Pressure Vessels, Piping, Valves, and Safety Devices
Pressure Vessels, Piping, Valves, and Safety Devices
This domain covers pressure-vessel protection, piping layout, valve selection, expansion and support, and safety devices. Questions often compare relief valves, safety valves, and rupture discs, or ask why piping needs flexibility.
Core rules
- A pressure-relief valve protects vessels and piping from overpressure; a safety valve is typically for steam or gas service.
- A rupture disc is a non-reclosing device and may be used alone or upstream of a relief valve.
- Gate valves isolate, globe valves throttle, check valves prevent reverse flow, and ball valves give quick shutoff.
- Piping must accommodate thermal expansion using loops, offsets, or expansion joints; supports carry weight and control movement.
- Hydrostatic testing verifies strength and tightness, but test pressure and duration follow the applicable code.
Worked example
A 100 ft carbon-steel pipe is heated 100°F. Using a typical expansion coefficient of 6.5 x 10^-6 in/in/°F: expansion = 100 ft x 12 in/ft x 6.5 x 10^-6 x 100 = 0.78 in. Reason: unrestrained expansion can overload anchors and nozzles, so the layout must absorb about 0.78 in of growth.
Traps
Do not use a relief valve as an isolation valve; do not install a rupture disc without considering its burst tolerance and fragments; do not block expansion by rigidly anchoring both ends; and do not assume a valve's pressure rating equals its temperature rating.