Complete Maintenance of Auxiliary Marine Boiler

As an on-duty engineer, you should follow the maintenance procedures to ensure a trouble-free performance of boilers. The boiler maintenance should always be carried out according to the maker's manual, rules and regulations defined by classification societies.

The essential precaution and safety measures are to be taken before starting any maintenance. The risk assessment of that maintenance job is also to be carried out.

Water in the boiler is subject to contaminants such as oil, salt and other impurities. These contaminants lead to corrosion, scales, blocked lines, etc. Since high temperatures are encountered while working on the steam systems, boiler maintenance requires a regular shutdown for cleaning. inspection and repair. Once the maintenance is complete, the boiler is put back into operation, however, it is regularly checked to ensure a safe and smooth operation.

Boiler Maintenance

Shutting down and draining of boiler

What are the dangers associated with the boiler?

1. It is a pressure vessel.
2. It has hot stains.

The hot stains make it very difficult to carry out maintenance on any part of the boiler while it is in operation.

Therefore, a major part of the maintenance is carried out by shutting down the boiler completely.

You must always follow the correct procedures as given in your manual to avoid injuries and accidents.

You will find it easy to follow these steps to shut down this boiler.

• Carry out external inspection when the boiler is still under pressure so that you can identify few exhaust, stains and water leakages.
• Inspect all round glands, manhole doors, furnace doors and funnel exhaust.
• During firing, inspect the boiler furnace through the side glass to analyze the quality of flame.
• This will give you a good indication of the air-fuel ratio whether it's proper, less or more.
• Stop the firing and purge the furnace for about 5 minutes.
• Then switch of the first draught fan and close all air registers.
• Next shut the fuel before the burner and check that there is no fire in the furnace.
• Then take out the burners and insert them into cleaning oil.

• Stop the fuel oil pump, feed pump and then shut off the feed valves.

Now blow through the gauge glass to ascertain correct water level.

• Open the shift side valves first and then the scum valve on the steam side to complete the scum blowdown.
• Blowdown the remaining through the bottom blow-down valve.
• To prevent vacuum from forming inside the boiler, open-air vent cock when the pressure reaches about 0.5 bars.
• When boiler pressure is zero, first close the blow down valve and then close the ship side cock.
• The boiler is now successfully shut down and drained.

Now explains how the inspection and maintenance procedures carried out on boiler.

• Open the burner door for furnace inspection.

• Check the condition of the refractory and build it up wherever necessary.
• Note that too much carbon deposit of breakage in the refractory is an indication of bad combustion.
• Inspect the inside of the tubes for carbon deposits and bottle leaks.
• Then open the water side manual door and check for scale, rust and all deposits.

• Clean them by brushing or a recommended chemical to ensure a heat transfer and optimum tube performance.

Before startup:

Before you start up the boiler plant you need to do some general work and checks.

• First close the main steel valve, bypass valve, circulation valves if provided, scum valve and blow valves and open the air vent valve.
• Then open the feed water valves and fill the boiler with water after approximately 15mm below normal water level because the water will expand to its normal level when it is heated.
• In case you are filling a pressure less boiler make sure that you are throttled to shut off valve after the feed water pump.
• This will prevent the pump motor from being overloaded.
• Check the water level in the water level gauges more frequently.
• During complete start-up, low down the water level gauges several times to ensure a correct indication of water level.
• Ensure that the water level control system is connected and operational.
• Next check the oil systems and stop the fuel oil supply pump.
• Preheat the fuel oil if the burner should operate on heavy fuel oil.
• Check safety instructions with the burner from the separate manual provided.
• Now your boiler is ready for startup and raising steam.

Startup:

• At commissioning the startup of the boiler, and after any repair work on the refractory it is very important to further reduce the firing arc rate.
• This is the cause that the refractory will still contain a small amount of water which expands when heated leading to fishers and cracks in the refractory.
• The firing arc rate at the startup should not be too high as this might cause undue thermal stress on the boiler material.
• The burner must therefore only be operated at minimum load and at intervals of 1 to 2 minutes for the first few hours.
• Between each operation interval, the burner should remain stopped for approximately 8 to 10 minutes.

