55 Boiler Operation Maintenance

Learning Objectives

  • Describe startup steps and possible abnormal conditions
  • Describe daily check operating conditions
  • Explain emergency conditions and accidents that can occur during boiler operations

Essential Question

What are signs that a boiler is operating normally? Or abnormally?

Introduction

This chapter focuses on general guidelines on boiler operation and maintenance. Always check the manufacturer instructions for guidelines specific to the equipment in order to have safe and effective usage of the equipment.

Always keep a written record of all inspection and maintenance completed for all equipment.

Startup Procedure

This section describes in detail a general startup procedure for boilers.

The information in this section is taken from PanGlobal (2017) under the fair use policy.

Preparation for Startup

The following are some preliminary steps that should be taken:

  1. Make sure that the boiler has a valid inspection certificate. Without the certificate, the boiler may not be legally started up. The certificate should be conspicuously placed adjacent to the boiler or retained and safeguarded in a manner approved by the inspector. Be aware that if there is no certificate, it may take some time to get one.
  2. Inspect the fireside and waterside of the boiler to make sure that no foreign matter, such as tools or tags, is left behind.
  3. If the waterside of the boiler is dirty or coated with grease or oil, clean the boiler chemically first.
  4. Before filling the boiler with water, make sure that the firing equipment is ready for startup. This is necessary because the boiler should be fired up as soon as it is filled with water, to heat the water sufficiently to drive off the dissolved gases in order to prevent corrosion.

In order to prepare for the startup, the following procedure should be completed.

Note: the water system should already be filled, the boiler stop valves in the supply and return lines should be closed, and the steam unit should be a single unit.

  1. Review the manufacturer’s recommendations for start of the boiler.
  2. Before closing manhole and hand hole openings, make sure that the seating surfaces are clean. Traces of old gaskets left behind may cause leakage. Use new gaskets coated with powdered graphite or a gasket compound. This makes removal easier the next time the boiler is opened up.
  3. Before filling the boiler, ensure that manhole and hand hole covers, and/or washout plugs, are in place and properly tightened. Check that the blowoff valves on the boiler and the drain valves on fittings and controls are closed.
  4. Open the boiler vent and fill the boiler with water to the desired level. Add chemicals if and as required.
    • Water: fill the boiler completely until water exits the vent, then close the vent valve.
    • Steam: ensure the gauge glass is in full service. Fill boiler to desired level (slightly below normal working level to allow for expansion) and leave vent valve open.
  5. Check all points for leakage such as manholes, hand holes and drains.
  6. Water
    • When the boiler is filled, open the stop valves in the supply and return lines to the boiler and check that all other stop valves in the system are in the open position.
    • Check the altitude gauge on the boiler to see that the system is under the minimum static pressure required to maintain a positive pressure at the highest point in the system during operation. If the boiler is equipped with a combination altitude-pressure gauge, the pressure will be indicated by the movable hand. Align the stationary hand with the movable hand, so that when the boiler and system are heated up and in operation, it can be seen at a glance that this minimum pressure is maintained.
    • Check the level in the expansion tank. It should be in the lower part of the gauge glass.
    • Start the circulator and vent the air at high points in the system.
    Steam
    • If the heating system is going to be warmed up with the boiler, open the suction and discharge valves on the vacuum or condensate pumps, and set the pump switches to the ON position. Open the water supply to the feeder valve, if there is one.
  7.   Check that fuel is available up to the stop valves in the pilot and main burner supply lined. If fuel oil is used, also open the stop in the return line and make sure that the lines, filter, and fuel pump are properly primed and free of water.
  8.  Check that the fresh air supply to the boiler room is obstructed.
  9. Check the settings of the operating and limiting controls.
  10. On boilers with a high-low fire control, set the control switch on the panel to low unless advised otherwise in the manufacturer’s manual.
  11. On boilers with a modulating control, set the manual-automatic switch on manual and the flame control switch in the lowest position.
  12. Reset all limit switches, such as low water, which could have been tripped or opened during shutdown.
  13. Check that the boiler control switch on the panel is in the OFF position.

