Question 25 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B **Explanation for Option B (Treating with carbon penetrating solvent):** Hard carbon deposits (soot and baked oil residue) found in diesel exhaust systems—such as mufflers, pipes, and turbocharger outlets—are notoriously difficult to remove by mechanical means alone (scraping or wire brushing). A carbon penetrating solvent (often formulated specifically for diesel deposits) is the most effective chemical technique used in conjunction with mechanical cleaning. The solvent works by dissolving the binder materials in the carbon, softening the hard crust, and penetrating the layers, making the deposits easier to scrape off, brush away, or flush out. This reduces the amount of strenuous manual labor required and ensures a more complete cleaning. **Explanation for Incorrect Options:** **A) Baking off carbon with heat lamps:** While high heat (thermal cleaning, like using an oven or torch) is used in industrial settings (e.g., DPF cleaning), using consumer-grade heat lamps is impractical and ineffective for achieving the necessary high temperatures to efficiently "bake off" or incinerate thick, stubborn carbon deposits within the complex shapes of large marine exhaust systems. Furthermore, applying intense heat unevenly can warp metal components. **C) Sand blasting with diamond dust:** Sand blasting (or abrasive blasting) is an overly aggressive technique for cleaning routine maintenance areas like exhaust pipes and mufflers on a tug. Using diamond dust is prohibitively expensive, and standard abrasive media (like silica or glass beads) can damage critical, high-tolerance surfaces (like turbo blades or flange faces) and leave behind residual grit that could enter the engine or turbocharger upon reassembly, leading to catastrophic failure. **D) Treating with carbon tetrachloride solvent:** Carbon tetrachloride ($\text{CCl}_4$) is a highly toxic, carcinogenic, ozone-depleting substance whose use is heavily restricted or banned globally, especially in marine and industrial environments. While it historically had some industrial solvent applications, it is not used today for general carbon removal due to extreme health and environmental hazards. Safer, purpose-built carbon penetrating solvents are used instead.