Maintenance, Inspection, and Testing
Core concepts
Inspections are scheduled by code and by condition. Power boilers normally get an annual internal and external inspection, with the interval set by the jurisdiction; the NBIC governs repairs and alterations and requires permanent records. Preparation matters: cool and drain, isolate and lock out, open all manholes and handholes, remove plugs, and clean fireside and waterside surfaces so defects are visible.
Typical findings: waterside scale, pitting, caustic gouging, cracked or bulged tubes, leaking rolled joints, deteriorated refractory, external corrosion of the shell, and defective fittings. Non-destructive testing includes visual inspection, ultrasonic thickness, radiography, magnetic particle, and dye penetrant.
Tests: hydrostatic test at 1.5 times MAWP with safety valves removed or blanked and air vented; safety valve setting verified by qualified personnel; low-water fuel cutoff proven by blowing down the float or probe chamber and confirming burner shutdown; gauge glass and try cocks proven; alarms and interlocks function-tested.
Traps
Watch for a test pressure that is too low, a hydro test run with the safety valve gagged instead of removed, or an operator adjusting a safety valve in service.
Worked example
A boiler with 200 psig MAWP is hydro-tested at 1.5 x 200 = 300 psig, with safety valves removed and all air vented before pressure is applied.