Question 50 OSE02 - Assistant Engineer - OSV

The Correct Answer is B **Why option B is correct:** Sacrificial zinc anodes (or other active metals like aluminum) are designed to corrode preferentially, thus protecting the adjacent, more noble metals (like the steel or bronze components of the cooler) from galvanic corrosion. This process relies on direct electrical contact between the anode material and the electrolyte (seawater). When scale (often composed of calcium carbonate, rust, or marine fouling byproducts) builds up on the surface of the zinc anode, it acts as an insulator. This insulating layer significantly increases the electrical resistance between the anode and the surrounding seawater, effectively "blinding" or passivating the anode. A passivated anode cannot effectively release electrons and perform its protective function. Therefore, the scale must be physically removed (scraped or brushed off) to expose fresh, clean zinc metal (making it "shiny") to restore the electrical contact with the electrolyte and ensure proper cathodic protection of the cooler components. **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.** This is incorrect because replacement is only necessary when the zinc anode has been substantially consumed (usually 50% or more deterioration). If the anode still has adequate mass but is covered in scale, cleaning the scale off (as described in option B) is the correct and necessary maintenance action, making immediate replacement wasteful and unnecessary. * **C) Any accumulated scale build-up on sacrificial zinc anodes should be left intact to ensure proper protection from galvanic corrosion.** This is incorrect. As explained above, scale build-up passivates or insulates the anode, stopping the flow of protective current and rendering the anode ineffective. Leaving the 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, especially in warm seawater environments or when operating cooling systems, is a common and predictable phenomenon (e.g., calcareous deposits, fouling) and is the primary reason why anodes must be periodically inspected and cleaned.