Boilers and Pressure Vessels
Core concepts
This domain tests your grasp of steam and hot-water boiler types, pressure vessel construction, and the safety devices that protect them. Know fire-tube versus water-tube designs and where each is applied. Understand saturation temperature versus pressure, superheat, and why steam quality matters. Study the roles of safety valves, relief valves, pressure gauges, water-level indicators, low-water cutoffs, and feedwater controls. Familiarize yourself with the ASME Boiler and Pressure Vessel Code structure, maximum allowable working pressure, hydrostatic testing, and the meaning of stamping and nameplate data. Combustion basics, excess air, and efficiency loss through stack temperature are also fair game.
Traps to watch
Questions often blur the distinction between a safety valve and a relief valve, or between an operating control and a limiting safety control. Another trap is assuming a boiler can be fired at low water level if the cutout has not tripped. Remember that safety devices must fail safe and that bypassing a low-water cutoff is a serious violation. Watch for items asking which component absorbs thermal expansion or which protects against overpressure during a hydro test.
Worked example
A boiler rated 1,000 kg/h of steam at 10 bar gauge needs a safety valve capacity at least equal to the maximum generating rate. Rule of thumb: size the safety valve for the full rated capacity, never for average load, and verify set pressure does not exceed the vessel's maximum allowable working pressure. If the nameplate shows a design pressure of 11 bar, a valve set at 10.5 bar is acceptable only if the code and accumulation limits permit the overpressure.