The Bores cope Inspection Report of Gas Turbine

�? Inspection Time: 4^th Dec 2009

�? Inspection Place: *** Rental Power Plant, Bangladesh

�? Gas Turbine Model: France Alsthom PG6541

�? The State of Gas Turbine

Fuel: dual fuel system gas turbine, now natural gas burned

only

The unit was installed in Finland formerly and overhauled at 2008. After 2000 hours running, it was removed to *** Rental Power Plant, Bangladesh

Before the bores cope inspection, the history of the unit as follows:

That can be got according to above form:

1. Since overhauling, the unit runs 5881 hours totally before borescope inspection.

2. In *** Power Plant, Start-up is 79 times, Emergency trip is 19 times.

3. The running state after overhauling in Finland only was noted total running hours. But there is not any data about start-up and emergency trip.

�? Inspection Instrument

American Weilin Co. Ltd     Industrial Endoscope XLG3

�? The Item and Position of Inspection

Item A                                                                                         

1. Observe the first-stage nozzle trailing edge

2. Observe the first-stage bucket leading edge

3. Observation hole: K1、K2、K3、K4

Item B

1. Observe the first-stage bucket                                          

trailing edge

2. Observe the second-stage nozzle leading edge

3. Observation hole: K5

 

 

Item C

1. Observe the second-stage nozzle  trailing edge

2. Observe the second-stage bucket       leading edge

3. Observation hole: K6

Item D

1. Observe the second-stage bucket  trailing edge

2. Observe the third-stage nozzle leading

3. Observation hole: K7

Item E                                                                                    

1. Observe the third-stage nozzle trailing edge

2. Observe the third-stage bucket leading edge

3. Observation hole: K8

Item F                                                                                                      

1. Observe the compressor       seventh-stage blade

2. Observation hole: K9

Item G

1. Observe the third-stage bucket and nozzle

2. Observation point: exhaust diffuser

 

�? Inspection Result

1. The cracks are found on the inspected first-stage nozzle. Two of them are obvious. See photos 4, 5, 6, 7,140 and 141.

2. One crack is found on the inspected second-stage nozzle. See photo: 1, 51.

3. In the inspected first-stage buckets, several buckets have obvious defects and cracks, see photos 15,145 and 153. Some first-stage buckets have burning damage at some degree.

4.  Several cooling hole is distorted and burned in the inspected nozzle.

5. Some inspected nozzles and buckets have corrosion and sediment incrustation. The coating of them has abscission and damage at some degree.

6. There are several pits on the inspected compressor blades. The corrosion and sediment incrustation problems are serious.

7. We do not find any foreign body in the inspected flow path. Remark: the time on the photo is Beijing time   only some inspection photos are selected in the report.

 

�? Advice

Please pay more attention when the unit runs, for example:

The emergency trip ( or fast start ) makes the temperature of the components in the gas turbine hot path cooling rapidly ( or heating-up ). So among each part of every component in the hot path, the great temperature difference is occurred. In other Words, the temperature stress is occurred in a component’s interior. This stress of components interior is a reason that can create cracks and make the exist cracks extended. In the same sense, when the unit runs under a certain electric loading, if increase rapidly (or reduce) the unit’s electric loading, that also is a reason that can create cracks on the hot path components and make the exist cracks extended.

The advises are as follow:

1. The action of start-up, synchronization with the grid, increasing (reducing) the load and shutdown must follow the relative regulation; so that the thermal impact being suffering on hot components can be limited in the allowable range. And crack occurrence and extension can be controlled effectively. In order to safety operation, emergency trip must be prohibited.

2.  When the unit is running, the exhaust temperature, exhaust temperature dispersity  and wheel space temperature must be sure at the range of the standard value. If they are out the range of the standard value, engineers should analyze, find out the reason and solve the problem.

3. In the future bores cope inspection; the phenomenon that the crack of the first-stage bucket tip extends must be paid more attention.

4. According to the GE regulation, the natural (e) gas firednew model gas turbine should proceed to combustion inspection after running 12000 hours. However, some old kind model gas turbine like PG6541B should be checked after running 8000 hours. This gas turbine was overhauled at Finland before, the replacing of the combustion parts is not clear. But until now, it has run 5881 hours totally after overhauling. It should be proceed to combustion inspection as early as possible. And at the same time of combustion inspection, the follow item should be done:

4.1 Compressor IGV inspections. When the unit is under the quiescent condition, it is achievable to open the IGV to 84 degree.

4.2 Dismantle the parts used for oil-fired system, and block and seal the orifice of dismantled parts.

4.3 Solve the problem of the load gear box.

4.4 Research and discuss the gas turbine control mode. At present,  the  gas  turbine  is  simple-cycled (  is  not combine-cycled        ) operation,  but the  control  mode is  set

According to combined cycle operation (i.e. IGV control). So that under the low load, the temperature of hot path  components would be higher. We suggest that control mode should be changed from combined cycle to simple cycle

.4.5 Other item needs to be treated or modified on unit.

 �? Inspection Photo:

Item A Photo ( Hole K1-K4 )

NO.002 the first-stage bucket