Parameters for 15mw Steam Turbine

"However we planned to replace the front end bearing even though it was perfect. The rear side bearing was kept as it is and assembled back.

The machine was rolled and we found this time only rear brg temp went high and front was in normal condition".

You've answered your problem. Changing the rear bearing will bring it to nioraml condition. If BHEL would've done the maintenace they'd have replaced both at the same time.

Had a similar problem with a 2.7 MW Steam Turbine. Learn't only one thing - Replace all bearings that are prone to give problem later on and to heck with the owner's budget for, when things go wrong the same owner turns his back on you saying, " If I spent so much i could've spent a little more" . Before " I'm a poor man please please do it in my budget".

Replace all bearings "just for the hell of it" is a very strange engineering solution.

I guess it works for you becouse you know all there is to know about bearing replacement and others do not.

Should we not be trying to give an engineered answer to this mans problem?

I do not work too often on 5 pad tilting bearings, I guess they are a US design, possibly even GE. But there are fundamental Q's to ask.

Were the temp probes put back into the bottom pads to the same penetration as before, or are they now sitting closer to the Babbitt?

Were the bearing heights changed during this maint activity, such that the loadings are now different?

You bet it is a strange engineering solution and should not be recommended but, after 24 years of experience I've had had my pants literally taken off because, " I took the responsibility and therefore, i'm the one to be blamed hence, I and only i've to correct it and at my expense". It's a reputation at stake which I'm not willing to take.

Based on my pratical experience then, I take certain decision "to do or not to do".

You are 100% right . This may not work with everybody.

Should we not be trying to give an engineered answer to this mans problem?

He answered himself. If you read. Replacement of one side solved his problem whereas the other did not.

The only engineering answer I can give you is X-Ray both the present and a New bearing and then decide whether to put back the old one or replace it.

t

THANK YOU SIR,

YOUR APPROACH TO THE PROBLEM IS RIGHT. I WOULD LIKE TO INFORM YOU THE FOLLOWING POINTS WHICH MAY FURTHER GIVE YOU CLEARITY.

THE QUESTION WHAT YOU HAVE ASKED ABOUT THE INSERTION OF RTD IN THE BEARING PAD IS VERY DIFFICULT TO ANSWER.

THERE ARE TWO PADS COMING IN THE BOTTOM SIDE AND EACH PAD HAS PROVISION TO FIX TWO RTDs. IF YOU SEE FROM THE STEAM FLOW DIRECTION THE DIRECTION OF ROTATION IS ANTI CLOCKWISE. WE HAVE FIXED TWO RTD ONE AT EXTREME LEFT AND ONE AT EXTREME RIGHT.THE RTD AT EXTREME RIGHT IS SHOWING LESS AND THE RTD AT EXTREME LEFT IS SHOWING HIGH. THIS IS SAME IN BOTH FRONT AND REAR BEARINGS.

WHETHER THE ABOVE POINT GIVES YOU ANY CLUE.

REGARDS

M.RANGACHARYA

This is a confusing situation for me.

1. Steam flow direction. I work on many types of turbines, but not yet BHEL. Most have steam flow from the front to the rear (toward the generator) but some have steam flow from rear of turbine to the front. So to say "looking in direction of steam flow" still leaves me guessing.

Is the steam flow toward the rear of the machine or toward the front of the machine?

2. DOR. In my world this is always stated with respect to looking from the front of the machine to the back, regardless of steam flow directions mentioned above.

So regardless if your steam flow is from front to back, or back to front, if you are looking from front of machine to the back, you can now quote the DOR.

3. Rotor running position with respect to DOR (within a plain bearing). Initial run up will see the bearing try to climb the wall of the bearing at the side to which the top of the rotor turns. During run up it moves away from this side due to the establishment of the oil wedge. At full speed it sits over to the other side of the bearing, i.e., the side to which the bottom of the rotor turns.

The above is for a plain journal bearing type. The 5 tilting pad bearing you speak of may well have separate oil feeds to each pad. It may also be a simple oil flooded type. Which one is it?

It is almost always the case that the hottest portion of the bearing is the lower section quarter that the rotor is running at with respect to the above text. Is this the case with your rear bearing?

4. What else did you do and not do during your maintenance that you are not telling me about? Did you take before and after bridge gauge heights each time? Did you change the height of any other bearing? Did you record pre coupling break concentricity and post coupling break alignment? Did you perform rebuild concentricity?

I await your reply.

How is the machine running now?

TO YOUR FIRST QUESTION

DOR : LOOKING FROM FRONT (TURBINE IS SINGLE CYLINDER AND STEAM FLOWS FROM FRONT TO REAR)

THE TILTING PADS I AM TALKING IS OF WITH SEPERATE OIL FEEDS.

Dear Markathome,

Please read my first question bit carefully then you may understand the problem.

As i have told you each bearing has five tilting pads and out of five two pads are in the bottom. The bottom pads are only having temp measurements provision. When you look from the front the rotor direction is anti clockwise and the RTD connected to the extreme right port is indicating temp of 100 deg c and the RTD of extreme left port is indicating 76 deg c. The case is similar to Rear bearing side also. i would like to conclude that the RTD connected to extreme right are indicating high temp and rtd connected to extreme left are indicating less temp. How is this possible i am getting two temp in the same bearing that too the difference is of the order of 30-40 deg c.

I request you to think in the direction of bearing profile and its position during full speed.

rangacharya

Hello Rangacharya.

Firstly. I hope that the machine is still stable, as I do not promise any quick and resolute answers to this problem.

Second. I have no experience with 5 tilt pad bearings, so I am looking at this with only shell bearing experience.

There is still the possibility that the probes are penetrating into the bottom of the bearing pads at different amounts as was before the maintenance.

You have not mentioned if you did check pre strip-down concentricity or post strip-down alignment, or if you checked these again on rebuild. Also Bridge gauge readings. If you have replaced #2 bearing at a taller height you will have increased its loading. Conversely this will have unloaded #3 bearing next to it. Is bearing #3 running cooler than before? Did you record concentricity and alignment on strip and rebuild.

Are any of the bottom two pads fitted with Jacking Oil. If so, does the Jacking Oil supply have Non Return Valve fitted. If so, you may be able to see hydrodynamic oil wedge pressure in the Jacking Oil system pipework (when Jacking Oil Pump is shut down). If this pressure is greater than before (or #3 less than before) this is another indicator to the change in load on the bearings. You make an interesting point about the differential temperature between the two RTD's in the same bearing. What is the normal differential for #2 & #3?

I still advocate that replacing bearing just for the hell of it (as has been suggested) only works for some because they know how to set the new ones up properly. My questions about alignment and concentricity are all part of setting the bearing up properly.

Regard

Dear Friend,

A peculiar type of problem. WHAT is coming to my mind is

1. Did you check up oil flow to bearings, for its quantity and pressure.?

2. What about oil character.?

3. Have you called turbine Manufacturer's Engineer to site and what did he say.?

RAJESWARI.