Boiler Construction, Design, and Fittings
What the exam tests
This domain checks whether you can connect boiler geometry and materials to the fittings that keep a fired boiler safe. Expect questions on ASME Section I power boilers versus Section IV heating boilers, stayed and unstayed surfaces, tube holes and ligaments, inspection openings, and required trim: safety valves, steam gauge with siphon, water-level indicators, water column, try cocks, low-water fuel cutoff, feed check valve, main steam stop, and blowdown valves.
Core rules
- A safety valve protects the boiler; a relief valve protects piping or vessels. Safety valves must be sized for the boiler's maximum generating capacity and set no higher than MAWP.
- The water column steadies the gauge glass and provides a visible working range; its connections must be independent and not used for other fittings.
- Gauge glasses need two isolating valves and a drain; the lower connection must be above the lowest permissible water level.
- Openings in shells and heads need compensation; staybolts and ligaments carry pressure loads.
Worked example
A boiler has MAWP 150 psig and a safety valve set at 150 psig. With 6% accumulation, pressure may rise to 150 x 1.06 = 159 psig during full relieving. If the operating limit is 140 psig, the valve is not set too low; the accumulation allowance explains 159 psig. The exam may ask whether a 150 psig set point is legal: yes, provided capacity is adequate and the valve is rated and stamped for steam service.
Traps
Do not call a safety valve a relief valve; do not confuse set pressure with reseat pressure; do not place the gauge glass below the lowest permissible water level; and do not treat Section IV rules as automatically applying to a Section I power boiler.