Boiler Inspection, Testing and Maintenance
Inspection types
Understand the difference between external inspection while the boiler is in service and internal inspection when it is shut down and opened. Know what the inspector looks for: scale, corrosion, cracking, bulging, stay condition, tube ends, firebox condition and safety valve condition. Know the purpose of a hydrostatic test and when it is required, and why it is done at a specified multiple of working pressure.
Testing
Know the tests a candidate must be able to describe: hydraulic test, steam test of safety valves, accumulator test for safety valve lift, low-water alarm test, gauge glass proving and pressure gauge comparison. Understand non-destructive testing such as ultrasonic thickness measurement, magnetic particle and dye penetrant inspection, and radiography.
Maintenance
Understand planned maintenance: tube cleaning, scale removal, refractory repair, valve overhaul and safety valve resetting. Know why records of inspection and repair must be kept.
Traps
Questions often ask which test is done with the boiler cold versus hot, or what a hydrostatic test proves. It proves strength and tightness, not the correct setting of safety valves. Another trap is confusing ultrasonic testing (thickness) with radiography (internal defects).
Worked example
If a boiler is to be returned to service after repair to pressure parts, reason: complete the repair, carry out a hydraulic test, then reset and steam-test the safety valves before returning to service.
Rule of thumb
Inspect internally when cold and open; test safety valves on steam before service.