STRANGE VIBRATION IN BOLT OF IB BEARING BOX (19 MW STEAM TURBINE)

DEAR ALL,

please share your comments about one vibration found in bolt  of Bearing box of Steam Turbine (Condensate Steam Turbine), I attached spectrum in Axial direction (16 mm/sec), this vibration is the highest in machine.

have you been this kind of vibration before?

what is the cause of high vibration in axial direction in this bolt?

Ramon Ruiz (vibration CAT II)

Attachments

Original Post

Thanks for your comment, 

we need to wait next shut down to check tighten. 

6 month before this machine suffered damage at IB side of rotor, because the bearing box was down more than 2 millimeters, and 3300 BN system does not  showed high vibration. 

Best Regards

RRR

 

Hi Jhon,

of course, the spectrum is from accelerometer with magnetic mounting, and, bearing housing has two X and Y displacement probes, the probes are not contact BN 7200 system, are connected with rack BN 3300 at control room, but I dont know about his configuration. I took readings from BNC plugs from BN 3300, but I didn´t see high vibration before failure.

as BN not showed spectrum with high vibration, also in control room display the operator didn´t see any abnormal behavior.

I began to check phase and vibration in components of bearing box, to detect the cause of the bearing housing was down.

 

ramonruiz posted:

Hi Jhon,

I took readings from BNC plugs from BN 3300, but I didn´t see high vibration before failure.

 

 

If you aren't doing so already, you should be checking the DC gap voltage on the proximity probes.  If you don't have analysis hardware/software to do this automatically, then I suggest you connect a simple digital (preferably) voltmeter to the front panel of the rack and start logging the DC gap voltages on a regular basis.

Ramon,

It would help to identify shaft speed on your spectrum.

The "bolt" does not look like a normal hex-head bolt. It might even be a thin metal cap! Just make vibration measurements on the housing close to the bolt. If the vibrations are much lower, then no worry. Check the turbine manual or ask OEM or service company for description of the "bolt" and its purpose. Note that it may have to be slightly loose to accommodate sliding for differential thermal expansion. I would not try to tighten this "bolt" without knowing its purpose and torque specification.

Walt

I would first check two things. Torque on the main vertical bolt marked. And position locking bolt between two halfes of the housing. Take it out, tighten the main bolt and see the difference. Sometimes some rust or other crap can be found in the hole. Or the thread hole alignment between the halfes is not  appropriate. 

Ramon, regarding your pictures, you can't say the plates are not twisted. They could be twisted across the shaft not just axially. I hope you checked the bolts' tightness. Thereafter there are possibilities of:

- dirty/rusty surfaces

- lack of sealing locally

- bad surface tolerances / twisted material / bad machining / fatigue

It is a old machine, do you have vibration problems? Make sure you don't create them if you don't have them old machines may hide some secrets. On the other side, when it is operating verify that you have the similar vibration on both sides of the opening, if so it may indicate that they at least move as one object. If on the other hand you have a serious difference in vibration on each side it would indicate that they are not connected as good as they should and need to be verified. If it not broken, don't fix it but if it is broken you have to fix it.

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