4 x 210 MW : CSTPS : CHANDRAPUR EVENT ANALYSIS REPORT UNIT NO. 1

1. Event No. – 1 Time – 12:22 hrs. Date – 06.03.2008

2. Operating conditions at the time of Event :

Load Coal Cycles in service Oil Support

60 MW C 5 Guns

3. Nature of Event : Unit was withdrawn for Both ID Fans blade repairing & balancing work as both were having heavy vibration.

4. Observations :

As a preventive check Hydraulic test was carried out on date 07/03/08 at 5:00 hrs.Pin hole observed at tube no.-196 of rear Water Wall at rear arch.

After attending W/W tube leakage next Hydraulic test at 135 KG/CM2 was Carried out on date 10/03/08 at 10:15 Hrs & Boiler light up at 12:00 hrs.

Turbine Rolling started at 18:45 hrs and when turbine speed reached to 2400 rpm at 19:10 hrs, MS-1 Bypass (MS-3 valve) line bend puncture observed.

5. Analysis –

ID Fan A&B Vibrations increased. ID-1A Impeller found eroded severely, out of 24 blades 16 found punctured. ID-1B Impeller found eroded severely

Boiler tube leakage at rear water wall at rear arch. Primary failure Tube no. 196 on rear arch found pin hole.(T12 from RHS). Cause of failure- rear W/W panels got overheated and the external surface of the tubes facing the firing got oxidized.

MS-1 Bypass line bend punctured due to errosion.

6. Works carried out by maintenance section –

B/M: 1) Both ID Fan –A & B Weld repaired, cleaning, hard facing and balancing carried out. 2) Tube no. 195 & 196 of rear Water Wall at rear arch cut & new spool piece of

1500mm length introduced & welded. Total no of joints-six

T/M: 1) Punctured bend of MS-3 is replaced. 2) Thickness measurement of other three bends on the bypass line was carried out.

7. Works carried out for the restoration by operation :

Boiler lighted up Time - 21:30 hrs. Date – 11.03.2008

T-A Set Synchronised Time - 06:46 hrs. Date – 12.03.2008

8. Recommendations to avoid reoccurrence : a) Short term –

The failed W/W tube was further cut in length till the clean surface without any internal scaling observed .Tube no. 195 was cut & inspected, no scaling seen on internal surface.

b) Long term –

ID A&B: 1) Replacement of impeller is to be done in O/H. The procurement action for two impeller has been initiated. 2) Provision of Guillotine Gate: - The abnormal erosion and unbalance is due to running of ID fans with heavy stack emission .A proposal against R&M scheme has been send to HO for supply and erecting of Guillotine Gates. After making the provision of Guillotine Gates, the outage on one ID and half side of ESP can be taken. 3) The Existing impeller is having hollow blades. These are to be replaced by solid blades impeller.Water Wall: 1) Scanning of all tubes in rear water wall will be done to know exact condition of tubes. 2) Replacement of water wall panels is already included in station R&M plan.

9. Remarks – Nil

General Manager-I