with fluorescent wet methods, offers high sensitivity for detecting surface-breaking and shallow subsurface discontinuities. While Eddy Current Testing (ECT) can detect surface flaws, MT often provides better resolution and is less affected by minor surface contaminants for this specific application. PT requires a clean, bare surface, and UT is primarily for subsurface flaws, although phased array UT can sometimes detect surface flaws, MT is more direct for surface/near-surface on ferromagnetic base metals.