.boiler tube failure .btf .rbt
Causes of boiler tube leakage:
- Erosion corrosion at tube inlet
- Excessive scale formation due to improper water treatment
- Overheating due to excessive soot buildup
- Flame impingement
- ‘Forcing’ of boilers
- Vibration due to slack bracing
Indications of excessive tube leakage
- Unable to maintain water level
- Unable to maintain steam pressure
- High feed water consumption
- Hotwell low level alarm
- Steam emission at funnel
- ‘Bursting’ noise
- Possibility of flame being extinguished if water gets into furnace
- When seen through furnace sight glass, furnace looks ‘misty’
Action
- Inform C/E
- If unable to maintain water level, stop firing and switch off burner control panel power supply
- Stop feed pump
- Change over to DO
- Close main steam stop valve
- Necessary to identify and plug leaking tube/s
Prevention
- Regular soot blowing and water washing
- Proper boiler water treatment
- Cold starting and firing procedure should be as per makers’ instruction
While it is recognized that plugging of 10%-15% of the total number of tubes within the tube nest generally reduces operational efficiency of the pressure plant, this level of plugging can be tolerated
Stresses acting on boiler
- Thermal stress
- Longitudinal stress
- Circumferential stress or hoop stress
How do you differentiate between white smoke and steam smoke seeing in the funnel smoke?
- Answer: if it is white smoke, it will leave trail means it will travel some distance before disappear where the steam will not leave any trail it will disappear very quickly.
When and How would you carry out a hydrostatic pressure test on a boiler?
.boiler pressure test .bpt .blr pressure test
Hydrostatic pressure test is usually carried out when:
- When there is a major tube replacement
- When repairs/partial replacement is done to the boiler pressure part like partial repairs to the shell
- Surveyor may decide whether or not the pressure test should be done.
Procedure for test
- All welding must be done by graded welders acceptable to Class
- Ensure all mountings are in place and shut
- The safety valves’ mounting is blanked off
- The gauge glasses are removed or isolated by shutting the steam & water cocks
- The air vent valve is opened and water can be filled manually by the feed pump until water flows out from the air vent.
- Shut air vent valve
- Fix pressure pump and connection at the top usually at safety valve mounting
- Press up to 1.5 times the max. allowable working pressure
- Surveyor usually wants pressure to hold steady for at least 30 minutes and look for signs of leakage
Why can’t we use diesel engine exhaust gas for inert gas production?
Answer: As now a days most of the engines are super charged and in supercharged engine the amount of oxygen in exhaust gas is almost 17% but in inert gas system the oxygen content must be below 8% that is why main engine exhaust gas cannot be used.
Boiler Materials
- Shell – all-welded construction – seamless steel
- Tubes – ERW seamless steel (Electric Resistance Welded (ERW)