Boiler Construction, Fittings, and Appurtenances
Domain focus
This domain covers the pressure-containing parts of a boiler and the fittings that make it safe to operate. The exam expects you to know which code applies, what each fitting does, and which fittings may never be valved off or substituted.
Code basis and construction
ASME Section I applies to power boilers, generally those operating above 15 psig steam. ASME Section IV applies to heating boilers: steam boilers at 15 psig or less and hot-water boilers at 160 psig or less with temperatures at or below 250°F. Connecticut adopts these codes, so a new boiler must be stamped and installed per the approved design. Pressure parts include the shell, heads, tubes, tube sheets, staybolts, and ligament areas. Welding, post-weld heat treatment, and hydrostatic testing must be done by qualified organizations.
Access and inspection openings
Manholes and handholes allow internal inspection. They must be kept sealed in service, but the cover plates, gaskets, and bolts must be maintained so an inspector can open them. Never weld over an inspection opening or obscure the stamping.
Fittings and appurtenances
- Safety valve or safety relief valve: spring-loaded, set to the boiler MAWP, with no shutoff between it and the boiler.
- Gauge glass: shows water level; has upper and lower shutoff valves and a drain.
- Water column: provides a steady level indication and mounting point for controls.
- Pressure gauge: marked with the MAWP; a siphon or pigtail protects it from steam.
- Try cocks: independent level verification.
- Bottom blowoff: removes sludge; usually a slow-opening valve, with the boiler valve closest to the shell.
- Feedwater check valve: prevents backflow from the boiler into the feed line.
- Stop valves: isolate steam or water; not permitted between the boiler and safety valve.
Worked example
A feedwater line has a pump, a check valve near the boiler, and a gate valve for isolation. Why is the check valve next to the boiler? Reasoning: when the pump stops, boiler pressure would otherwise push water backward through the feed line. The check valve blocks that reverse flow and protects the pump and water treatment. The gate valve is for maintenance isolation only and must be open in service.
Traps that cost marks
- Putting a shutoff valve between the boiler and its safety valve.
- Calling a hot-water relief valve a "steam safety valve" in a code answer.
- Using a hydrostatic test as a substitute for a safety-valve test.
- Replacing a gauge glass with pipe or plugging a try cock.