Top 10 common incidents in boiler operation, causes, and solutions
GENERAL PRINCIPLES FOR HANDLING INCIDENTS
- Operators are responsible for applying incident handling measures as prescribed to promptly resolve incidents and prevent their spread.
- Identify the exact cause of the incident to determine the best, fastest, and least damaging solution for the system.
- When abnormal equipment signs (incident indicators) occur, immediate action or timely response plans should be executed to avoid passive incidents.
- Boiler operators should have a good understanding of the system and incident handling procedures to react, identify, and rectify incidents promptly.
- After an incident occurs, it should be reported to other relevant departments to work together on long-term remedies.
1. SEVERE WATER SHORTAGE IN THE BOILER
- Low water level warning and alarm on the HMI, sirens in the control room.
- Unable to observe the water level through the sight glass, abnormal steam pressure, abnormal main steam temperature.
- If the combustion chamber door is opened, a fierce fire is observed inside, and the boiler walls are hotter than usual.
- Abnormally high smoke temperature, metal expansion noises inside the boiler body.
- Due to operator negligence, the water supply pump was not activated promptly.
- Severe damage to a heat exchange tube or bottom blowdown valve in the boiler that prevents maintaining the water level.
- Pump malfunction that allows the pump to run but not supply water (pump entrapped air, pump motor running but impeller not functioning, pump motor overload, etc.).
- Source water supply system encountering a problem that prevents water supply to the feedwater tank, causing the water source to deplete.
- Failure of the water level sensor system, causing the water pump not to function.
- When a severe water shortage is confirmed, the boiler must be urgently shut down [Emergency stop]. Starting is strictly prohibited.
- Turn off all switches of the water supply pump equipment to the Off position, turn off the power circuit breaker (CB) of the water supply pumps.
- Turn off all feeding equipment, smoke fan, and air fan. Let the boiler cool naturally.
- After the boiler has cooled down, the incident should be assessed based on the incident's cause.
- Inspect the steam generating tube bundles from the inside and assess deformations.
- If no abnormal deformations are found, the boiler can be restarted.
2. NORMAL WATER LEVEL IN THE BOILER
- Low water level warning and alarm on the HMI and control room screen.
- Water visible in the sight glass, water level suddenly rising at the base of the sight glass, or water appearing in both sight glasses after opening the bottom blowdown valve for 3 seconds and then closing it abruptly.
- The boiler reports a water shortage after draining the sight glass tubes.
- Failure to switch the water supply pump to Auto mode.
- Pump overload causing the pump to be unable to supply water.
- Pump entrapped air causing the pump to run but not supply water.
- The boiler reports a water shortage after draining the sight glass tubes due to a leak in the bottom blowdown valve of the sight glass assembly.
- Inadequate water source system.
- Reset the pump to Auto mode and restart it.
- If the water level does not rise or continues to decrease after the pump is restarted, check for pump overload or entrapped air and resolve it.
- If water leakage is found at the bottom blowdown valve of the sight glass assembly, close the valve and replace the gasket.
- If the water source is inadequate, assess the water source equipment's operating condition and resolve the issue.
3. BOILER WATER LEVEL ABNORMALITIES
- The pump continues to supply water, the boiler is operational, but the water level in the sight glass remains unchanged, or water is not visible in the sight glass. The sight glass is misaligned with the water level sensor.
- The water level in both sight glasses appears normal, but the boiler system issues low water or high water alarms, indicating a discrepancy in the positions of the two bright sight glasses.
b. Causes and Remedies:
- The water level in the sight glass remains still or is in an incorrect state relative to the water level sensor (false sight glass reading) due to clogged water or steam passages to the bright sight glass or improperly closed or obstructed valves.
- A leaking sight glass drain valve or its position can also cause false water level readings in the bright sight glass.
- Inspect the isolation valves for proper opening and closing positions and clear any obstructions inside the sight glass passages.
- Ensure that the water levels in both sight glasses are equal after rectification.
- Normal water levels in the sight glass but boiler reports low or high water conditions (false water level sensor readings) are often due to short-circuited or broken signal wire connections of the water level sensor. Check and address the following points:
- Inspect signal wire connections to terminals for oxidation or breakage.
- If the wire connections are normal, check the entire signal wire for rodent bites or breaks.
- Examine the water level probe terminals inside the water column to ensure they are not misaligned and causing circuit contact.
4. STEAM PIPE RUPTURE OR EXPLOSION:
- Steam and water are observed spraying into the combustion chamber.
- The water level in the water column drops rapidly.
- Abnormal noises may be heard inside the boiler.
- Improper quality of supplied water, leading to deposits and buildup inside the pipe walls.
- Disruption of water circulation within the boiler, damage to insulation, or damage to water pipe joints.
- Uneven heating of the steam pipe during boiler operation (cold air entering the combustion chamber) or uneven heat transfer.
