Bearing Temperature Increases Along with the Load

Friction. Is the temp within specs?

Yeah friction.... This I have already mentioned.

Temp. is within a limit but it does not mean that we can be relaxed. The trip limit on bearing temp is 110 C deg. We had readings up to 97 C deg with max load of the unit.

It is too close to limit and means that something is wrong.

What is the relation between temp and load?

More load = more torque on shaft.

Is there water in the oil......milky colored. Maybe a bad steam seal allowing steam into oil chamber.

This could take a long time on here. Have you checked the troubleshooting section of your documentation. Did you try google?

1. What are the factors that contribute to bearing failure in a steam turbine?
2. Answers:
3. Improper lubrication. Only the recommended lubricant should be used.
4. Inadequate water-cooling.
1. The jacket temperature should be maintained in the range of 37-60°C
2. The flow of cooling water should be adjusted accordingly.
1. Misalignment. It is desirable that ball bearings should fit on the turbine shaft with a light press fit. If the fitting is too tight, it will cause cramping. On the other hand, if the fitting is too loose it will cause the inner race to turn on the shaft. Both conditions are undesirable. They result in wear, excessive vibration and overheating. And bearing failure becomes the ultimate result.
2. Bearing fit.
3. Excessive thrust.
4. Unbalance.
5. Rusting of bearing.

Definitely Friction. Higher load creates more pressure to surfaces in contacts instead of surface->lubricant->surface scenario for journal bearing. Consult experts on lubrication and bearing provider. They will probably have recommendations like changing type of lubricant(best) or system cooling at higher loads. But, when temperature is at tolerable range, its part of its service.

Generally high speed machines are fitted with bearing having hydrodynamic lubrication system. The bearing temperature variation is observed once the dynamics of oil film are change due to some foreign particle or layer on the bearing surface. Many times small sludge of oil comes on the bearing and forms a very thin layer, which restict the heat transfer in normal way and thus bearing temperature increases with load. You have to check the bearing in next opportunity.

First you must check whether this is happening regularly or sporadically. Heat is generated mainly in bearings due to frictional forces which is normally taken care by proper lubrication. If it is happening regularly then it could be due to additional heat coming from other sources apart from friction. You must also check the lubricant's condition as the lubricant gets degraded depending upon the heat generated. In that case if the lubricant is not changed then also you will notice additional heat.

But it is better you try to go to the root cause of this problem. In case you need more help please send mail

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It seems to me that the bearing temperatures should increase with an increase in the turbine load. If it does not increase, then the real question is why not? Temperature increase is a relative change, so what you get is greater amounts of power loss associated with greater amounts of power produced. Let us assume the bearings are either sleeve or roller bearings, creating either sliding or rolling friction. The vast majority of the frictional losses will express as heating of the parts in contact (lesser amounts in sound, vibration, wearing of parts, etc). To draw more power from a turbine, there needs to be an increase in torque, in speed, or in both torque and speed. Usually there is an increase in fuel consumed as well as an increase in temperature and gas throughput. The forces applied through the bearings keeping the parts in correct relative positions need to be greater to correct greater amounts of divergent forces. With good bearings, these will not be large, but the relative amounts will be greater. I assume you understand how friction creates heat, through transfer of motion from the macro-scale to the molecular scale. The increase of gas temperature associated with increased power production and the increase of gas flow-rate both will transfer more heat to parts in contact with the gas, and ultimately to any parts in thermal contact. It is possible, if you so choose, to control the increase in bearing temperatures, but you need a good reason, and the reason is xxxxxxxxxx.

Thank you all for an info you have provided so far.

I should have put more info and I am going to fill this gap just now.

Steam turbine is new and during commissioning phase. It has 8 bearings (#7, #8 are GT bearings) current load is 400 MW (600 MW is max ) bearing temp's are :

#1, #2 = ~ 90 C deg, #3, 4, 5, 6, 7, 8 ~ 75 C deg.

The trip limit on bearing temp is 110 C deg.

Bearing # 2 is radial-thrust bearing. Brg #1, #2 have the pads and #2 is thrust one. The rest of brg's are "lemon" shape bearings - elliptical ones.

We are not going to accept this high brg temp's and want contractor to open the bearing and check them.

P.S.

This is Chinese turbine erected by Chinese contractor

"This is Chinese turbine erected by Chinese contractor", I think that explains it.

I was in 100% sure that this remarks is going to be commented in this way :-)

Higher loads mean greater thrust pressure. So your thrust bearings are heating up. If they are heating up too much, then they are too small or insufficiently cooled.

Bill

The temp measurement of the thrust bearing pads is in place and readings do not make us worried

Your additional information provided the answer. #2 is the thrust bearing, which positions the shaft along its axis. The greater the load carried by the turbine, the greater the pressure drop across the turbine, and the greater the axial loading. Regardless of whether the thrust bearing is a simple flat bearing or a roller bearing, the the added thrust load increases the shearing of the oil, which raises the temperature.

