BOILER OPERATION AND MAINTAINANCE

 PROCEDURES OF RAISING STEAM FROM COLD ON A WATER TUBE BOILER

PREPARATION

1. I the internal surfaces to ensure they are clean, all openings to the boiler mountings clear, and tubes proved to be free of obstruction.

2.Replace any internal fittings which have been removed, checking to ensure they are correctly positioned and secured. 

 

 3.Check the gas side of the boiler is clean and in good order. Make sure the soot blowers are correctly fitted, and operate over their correct traverse.

4.Check the direct reading water level gauge isolating cocks, together with all boiler vents, alarm and pressure gauge connections. The superheater drains are also opened.

5. Check  that all other drains and blow down valves are closed. 

PROCEDURE -

1. Fill the boiler with hot deaerated water. At this stage the initial dose of chemical treatment can be added Continue to fill until water just shows in the water level gauges. 

2. Remove the funnel cover,  and make sure that the forced draught fans are in working order. 

3. Check the fuel oil system to ascertain it is in good order. Start up the fuel oil service pumps and check for leaks

4. Start the forced draught fan, and with all the air checks full open purge the boiler.

5. Make sure water level gauge cocks are open, water is showing in the glass.

6. Now close all the air checks except for the burner to be flashed up, this being done by means of ignition equipment. 

 7.Use  the lowest possible firing rate. Adjust the air supply so as to obtain the best combustion conditions.

8. After about one hour steam should show at the drum and superheater vents.

9. When the steam pressure has reached a value of about 300 kN/m² blow through the water level gauges to ensure they are working correctly. 

10. At a pressure of about 1400 kN/m2 open the auxiliary stop valve and warm the auxiliary line through. Now fully open the auxiliary stop valve.

11. Bring the boiler up to working pressure, keeping the firing rate as steady as possible, and avoiding intermittent flashing up. Check the water level alarms. 

12. Open the main steam line drains, and crack open the main stop valve and warm through the main steam line. Then close the drains and fully open the main stop valve. 

PROCEDURE OF RAISING STEAM FROM COLD ON SCOTCH BOILER (Fire Tube)

1. Check that all internal pipes and fittings to see that they are in place, and properly fitted.

2. Check Blowdown valve is clear. 

3. Fit lower manhole door. Check external boiler fittings to see they are in order. 

4. Check all banks are removed from safety valves, blow down line.

5. Fill Boiler with water to about one-quarter of the water level gauge glass. 

6. The initial dose of feed treatment chemicals, mixed with water, can added to feed water

7. Make sure air vent is open. 

8. Set one fire away at lowest possible rate. After about one hour start to circulate the boiler by means of auxiliary feed pump .

9. Continue firing at lowest rate until the boiler is well warmed through especially below the furnaces. 

10.  Continue circulating for about four hours, raising the temperature of the boiler at a rate of about 6° to 7° C per hour. 

11. When water temperature below 100°C. At the end of this time set fires away in all furnaces, still at the lowest rate. Close the air vent. 

12. Circulating the boiler can now be stopped, and steam pressure slowly raised during the next 7-8 hours to within about 100 kN/m² of the working pressure. 

13. Test the water gauge. The boiler is now ready to be put into service.

14. About 12 hours should be allowed for the complete operation provided some means of circulating the boiler.

SURVEY PROCEDURE TO BE CARRIED OUT ON A MARINE BOILER

Survey Timeperiod

1. Main water tube boilers of passenger ships are surveyed annually, while for cargo ships bi-annual survey is sufficient. 

2. Then normal procedure for auxiliary boilers is bi-annual for the first eight years.

3. Thereafter annual  although a concession may be made for auxiliary water tube to continue on a two year cycle, provided that they are in good condition.

Inspection to be done-:

1. The survey will cover the boiler from burner front, or exhaust gas inlet, to funnel top, including all pressure containment parts, valves and fittings .

2. During the survey the boiler, economiser and air heater are to be examined both internally and externally as far as access 

3. Necessary  parts subjected to a hydraulic test. Thickness of plates and tubes is to be determined usually by ultrasonic test equipment.

4. The principal boiler mountings are to be examined externally, and opened up for inspection where considered necessary. 

5. Boiler casings, supports etc. will be examine to see they are in good order, and allow for free expansion.

6. Automatic control equipment for water level and for fuel oil is to be checked, with special regard to safety cut-outs.

7. Isolate the boiler from all working systems, and open up both water and gas sides, remove  any internal  necessary for a proper visual examination. 

8. Previous records should be examined and note taken of any previous defects repairs, so these can be given special attention.

 Typical procedure will as follows 

1. The steam drum is examined internally and externally together with its mountings.

2. Then all top headers and the burner positions, including carriers and associated pipework. 

3. Economiser and superheater headers can be inspected before entering the water drum. 

4. Do not carry out any gas side inspections until all internal examinations are complete, in order to avoid carrying grease, dirt etc. into the water spaces.

5 . On the fire side, start with the furnace. Then in turn the superheater, economiser, and air heater can be inspected.

6. A note pad with pencil securely attached , an unbreakable torch and a mirror on a rod should  be available, together with other items if desired such as a straight-edge, an introscope to examine tube bores, and a polaroid camera to record any defects found.

 7. The survey is not complete until the boiler has been examined under steam, and the pressure gauges checked against a test gauge.

8. The water level indicators and protective device  must be tested, and the safety valves adjusted to their correct blow-off pressure. 

NORMAL DAMAGE ARISE IN MARINE BOILER

1. Corrosion -: There are two principal forms of corrosion. One is direct chemical attack and mainly occurs in superheaters due to the high metal temperatures involved. It can result in pitting or cracking in tube bores, or in scaling or flaking on the gas side of tubes This form of corrosion also occurs when loss of water circulation causes the metal to overheat in the presence of steam.

The more common form ofcorrosion found in boilers is the result of electro-attack usually involving acidic water conditions in the presence of dissolved oxygen.

2. Erosion -:  It is a mechanical wearing away of the boiler metal due to water, steam or gas flowing over the metal surface. Thus tubes can wear thin in the region of bends, due to water impingement.

3. Overheating-: In service  boiler  matter subjected to the heat of combustion must be continually  cooled by water or steam. If for any reason this cooling affect is lost greatly reduced, the boiler metal overheats, loses strength and distorts. 

4. Cracking -: Welded boilers are especially vulnerable to fatigue cracking resulting from bad design , poor workmanship or both . Fatigue cracking is  also associated with thermal cyclic stressing, which can resultfrom poor steam-raising pro cedures, lack of expansion.