The boiler is now ready for startup.

Startup
  1. On gas-fired boilers with a standing pilot, open the pilot valve and light the pilot. Follow the lighting instructions given on the instruction plate attached to the burner manifold or automatic valve. When the pilot is lit and burning satisfactorily, open the stop valve in the fuel line to the main burner.
  2. On the boilers with an intermittent, or interrupted pilot, open the stop valves in the fuel line to the pilot and to the main burner.
  3. Close the main switch to supply power to the boiler.
  4. Turn the boiler control switch to the ON or START position. The programming relay or control will take over and start up the boiler in the proper sequence.
  5. Warm the boiler up slowly to prevent excessive stresses in the boiler metal due to uneven expansion and thermal shock.
  6. Inspect the boiler frequently during the warm-up period. Observe the operation of the burner. Check for leakage at hand holes, washout plugs, valves, and pipe connections.
  7. Water
    • Do not leave the boiler until the operating control reaches its cut-out temperature. Make sure that the control shuts off the burner.
    • When the burner shuts down, check the water pressure on the altitude gauge and the water level in the expansion tank.
    • Check the safety relief valve for evidence of leaking. Perform the try lever and pop tests.
    Steam
    • Close the vent valve when the boiler pressure reaches 15-20 kPa (2-3 psi). All the air should have been driven out of the boiler.
    • When the boiler is thoroughly warmed up, steam is being produced and good water circulation has been established, the firing rate may be increased slowly.
    • While the boiler is building up pressure, blow down the water column and gauge glass to ensure the connections are clear and the level is correct. Also, test the low-water cut-offs by opening the drains on their housings.
    • Stay with the boiler until the operating control reaches its cutout point. Make sure it shuts off the burner at the right pressure.
    • Check the safety valve for evidence of simmering. Perform the try level and pop tests.
  8.  Enter the following in the log book:
    • Date and time of startup.
    • Any irregularities observed and corrective action taken.
    • Time when control shut off the burner at established temperature/pressure, tests performed, etc.
    • Signature of operator.

Routine Operation and Maintenance

It is really important to regularly and carefully inspect boilers to ensure they are working safely and effectively. There are some checks that should be held on a daily basis.

Pressure and Temperature Checks
Water Units
  • Check the operating pressure and temperature of the hot water boilers.
  • The temperature should be at least 77° C (170° F), and maximum should be the required temperature to properly heat the building.
  • The pressure depends on the type and size of building. A general recommendation is to have a difference of 69 kPa (10 psi) or 25% between the safety relief valve set pressure and the boiler operating pressure.
    • Ex. the safety relief valve is set to open at 250 kPa,
  • There should be a large difference:
    • Safety Margin: It provides a buffer to accommodate pressure fluctuations and prevents accidental discharge of steam or fluids during routine operations.
    • Prevention of Overpressure: It ensures that the relief valve opens only when pressure exceeds safe limits, minimizing the risk of system failure or explosion.
    • System Stability: Maintaining a substantial difference between set pressure and operating pressure helps stabilize the system by reducing wear and tear on the valve.
Steam Units
  • The pressure should remain within the prescribed high and low limits as set by the operating control.
  • The maximum operating pressure should be set 20-30 kPa (3-5 psi) below the operating pressure of the safety valves.
  • The discharge pressure of the safety valves must not surpass 103 kPa (5 psi).
  • The pressure differential is essential to enable the valve to seal tightly after it has been forced open by pressure.
Water Levels
Water Units
  • Sometimes, there are very small leaks, that require additional water to be added to make up for that water loss.
  • If there is additional water required regularly, there may be leaks in piping and valves, leaking packing or seals on the circulator pump shaft, or a leaking boiler.
  • The first sign of constant leaking is reduced pressure, then a drop of water level in the gauge glass of the expansion tank, and finally the upper part of the system will become dry.
  • This can result in a loss of heat in the areas furthest from the boiler (ex, if the boiler is in the basement, the 5th floor may not get enough heat)
  • It is important to regularly check the water levels ensure that the heating system is completely filled with water.
  • Regular checks will prevent a structural loss and a financial loss.
Steam Units
  • Do not depend completely on water level controls, emergency water feeders or automatic alarms. There is a margin for error.
  • Always check for the right water level in the boiler in order to have safe operation.
  • You should blow through the gauge glass, water column, and connecting lines regularly (weekly) to ensure that the connections are clear. This should also be done often if a lot of make-up water is being added.
  • Make sure the gauge glass is always clean in order to get a clear and accurate visual of the level.
  • Check for rust.
  • Check for the right concentration of the water treatment chemicals.
  • Check for a steady water level. Water should not be foaming. Only slight foaming is normal. If there is excessive foaming, lower the level by 5-7.5 cm. and refill to the normal level. Repeat many times. If this continues, cool and rain the boiler. Wash it and refill it.
Burner Operation

