Boiler Feed Water Pump Thrust Bearing Failure

Coupling alignment?

Cheap bearings ...bearings inserted incorrectly ..ie wrong way for the application.
Have you just rebuilt them or installed them?

Could you describe/define the failure?

You have not defined briefly enough. If it is a LOUD WHINEING sound it is a non aligned coupling.

Internal Hydraulic Balancing may be irregular. Check for closed/pinched valve (if any) in the balancing line or blockage in the balancing line. If ok, suspect the damage/heavy rub on the labyrinth of the balancing disk/drum. This quite possible, you have changed the bearing as that would have failed. With failed bearing, there is every possibility for this labyrinth to have a Savior rub, which could cause a heavy through flow and disturb the balancing. Such a loss of hydraulic balancing would impose huge axial force on the thrust bearing, leading to a ultimate failure.

How could you have grease-lubricated bearings for a multistage BFP?

It must be oil-lubricated.

motor bearing are normally grease lubricated internal temprature of motor is always near 100 degree celcius

We are talking about pump bearings here, not motor bearings

It seems to me that face to face mounting is incorrect. Mounting the bearings in the tandem duplex arrangement will take the highest thrust load. Face to face accepts thrust in both directions and if the thrust load is above the bearing's capacity you will quickly destroy the one that accepts thrust in the opposite direction. That bearing will come apart and the metal shavings and pieces of the cage etc will destroy the other one. Be sure the bearings are mounted in the proper direction to accept the thrust load. There could also be a problem with the fit to the shaft - Is the bearing slipping on the inner ring? This would cause the grease to melt and run out of the bearing. How are you mounting them? They should be pressed on by the inner ring only - No hammering or pressing on the outer ring as this would damage the races and balls. I concur with the comment from Satish Kallakuri concerning oil lubrication. Bearing manufacturers such as SKF publish photographs of typical bearing failures. Looking there would be a start. Best of luck to you. Ed

Yesyen and Satish are both making good points. I would pull the pump and have the bearing seats rebored by a big pump shop, replace the labrynth and coupling. Have SKF or the pump manufacturer recomend/supply the bearings. Totally refresh or replace this pump. Assuming the bearings weren't pounded into it by an idiot.

I have come across multi-stage boiler feed water pumps with grease-lubricated bearings running for years. There had always been debates among pump technicians and service engineers about mounting. Looking at bearing catalogs (the table in woodygb's post), all the three mountings are recommended by bearing manufactures. Referring pump manufactures' catalog is always wise.

We do not know for how long this pump was running successfully, since commissioning. Had it been running 3 / 4 years well and failed on normal wear and tear, why to think of changing the type of OEM suggested bearing mounting? Nor think of going to oil lubrication? Imagine the issues related to modifying a grease application to oil application in an existing pump.

Talking of angular bearing mounting, pump specialists tend to recommend 'back to back' over 'face to face' due the former mounting is capable of sharing greater moment load. But both the arrangements exist successfully as long as the 'residual axial load' is bearable by one bearing (other bearing is non active).

Talking of 'axial load' pertained to multi-stage pump with 'hydraulic balancing arrangement', understanding the design is a bit farfetched for maintainers. In a new pump, with proper (balancing) drum/piston and its new labyrinths, do we (maintainers) know whether the axial load is 100% balanced or an amount of (residual) load is left unbalanced? I heard from the designers that an amount is left unbalanced intentionally, as to take care of rotor assembly from axial jog/vibration. Sound very logical, but to which direction this residual unbalance axial load is preferred, towards in-board or out-board? Some OEM field specialist say in and some say out ! I do not know the expertise of such OEM field specialists on such intricate design details. And poor maintainers mostly may not have the contact with OEM's design group. Some experts from our forum, knowledgeable on this subject could through more light for the benefit of all. Let us say in a particular pump, this unbalance load is acting towards in-board and the thrust bearing are mounted in tandem orientation, but also acting towards in-board (say, both the bearing are non-active), the consequence could be catastrophic !

So the failure history and the manufactures' recommendations are very important before taking any drastic modification steps.

actually this is the first time i noted that there are boiler feed water pump uses grease for lubrication. you know why? mostly boiler feedwater pump i work with are either driven by a high speed motor (3600 rpm or above) or a steam turbine. at this speed i dont know what kind of grease you are using. what is the speed of your fwp?anyways, mostly trust bearing fails due to wrong installation, wrong bearing clearance and wrong lubrication. if you insist that you are using grease since the start then make sure you installed back the spacer you remove or check the bearing allowable clearance. sometimes our naked eye cannot identify a bend shaft. check the shaft too. it could be unbalance impeller also. are you sure face to face is the original bearing set up not back to back?

pump running rpm are 3000 can we use oil in place of grease what arrangement need to accommodate oil can we use bearing in ten dam arrangement

Please tell us for how long this pump with great lubrication working successfully since commissioning? This is a vital information to decide whether any modification like 'grease to oil' or 'face to face' to 'back to back' or 'tandem' mounting are required.

