Exam Question

### (a) Reasons for Employing Double-Walled Fuel Pipes for High-Pressure Fuel Lines (6 Marks)
Double-walled fuel pipes are a critical safety and environmental feature mandated for high-pressure fuel oil lines in marine diesel engines. Their employment is driven by several crucial factors:
* **Fire and Explosion Hazard Mitigation:** High-pressure fuel lines, operating at pressures up to 1800 bar or more, carry fuel at temperatures typically above its flash point. In the event of a rupture or pinhole leak in the inner pipe, fuel would be released as a highly atomized spray. If this spray comes into contact with hot surfaces (e.g., exhaust manifolds, turbocharger casings, steam pipes) which can exceed 220°C, it would immediately ignite, leading to a catastrophic engine room fire. The outer pipe acts as a secondary containment barrier, preventing the atomized spray from reaching these hot surfaces, thus significantly reducing the risk of fire and explosion.
* **Environmental Protection and Pollution Prevention:** A leak from a high-pressure fuel line would release fuel directly into the engine room bilges or potentially overboard if not contained. This constitutes a severe environmental pollution hazard, which is a contravention of MARPOL Annex I regulations. Double-walled piping ensures that any internal leak is contained within the annulus, preventing uncontrolled discharge of fuel into the machinery spaces or the marine environment.