To Reduce Steam Turbine Eccentricity Back to Normal

This is like sending your doctor an e-mail saying "Doc, I have this terrible pain in my chest. I took an aspirin but I still hurt. What's wrong with me?"

It is impossible to diagnose this type of problem without a lot more information from your engineers.

Thanks Lyn. May I know what are the information required in order to diagnose this kind of problem?. i.e all the turbine supervisory system parameters?

Would you ask your doctor over the phone what are all of the symptoms to diagnose your pain?

When did the call go in to the original equipment maufacturers and what was the response? Why is it deemed necessary to disregard that advice and seek a reponse from an anonymous internet forum instead?

Because our advice is best and tariffs . . . . . you cannot steal it for cheaper.

Just bring in your local blacksmith. One good whack can easily move the shaft 150 microns. If it doesn't then there's always C4!

High Vibration may be a reason of bent shaft due when the turbine is stationary and thermal arching or bowing of the shaft has occured or the shaft has sagged under its weight. Rotate the turbine slowly (barring) monitor both on full speed and barring.

Straighten the bent shaft then monitor again.

You are you asking us? Where is your Steam Turbine supplier??? OH! you bought a used one probably?

The bearings were replaced using this opportunity that turbine is stopped, right?. I cannot find real correlation between minor withe metal scratches and rotor's eccentricity.

If the scratches (you wrote "minor") are not serious ones and in line with recommendations given by bearing supplier (you can use ISO/Alstom/Siemens norms instead ), I do not think that the repleacement was really necessary and especially for top part of the bearing.

I would check rather the clearances of rotor in bearings and the working marks.

Was this turbine start up the first one after overhaul? If yes, have you done something with the rotors coupling surfaces? I mean any coupling's machining?

If the start-up took place after long shout down, you needed to put the rotors on barring gear long enough to get rid off this natural rotor's sag and warming them in parallel. Anyway start up procedure should be clear defined and known for your Operation team.

Check the control room readings related to casings temperature, soaking time, etc.

If there was not the after overhaul start-up I would suspect operation mistake.

1st you should have been at turning gear speed until heat soak was completed or a maximum of 500 rpm until heat soak was completed. Then monitoring the vibration as you came up in speed. You more than likely got into a rub and bowed your rotor. 24 hours on turning gear should bring the eccentricity back into startup range. Then go through a normal start up and monitor vibration. If you have normal vibration until after you go above 1000 rpm's then you are proably getting into a rub. At this point you lower the rpm back to 1000 or lower and watch the vibration until it comes back into normal range and then take it back up in speed. This process will eventually rub the vibration out and you can come to speed and get on line.

What I could recollect from some of my saved notes. maybe it will help you.

Eccentricity is an extremely important condition to know about before trying to go to high speed on a turbine shaft.
It tells you the shaft is more like a banana than a pole if high. Severe damage could result to blades and seals as they are not vertical in the casing. Measuring eccentricity is accurate before the shaft establishes an oil wedge in the bearing. This is what is meant by becoming dynamic ie it is floating.
Eccentricity is not an issue at full speed and is often not available as an indication. The almost equivalent condition at full speed is bearing vibration..

Steam Turbine Turning Gear - Turning gear is utilized on turbines to reduce eccentricity or out of round of the rotor. When a rotor is standing still it has a tendency to sag due to its weight.
While running a turning gear which is a separate motor that turns the rotor slowly 10-50 RPM through a clutching mechanism. This rotation keeps the rotor in balance.
It is very important to run the turning gear on shutdowns and start ups. The time required to run is dependent on the size of your unit.
Typically the turning gear must be on for 12-36 hours for small to large steam turbines after shutdown and 2-16 hours prior to a turbine start.
If a turning gear is not utilized the rotor will become eccentric and may cause vibration up to wiping rotating parts with the stationary parts causing catastrophic failure.

I work on many turbines that do not have turning gears. They have to be slow rolled with steam for 30 minutes to an hour to straighten them out. I have been repairing them since 1971 and have run into many different senarios. Rubs bent shafts broken buckets ect: General electric will allow a unit to be taken off turning gear at 1000 degrees F in an emergency. It just has to be on turning gear until the ecc corrects it self prior to start-up. The question indicated that he did not know why he was vibrating and since it was at startup they got into a rub and it could have been from going rotor long from too much heat on the rotor and the shell not growing fast enough. Seen that happen also as I do a lot of startups on steam turbines.

I need to keep in touch with you . Please send me a mail on my email : duconems at the rate yahoo dot com . ( trying to beat CR4 with this coded email address)

All of the advice given so far has been good and applicable. In the interest of elaborating on some of the advice I would like to add the following;

True vibration is an indication that the center of mass does not coincide with the center of rotation.

Your statement that you tripped at 2200 rpm (HP trip) would suggest to me that it is quite possible you were at or near the first critical speed. Most large turbines will alarm at about 6 mils and trip at around 10 mils. If you had picked up a rub at or near the critical the effect would have been more pronounced than at any speed other than critical. Even if this were the case the rotor bow should have returned to normal after a sufficient time on the gear. It is possible that if the rub were severe enough, it could cause a permanent bow in the rotor. Permanent bows over 30 mils have been recorded caused by rubbing or water induction.

When reading an eccentricity indicator most operators look for a "normal" reading versus a maximum reading. I have personally seen meters that had normal readings as low as 1/2 mil and as high as 3 mils. Normal being the operative term.

A usual recommendation relating to turning gear operation is to operate the turning gear for 4 hours or until the eccentricity is normal prior to rolling the unit. Most OEM's give some guidance as to special situations such as are encountered when setting the overspeed trip or other situations that require stopping the shaft when it is at or near operating temperature. This is usually called out in the instruction book as 10 minutes on the gear for every stopped minute up to a maximum of 4 hours, these guidelines are usually provided with the provision that eccentricity must be normal prior to rolling the turbine.

I would suggest that you check your instrumentation and if possible confirm the readings with a dial indicator or another proximity probe.

If the instrumentation is correct you should get some input from the OEM, the consequences of operating with a severely bowed rotor can be quite costly.