Dears,

We have experienced dramatic change of vibration over GT24 "SGT600"  where bearing 3, 4.

We have stopped the unit and start it again and vibration trend still high, specially bearing 3.

We also carried out NDT test on PT coupling shaft but found no trails for cracks!

The high vibration parts are shown in following schematic:

 

GT24

 

the attached files contains all the required data.

any suggestions about this?? it will be appreciated 

 

Attachments

Original Post
chitrang.nanavati posted:

Hi Hisham,

Can you provide the spectrum of bearing 3 ? At what frequency vibrations are coming

What is the history of this bearing, can you trend the vibration over 4 months ?

Dear chitrang.nanavati,

           Thank you for your reply & sorry for the delay, I have attached the spectrum trends for for Bearings 3 & 4.

thank you again. 

Attachments

The report by Siemens offers a hypothesis that the vibration changes with load and torque. They recommended an inspection of the shaft couplings. You have already done an external visual inspection that did not reveal anything significant with the disk packs. The vibration phase angle data does not change that much with changing load, indicating that the apparent unbalance phase angle remains the same while unbalance increases. The spool piece part of the coupling would have to be shifting relative to the shaft-mounted coupling hub. I would guess that the only way that this hypothesis can be proven is to completely disassemble both of the disk packs and inspect for wear and cracks on the discs and bolts. These components should probably be replaced and the coupling rebalanced.

I suggest you also measure gear case vibrations with the maximum frequency of 2 to 3 times tooth mesh frequency. This measurement could indicate how your vibrations are affected by load and to what extent the tooth mesh vibrations are modulated by turbine speed.

Another hypothesis that may or may not be relevant is that the turbine rotor changes shape due to axial thrust, and the shape change causes unbalance. Some gas turbine rotors are susceptible to shape changes while reaching normal operating temperature and load.

What type of bearings are used, and have you made any measurements to assess their condition?

Walt

Walt Strong posted:

The report by Siemens offers a hypothesis that the vibration changes with load and torque. They recommended an inspection of the shaft couplings. You have already done an external visual inspection that did not reveal anything significant with the disk packs. The vibration phase angle data does not change that much with changing load, indicating that the apparent unbalance phase angle remains the same while unbalance increases. The spool piece part of the coupling would have to be shifting relative to the shaft-mounted coupling hub. I would guess that the only way that this hypothesis can be proven is to completely disassemble both of the disk packs and inspect for wear and cracks on the discs and bolts. These components should probably be replaced and the coupling rebalanced.

I suggest you also measure gear case vibrations with the maximum frequency of 2 to 3 times tooth mesh frequency. This measurement could indicate how your vibrations are affected by load and to what extent the tooth mesh vibrations are modulated by turbine speed.

Another hypothesis that may or may not be relevant is that the turbine rotor changes shape due to axial thrust, and the shape change causes unbalance. Some gas turbine rotors are susceptible to shape changes while reaching normal operating temperature and load.

What type of bearings are used, and have you made any measurements to assess their condition?

Walt

Dear Walt,

thank you for your reply, I have contacted the Mechanical department for your inquiries. They have already visually inspected the gearbox, nothing have been found, also the vibration on the gearbox seems quite normal over the loading scale.    

 

Regarding the bearings: they haven't conducted any test except lowering the Lub oil supply pressure from 200 kpa to 170 kpa which showed no effect on bearings 3 & 4 vibrations.

Beaering types:

           Bearing 3 : Journal

            Bearing 4: combined thrust & Journal as shown belowPTUntitled

Attachments

Photos (2)

Dear Hisham4ever ;

I’m not familiar with Siemens GT, I’m more GE HDGT (General Electric Heavy Duty Gas Turbine)…

What’s happened on June 2014? What did you find after the feeder trip? And what was the relation between the FEEDER TRIP and the high vibration on #3 and #4 bearings??

