Boiler Water Treatment
Correct chemical dosing and a controlled TDS prevent scale formation and foaming/priming: water chemistry, not just the safety devices, determines the boiler's service life.
Operational Explanation
Chemical treatment of boiler water prevents two distinct but related problems: the formation of scale on heat exchange surfaces, which reduces efficiency and can lead to localized overheating, and the phenomenon of foaming/priming, caused by an excessive level of total dissolved solids (TDS) that compromises the quality of the steam produced.
Polyelectrolyte treatment is today considered superior to traditional alkaline/phosphate treatments for auxiliary boilers, provided the correct alkalinity level is maintained so as not to neutralize the polyelectrolyte's electric charge.
Regulatory Reference
There is no single IMO standard dedicated to chemical treatment of boiler water; operating practices derive from the boiler manufacturer's manuals, P&I guidelines and industry good practice, with recommended daily tests of pH, chlorides, phosphates, dissolved oxygen, TDS and hardness.
Scope of Application
Ships fitted with an auxiliary boiler, with responsibility resting on engine room personnel to maintain chemical dosing and TDS monitoring within the correct parameters according to the manufacturer's manual.
Procedure / How to Complete It
- Carry out daily tests of pH, chlorides, phosphates, dissolved oxygen, TDS and hardness of the boiler water according to the manufacturer's procedure.
- Dose the coagulant/polyelectrolyte directly into the boiler through the intended dosing system (bypass pot feeder on the feed line), according to the indicated quantities.
- Adjust surface blowdown based on the TDS levels detected, keeping conductivity below the threshold indicated by the manufacturer (typically below 1,000 µS/cm) to avoid foaming/priming.
- Maintain the correct alkalinity level when using a polyelectrolyte treatment, so as not to neutralize its electric charge and compromise its effectiveness.
- Systematically record test results and dosing/blowdown actions, to build a history useful for identifying anomalous drifts over time.
Practical Example
Example log entry for boiler water treatment: "Daily test: pH 10.8, TDS 850 µS/cm, chlorides within threshold. Surface blowdown adjusted to 15 minutes/watch to keep TDS below 1,000 µS/cm. Polyelectrolyte dosing: 0.2 litres, consistent with boiler capacity."
Real Cases
Common Mistakes Mistake Library
| Mistake | Consequence | How to avoid it |
|---|---|---|
| Boiler water tests carried out occasionally instead of with a systematic daily frequency | TDS or pH drift not detected in time, with risk of scale or foaming | Carry out daily tests systematically, regardless of perceived workload priorities |
| Surface blowdown not adjusted in response to rising TDS | Foaming/priming with carryover of water into the steam system | Always adjust blowdown based on detected TDS levels, not according to a fixed schedule independent of real data |
| Alkalinity not monitored when using a polyelectrolyte treatment | Neutralization of the polyelectrolyte's electric charge, with loss of treatment effectiveness | Monitor alkalinity together with the other parameters when using this type of treatment |
PSC Observations
Operational Tips
- Don't treat daily tests as a formality: they are the only way to detect a drift before it becomes a structural problem.
- Always adjust blowdown based on real TDS data, not according to a predefined fixed schedule.
- If using a polyelectrolyte treatment, monitor alkalinity with the same attention as the other parameters: it is the condition for its effectiveness.
Checklist
- Daily tests of pH, chlorides, phosphates, dissolved oxygen, TDS and hardness carried out systematically
- Chemical dosing carried out according to the quantities indicated by the manufacturer
- Surface blowdown adjusted based on detected TDS levels
- Alkalinity monitored when using a polyelectrolyte treatment
- Log of tests and dosing/blowdown actions systematically maintained