Question 29 AEL01 - Assistant Engineer - Limited

The Correct Answer is B **Why Option B ("Monel metal or stainless steel") is correct:** Fuel oil often contains trace amounts of water, sulfur, and various acidic contaminants (especially if poor quality or high-sulfur fuel is used). These impurities make the fuel highly corrosive. Strainer components (disks, spacers, and scraper blades) are constantly exposed to this aggressive environment and must operate reliably without seizing or failing. * **Stainless Steel (e.g., 300 series):** Offers excellent resistance to oxidation, sulfur corrosion, and general acidic attack due to its chromium content, making it highly durable for filtering applications. * **Monel Metal (Nickel-Copper Alloy):** Is superiorly resistant to corrosion by a wide range of acids, alkalis, and particularly saltwater and brackish water (which might contaminate marine fuel systems). It is also strong and maintains its integrity under operating temperatures, making it a premium choice for critical fuel system components where corrosion must be minimized. Using these materials minimizes system maintenance, prevents component failure, and avoids introducing corrosive products (like rust) into the engine's injection system. **Why the other options are incorrect:** * **A) Copper:** While resistant to some forms of corrosion, copper is susceptible to attack by sulfur compounds (forming copper sulfide) commonly found in fuel oil. More importantly, copper ions released into the fuel can act as a catalyst, accelerating the oxidation and degradation of the fuel itself, leading to sludge formation and filter clogging. * **C) Iron:** Standard iron (or carbon steel) is highly susceptible to rust (iron oxide) when exposed to moisture and oxygen. It is also easily attacked by sulfur and organic acids present in fuel oil. Using iron would lead to rapid component degradation, system fouling, and frequent need for replacement. * **D) Brass:** Brass is an alloy primarily made of copper and zinc. Like pure copper, it is susceptible to sulfur attack and can contaminate the fuel, accelerating degradation. Furthermore, brass can undergo dezincification (where the zinc component leaches out), leading to a porous, weakened, and brittle structure, making it unsuitable for long-term critical straining applications.