Inspect the burner flame. Check for :

  • Burning brightly and evenly
  • Signs of smoking
    • If there is smoking, check the air intake in the boiler room for any obstructions (snow, ice, bags, etc.).
    • Other possible reasons, check if the burner nozzle is dirty: dirty burner nozzle, low fuel temperature, incorrect fuel-air ratio.
    • Adjust the above to stop the smoking.
Stack Temperature

Flue gases’ temperature can be checked using a stack temperature. It shows if the heat exchange between the flue gases and water in the boiler is working. If the heating surfaces on the fireside and waterside are both clean, the maximum amount of heat can be exchanged, and in this case, the stack temperature will at its lowest for each specific firing rate. Heat transfer can be negatively impacted by the following:

  • Soot deposits on the fireside due to improper combustion.
  • Scale and sludge deposits on the waterside due to incorrect water treatment or a lack of water treatment.

The gases leave the boiler at a higher temperature which has a negative impact on the boiler efficiency. The stack temperature should be observed and recorded so that any changes can be analyzed, and any problems can be fixed (for example, cleaning). A slight change is not harmful towards the equipment, but a large difference will cause issues, such as furnace explosions, damaged tubes, etc.

Water Treatment & Make-up
Water Units
  • Water treatment is done to prevent corrosion.
  • The boiler water should be analyzed before deciding the exact treatment.
  • Water should continuously be tested after the treatment.
  • Water treatment is not required for scale IF additional water treatments are being done while adding make-up water.
Steam Units
  • Tests should be done for the boiler water, make-up water and the condensate at different intervals.
  • Analyze the test results to decide the exact chemicals and the quantity needed for best treatment and protection.
  • Blow down as needed.
  • If external water treatment equipment is being used, keep an eye on its function.
  • Try to limit make-up water to be added because this has oxygen in it, and we do not want oxygen entering the boiler.
  • If there is a condensate return tank, feed the make-up water into the condensate return tank instead of into the boiler.
Blowing Down
Water Units
  • Regular blowing down is required when there is regular or significant make-up water being added.
  • Generally, blowing down, cleaning, or emptying is not needed between the 2-year inspections.
  • Consult your manufacturer’s instructions for more information.
Steam Units
  • Only blow down the boiler as needed to ensure that the levels of dissolved and suspended solids remain within acceptable limits and to eliminate any sludge accumulation.
  • If little or no make-up water is being added, blowing down once a week is enough.
  • If there is more make-up water being added, blow down more often.
  • Note: the more you blow down, the more expensive it gets.

Intermittent Blow Down Valve

Continuous Blow Down Valve:

Example:

Inspection

It is important to regularly and properly completing inspections in the boilers. Generally, the following should be inspected:

  • Leakage
    • safety relief valves
    • manholes
    • hand holes
    • clean-out plugs
    • valves
    • pipe connections
  • Unusual noises or conditions
  • Equipment
    • circulating pumps
    • chemical feeders
    • air compressors and feedwater
    • condensate
    • vacuum pumps
    • fuel pump (if oil-fired)
    • fuel level (if oil-fired)
  • Cleanliness/Housekeeping
    • oil spills
    • storage of rags
    • no boxes or flammable materials need the boiler
Safety Relief Valve
Pipe Connection Union
Connection Elbow
Connection T

NOTE: ensure to keep a record of all inspections, checks, testing, etc.