On HDGT when TRIP occurs, automatically the auxiliary lube oil pump starts time to cooldown the machine rotors and theirs bearings. If , for any raison like electrical power cut, the auxiliary pump doesn’t work, the emergency lube oil pump will start to cooldown the rotor and bearings. But if (for any raison) the cooldown process wasn’t correctly performed damages may happen on bearings also rotor bow may happen?!!!..

If on June 2014, the cool-down process wasn’t correctly forwarded, the bearings will be stressed and overheated and this could lead to a partial Babbit melting (bearing white metal) consequently high vibrations will appear!

What about your generator?

Usually 4 poles generators are driven by gas turbines that means their speed is about 1500 or 1800 rpm depending if you are using 50 or 60 Hertz Frequency.

HDGT Rotor exhibits the first RESONANCE between 1100 and 1600 rpm. So if your generator is experiencing any problem leading to a small abnormal level of vibration it will be amplified at the Power Turbine side because it matches with its 1st balance resonance.

Hope this is heplpful

Regards

Karim

Walt Strong posted:

The report by Siemens offers a hypothesis that the vibration changes with load and torque. They recommended an inspection of the shaft couplings. You have already done an external visual inspection that did not reveal anything significant with the disk packs. The vibration phase angle data does not change that much with changing load, indicating that the apparent unbalance phase angle remains the same while unbalance increases. The spool piece part of the coupling would have to be shifting relative to the shaft-mounted coupling hub. I would guess that the only way that this hypothesis can be proven is to completely disassemble both of the disk packs and inspect for wear and cracks on the discs and bolts. These components should probably be replaced and the coupling rebalanced.

I suggest you also measure gear case vibrations with the maximum frequency of 2 to 3 times tooth mesh frequency. This measurement could indicate how your vibrations are affected by load and to what extent the tooth mesh vibrations are modulated by turbine speed.

Another hypothesis that may or may not be relevant is that the turbine rotor changes shape due to axial thrust, and the shape change causes unbalance. Some gas turbine rotors are susceptible to shape changes while reaching normal operating temperature and load.

What type of bearings are used, and have you made any measurements to assess their condition?

Walt

Walt Strong posted:

The report by Siemens offers a hypothesis that the vibration changes with load and torque. They recommended an inspection of the shaft couplings. You have already done an external visual inspection that did not reveal anything significant with the disk packs. The vibration phase angle data does not change that much with changing load, indicating that the apparent unbalance phase angle remains the same while unbalance increases. The spool piece part of the coupling would have to be shifting relative to the shaft-mounted coupling hub. I would guess that the only way that this hypothesis can be proven is to completely disassemble both of the disk packs and inspect for wear and cracks on the discs and bolts. These components should probably be replaced and the coupling rebalanced.

I suggest you also measure gear case vibrations with the maximum frequency of 2 to 3 times tooth mesh frequency. This measurement could indicate how your vibrations are affected by load and to what extent the tooth mesh vibrations are modulated by turbine speed.

Another hypothesis that may or may not be relevant is that the turbine rotor changes shape due to axial thrust, and the shape change causes unbalance. Some gas turbine rotors are susceptible to shape changes while reaching normal operating temperature and load.

What type of bearings are used, and have you made any measurements to assess their condition?

Walt

dear walt 

pls give me your idea about my post that you can find it by searching 

Unexpected high vibration sgt 600gas turbine)

 

It is not professional to hijack other postings to draw attention to your posting. The best way to get attention is to add information to your posting. A large font and the request to search for your original posting is not going to improve your chance for help from me or anyone else. 

Walt

Walt Strong posted:

It is not professional to hijack other postings to draw attention to your posting. The best way to get attention is to add information to your posting. A large font and the request to search for your original posting is not going to improve your chance for help from me or anyone else. 

Walt

Dear walt 

I am sorry about that. I have search for sgt turbine and find your comment at this post.

Because i couldnt send private message to you. I apologize again .

Best regards

I would look further at the coupling as OEM suggest they would have seen it before, another thing to look at that may not be so complicated would be the mounting of the end of the machine. If you had a none standard shutdown so parts that normally can move got stuck some way or have increased friction to move may create problems.

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