In many power stations which are using coal as fuel, boiler tube leakages are common factor for forced outage of the Unit. In states already reeling under power shortages/load shedding such outages add to further load reduction. Common man is sufferer in spite of paying the huge electric bill. Major reasons contributing for boiler tube leakages are :
1. Erosion due to ash
2. Furnace temperature maintaining high
3. Low boiler drum level causing starvation.
4. Stuck up wall soot blower/deslagger
5. Hydrogen embrittlement
6. Air erosion due to air ingress from furnace insulation, inspection door opening
7. Low Ph of feed water causing acidic erosion from inside the water wall tubes.
8. Over heating due to delayed combustion of coal particles due e to higher particle size.
Boiler Maintenance Engineers are always looking for permanent solution to this problem as an outage due to tube failure requires Unit shut down for a period of 12 to 24 hours depending on location of tube failure, temperature in that zone, secondary tube leakages etc.
The usual remedies are periodic inspection, charting/mapping previous failures, shielding tubes by cassettes, wear resistant coating/welding, hydro pressure testing, Coal burner geometry, land flow test (cooling rate test for determining blockages in tubes), Observing hot spots during boiler running are some of the measures.