a) Why grey cast iron is not a suitable material for ship’s side valves.
Grey cast iron is not a suitable material for ship’s side valves for several reasons:
- Brittle: Grey cast iron is brittle, which means it is more likely to crack or break under stress than other materials. This is a major concern for ship’s side valves, which are subjected to high stresses from waves and currents.
- Poor corrosion resistance: Grey cast iron is not very resistant to corrosion, especially in seawater. This means that it is likely to rust and deteriorate over time, which could lead to leaks and failures.
- Weak in tension: Grey cast iron is weak in tension, which means that it is not able to withstand pulling forces very well. This is important for ship’s side valves, which need to be able to withstand the pulling forces of the piping system.
(b) Three suitable materials for ship’s side valves, with reasons:
There are a number of materials that are suitable for ship’s side valves, but three of the most common are:
- Ductile iron: Ductile iron is a type of cast iron that has been treated with magnesium or cerium to make it more ductile and less brittle than grey cast iron. This makes it a much more suitable material for ship’s side valves.
- Bronze: Bronze is an alloy of copper and tin, or copper and aluminium, that is strong, corrosion-resistant, and ductile. This makes it an excellent choice for ship’s side valves, especially in applications where seawater is present.
- Stainless steel: Stainless steel is a steel alloy that is resistant to corrosion and has good mechanical properties. It is a more expensive option than ductile iron or bronze, but it can be a good choice for ship’s side valves that need to be particularly strong and durable.
Q7
(a) Aft deck bollard
- Material: Typically made of cast steel for its high strength and durability. Cast steel can withstand the high pulling forces exerted on the bollard when ships are being moored or towed.
(b) Anchor windlass
- Material: Often made of cast iron or cast steel for their strength and affordability. In some high-performance windlasses, duplex stainless steel may be used for its superior strength-to-weight ratio and corrosion resistance.
(c) Deck handrails
- Material: Typically made of stainless steel due to its strength, corrosion resistance, and ease of maintenance. In some cases, aluminium or fibreglass reinforced plastic (FRP) may be used depending on the desired weight and cost considerations.
(d) Mooring lines
- Material: Traditionally made from natural fibres such as manila or sisal for their high strength and shock absorption properties. However, synthetic fibres such as nylon or polyester are increasingly being used due to their superior strength, durability, and resistance to rot and mildew.
(e) Davit fairlead rollers
- Material: Often made from a polymer alloy with high wear resistance and low friction, such as acetal or UHMWPE (ultra-high-molecular-weight polyethylene). These materials help to protect the mooring lines from chafing and wear as they pass through the fairlead.