The temperature is within the allowable specification, with an adequate margin (13-20 deg C). The trip limit is probably much lower than the temperature where catastrophic failure will occur. If the temperature is stable, then let it run, but monitor it. If there is a problem with the bearing, you will see the temperature climb in the near future. If that happens, then shut down, tear down, and diagnose the cause.

"Let run it" - I would say that this explanation is on this same level like we have from Chinese contractor (with full respect to You - McTech).

We have had in service the another turbine - let's name it "B" (the same type, OEM & etc) since September previous year, it means I have comparison. At turbine "B" bearings temp is ok.

The lub. oil is the new one , so should be ok. but based on my experience with this Chinese contractor everything is possible. Certainly the analysis is going to take place.

There is a schedule to take turbine to max load. Let's see what will happen... .

I suspected wrong coupling alignment but the shaft vibrations in such conditions would be high - they are below 50 microns which is very good for new machine.

The decision has been made to not accept this failure. The bearings are going to be checked.

Watching Chinese way of lub. oil flushing I have my doubts if the strainers we have in the lub oil inlet lines are choked. There is no indication of pressure difference, so hard to asses just now. On the other hand it would be real disaster if the strainers were choked but to be honest it is possible. Why not?

Let me give you another example. The generator stator winding cooling water conductivity is more than 0.5 mS. According to provided by Chinese manual should be less than 0.2, which is in line with international practise. Explanation given by them is that 0.2 is the manual print mistake and in fact even up to 5 mS is ok. Could you believe it?

I would check the coupling, If it's not a floating coupling when the driver or driven side starts to heat up the thermal growth is going to put axial pressure on your thrust bearing causing it to heat up. Just another suggestion...good luck.

Bigger axial force would make the thrust bearing pads temperature high, which is not the case. The pads temp;s are ok

You are saying that pad temps are OK but your previous post mentions #1 and #2 are thrust pad bearings (with high temperature?)

What are the location of the bearings?

Is there a possibility of the steam leakage entering the bearing housing?

The temperature rise with the load - I would have assumed due to excessive thrust load (may be far in excess of the designed load) since that would cause the higher than acceptable specific loading on the bearing and squeeze out the EHD oil film.

But then you are mentioning that the thrust pad temps are OK. Then where in these bearings temp is high?

In certain cases - due to bearing fault we have seen this happening - in thrust pad as well as the journals when the profile were wrong or pads were not on the same plane.

The bearing # 1 is radial bearing with radial tilting pads. The bearing # 2 is radial bearing as well. Additionally close to brg # 2 we have thrust bearing.

The readings I have given are related to temp. of the radial bearing's white metal.

I did not put readings of thrust pads as they are ok.

If we have had increase of the axial force we would have observe the higher temp of thrust bearing pads which is no the case as I have already mentioned.

Today, I had possibility to see brg # 1, #2 changes due to load changes. The relationship is strong:

- load 400 MW brg # 1 temp - 90/89 deg C , brg #2 temp - 87/79 deg C

(we have two measurement places at these bearings)

- load 220 MW brg # 1 temp - 81/84 deg C, brg #2 temp - 82/76 deg C

- load 109 MW brg # 1 temp - 77/79 deg C, brg #2 temp - 78/73 deg C

As trip set is 110 degC, there is no harm in running continuously for longer observation. But it will be better to open the bearings for inspection and recheck its clearances, interference and skewness and ensure as per norm. A through flushing play a very important role in pre-commissioning activities.

You have not mentioned the alarm set point, normally it is 5 degC lower than trip set point. In new machines bearing temp at rated load should be at least 20 degC lower than alarm set point (assumed 105 degC) for such rotating machines. Also, if you observe that the steady state bearing temp at rated load in some cases are much lower, say 40 degC lower than alarm set point, then alarm & trip set points should be lowered than recommended.

The high alarm is at 110 deg C, the trip at 115 deg C. This I double checked and given values are right ones.

The bearings check should be done but I do not think that it will be done. There is a bit "politic" involved and technical point of view is going to be bypassed, I afraid

Is it so difficult to open a bearing for insection? If you consider it's an abnomility, you should make them agree for it by convinsing technically.

I remember a mechanical run test of a 6 MW centrifugal compressor at supplier's premises in Germany for which I was part of inspection team from purchaser's side. During run, one of its journal bearing temp behaved abnormally, even though well within the alarm limit. Inspection was not cleared & decided for inspection. When checked minute dimentional deviations found in bearing (not in assembly). Bearing was replaced & problem was solved.

Pritam,

You mentioned about inspection in Germany. There is different supplier attitude than we have here.

