7/31/2019 Commissioning Experience and Learning

1/15

COMMISSIONINGEXPERIENCE AND

LEARNING

NTPC VINDHYACHAL STG-III

(2X500MW)

7/31/2019 Commissioning Experience and Learning

2/15

PAPER PREPARED BY

S.S SEN DGM (COMMSG)

S.K ROY SR SUPDT. (COMMSG)

SATYA NARAYAN ENGR. MD. AKHTAR ENGR.

7/31/2019 Commissioning Experience and Learning

3/15

INFERIOR QUALITY OF TEMPORARY PIPING BEINGUSED DURING CHEMICAL CLEANING/STEAM

BLOWING ACTIVITIES.

All temporary piping should be identified with tag nos,similar to other pr. parts with separate PGMA, DU etc.

Proper drawing with quality plan support detailsdrains vents and location of isolating valve should beclearly mentioned.

Temporary piping drawings should be duly approvedby corporate engg. And CQA.

The hydro test/NDT requirements should be clearlymentioned in the drawings.

The first isolating valve must be located nearest to thejunction with permanent system.

7/31/2019 Commissioning Experience and Learning

4/15

INADEQUATE CAPACITY OF SUCTION LINES OF ACIDINJECTION PUMPS USED DURING CHEMICAL

CLEANING PROCESS. As per scheme three acid injection pumps (3X50%) were

designed to take suction from a common header having 80Nb dia. and discharging into a common header having thethe same dia.

During mock trial it was observed that while running twopumps at a time one pump was getting starved,Consequently pump was getting hot and its gland wasgetting damaged with in few minutes.

One additional suction line was drawn directly from mixingtank and acid storage tanks and thus problem of pumpstarvation was solved.

7/31/2019 Commissioning Experience and Learning

5/15

Insufficient gap between RH coil bottom and

rear arch tubein unit #9

As per drawing clearance between RH coils bottom and reararch is 350mm.But on measurement the value of clearance insome of the coils was in the range of 250mm approximately.

Later BHEL revised the minimum clearance as 285mm.Revision

was accepted by the site and modification was carried out. To obtain minimum 285mm clearance gap between the tubes of

coil at the bottom was reduced to 15mm, Which is as perdrawing.

In this exercise 2 to 7 loops of different panels were shortened

and available clearance between the tubes is shifted toclearance between coil bottom and arch.

Out of 74 ,51 coils were modified and 186 circuit loopsshortened involving 372 butt joints.

7/31/2019 Commissioning Experience and Learning

6/15

7/31/2019 Commissioning Experience and Learning

7/15

PROBLEM OF OFFSET ANDORIENTATION IN NMEJ OF UNIT#9

It was observed that offset of NMEJ was in reverse direction ataround 6 no. of locations e. g wind box (L&R), ECO outlet(L&R), hot SA duct (L&R).

Later on all the above NMEJ were attended in situ.

7/31/2019 Commissioning Experience and Learning

8/15

PROBLEM OF PA FAN BLADE PITCHGETTING FULLY CLOSED IF FEEDBACK

BECOMES BAD

As per logic implemented PA fan blade pitch gets fully closed iffeedback gets disturbed due to any reason. It has been decidedto modify this logic and the blade pitch in this situation willremain stay put.

7/31/2019 Commissioning Experience and Learning

9/15

COAL MILL FINENESS POOR IN (+50)

It was observed that coal mill fineness was poor in chemicalanalysis. later on spring compression was set at 10.5 tonnesagainst 8.5 tonnes and classifier setting was changed from 4 to6 on its scale.

7/31/2019 Commissioning Experience and Learning

10/15

PROBLEM OF VALVES PASSING LIKE

CBD,EBD,IBD, SH &RH SPRAY

It was observed that these valves are passing heavily after fewmonths of operation, on inspection it was found that their seatswere in badly damaged condition.

Later on these valves were attended for passing by lapping.

7/31/2019 Commissioning Experience and Learning

11/15

HIGH VIBRATION (AXIAL &RADIAL) INPA FAN-9A

PA Fan-9A fan DE brg. was having high axial andradial vibration of the order of 8-9 mm/sec. Duringrecent overhaul its rotor assembly was dismantledand it was observed that there was loose rust

(around 500 grams) inside the rotor assembly. Afterremoval of loose rust the fan brg. vibration camedown to normal level (2-3 mm/sec).

It is suspected that due to improper storage of thefan rotor during erection stage, there was ingress of

moisture inside the rotor causing formation of rust.These loose rust particles were creating unbalanceduring frequency change.

7/31/2019 Commissioning Experience and Learning

12/15

PROBLEM OF HIGH METAL TEMP OF RHOUTLET COILS

It has been observed that few no of RH outlet coils e. gcoil no 66&70. are maintaining high metal temp of theorder of 580-590 deg C.

Total 71 nos. of TCs are provided.55 nos. outside thegas path, 06 nos. at the outlet front header,06 nos. at theoutlet rear header

Assembly no. 18,38 and 58 have 11TCs full depthmeasurement. As per experience of unit no.-9,.Assemblyno. 66&70 are experiencing higher metal temp. thanassembly no. 38 and 58.in which full depth TCs areinstalled. Hence thermocouples from assembly no. 58

be shifted to assembly no. 56 and thermocouples fromassembly no.-38 be shifted to assembly no.

Also additional thermocouples should be installed.

7/31/2019 Commissioning Experience and Learning

13/15

EXPERIENCES AND FEEDBACKS

No provision of approach/platform for valves/dampers of airand FG circuits of APHs. ( especially FD and DDs of APH).

No clearance of boiler pressure parts insulation beforecompletion of fin welding.

HFO/LDO lines to be air and steam charged before oilcharging & hot tightening of all flanged section bolts.

Location of boiler side cable trays beneath the HFO/LDOstation.The boiler area main cable route to be shifted in LHSof boiler to avoid fire hazard due to HFO/LDO lkg.

Proper checking of blade pitch mechanism locking duringcommissioning stage itself.

7/31/2019 Commissioning Experience and Learning

14/15

Provision of SS lines in mill lub oil return in place of MS line-lub oil supply lines for upper and lower radial bearing are ofSS make but the return line and excess discharge line are ofMS make lub oil picks up mechanical impurities during thereturn cycle and welding& fit up, acid pickling , and lub oilflushing of these lines takes lot of time. the cycle time of theabove activities can be reduced by using the SS lines.

Acoustic steam leak detector to be installed in boiler forquick identification of BTL.

Flame monitoring camera yet not cleared from corporateengg.

Provision of ladders inside the wind box for checking ofSADs.

The very first requirement of commissioning e. g platformproper approach, boiler lift and area lighting gets satisfied atthe tag end of commissioning.

7/31/2019 Commissioning Experience and Learning

15/15

NEED TO REVIEW TWO STAGEHYDRO TEST (DRAINABLE/

NON DRAINABLE) OF BOILER.

After completion of stage-I hydro test ofboiler a lot of cutting & welding is done forcompletion of balance work on pressure

parts.