Unexpected high vibration sgt 600gas turbine

Dear all

I face to strange behavior vibration of gas turbine.sgt 600 is double shaft gasturbie. Compressor turbine and power turbine. Compressor turbine consist two journal bearing .operational speed is about 10000 rpm for compressor turbine and 7500 rpm for power turbine. Alarm limit is 7 mm/s and the trip limit is 15 mm/s .we have just one accelerometer on the casing near the bearings for measuring and monitoring. overal vibration of both bearing of compressor turbin increase by the same about 6 mm/s and both phase of bearings around 9000 are stable so by increasing a little  rpm above 9000,for example 9100.fft of bearing number 1 have (1x,2x,3x)that have same amplitude all peaks near 5mm/s and bearing number 2 just have a 1x with 7 mm/s.by this condition machine were stable about 2 minute but suddenly vibration of bearing number 2 increase up to trip limit .my question is what cause of this behavior after 9000 rpm for bearing number 2?   

I need to mention that by checking the some part of compressor turbine by borescope  ,we find some partial touch at tip of impeller in last stage of compressor .

Pls share your idea 

Best regards

Original Post

Did you restart? How old is it? Have you stable brg. temp and pressure? Any other none normal happenings? Have you inspected mounting of the machine to the foundation? I have another AFAIK unsolved case same machine elsewhere where inspection gave the same result but it create a vibration of the same freq. on all bearings that seem to be unrelated to any speed or other so it would be likely a resonance that is excited from something but your machine seem to have a "better" vibration picture that with this limited info would point to some looseness somewhere due to some event. But it is no more than a guess, on the other hand the mountings of gasturbines that need to cope with thermal expansions are various and tricky things and if they misbehave it may give interesting problems. If you have SSS couplings somewhere they have created interesting problems to due to getting worn and having tiny springs spreading inside it too giving vibration trouble.

OLI posted:

Did you restart? How old is it? Have you stable brg. temp and pressure? Any other none normal happenings? Have you inspected mounting of the machine to the foundation? I have another AFAIK unsolved case same machine elsewhere where inspection gave the same result but it create a vibration of the same freq. on all bearings that seem to be unrelated to any speed or other so it would be likely a resonance that is excited from something but your machine seem to have a "better" vibration picture that with this limited info would point to some looseness somewhere due to some event. But it is no more than a guess, on the other hand the mountings of gasturbines that need to cope with thermal expansions are various and tricky things and if they misbehave it may give interesting problems. If you have SSS couplings somewhere they have created interesting problems to due to getting worn and having tiny springs spreading inside it too giving vibration trouble.

Thanks dear oli

Temp and pressure are stable.phase vibration is constant .we start more than 5 time at different days. sometime  we find the turbine 2 days in service with out increasing vibration. But after shutting down and starting at another day we face to unexpected behavior .

Thanks in advance    

OLI posted:

Did you restart? How old is it? Have you stable brg. temp and pressure? Any other none normal happenings? Have you inspected mounting of the machine to the foundation? I have another AFAIK unsolved case same machine elsewhere where inspection gave the same result but it create a vibration of the same freq. on all bearings that seem to be unrelated to any speed or other so it would be likely a resonance that is excited from something but your machine seem to have a "better" vibration picture that with this limited info would point to some looseness somewhere due to some event. But it is no more than a guess, on the other hand the mountings of gasturbines that need to cope with thermal expansions are various and tricky things and if they misbehave it may give interesting problems. If you have SSS couplings somewhere they have created interesting problems to due to getting worn and having tiny springs spreading inside it too giving vibration trouble.

The age of machine is 3 years 

So shutdown is normal part from where it trips? Would the vibration be high from start when having a bad start or when do it increase? How old is it? When was bearings checked last time? Can you take a look at the mounting of the machine so nothing misbehave?

OLI posted:

So shutdown is normal part from where it trips? Would the vibration be high from start when having a bad start or when do it increase? How old is it? When was bearings checked last time? Can you take a look at the mounting of the machine so nothing misbehave?

Yes, the shutdown is normal . At the starting vibration increase at bearing  of compressor  up to alarm limit but vibration of turbine is good. By passing the critical speeds ,vibration of bearing of compressor decrease but at this time beaing of turbine increase to alarm limit(7mm/s). After that by increasing  a little speed of power turbine ,suddenly vibration of bearing of turbine reach to 15mm/s(trip).

Age of machine is 3 years .bearing wasn't checked until now . 

Best regards

OLI posted:

Did you restart after the event? If so how was that? Has this only happened once? How much speed increase about was it for the PT?

Yes we start after event ,vibration some time increase earlier or later .

Compressor ideal speed is around 9600 rpm and the pt speed for that is 7300 rpm.

By increasing the pt speed to 7500 event will be occur 

Add Reply

×
×
×
×