Pipe, Fittings, Valves and Materials
What this domain tests
This domain tests material selection and component identification: pipe, fittings, valves, gaskets, and fasteners. The exam expects you to match material to fluid, temperature, pressure, and corrosion risk, and to recognize where a valve type is unsuitable.
Core rules
- Carbon steel is common for fuel oil, lube oil, compressed air, and fresh water. It is not suitable for seawater without protection.
- Copper-nickel, commonly 90/10 or 70/30, is widely used for seawater cooling and ballast because it resists marine corrosion.
- Stainless steels such as 316L suit many chemicals and fresh water but can suffer chloride stress-corrosion cracking in hot seawater.
- Valve selection follows function: gate for isolation, globe for throttling, check for backflow prevention, butterfly for space-saving isolation, and ball for quick shutoff.
- Pressure class, temperature rating, and end connection must match the line specification; a valve’s body rating is not the same as its seat rating.
Worked example
A seawater cooling branch is specified. Carbon steel would corrode rapidly, and a galvanized pipe is not a seawater material. Select 90/10 copper-nickel pipe with compatible copper-nickel or bronze valves, and confirm the valve pressure class exceeds the pump shutoff head. Use insulating gaskets and separate the line from carbon-steel supports where galvanic corrosion is possible. Reasoning: the material must resist the fluid, and the valve must survive both pressure and marine conditions.
Traps
- Creating a galvanic couple by joining copper alloy to carbon steel without isolation.
- Choosing a gate valve for throttling service.
- Ignoring temperature derating of a valve or gasket.
- Assuming all “stainless” grades are equal in seawater.