Question 42 OSE02 - Assistant Engineer - OSV

The Correct Answer is B **Explanation for Option B (50%):** Sacrificial anodes, such such as zinc, aluminum, or magnesium, are installed in seawater systems (like the raw water boxes of freshwater coolers) to prevent corrosion of the more expensive metallic components (like the cast iron cooler body or copper piping/tubing). They protect these components by preferentially corroding. Industry standards and best maritime practices, as mandated by classification societies and engineering manuals (especially concerning cathodic protection systems), dictate that sacrificial anodes should be replaced when they have deteriorated by approximately $50\%$ of their original mass or volume. This threshold ensures that the anode retains sufficient mass and surface area to provide adequate cathodic protection until the next scheduled maintenance interval, preventing the underlying machinery from becoming vulnerable to corrosion damage. **Why other options are incorrect:** * **A) 25%:** Replacing the anodes at only $25\%$ deterioration is unnecessarily premature. The anode still has $75\%$ of its life remaining and substantial protective capacity. While not harmful, it wastes time, materials, and maintenance resources. * **C) 75%:** Replacing the anodes at $75\%$ deterioration (meaning only $25\%$ is left) is generally considered too late. At this stage, the surface area and mass of the anode may be insufficient to provide adequate current density for effective protection of the entire system, potentially exposing the cooler boxes and heat exchanger elements to accelerated corrosion risk before the next planned inspection or replacement. * **D) 100%:** Waiting until $100\%$ deterioration means the anode is completely consumed. At the point of complete consumption, there is absolutely no cathodic protection being offered to the machinery, leaving the expensive components fully exposed to galvanic corrosion, which could lead to immediate and rapid failure of the raw water box or cooling elements.