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CHEMICAL CLEANING OF BOILER IS CARRIED OUT IN THREE CONDITION :-

1.  BEFORE INITIAL START OF BOILER.
2.  IN CASE OF HEAVY OIL CONTAMINATION.
3.  IN CASE OF HEAVY SCALING OR CORROSION.

ACID CLEANING :-

ACID CLEANING IS CARRIED OUT IN CASE OF HEAVY SCALING INSIDE THE BOILER.

PROCEDURE :-

1. CHEMICAL CLEANING PUMP AND TEMPORARY PIPING SHOULD BE INSTALLED TO ALLOW COMPLETE CIRCULATION OF BOILER WATER.
2. COMPLETELY FILL THE BOILER WITH CLEAN, FILTERED AND SOFTENED WATER.
3.  HEAT TILL BOILER METAL TEMPERATURE REACHES 60-90°C.
4.  ADD FOLLOWING CHEMICALS :- 5% OF HCL, 0.5% OF AMMONIUM BIFLOURIDE AND 0.1 TO 0.2% OF INHIBITOR.
5.  CIRCULATING SOLUTION IS MONITORED FOR FERROUS CONTENT WHICH INDICATES THAT ALL SCALE HAS BEEN REMOVED AND ACID IS NOW ATTCKING METAL.
6. ACID SOLUTION DRAINED AND BOILER IS THEN FLUSHED.
7. OPEN VENTS AND FIL BOILER AND ECONOMIZER WITH CLEAN AND SOFT WATER.
8. RINSE TILL pH OF WATER DRAINED DOES NOT BECOME MORE THAN 5.
9. CARRY OUT NEUTRALIZATION.

NEUTRALIZATION:-

IT IS CARRIED OUT AFTER ACID CLEANING TO ELIMINATE ANY ACID SOLUTION LEFT AFTER ACID CLEANING WHICH MAY CAUSE CORROSION INSIDE THE BOILER.

PROCEDURE :- 

1. OPEN THE DRUM VENT.
2. THROUGH CHEMICAL CLEANING HEADER, COMPLETELY FILL THE BOILER WITH DISSOLVED CONCENTRATED SODIUM CARBONATE WHICH SHOULD BE EQUIVALENT TO 0.5 TO 1% SODIUM CARBONATE WHEN BOILER IS COMPLETELY FILLED.
3. DRAIN THE WATER BACK TO NORMAL WORKING LEVEL.
4. FIRE THE BOILER TILL 7 BAR IS REACHED AND HOLD IT FOR 4 HOURS.
5. AT COMPLETION OF BOIL OUT, COOL BOILER TO 1 BAR AND DRAIN.

PASSIVATION :-

WHILE UNIT IS STILL HOT, ADD CONCENTRATED SODIUM NITRITE SOLUTION TO OBTAIN 0.5% SODIUM NITRITE AND COMPLETELY FILL BOILER AND ECONOMIZER. AFTER 1 HOUR, DRAIN BOILER AND ECONOMIZER TO WASTE.

INSPECTION AND FLUSHING :-

INSPECT FOR ANY LOOSE SCALE OR IRON OXIDE PRESENT IN STEAM DRUM.