Boiler Maintenance and Maintenance: Methods and Scope

I. OBJECTIVE OF MAINTENANCE AND MAINTENANCE WORK

• Maintenance and maintenance are technical care activities that involve adjusting, repairing, and replacing certain components and parts inside equipment and machinery to maintain or restore normal operation after a period of use. Maintenance and maintenance efforts also help users detect potential damage early for timely intervention, avoiding significant damage to the equipment.
• Boilers comprise various equipment, operate differently, and have different maintenance conditions. Understanding the process is essential to perform thorough and proper maintenance on the equipment, avoiding wasting time and excess maintenance materials.
• When maintenance and maintenance work is ensured, boilers will operate safely and reliably, preventing unexpected failures that could cause significant disruptions to the production process.

II. MAINTENANCE METHODS FOR BOILERS WHEN THEY ARE OUT OF SERVICE

1. DRY MAINTENANCE METHOD

Applicable when the boiler is planned to be out of service for more than 1 month.

• After stopping the boiler, wait for it to naturally cool down, with the chamber temperature dropping below 150°C and steam pressure ranging from 0.2bar to 0.5bar.
• Turn off the control power.
• Open the quick drain valve and drain all the water from the boiler. Pay attention to draining from all bottom drain valves to clear pipes, dark water assemblies, bright water assemblies, and heating units.
• Use a small firewood fire to dry any residual water inside the boiler. Be careful to keep the fire small to avoid damaging the boiler, as there is no cooling water inside the pipe system. Control the temperature of the combustion chamber not to exceed 200°C and prevent pressure from building up inside the boiler.
• When you observe that the steam escaping from the quick drain valve is gradually decreasing, you can stop the fire, allowing the boiler to cool naturally. Close all bottom drain valves, gas drain valves, and quick drain valves.
• Place 25kg of live lime with 20mm to 30mm-sized particles in a stainless steel or aluminum tray and put it in the steam drum. Close the steam drum's doors.
• Regularly, about once a month, open and check if the lime particles are broken; if so, replace them and then close the steam drum's doors again.

2. WET MAINTENANCE METHOD

Applicable when the boiler is planned to be out of service for less than 1 month.

• After stopping the boiler, wait for it to naturally cool down, with the chamber temperature dropping below 150°C and steam pressure ranging from 0.5bar to 1bar.
• Turn off the control power.
• Open the quick drain valve and drain all the water from the boiler. Pay attention to draining from all bottom drain valves to clear pipes, dark water assemblies, bright water assemblies, and heating units. After confirming that the water has been completely drained, close the bottom drain valves. The quick drain valve remains open.
• Replace with treated clean water that meets the standard into the boiler.
• Heat the boiler until it reaches 0.3bar and control the combustion to ensure that the pressure does not exceed 0.5bar. There should be steam escaping from the quick drain valve. Maintain this pressure at 0.3bar for 20 minutes to vent all the oxygen in the water, then stop the heating. Close all gas drain valves.

III. CHECKING AND MAINTENANCE CATEGORIES DURING BOILER OPERATION

1. HOURLY

• Check the normal operation of the equipment in operation.
• During each shift, check the quality of the water supply and boiler water to ensure the quality of the water being used.
• During each shift, drain boiler water and the assembly of sight glasses, checking the proper operation of water level monitoring equipment.
• During each shift, drain condensed water from compressed air systems and compressed air tanks.
• Check the stability of the incoming fuel.
• Check continuous operation of ash removal equipment without interruption and without releasing dust into the environment. Check the ash funnel of dust collection equipment for normal operation without blockage (check for ash accumulation in the funnel, check for suction at inspection points).
• Check the water levels in the boiler system, including water level screens and sight glasses, water tank levels, and source water supply systems.
• Check the water levels in dust settling tanks and wastewater settling tanks. Take prompt action when there are signs of shortages or fullness.
• Check the pressure at the inlet of boiler feedwater pumps, intermediate water pumps, and other auxiliary water supply pumps to detect pump malfunctions, water loss, or damage in a timely manner.
• Check the temperatures of bearing housings and motors in operation. If temperatures exceed 70°C, immediately notify mechanical maintenance staff or maintenance personnel and continue monitoring.
• Check rotating equipment for abnormal noises, jamming, or blockages.
• Check auxiliary equipment, air compressors, for normal operation.
• Record equipment parameters for monitoring and tracking purposes.

2. DAILY

• Compile and compare data.
• Check and record all relevant indices: electrical consumption index, water consumption index, fuel consumption index, steam production index, and ash content index.
• Check daily operational parameters. Compare current operating parameters with previous days and months to detect abnormalities.
• Check the operation of Main and Auxiliary Engines throughout the entire boiler system.
• Clean the area around the boiler house and remove ash for disposal.
• Record daily shift tasks.

3. MONTHLY

Minor maintenance.

• Check the operation of safety valves at 15-day intervals at working pressures for all valves.
• Check pressure gauges for normal operation.
• Clean filter screens and Y-type water filters.
• Check steam traps for normal operation.
• Open sight glasses and flush bright water assemblies if they appear cloudy.
• Clean electrical equipment.
• Check the connection of the electrode probe assembly of the sight glass. Inspect connections for loose connections and oxidation.
• Overall cleaning of the boiler: Clean and remove deposits inside heat exchanger pipes, heating units, recuperators, flue gas ducts, and dust collection systems.
• Inspect lubricants and check bearings and drive belts, gearboxes.

4. SEMI-ANNUAL

Intermediate maintenance.

• Open the steam drum and water drum doors, inspect the inside of the pipes for deposits.
• Open the cleaning doors of the combustion chamber and drum, check for deposits or foreign matter.
• Completely replace lubricants, oils, or bearings in equipment.
• Check all electrical equipment and electrical connections of the equipment.
• Check air ducts in the combustion chamber. Check air duct openings for blockages and clean if necessary.
• Check the operation of the boiler feedwater treatment system. Regenerate and measure water quality before and after regeneration.

5. ANNUAL

Major maintenance.

• Inspect the refractory brick walls of the furnace and repair any cracks or structural damage.
• Clean and repaint rusted areas and components.
• Inspect or replace blocked air nozzles.
• Inspect or replace bearings, bearing housings, drive belts, etc.
• Inspect fan blades and fan bodies for dust accumulation or corrosion.
• Check the water supply system and perform maintenance on the water softening system for feedwater.
• Inspect and maintain all open-close valves, safety valves, and steam control valves.
• Maintain the pressure reducing unit.
• Check the inspection deadlines for all boiler equipment for re-inspection or schedule inspections as required. According to Circular No. 54/2016/TT-BLĐTBXH of the Ministry of Labor, War Invalids and Social Affairs, periodic inspections are conducted every 2 years. For boilers in use for over 12 years, the inspection interval is annually.
• Inspect and clean deposits inside the boiler.