Boiler Construction, Design, and Fittings
This domain tests how boiler pressure parts are designed and how required fittings protect the boiler. Expect ASME construction logic, maximum allowable working pressure (MAWP), seams, stays, openings, and the function of fittings.
Design basis
- Power boilers follow ASME BPVC Section I; heating boilers follow Section IV. The nameplate MAWP is the ceiling; operating pressure must stay at or below it.
- Shell thickness depends on pressure, diameter, allowable stress, and joint efficiency. A longitudinal seam carries about twice the hoop stress of a circumferential seam, so its efficiency normally governs shell thickness.
- Stays support flat surfaces; staybolts may have telltale holes that leak before a crack becomes catastrophic. Openings need compensation.
Fittings
Safety valve, pressure gauge with siphon, gauge glass with isolation and blowdown valves, water column, low-water fuel cutoff, main steam stop, feed check and stop valves, blowdown valves, and fusible plugs where required. Fittings must be rated for the pressure and temperature.
Worked example: A boiler is stamped MAWP 150 psig. A safety valve set at 160 psig is offered. Reject it. The set pressure cannot exceed MAWP, and capacity must equal or exceed boiler capacity. A correct valve is set at 150 psig or lower as designed, with operating pressure below the set point.
Traps: treating operating pressure as MAWP; accepting a valve without capacity data; omitting a gauge siphon; ignoring telltale holes; allowing non-code welding on pressure parts.