Materials Selection Flashcards

In DP vessel engine room design, which material is specified for fuel oil piping in high-pressure injection lines to prevent fire hazards?

Answer: Seamless carbon steel with double-walled construction

SOLAS and class rules require high-pressure fuel lines to use double-walled (jacketed) seamless steel piping with a drain/alarm on the annular space to contain leaks and prevent engine room fires.

When selecting materials for DP vessel moonpool structures, which property is most important to resist the cyclic wave-induced fatigue loads?

Answer: High fracture toughness combined with adequate fatigue crack growth resistance

Moonpool structures experience cyclic hydrodynamic loads; materials must resist crack initiation and propagation (fatigue), and arrest cracks before catastrophic failure (fracture toughness).

For DP thruster thruster-to-hull interface bolts submerged in seawater, what material and surface treatment combination is used to prevent galvanic corrosion?

Answer: Titanium Grade 5 (Ti-6Al-4V) with anodizing

Titanium Grade 5 offers excellent seawater corrosion resistance and is galvanically compatible with aluminum thruster housings; anodizing further improves galling resistance on threads.

Which parameter defines the suitability of an elastomeric coupling material used in DP thruster shaft couplings for vibration isolation?

Answer: Dynamic stiffness and loss factor (damping coefficient)

Dynamic stiffness determines the coupling's natural frequency tuning, while the loss factor quantifies energy dissipation; both must be matched to thruster excitation frequencies for effective vibration isolation.

On a DP vessel, which material consideration is paramount when selecting gaskets for seawater heat exchanger flanges on the main thruster cooling system?

Answer: Compatibility with seawater, resistance to creep relaxation, and clamp load retention

Heat exchanger gaskets must resist seawater attack, maintain sealing force under thermal cycling, and not creep under bolt load, preventing leaks that could cause thruster cooling failure.

For DP vessel bilge piping systems, why is PVC (polyvinyl chloride) piping generally not accepted by classification societies in machinery spaces?

Answer: It releases toxic chlorine gas and melts in fires, violating fire safety rules

Classification societies prohibit PVC in machinery spaces because it burns with toxic HCl gas emission and collapses rapidly in a fire, compromising bilge system integrity during emergencies.

When evaluating steel grades for DP vessel deck plating subject to topside equipment impact loads, which test verifies adequate toughness at low ambient temperature?

Answer: Charpy V-notch impact test at specified temperature

The Charpy V-notch test measures absorbed impact energy at a specified test temperature (e.g., −20°C), confirming the steel grade's resistance to brittle fracture under impact loading in cold conditions.