 

Emergency Conditions

Emergency situations and unforeseeable conditions can occur while operating steam boilers. Read the different situations below to better understand these situations and the causes that lead to such situations.

Abnormal Water Loss

This can occur when make-up water is consistently needed or when water treatment chemicals are required to be adjusted to maintain the correct concentration levels in the boiler. Increasing or continuing water treatments is NOT the solution. The boiler and all its parts should be inspected to find the cause of this issue in order to repair the issue as soon as possible.

To do so, tightly close the blowdown valve and close all drain valves. Check and inspect all parts, including but not limited to, pumps, valves, pipping, terminals, etc. If there is no issue found, it may be necessary to shut down the boiler and conduct a hydrostatic test to ensure that there are no leaks or issues with the pressure.

Low Water Level

If the water level continues to drop, this may be caused by one of the following:

  • feedwater level controller not working properly.
  • feedwater or condensate pump failure.
  • water supply to the pump is being interrupted.
  • ruptured firetubes or open blow-off valves that lead to leakage from the boiler.

The boiler should shut off automatically if the water level drop below the cut-off point. If this does not happen automatically, the operator should check the glass gauge to see the water level (open it if you need to confirm). If the water level is low, immediately shut down the boiler. Once the boiler is cooled off, drain it. Check for any damage due to overheating. If there is damage, contact the Boiler Inspector. If there is no damage, fill up the boiler, but do NOT start operating it until the issue is determined and resolved.

High Water Level

The information in this section is taken from PanGlobal (2017) under the fair use policy.

Should the water in the gauge glass of a steam boiler show a higher than normal level or even climb out of sight, the level should be brought back to normal to prevent carryover of the water with the steam.

If the cause of the high water level is a malfunction of the boiler water level control devices, it is imperative that the feedwater system be shut down immediately. Any attempt to lower the water level before stopping the feedwater input will result in the control system trying to maintain the level, which is not what is wanted. Further, opening the blowdown valves can result in a pressure drop and this can result in boiler water “swell”, a condition in which the water volume tries to increase. Remember, feedwater temperature is much lower than the boiler water temperature; stopping its flow should result in a slight boiler pressure increase. This in turn will cause “shrink” of the boiler waiter, a positive factor in the situation we are trying to resolve.

It is in this condition of boiler water swell that results in no boiler having a high water level fuel cut-off device. Any drop in pressure will cause this, therefore it is important to maintain pressure.

Should there be “priming” and resulting water hammer, the operator should stop the feedwater input then close the steam outlet valve. The boiler will then trip on high steam pressure. Whenever there is evidence of water hammer, it is imperative to always isolate the system at the source and not open drains or any other valve that would cause glow to happen or the pressure to drop. Should water hammer result, the boiler must be removed from service immediately and thoroughly inspected by a jurisdictional boiler inspector, an insurance company inspector, and an inspector from the plant operations group before the unit can be returned to service.

The cause of trouble, a defective feedwater control, should be repaired as soon as possible.

Blower Failure

If the blower or fan fails, the combustion air supply will stop. In this situation, the fuel supply has to be shut off immediately to avoid a furnace explosion. Most boilers will have a low-air cur-off switch that will automatically cut off the power to the fuel valve immediately after the level drops below the minimum safe value.

Flame Failure

Following are the possible causes that could lead to flame failure:

  • insufficient fuel oil supply because of a plugged filter.
  • presence of water in the fuel.
  • an excess of air supply.
  • insufficient gas pressure.

When this happens, the fuel flow to the burner has to be stopped immediately so the furnace does not fill with unburned fuel which can lead to an explosion. A lot of boilers now have flame detection devices that will stop the fuel supply right away. It is therefore really important to regularly test these devices to ensure these safety precautions fall into place when they are needed!

