How was sensitivity increased for railway LPI?

• A. submerging longer in oil
• B. dye concentration increase
• C. striking the object with a hammer
• D. using a brighter light source

Answer: (C)

In liquid penetrant inspection, sensitivity means the ability to reveal the smallest surface-breaking flaws. For railway components, a controlled mechanical shock—tapping or striking the part with a hammer before applying penetrant—increases this sensitivity. The impact creates tiny surface discontinuities and briefly opens micro-cracks, letting penetrant enter more easily. After removing excess penetrant and applying the developer, these indications become larger and more easily seen, allowing detection of smaller defects that might otherwise be missed.

Other methods are less directly effective in this railway context. Submerging longer in oil can help penetrant entry but may also waste time and blur indications; increasing dye concentration boosts color intensity but not the smallest flaw visibility; a brighter light helps illumination but doesn't enhance the actual penetrant penetration into tiny defects.