Just started a new career in a coal station as assistant and looking to know the tell tale signs of a boiler tube leak

 

well , the leak detection can vary depending on the type of boiler design and the area of the leak , i have worked in membrane tube boilers and one primitive mud drum boiler. I will share my experiences here for the same.

1. Economiser tube leak - this is the most common type of leak as it is at the fag end of the flue gas path and is prone to cold end corrosion caused by sulphur deposits. economizer tube leak can be deduced by

a. difference in the steam and the water flow in the boiler. ie during a tube leak given that the level controller in the boiler is working well and maintaining a steady level in the drum. the water flow into the boiler will be higher than the steam flow. the difference in the water/steam flow will depend on the extent of the leak.

b. there will be a reduction in the temperature in the economizer zone and in all subsequent zones as the boiler cannot get sufficient heat gain due to the leak.

c. Due to the presence of the economizer near to the stack the stack temperature also falls down.

2. Evaporator and downcomer leak - in membrane wall designs the downcomer is outside the boiler flue gas zone. the chances of leak is very minimal and can be seen visually when it is developed. Minor leaks in the downcomer cannot be detected. as for the evaporator tubes, thermal shock and material failure due to aging or misplaced material is the common mode of failure. the leak here is also detected by the mismatch in the steam/water flow in the boiler. for a mud drum boiler with downcomer inside the flue gas zone this equation is used:

2P - M > 0 . where P is the P alkalinity and M the M alkalinity in the drum sample. if this reaches zero or below this value then it is a case of downcomer or evaporator leak in a mud drum design boiler.

3. superheater coil leak - prone to materiel failure due to thermal shock and due to aging. by design all boiler and furnace tubes are designed for 100000 hours of operation. however due to the nature of operating or due to the design flaw the superheater coil may fail. small leaks in the superheater are near impossible to detect. The steam / water ratio is again a indicator of the leak. the temperature is not a indicator in this case. i have also seen inspection people detect leak using acoustic methods. however i do not have idea of how it works.

so based on the plant DCS operation parameters this is how you can detect a boiler tube leak .

 

The simple way to find out leak is to analyze the condenser make up. If you make a trend of condenser make up data you will find when the leak is occurred following a increment of make up water.

If a Economiser tube leak is occurred the make up water consumption increases slowly due to low pressure at economiser side. It also decrease the flue gas temperature at stack outlet.

If a Evaporator tube leak is occurr ed you will experience a fluctuation of boiler water chemistry.

If a superheater tube leak is occurred it will detected by the reduction of the production of steam turbine. Analyze water/steam ratio will be more helpful to find a tube leak.

 

well , the leak detection can vary depending on the type of boiler design and the area of the leak , i have worked in membrane tube boilers and one primitive mud drum boiler. I will share my experiences here for the same.

1. Economiser tube leak - this is the most common type of leak as it is at the fag end of the flue gas path and is prone to cold end corrosion caused by sulphur deposits. economizer tube leak can be deduced by

a. difference in the steam and the water flow in the boiler. ie during a tube leak given that the level controller in the boiler is working well and maintaining a steady level in the drum. the water flow into the boiler will be higher than the steam flow. the difference in the water/steam flow will depend on the extent of the leak.

b. there will be a reduction in the temperature in the economizer zone and in all subsequent zones as the boiler cannot get sufficient heat gain due to the leak.

c. Due to the presence of the economizer near to the stack the stack temperature also falls down.

2. Evaporator and downcomer leak - in membrane wall designs the downcomer is outside the boiler flue gas zone. the chances of leak is very minimal and can be seen visually when it is developed. Minor leaks in the downcomer cannot be detected. as for the evaporator tubes, thermal shock and material failure due to aging or misplaced material is the common mode of failure. the leak here is also detected by the mismatch in the steam/water flow in the boiler. for a mud drum boiler with downcomer inside the flue gas zone this equation is used:

2P - M > 0 . where P is the P alkalinity and M the M alkalinity in the drum sample. if this reaches zero or below this value then it is a case of downcomer or evaporator leak in a mud drum design boiler.

3. superheater coil leak - prone to materiel failure due to thermal shock and due to aging. by design all boiler and furnace tubes are designed for 100000 hours of operation. however due to the nature of operating or due to the design flaw the superheater coil may fail. small leaks in the superheater are near impossible to detect. The steam / water ratio is again a indicator of the leak. the temperature is not a indicator in this case. i have also seen inspection people detect leak using acoustic methods. however i do not have idea of how it works.

so based on the plant DCS operation parameters this is how you can detect a boiler tube leak .

These are very good discussions. When water walls tube leak occurs in drum type boiler, what happens to drum pressure?