Question 38 MODE01 - Chief MODU Engineer

The Correct Answer is C ### Why Option C (Water Contamination of the Lube Oil System) is Correct The bearing in question is a bronze liner with an overlay of lead-tin flashing. This overlay (or babbitt layer) is relatively soft and is designed to sacrificial wear and provide a conformable surface. A **milky-white color** (or sometimes a grayish-white) on the bearing surface, especially in patches, is a classic visual indication of **water contamination** (emulsified water) in the lubricating oil. This phenomenon is often referred to as "de-plating" or "tin bloom." When water is present in the oil, it can combine with additives or impurities to form weak acids or corrosive compounds. These contaminants chemically attack the lead-tin overlay, dissolving the tin component of the flashing, leaving behind a white, powdery, or milky residue primarily composed of oxidized tin or lead salts, and exposing the underlying bronze substrate in localized areas. ### Why the Other Options are Incorrect **A) improper break-in wear:** Improper break-in wear usually manifests as localized severe scoring, overheating (bluing or discoloration), pitting, or smearing of the overlay material due to excessive friction or load, not a uniform milky-white discoloration. **B) relocation of the overlay flashing:** Relocation (smearing) of the overlay material typically occurs due to high shear stress or overheating, resulting in the babbitt being pushed from high-pressure areas into low-pressure areas. This results in rough, uneven surfaces or plugged oil grooves, not a generalized milky-white chemical corrosion pattern. **D) proper break-in wear:** Proper break-in wear is characterized by a uniformly smooth, polished surface with full contact and typically a dull gray or silvery appearance (the original color of the lead-tin alloy), without localized corrosion or widespread exposure of the underlying bronze unless the operational hours are significantly advanced.