Boiler Tube Leak

Leaks in boilers, piping and feed water heaters are major contributors to power plant unavailability and performance losses. In their early stage, leaks are often undetected because they are inaudible and/or concealed by insulation.



1. Noisy at boiler area.
Operators should be identified the steam noisy are coming from de-aerator vents, soot blow activity or from boiler tube leak. It needs long term experience.
Others way, direct measurement of background noise is needed to determine the spectral characteristic. Using background noise and leak characteristic data, full scale test have been run to optimize sensor listening distance.

2. Condenser make-up consumption.
Causes de-aerator vents, soot blow activity and opening continuous blow down propose for getting good steam quality, normally consumption of condenser make up is below 35 T/h. If got boiler tube leak, condenser make-up can reach 60 T/h.

3. SSCC Sump.
Whenever got boiler tube leak at wall tube and secondary superheater (furnace area), submerged scraper chain conveyor (SSCC) sump is rapid full and The SSCC sump pump gets cut in frequently. But if the leak at back pass area is difficult to identified.


4. Furnace pressure.


Furnace pressure is tending to positive pressure whenever got tube leak. ID Fan inlet guide vane (IGV) get open widely. Let’s make different of opening IGV causes low performance of air heater leakage control system (LCS), high air heater differential pressure (DP) of boiler got tube leak.

So I collected data at full load and focus on ID Fan performance at the unit 10 which has low performance of air heater LCS and DP and unit 20 which has high performance of air heater LCS and DP.

Unit 30 / Unit 40

a. Total FD Fan Discharge Flow T/h 2397 2353
b. Secondary Air flow T/h 1777.4 1788.4
c. Primary Air Flow T/h 506.3 488.4
d. Total Air (b+c) T/h 2282.5 2277.4
e. Air Heater leakage (a-d) T/h 619.6 564.6

f. Heating Value of Coal kJ/kg 21637 23338
g. Coal Consumption T/h 294.8 267
h. Gas CO content ppm 121 14.5
i. Gas O2 content % 2.9 2.4

j. Air heater DP cmHq 16 11
k. Gas oulet to air heater mbar -10 -10
l. Gas outlet ID Fan mbar 19.1 18.6

m. FD Fan Blade % 85.8 77.7
n. PA Fan IGV % 57.5 38.5
o. ID Fan IGV % 97.1 78.3

Analysis only at unit 10
Furnace pressure -1.5 mbar
Boiler pressure area back pass -8 mbar
Inlet temperature ID fan 124C = 397K
Specific gravity of mercury SG Hg = 13.6
Molecular weigh of water =18.02 kg/kmol
Universal gas constant 8314 J/kmol.K

Density of air inlet ID Fan at temperature 124C = 0.876 kg/m^3
It is can calculated from ideal gas equation by assumed inlet pressure of ID Fan.

Inlet Pressure ID Fan
Boiler pressure area back pass + DP of Air Heater
-8 mbar – (SG Hg x air density x h)
-8 mbar – 13.6 x 0.876 kg/m^3 x 16 cm x m/100cm x Ns^2/kg.m
-8 10^-2 N/m^2 – 18.68 N/m^2
-818.68 N/m^2
Absolute pressure = 101325 – 818.68 = 100506N/m^2
Rise pressure = -818.68 N/m^2 + 19.1mbar = 2.72 kPa


Air flow through ID Fan
FD Fan flow + PA Fan flow
(2397 + 506) T/h x 1000kg/T x h/3600s
806.38 kg/s (2 x ID Fan)

Density of Water
P x v = R/M x T
v = (8314J/kmol.K x 397K)/(18.02kg/kmol.K x 100506N/m^2)
v = 1.822 m^3/kg
Density = 0.548 kg/m^3

Normal condenser make consumption = 35 T/h = 17.74 m^3/s
Condenser make up consumption if got tube leak = 60 T/h = 30.41 m^3/s

Air Flow = 806.38 kg/s x 0.876 kg/m^3 = 460.26 m^3/s

Air + (steam form soot blower) = 460.26m^3/s + 17.74 m^3/s = 472 m^3/s
ID Fan inlet vane will increase 2% (from ID Fan curve)

Air + (steam form soot blower & tube leak) = 460.26 m^3/s + 30.41 m^3/s = 490 m^3/s
ID Fan inlet vane will increase 5% (from ID Fan curve)

More information about Re-heater protection, click below this....
http://idpowerstation.blogspot.com/2009/06/re-heater-protection.html