- Accumulation of ash and slag inside the pipe walls or erosion of the pipes.
- Incorrect boiler operation, rapid firing, continuous pressure fluctuations, water shortage, continuous changes in boiler capacity, or excessively rapid cooling.
- Poor pipe quality.
- Excessive water impurities without proper bottom blowdown.
- Stop the boiler in case of a rupture.
- If the steam pipe rupture is significant and the amount of water supplied is less than the amount discharged, do not supply water to the boiler anymore.
- Quickly implement replacement or repair measures to resume boiler operation.
5. LEAKS IN PRESSURE-CONTAINING COMPONENTS:
- Steam escaping with a hissing sound.
- Poor quality of fabrication, repair, assembly, or installation.
- Ingress of cold air causing metal cracking.
- Poor water quality leading to localized corrosion, metal deformation, cracking, water shortage, or pipe bending.
- If the leaks in valves or flanges are minor, monitor them until the next scheduled repair or replacement. If the leaks are significant, reduce the pressure to P = 0 kg/cm².
- If there are leaks in pressure-containing components, stop the boiler to rectify the issue.
6. FAILURE OF WATER LEVEL GAUGES AND PRESSURE GAUGES:
- Explosive sounds may be heard.
- Steam and water may spray out.
- Sudden temperature changes or impact on water level gauges and pressure gauges.
- Eccentricity or overtightening during gauge installation, causing insufficient room for expansion and contraction.
- Wear and tear of water level gauges during operation.
- If the water level gauges or pressure gauges are severely damaged or without replacements, stop the boiler normally.
- If the pressure gauge is shattered, remove the water in the gauge by turning the three-way valve to drain.
- Replace the broken pressure gauge with a new one. The procedure is as follows:
- Close the three-way valve to drain the condensed water.
- Unscrew the fitting that holds the pressure gauge
7. MALFUNCTION OF WATER SUPPLY VALVE ASSEMBLY:
- Hot water returns to the pump.
- The pump is running, but no water enters the boiler.
- Dirt and impurities in the supplied water causing wear and tear on check valves and silver valves, leading to valve leakage.
- One-way check valve getting stuck, preventing water from entering the boiler.
- If the valve assembly is slightly damaged and there is only minor water leakage, continue boiler operation until the next scheduled repair within 1 month. If hot water returns to the pump, release hot water before operating the pump.
- If the valve assembly is severely damaged and water cannot enter the boiler, promptly stop the boiler and proceed with replacement and repairs.
8. BOTTOM BLOWDOWN VALVE MALFUNCTION:
- Even after closing the valve tightly, water continues to leak.
- Strong water discharge at the bottom blowdown valve, and the water level in the water column decreases.
- When opening the blowdown valve, no water is released.
- Corrosion of the check valve, preventing proper sealing.
- The valve stem is broken, bent, or the packing is completely worn out.
- Accumulation of water deposits leading to valve blockage.
- Close the valve tightly and check if water continues to leak. If water still leaks, stop the boiler operation.
- If the bottom blowdown valve is severely damaged, close the isolating valve and replace the faulty blowdown valve.
- If the valve is blocked, stop the boiler for maintenance.
- In cases where the valve assembly is slightly leaking, monitor its performance until the next scheduled repair within 1 month.
9. BOILER FEED PUMPS RUNNING LONG BUT INSUFFICIENT FLOW RATE:
- Main and standby pumps are running almost continuously, but the boiler frequently reports water shortage.
- The discharge pressure of the pump exceeds 1.8 times the working pressure of the boiler.
- Anomalies in the pump's current.
- Boiler operating at a load exceeding its rated capacity, causing the pump to operate under excessive load.
- The discharge pressure of the pump is too high compared to the boiler's pressure, often caused by severe clogging inside the water supply pipes or the outlet, resulting in high pump discharge pressure and insufficient flow rate.
- Abnormal pump current is usually due to air ingress or water loss in the pump's inlet, causing the pump to operate without a load.
- If the boiler is operating at an excessive load compared to the pump, replace the pump with a higher capacity and flow rate.
- When the pump's discharge pressure is excessively high due to severe pipe clogging, flush the water supply pipes thoroughly. Open the air vent to check for blockages in the water supply pipe outlets and address them. Ensure that the water treatment system meets the standards. Clean the pipes and boiler to remove deposits.
- Check the water source for the pump, and the water level in the supply tank should be above 50% to avoid air ingress. If there is air ingress, release the air.
10. BOILER FEED PUMP FAILS TO START:
- Manual start, but the pump does not operate.
- Automatic start, but the pump stops after 5 seconds.
- Start-up, but the pump does not run or runs with unusual noises, causing circuit breaker tripping or thermal overload of the pump.
- Manual start but pump does not run due to the pump being in a high-water level warning state.
- Manual start but pump does not run due to the circuit breaker not supplying