Maintenance Procedures

Regular and thorough maintenance can increase the safety, the lifetime and the efficiency of boilers. There are also legal requirements for specificized inspection intervals for boilers and pressure vessels. Follow the instructions specific to the boilers used at the facility. This section discusses general instructions for maintenance. Always refer to the manufacturer’s instructions. It is very important to take all precautions and steps to ensure the safe operation of all equipment.

General Maintenance
  • Always check for leaks in steam, water and fuel connections.
  • Check for the tightness of adjusting crews, locknuts, sheave setscrews, valve packing, etc.
  • Repair all issues immediately.
Lubrication
  • The burner and fan motor can have pre-lubricated sealed bearings which do not additional lubrications for about three years.
  • The burner and fan motor can also have standard ball bearings which require lubrication one time per year.
  • Always check the manufacturer’s instructions for more details and accuracy.
Washing out the Boiler After the initial three month of use, new boilers should follow this procedure:

  • shut down;
  • drain;
  • open it up;
  • flush with a high-pressure hose;
  • inspect.

During this, the tubes and tube sheets can be inspected for scale or pitting to see the efficacy of the water treatment. This entire should be repeated as often as needed.
Cleaning the Firetubes Follow this procedure:

  • Unlock and pull open the doors located at the front and rear of the reversing chambers.
  • If the tubes have soot on them, they need to be brushed to be cleaned. Before cleaning, take off the flame retarders, if they are being used. Brush eh tubes from both ends.
  •  Take out all the soot from the furnace and reversing chambers.
  • After you are done cleaning it, put the flame retarders back on and close all the doors. Before you close the doors, cover the door gaskets with graphite an oil, or an anti-seize compound so they don’t stick.
Refractory Maintenance
  • Every time the boiler is opened for cleaning, make sure to inspect the refractory and wash-coat it with diluted heat resistant cement on a regular basis to extend its life.
  • If there are cracks or joints, make sure to face them with the cement to prevent the damage from continuing.
  • Replace any burned out or broken liners (using the same material)
  • General deterioration will lead to the refractory to be renewed.
Burner Maintenance Regularly observe the burner flame during operation to ensure that the flame is symmetrical. That would mean that the burner is clean. Gas burners don’t usually need much maintenance, simply inspect once per year. Oil burners need to be cleaned regularly by following the procedure given by the manufacturer. Here is a general procedure:

  • Ensure that the power supply to the boiler and to the fuel pump is not turned off, including the manual stop valves being closed before taking out the burner.
  • Take out the fuel lines and the burner assembly from the front of the boiler.
  • Take apart the burner completely, but make sure to be careful with the nozzle and component parts.
  • It is recommended to use a monarch-brass nozzle wire brush to clean the carbon buildup. Do not use other wire brushes as this can cause damage and ruin the parts.
  • Use a good carbon solvent to soak all the parts and rinse them with hot water after. Use the labeling for details on how to use the solvent. Be careful and use PPE.
  • Using a lint-free cloth, dry all the parts and polish the orifice lightly with a round sharpened toothpick.
  • Clean your hands and tools before putting the burner back together.
  • Clean the diffuser, pilot, tube, and igniter. Put a cloth through the scanner to have a shiny surface. Wipe down the rotary damper and make sure it is moving smoothly.
  • Put the burner together and put it back in the burner head. Ensure that the nozzle is put back in place properly. Make sure everything is put back the way it was before.
  • Connect the fuel lines and ensure that it is tight.

Refractory:

How to clean out a Burnham oil boiler?

Additional Resources

Copyright © 2017 PanGlobal. All rights reserved. Under Fair Use Policy.

PanGlobal. (2017). In Boiler Operation Maintenance. Low Pressure Boiler Components & Operation (2nd ed.). PanGlobal Training Systems Ltd.

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SIGA Maintenance Worker Prep Copyright © by hrycaym. All Rights Reserved.

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