Inspection, Maintenance, and Testing
Core concepts
Inspection keeps the boiler safe between overhauls. Internal inspection looks for scale, corrosion, pitting, cracking, and proper staybolt condition; external inspection checks fittings, insulation, supports, and piping. The hydrostatic test verifies tightness and strength: the vessel is filled, vented, and pressurized, typically to 1.5 times MAWP for a new vessel, and inspected for leaks; it is not a substitute for an internal inspection. Safety valve testing includes pop testing and accumulation testing; the valve must relieve at the set pressure and reseat properly.
Know the low-water cutoff test (evaporate or drain to trip level, confirm fuel shuts off), the flame failure test (simulate loss of flame and confirm fuel shutoff), and the pressure limit test. Know the gauge glass blowdown procedure: open the drain, close the top connection, then the bottom, and reopen in reverse to prove both connections clear. Know that maintenance records, nameplate data, and inspection certificates must be retained and available.
Traps
Questions confuse the hydrostatic test pressure with the operating pressure, ask whether a hydro test replaces internal inspection (no), and test the order of gauge glass blowdown. Another trap: assuming a safety valve that weeps after popping is acceptable; it must reseat and be repaired if it does not.
Worked example
Rule of thumb: for a boiler with MAWP 150 psig, the hydrostatic test pressure for a new vessel is 1.5 × 150 = 225 psig; the test is held while the vessel is inspected for leaks, then pressure is released slowly.