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