Variation of Front Shaft Displacement in Steam Turbine

"45 to 70 microns"

How did you measure that?

70 microns is about the same as a few red blood cells all lined up.

What am I missing here?

Has it been properly balanced as per original manufacturer's procedure and specifications?

How to solve the problem?

Have a look at was left over in the parts bucket after the major overhaul.

Look at each 'spare' piece and decide whether it probably should have gone back in where it came from.

What was replaced/adjusted during the overhaul?

Overhaul it again this time do it right. And don't let anyone in purchasing order substandard parts to save cost. Or cut corners to save time and money.

Did you re-align the turbine to the driven equipment? If you did you have the turbine loe to the driven equipment and it is causing the front end of the turbine to be to lightly loaded. //also you have not given enough data to truly troubleshoot the problem. Does the turbine have only top inlet valves or upper and lower valves. Does it drive a gearbox or just a generator? Is it a condensing or a back pressure machine? After looking at the few answers you received, you need to disregard anything they write. If you did realign the unit you will have to raise the driven equipment by 5 mils and this will load the front of the unit enough to stabilize it. It is a good starting point.

5 mils?

please use SI or imperial units.

Where did you go to school? 5 mils or 5 thousandths. When aligning we use mils or thousandths. That will misalign the unit a total of 10 thousandths. This will load the vibrating bearing and make it not sentive to the inlet steam.

I was schooled in a metric (SI) environment.

The OP used microns which is an unambiguous SI unit. I don't know why you have reverted to imperial.

In the metric world's vernacular, taking off a few mils is taking off a few millimetres. Quicker to say.

Removing a few thou is an imperial world vernacular that I am familiar with for removing a few thoudands of an inch. One learns to span these two universes.

Back to your advice to the OP.

It sounds like you have found that deliberate (minute) misalignment can relieve vibration issues. Additional bearing load dampens the vibration you say.

Sounds like a rough fix to me.

If what you are saying is true then that would mean that the vibration is caused by excessive bearing lash in the first place. Right?

Sorry about that Wal but I am in the USA and i was not schooled in Metric's so I go by what I was taught. I convert when I have too and if you understood vibration and alignment then you woulld automatlicly figure out the difference. I have been working on steam turbine generators for the last 40 years. How long have you been working on them. I inspect them and repair then and the manuals are not always in english or the standard size for me but I have to translate and convert sizes ect: you have not added anything to this guys problem. Why don't you give him a solution. I asked the right questions and he has not replied. I am out of here.

Well, I understood what you were saying...but then I can translate between U.S.A and European

Drew K

Can you pl submit the timebase data? Are you sure, the area of the shaft facing the probe is free of scratches, burrs etc? Thermally induced misalignment may be another reason.

From my vibrations training course, a spike in the spectrum at the 1X in order of likelyhood:

Unbalance- 1x peak with low 2x peak and negligible other harmonic amplitudes.

Shaft/coupling misalignment- check for other frequency symptoms such as higher thanusual peaks at 2x and other lower harmonics check phase symptoms as well to distinguish from unbalance.

Sheave misalignment- often looks like unbalance except axial amplitudes are usually much larger than for unbalance.

Bent shaft- similar to static unblance except for 180° out of phase with axial readings

This is not all that was listed, just the highlights. Unbalance could be caused by eccentricity due to not placing it on the turning gear long enough before operating, or not allowing the unit to warm up during heat soak stages.

Drew K