Maintenance, Inspection, and Water Treatment
What is in the water
Hardness (calcium, magnesium), silica, iron, dissolved oxygen, carbon dioxide, alkalinity and dissolved solids. Scale insulates: as little as 1/8 in raises fuel use by roughly 10% or more and lets tubes overheat. Sludge settles in mud drums. Oxygen pits; carbon dioxide dissolves in condensate and eats return lines; high alkalinity and free caustic promote carryover and caustic cracking of stressed seams.
Treatment train
Softening removes hardness; deaeration removes oxygen (heat to saturation and vent); oxygen scavengers such as catalyzed sulfite mop up the rest; phosphate and polymer condition residual hardness; amines protect condensate; blowdown controls solids. Control cycles of concentration by conductivity or chloride. Remember that sulfite is not used in very high-pressure units, and more chemical is not better.
Inspection and maintenance
Internal and external inspections look at waterside deposits and pitting, fireside soot and refractory, tube ends, handhole gaskets and safety valves. Tests include hydrostatic, ultrasonic thickness, eddy current and pop testing of safety valves. Keep the log - trends catch problems earlier than any single reading.
Traps
- Setting pH too low (corrosion) or too high (foaming, caustic attack).
- Judging layup by adding chemicals and walking away.
- Skipping blowdown records.
Rule of thumb
Cycles = boiler chloride ÷ feedwater chloride. At 300 ppm and 15 ppm that is 20 cycles, so blowdown is 1/20 = 5% of feedwater flow.