HTC steam turbine front radial bearing high temperature issue

Transcription

1 HTC steam turbine front radial bearing high temperature issue HTC steam turbine type : T7635 condensation Turbine parameter: Rated RPM:6042, Rated power:32000kw. Design steam pressure : 8.935Mpa Design steam temprature:510c. Design flow rate:32.4kg/s The turbine is used to drive two compressors (Front end: BAC, Back end : MAC.) All the couplings between machines are disk type. Whole compressor train is design by Siemens

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4 Turbine running History: On 7/8 we did solo test for the turbine, At that time, vibration and temp is good Turbine running History: Also in the past two months we started up compressor train for pipe blowing and cold box cold test. During the period the turbine running status always is kept at the good status. But on date 10/22 8:50 we met the turbine first trip that is caused by high vibration at

5 radial bearing of turbine back end. (vibration suddenly goes up to trip value 75um), After checking running data and instrument we did not find any abnormalities on operating and turbine (the only small operating difference comparing with past operating parameter is that BAC load is more than before). We tried to start up turbine again for looking for some clues. In the initial three hours of turbine running we did not find any abnormalities on the turbine bearing vibration and temp. When operator started loading BAC for cold box cool down The temperature of radial bearing at the turbine front end started going up. And quickly rise to trip value. The turbine again trip due to high temp at the front radial bearing. Observation (turbine disassembly): 1. The front radial bearing of turbine is damaged. 2. The rear radial bearing and thrust bearing is good. 3. The other mounting data is same as before. Action : 1. Clean the shaft journal with fine sand paper. 2. Replace the damaged bearing with new. Then check the contact between new bearing and shaft journal. Found the contact also is not good, same as damaged bearing wearing shape. 3. Adjust the front bearing housing to make the contact between bearing and shaft journal is good. More than 80 percent. 4. At same time check the turbine rotor and casing alignment. After adjustment the data is with HTC tolerance. 5. Check the leveling (put water level on the shaft journal, back end :0.03mm/m toward MAC, front end : 0.025mm/m toward BAC.

6 6. Check the alignment at the turbine both ends, Also it is within the Siemens alignment tolerance. 7. Put back everything for turbine start up preparation. Running observation After this repair : At this time when turbine speed up to 5800 RPM, The front bearing temp started going up from around 74C, And after incasing to 85C at certain rate, suddenly went up to trip value. From situation it is worse than before. Observation during turbine disassembly : It is same as before. The front radial bearing is damaged and the wearing shape is same as before, uneven wearing. Inadditional information: during this time running we found the gas seal of turbine front end has serious gas leaking. ( Before, I saw there is some gas leakage existing on the front gas seal.)

7 Action: 1. Replace front radial bearing with new, And check the contact, it is good, Same as situation during last time repair. In other words, the contact is good as machine is cold. But it is changed as machine is hot. 2. Lift up the back end of turbine, make the back end of turbine is higher 0.24mm than the front end of turbine. Two purposes: 1). due to normal running status the front end height expansion is higher than back end. Attached is Siemens alignment data, Thereinto it also included this instruction. 2). Make reverse contact to insure it can has good contact during normal running (this is gotten based on current bearing damaged situation). 3. Increase the clearance of bearing leading side and trailing side. To further increase oil flow. 4. Check leveling. (put the water level on the shaft journal of turbine both ends, the back side :0.10mm/m towards MAC, the front side : 0.10mm/m also towards MAC. 5. To re-align the turbine both ends within Siemens tolerance. 6. For gas seal leakage issue, It will take long time to fix it (need to lift up top casing ), So customer hope it can deal with it in the future, At present HTC also gave out a temp method for this. 7. Measure vibration spectrum. ( this time not carry out )

8 Observation: The high temp again happened, still same as before. -Next plan to this issue from HTC 1. Take off the top casing of turbine to check internal parts for ok. 2. At same time fix the gas seal leakage issue. 3. Disassemble the front bearing housing for check. To re-polish the sliding surface on the bearing house and guide block. And reassemble it and assure every bolt on the bearing housing is tighten per HTC request. 4. Check coupling guard if there is any abnormalities that block the bearing housing expanding during turbine running. If necessary increase the clearance between guard and mounting plate on the bearing housing 5. Further polish the shaft journal with sand paper on site. 6. Use the bearing without bottom jacking oil hole. Other plan: 1. Measure the vibration spectrum at the next time. 2. Re-do alignment for steam turbine both ends, And make the alignment close to Siemens best request. 3. Siemens also need to re-calculate whole compressor train alignment request. Siemens also help on this troubleshooting. Observation during repairing: 1. the gas seal is good, The only problem is that some debris blocked the water drain hole on the gas seal.

9 2. On the front bearing housing found some nick on the bearing housing sliding surface and a bolt used to fix the support of bearing housing has a little loose re-polish the surface and re-tighten all the bolts during the bearing house adjustment. 3. Found there is a imprint respectively on the coupling guard and mounting plate. Seems the guard is blocking the bearing housing expansion during turbine running. 4. The front bearing wearing status is not same as before. Should be better than before. 5. Nothing abnormal found during bearing pedestal and gear box dismantling. However, one month ago, we already have resolved this problems. At present the machine is running normally. It seems the main issue was caused by coupling guards blocking the bearing house expansion during loading BAC side of turbine and a loose bolt on the guide support of bearing house.