In western world you can insist on some activity as a customer and seller will do it.

In normal case I would force to do it without any discussion. I hope that it will happen

Even in India, we had a gear box for Gas Turbines @5200RPM we had abnormal temperature rise and when opened we found already damage of the white metal has set in and result- as analysed by us was due to the bearing manufacturer has incorrectly machined the lobes (4 lobe bearing).

However in your cas it is tilting pad journal, on which I didn't comment due to my lack of practical experience and as far as my theoritical knowledge goes, it is a complex mechanism (unlike the tilting pad thrusts) and the temperature rise with load is really a puzzling phenomenon - unless the load is increasing the unbalance. Bearing temperature rise is associated with the oil film squeeze-out or turbulence.

The RPM being constant (irrespective of load) the turbulence can not set in so the other factor is the drop in oil film thickness.

This can happen due to increase in axial load beyond the bearing capacity- pad preload, etc various factors come to mind in addition to the wedge geometry.

BTW- any vibration level increase with load?

Errata :

This can happen due to increase in axial radial load beyond the bearing capacity.

BTW: did you do the vibration analysis wrt load?

You have suggested the temperature of the rotor - should affect other bearings too?

The load usually should create the thrust unbalance, which is not the case here. It seemes to create a radial unbalance amd some times it may shif the centerline of the rotor, a properly designed bearing should provide the wedge to counteract this movement beyound limit.

Thank you for your contribution. The vibration increase would open the new trace for further investigation but it is not the case - we have not observed this .

The clue here is that your axial bearings are heating up when you apply load, and presumably cool when you unload them. There is something wrong for sure.

Axial bearings should not heat up because of machine loading...the load on axial bearings is constant when speed is constant, and heating is solely a function of speed and weight on the bearing. If weight is constant and speed is constant, heat should be constant.

If your axial bearings are too tight, (new installation, fresh paint perhaps?) the inner races may be sticking to your shaft. The shaft may be pushing your inner races back under load, causing the axial bearings to run with a small thrust load which of course they are not designed to handle. The answer is to make sure that the axial bearings slide smoothly on the shaft. A drop of oil perhaps?

Is my analysis valid gentlemen of Conference Room four? This is not my field.

There is no problem with axial (thrust) bearing. The temperature is high for two radial bearings.

Ahh, you are right. Silly me. I was thinking that the axial bearings were the radial bearings. That terminology issue again! But of course...the axial bearing would hold the axial load! Grin! Mea Culpa. Of course, I meant the support bearings, the ones you call the radial bearings. The round ones!

But... the statement stands....the "radial" bearings are being thrust out of position. If they are sticking on the shaft and the inner races shift a bit sideways under load, this will cause heat problems. Fresh paint could cause this.

Did you try a drop of oil on the shaft to allow it to slip into place? Was the bearing damaged when installed onto a too tight shaft?

If anybody has a better idea...I would like to hear it!

I think again you are little out of track. "the inner races shift a bit sideways under load, this will cause heat problems. Fresh paint could cause this. Did you try a drop of oil on the shaft to allow it to slip into place? Was the bearing damaged when installed onto a too tight shaft?" These are applicable for antifriction bearings. The topic under discussion is about tilting pad journal bearings.

Hmmm. When did the OP suggest that they were solid journals? He said "bearings".
Clearly you are right in that I am off track.

Bearing two is both thrust and support. It is heating up under load. Poor lube was suggested by the OP and ignored so far. But it should be looked at more closely. Breakdown of the oil wedge will cause serious problems.

Bearing one is support only. It heats up under load. Should not happen. Do YOU have any ideas?

I agree. Breakdown of the oil wedge will definitely cause problems. It can be detected if opened for inspection by seeing the rubbing pattern. Improper bearing clearance, dimensional deviation of radial pads, wedge angle & stuck-up pads (not free to oscillate at its fulcrum) may cause breakdown of the oil wedge.

The oil wedge breaks causing dry friction and bearing temp is going high - ok.

Let's think what is the root cause that the oil wedge breaks. it has been mentioned that the poor quality of the lub oil, this is going to be checked.

Discussing with my friend who was a turbine operator, he suggested that the regime of regulations valve work could be one of the reason of bearing high temp.

The valves (in his turbine) can work in two ways in a parallel mode and in a sequence mode.

The parallel mode work of reg valves is in place when in the same time all of them are opened or closed. It gives the uniform force on the rotor and better temp deployment along the casing and rotor.

The sequence mode work takes place when the valves are opened or closed in some order. First valve no 1, than no 2 etc. It can generate the forces pushing/moving the rotor in the bearing and breaking the oil wedge.

The high temp of the bearing he had was during the sequence mode work of valves.

Please let me know your thoughts and opinion