Symptoms:

1.  The steam drum water level exceeds the specified maximum limit; in severe cases, the water level is no longer visible;

2.  Steam salinity increases;

3.  The instrumentation system triggers a high-water-level alarm and audible signal;

4.  Superheated steam temperature drops;

5.  Feedwater flow is abnormally higher than steam flow;

6.  In severe overfilling cases, water hammer occurs in steam pipelines, and steam leaks from flanges.

Causes:

1.  Operator negligence, insufficient monitoring of water level, or operational error;

2.  Failure of the automatic feedwater control system or malfunction of the feedwater regulating device;

3.  Inaccurate water level gauge readings leading to operator misjudgment and subsequent operational errors;

4.  Failure or deactivation of water level protection systems, preventing the emergency drain valve from opening;

5.  Significant load fluctuations without timely adjustment.

Corrective Actions:

1.  When the water level exceeds the maximum permissible limit for the steam drum:

(1) Cross-check and flush the water level gauges to verify the accuracy of the readings;

(2) Switch feedwater control from automatic to manual and throttle back (reduce) the feedwater flow.

2.  If, after the above measures, the water level continues to rise to +100mm:

(1) Further throttle or close the feedwater valve (if stopping feedwater intake, open the economizer recirculation valve); (2) Open the emergency drain valve;

(3) Depending on the drop in steam temperature, throttle or close the attemperator (desuperheater) water valve and notify the turbine operators to open relevant drain valves. 3. If the steam drum water level exceeds the upper limit of the visible range, immediately notify the turbine operator, report to the shift supervisor, and take the following measures:

(1) Immediately shut down the boiler and close the main steam valve (for a single-boiler unit, obtain the shift supervisor's consent);

(2) Stop feeding water to the boiler and open the economizer recirculation valve;

(3) Fully open all superheater drain valves and the main drain valve;

(4) Increase blowdown and monitor the steam drum water gauge for the reappearance of the water level;

(5) Restore the boiler unit to operation as soon as the fault is cleared;

(6) During the shutdown process, if the water level reappears in the steam drum water gauge and the temperature drops significantly, boiler operation may be maintained while taking steps to restore the water level to normal as quickly as possible.