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10/30/06 E:/wkg_fdr/ppt/slide_prsnt1.ppt
ECONOMISER TUBE LEAK ECONOMISER TUBE LEAK
IN BOILER # 6IN BOILER # 6DATE - 26.09.05DATE - 26.09.05
Sl. No. Section Date and Time
of IncidentDate and time of normalise Shift Shift
InchargeOperator Incharge
Equipment Description
Sub-equipment
detail
Brief Incident Description
1 PH3 26.09.05, 12:35 Hrs
29.09.0505:20 Hrs
A A. Seal Jitu Ram Boiler#6 EconomiserBoiler 6
Economiser tube leakage
Incident Detail
Failure Location Detail
1st coil of middle bank (ESP side), 15th row from top had
developed a 1.5 mm dia. pin hole.
This was between 2nd and 3rd column (from Boiler-5
side) of Economiser , behind a cross beam.
TUBE LEAKAGE AREA
Economiser of Boiler #6
Leakage area
ESP
Back
Economiser’s Middle Bank Tubes
Pin Hole
Back
Function of Economiser
To preheat the feed water of Boiler.
Water is supplied at the inlet manifold of Economiser, which
after passing through the tubes, goes into the Economiser
outlet manifold.In the process water picks up heat from the
flue gas.Hot water then goes into the steam drum.
Line Diagram
FRONT SHAFT REAR SHAFTSTOKER
LOWER
DRUM
UPPERDRUM
B. B. TUBES
DOWN COMER
CHECKVALVE
M
FEED WATER CONTROL STATION
EconomiserPry. Sup. Sec. Sup.
Gen. Tube
Attemperator
Spray waterSup. Steam to TG
Feed Water
Flue Gas
I.D.Fan Stack
Boiler
OBSERVATIONS
Thickness gauging was also carried out at bottom, top and middle levels of economiser tubes during RLA study by M/S TBW. There was no abnormal thinning.
Tube thickness measured & found o.k (original thickness 3.66 mm) near the failed tube area.
No thinning on straight portion of the tube.Thinning <1 mm for bend portion.
Tubes thinning
No abnormal deviation found
Inlet water temp. 1130C Outlet water temp. 2100CInlet feed water press. 68 Kg/Cm2
Inlet feed water flow 69 Tons/hr.Inlet flue gas temp. 4060C Outlet flue gas temp. 1780C
Inlet water temp. 1150C Outlet water temp. 2540CInlet feed water press. <81 Kg/Cm2
Inlet feed water flow 68 Tons/hr.Inlet flue gas temp. 4250C Outlet flue gas temp. 1770C
Deviation from operating parameter
Remarks / Action TakenObservationNormal ConditionProbable
Causes
OBSERVATIONS
- No corrosion / pitting was observed when tested during RLA study (03/09/05 to 08/09/05) done by M/S TBW, Pune. Since then there is no change in water quality. Corrosion inside is ruled out.- No action
Could not be seen inside.No corrosion on surface.Corrosion internal
- No corrosion / pitting was also observed when tested during RLA study (03/09/05 to 08/09/05) done by M/S TBW, Pune. - No action
- No corrosion No corrosion on surfaceCorrosion external
Remarks / Action TakenObservationNormal ConditionProbable
Causes
OBSERVATIONS
Less spacing between skin plate and the tube caused localised high flue gas velocity lead to corrosion.Baffle to be provided
Tube pitch – found ok.Spacing between skin plate and tube – approx 40 mm
Tube pitch – 75 mm Spacing between skin plate and tube – 60 mm (Considering no change in boiler parameter)
Localised high flue gas velocity
No action
- Not checked.- During RLA study it was found that tubes are of specified grade and of normal micro structure
Tubes grade – BS3059 1978 PT-2 S2 440 Cat.-2Micro structure – Normal
Tube’s poor Metallurgical state
Check for localised high flue gas velocity. (considering there is no change in fuel quality)
External flue gas erosion marks were present on the leaking tube and four other tubes nearby.
No erosion on surfaceTube’s erosion
Remarks / Action TakenObservationNormal ConditionProbable
Causes
Thickness Measurement
Pin Hole
Back
Errosion Marks on tube
Pin Hole
Severe Erosion marks
Back
Root Cause
Erosion of tubes by localised high flue gas velocity.
The gap between Economiser’s skin plate and the failed
tube area was relatively less causing relatively high flue gas
velocity in that zone.
Corrective Action
The pin hole was rectified by metal buildup by high
pressure welder.
The other eroded portion of the tubes (4 nos.) were also
rectified by metal buildup by high pressure welder.
Hydraulic test was done and found no leakage from the
Economiser tubes.
Rectified area
Back
Corrective Action
Preventive Action
To prevent high speed flue gas to escape in between the skin plate and
outer most tube surface, baffle plates were provided on the top of each bank so
that chances of erosion in the outer most tube will get reduce.
Similar baffle plates will be provided in other Economiser during its
shutdown.
Mapping is done for all the failed Economiser tubes.
All the failed tubes and the tube portions which having less thickness than
the desired, will be rectified during Boiler Gas Conversion.
Monitor thickness of bend and straight portion of the tube annually.
* In these case too, the fact remains that many areas of Economiser coils are not
approachable for testing as well as these area are prone to errosion.
Preventive Action
Back
Baffle plateSkin plate
High velocity area