Boiler Construction
Materials and pressure parts
Construction questions focus on pressure-retaining parts and the code rules that govern them: shell, heads, tubes, tube sheets, stays, and openings. Understand that thickness is calculated from design pressure, temperature, and allowable stress, with corrosion allowance and joint efficiency factored in. Traps: assuming thicker is always safer (it affects heat transfer and stress), and confusing design pressure with operating pressure - the safety valve is set at or below the maximum allowable working pressure (MAWP), never above it.
Stays, openings, and reinforcement
Flat surfaces need stays to carry load; every opening removes metal and must be reinforced to restore strength. Questions often ask why a handhole or manhole is reinforced, or why staybolts are drilled (tell-tale holes reveal a cracked or broken stay).
Welded vs. riveted construction
Modern boilers are welded; riveted seams are legacy. Know that welded joints are subject to joint efficiency and require qualified welders and procedures, and that post-weld heat treatment may be required for thick sections.
Worked example
A question asks where the safety valve should be set relative to MAWP. Rule of thumb: set pressure ≤ MAWP, with the valve capacity sized to relieve the boiler's maximum steam generation. Setting a valve above MAWP to "stop nuisance popping" is always wrong - fix the cause, not the setting.