Boiler Construction, Design, and Fittings
Two families, one code
Every boiler you will be asked about is either a firetube (hot gases inside tubes surrounded by water - HRT, Scotch marine, firebox) or a watertube (water inside tubes surrounded by hot gases). Be able to trace the gas path: furnace → combustion chamber or turnaround → convection tubes → breeching → stack, and identify pressure parts (shell, heads, tube sheets, crown sheet, stays, ligaments, furnace) versus setting parts (refractory, baffles, casing). Construction is governed by the ASME Boiler and Pressure Vessel Code: Section I for power/high-pressure boilers, Section IV for heating boilers.
A steam boiler normally carries safety valve(s), a steam pressure gauge with siphon and three-way cock, a water column with gauge glass, try cocks, a low-water fuel cutoff, feedwater check and stop valves, a steam stop valve, bottom and surface blowoff valves, and manhole/handhole access.
Traps the exam likes
A safety valve must be ASME-stamped, set at or below the MAWP, and must discharge to a safe location with no shutoff valve in its discharge line. You may never add weight, block, or screw down a spring to raise the set point. Section I requires two or more safety valves when heating surface exceeds 500 sq ft, and a superheater needs its own. The pressure gauge must be visible and connected above the water line with a siphon to protect it from steam.
Rule of thumb: total safety valve rated capacity must equal or exceed the boiler's maximum generating capacity - an undersized valve is no safer than no valve.