Marine Engineering Study Materials

The boiler maintenance should always be executed with skill and in accordance with valid rules and regulations from the authorities, and below are given some recommendations for periodical inspections and maintenance.

Daily Operation

During normal operation of the boiler some work and check procedures have to be considered every day.

1. Check the boiler steam pressure and the water level.
2. Check that the feed water control system is operational.
3. Check the boiler water condition and make necessary countermeasures with regard to the feed and boiler water treatment. If necessary blow-down the boiler.
4. Check the function of the oil burner at different capacities through the inspection holes on the boiler.
5. Check the flue gas temperature after and/or the draft loss across the boiler. If either the temperature or the draft loss is too high, the pin-tube section must be cleaned.

Weekly Routine Checks

1. Drain each water level glass for about 10-15 seconds.
2. In case of contaminated boiler water or insufficient water treatment, the draining of the water level glasses must be done more often.
3. Check the safety water level device.
4. Depending on the boiler water tests blown-down the boiler. Open the blow-down valves quickly for a few seconds, and then close and open again for about 5-10 seconds.
5. Repeat this operation when required according to the boiler water tests.
6. Perform scum blow out by means of the scum valve when required. The scum blow out must be carried out until the drained water is clean.

Monthly Routine Checks

1. Test all stand-by pumps.
2. Check all boiler mountings for damage or leaks and repair/replace if necessary.
3. Check the function of the high steam pressure switch by lowering the set point or by raising the steam pressure, e.g. by closing the main steam valve slowly. The burner must stop automatically.

Inspection of Furnace

The furnace should be inspected at least twice a year. During this inspection the following issues should be taken into consideration:

• Check for cracks at the refractory lining and that the furnace walls are free from excessive soot deposits.
• Examine carefully the area opposite the burner. Too much soot deposits indicate that the burner should be adjusted.
• Check that the pin-tube elements are intact and that soot deposits are within normal limits.

Inspection of Boiler Water Side

1. The boiler water side (interior) must be carefully inspected at least twice a year. This inspection of great importance and no doubt the most important of all the maintenance measures, since it has a direct influence on the boiler longevity and on the security.
2. At these inspections, hard deposits, corrosion and circulation disturbances can be found at an early stage, and preventive measures must be taken to avoid unexpected material damage and boiler breakdown.
3. Presence of hard deposits at the furnace wall and the pin-tubes reduces their heat transfer properties and decrease the capacity of the boiler.
4. Further, it is possible to make out if the feed water treatment has been satisfactory and if the blow-down has been carried out sufficiently.
5. Incorrect feed water treatment is commonly causing hard deposits or corrosion.
6. Insufficient blow-down will cause sludge deposits in the tubes and accumulation of sludge in the bottom of the boiler.
7. If hard deposits are not removed, it may lead to overheating in the boiler plate material which is exposed to the flame in the furnace wall area. This may cause material damages.
8. Incorrect feed water treatment does not always lead to hard deposits. For example, a too low or too high a pH-value may give an electrolytic reaction, causing corrosion in the boiler.
9. When the boiler interior is inspected, examine all parts carefully and be attentive to deposits, corrosion and cracks. It is advisable to pay special attention to this inspection.

Procedure and Remarks for Inspection

1. Shut off the boiler and allow it to cool (below 100°C). The boiler should NOT be depressurised by lifting the safety valves and then filled with cold feed water since the stress induced by too rapid cooling may cause damage.
2. Empty the boiler and close all valves. If the boiler is connected to a second boiler, check that the valves between them are closed.
3. Unscrew and remove the manhole hatch(s) on the boiler and enter the boiler when it is sufficiently cold. Check the welding in the boiler. A careful examination should be carried out with respect to any possible corrosion or crack formation.
4. Special care should be taken to the water line area in the pressure vessel where oxygen pitting may occur.
5. If deposits are found to be forming in the boiler tubes, the boiler should be chemically cleaned.
6. It is advisable to consult a company of cleaning specialists who will examine the boiler deposits and treat the boiler accordingly.
7. After chemical treatment the boiler should be blown-down at least twice a day for approximately one week. This will ensure that excessive sludge deposits due to chemical treatment do not collect in the bottom of pressure vessel.

Contamination

If the boiler is contaminated with foreign substances like oil, chemicals, corrosion products etc., it is very important to act immediately to avoid damages to the boiler.

Layers of thin oil films, mud, etc. exposed to the heating surfaces causes a bad heat transfer in the boiler, leading to overheating followed by burned out pressure parts. In order to remove such contamination, a boiling out or acid cleaning have to be performed immediately.

Corrosion products from the pipe system or insufficient boiler water treatment may result in corrosion in the boiler itself. It is therefore important to observe that such circumstances do not occur in the system.

Reference:

MISSION™ OL Boiler Manual by Aalborg Industries