Question 60 UFIV01 - Chief Engineer - UFIV

The Correct Answer is C **Why option C is correct:** Sacrificial zinc anodes (zincs) are installed in seawater-carrying components, such as water boxes of heat exchangers, to prevent galvanic corrosion of the surrounding metal (usually bronze, steel, or cast iron). The zinc is more reactive than the surrounding metal and corrodes first, providing protection. Scale build-up (often calcium carbonate or corrosion products) on the surface of the zinc anode is highly undesirable because it acts as an insulator, significantly increasing the electrical resistance between the anode and the seawater electrolyte. This reduces or stops the flow of protective current, making the anode inactive and rendering the protected metal vulnerable to corrosion. Therefore, during periodic maintenance and inspection, any accumulated scale or corrosion film must be physically removed (scraped or wire-brushed) to expose the clean, active zinc surface, ensuring a low-resistance electrical path and restoring proper cathodic protection. The goal is to make the zinc "shiny" or clean metal. **Why the other options are incorrect:** * **A) Any sacrificial zinc anodes with accumulated scale build-up should be replaced regardless of the degree of deterioration:** While zincs are replaced when they are significantly consumed (usually 50% or more deteriorated), replacement due solely to scale is unnecessary and wasteful if the zinc still has substantial mass remaining. The correct action for scale is removal (cleaning), not immediate replacement. * **B) Any accumulated scale build-up on sacrificial zinc anodes should be left intact to ensure proper protection from galvanic corrosion:** This is fundamentally wrong. Scale acts as a barrier (insulator) that prevents the zinc from sacrificing itself and generating the protective current needed for cathodic protection. Leaving scale intact *guarantees* improper protection. * **D) There is no need to check for scale build-up on the sacrificial zinc anodes as this phenomenon is not physically possible:** This is incorrect. Scale build-up (fouling) is a common and predictable phenomenon in seawater systems, especially in coolers and on anode surfaces, particularly if the water box temperatures are elevated. Inspection for and removal of scale and fouling is a standard and critical part of marine maintenance.