Raise in steam:

To raise steam in a boiler you need to follow some general work and check procedures.

• Check that the valves for the pressure gauges are open.
• If the boiler pressure is below 1 bar ensure that the air vent is open and then stop the burner.
• Switch on the manual control and low load to avoid thermal shock.
• Ensure that the water level does not rise too high during the pressure rising period. If the water level is too high drain via the blow down valves.
• Close the air vent valves when steam blows up through it.
• Note that a pressure reading should be indicated on the boiler pressure gauge before the air vent valve is closed.
• Tighten all covers such as man holes, hand holes, inspection doors etc.
• During the pressure rising period, if required, check all flange joints on the plant.
• Change to automatic control of the burner when the boiler pressure is 0.5 bars lower than the working pressure of the boiler.
• It is highly recommended that you allow at least four hours to lapse between flashing up and attaining full stream pressure.

While the steam is being raised, you need to perform some inspections.

• Check for leakages from manhole, hand holes and all boiler mountings.
• Check for flame quality through the side glass provided and adjust the air-fuel ratio accordingly.
• Check that the water level in both the gauge glasses is same.
• Check the colour of smoke from the funnel and readjust the air-fuel ratio if necessary.
• Check if the blow down line is hot.

If the checked results are not found normal, the boiler may have to be shut down and the abnormalities have to be rectified.

Next, open the bypass valve slowly to heat up and pressurize the steam system.

If the boiler is not provided with the bypass valve then the main steam valve should be used to heat up and pressurize the steam system.

Check the low water level safety arrangements and then open the main steam stop valve. Close the bypass valve.

Open the valve of the steam consumers carefully to avoid water shocks to the pipe lines.

When the boiler is in normal operation check that the water level control system and the gauge board functions are fully operational.

Your boiler is now ready for use.

The boiler is provided with various alarms and trips for safety of the equipment and its operator.

You must take action, when one of the alarms sounds.

Low water level alarm:

• If the low water level alarm sounds, shut off fuel and confirm level from the gauge glass.
• Increase the feed flow rate.
• If the water level still keeps failing, switch off the burner and start checking for leaks.

High water level alarm:

• If the high water level alarm sounds, shut off fuel and confirm level from the gauge glass.
• Decrease the feed flow rate. If the level is still too high, stop the feed totally and wait for it to come down.
• You may have to blow down if necessary.

Burner flame failure alarm:

• If the burner flame failure alarm sounds, shut off the fuel.
• Purge the furnace with a forced draught fan for 5 minutes or more.
• Inspect the furnace through the burner door.
• If there is no oil accumulation inside, relight the burners.

Low control air pressure alarm:

• If the control air pressure is low increase the air supply.

Low fuel pressure alarm:

• If the pressure low alarm sounds, check whether any valve in the fuel line is closed.
• The suction strainer before the burner or the fuel pump is choked or the fuel level in the service tank is low.

Low feed water pressure alarm:

• If the feed water pressure alarm sounds at feed pump discharge, check the water level, temperature or for any airlocks in the lines.

Low steam pressure alarm:

• If low steam pressure alarm sounds it means that the steam consumption is high. Therefore, increase the number of burners.

High steam pressure alarm:

• If the high steam pressure alarm sounds it means that the steam consumption is low. Therefore, reduce the number of burners of their load.

Low fuel oil temperature alarm:

If low fuel oil temperature alarm sounds, increase the steam to the steam heater to bring the temperature back to normal.

Automatic boilers will shut off when the following situations arise:

A) low low-water level

B) high-water level

C) flame failure

D) low combustion air pressure or fan failure

E) loss of control of system power

F) burner door is open

G) low automating steam pressure