Had it been running for reasonable time like 3 years or even one year, no basic change might be required. If the problem is elsewhere, as mentioned, alignment, bent shaft, imbalance, worn out internal labyrinths, assembly error, your modification to oil lubrication could only give a marginal addition to MTBF. Besides it may not be that easy to modify to oil lubricated system unless you involve OEM.

my dear this problem is since newly installed pump it run only 24 hour continuously with out problem normally it give problem after two or three hour of startup

Dear Guest, presume you are the OP.

You mean it failed after a brief, satisfactory run for 24 hours?

Is the failure pattern more resembles, Case-1 or Case-2 ?

my dear like case one

my dear can you give the brand, model no, type of the pump you are using, let us search the detailed drawing of the pump. if you have that drawing much better, /is there any cooling system on the bearings?

my dear pump brand SIHImulti-MSL/MSM 032-100

Is this model you have?

my dear same model with top suction top discharge suction side is toward diver end having deep grove ball bearing with grease lubrication thrust bearing is toward non drive end [discharge end] bearing is angular contact single tow pair mounting,.

my dear you mentioned you have 6 active pump of the same model. why dont you open another one and compare it to the one that having a problem. also carefully read again the pump manual (schematic diagram). if this pump had been operating before so most probably you mislook something during assembly. Did you notice any water that mixed with the grease at the bearing when you open?

no my dear i am sure i mention wrong in first subscription we have two pump having six stages both are suffering same problem one is turbine driven othher is motor driven

can you show the schematic of the pump, i prefer part list if available. i am trying to download but there is some problem with translation.

sorry i just read some of your answers. i believe since the problem start from the beginning, it is better to refer to the manufacturer. and install a new pump. or better try another type of feed water pump. are you running a high pressure (superheated) boiler? maybe the pump design is not suitable for your need?

Fine, the bearing arrangement should look like this, right?

The bearing 'IN' is towards the pump and the bearing 'OUT' is on the outer (adjacent to lock-nut).

Please tell, which bearing suffered worst damage, inner or outer or (don't say) both?

dear sir bearing 'out' looks more damage than bearing 'in' in pump which is driving by turbine in the other pump which is driving by motor bearing 'in' looks more damage than bearing 'out'

If you are sure of your observation that, "outer bearing in turbine driven pump and inner bearing of motor driven pump fails often", it leads not to suspect common problems between these pumps.

Common problems like, 'improper internal unbalanced axial trust or mounting procedures/mistakes', would lead to failure on either inner or outer bearing. Not inner in one pump and outer in the other pump.

You need to endorse your observation by double check.

Taking your observation valid, it leads to suspect of an influence of some disturbance form outside the pumps not within.

Disturbance from coupling, misalignment, thermal growth of equipment and last but not the least: thermal growth of pipelines.

What is the type of coupling used on these pumps?

Are they 'flexible disc type'?

Is the DBSE (Distance Between Shaft Ends) recommended by supplier and maintained on field? If not, what are the existing DBSEs and what are the 'Spool piece distances'? What are the pre-stretch of the flexible members, are they recommended and within the recommendation?

In the turbine driven pump, is the thermal expansion of turbine shaft pushes the pump shaft unduly, beyond the flexible limit of the coupling member; thereby the outer bearing suffers greater damage?

In the motor driven pump, is the DBSE is much more than the recommended value; such on coupling the pump shaft is pulled in and unduly loads the inner bearing?

Hope these questions helps, though not solving the problem but at least eliminating the influence of a dominant source, 'disorders from coupling'.

These pumps are connected with hot pipelines all around, steam and condensate. If the pipeline expansions are not duly considered and managed they are sure to exert on pumps. Often the slender 'holding down bolts' are no match for huge thermal expansion of piping. Alignment and Thrust bearings are often victimized due to undue pull or push of the pipe expansion.

on the drawing shown it shows that the outboard bearing (trust bearing) is covevered by the condensate. condensate temperature is 94 to 98 c i assumed. maybe this affect also the bearing performance. by the way try running the pump on a cooler water, say normal tap water temp. Dont run your boiler. although yesyen consider pipe expansion to affect your alignment. in this regards check the piping support. i am sure the pipings have already bend and loops for expansion consideration.

"drawing shown it shows that the outboard bearing (trust bearing) is covered by the condensate."

But OP in his reply 20, clarified, "same model with top suction top discharge, suction side is toward diver end having deep grove ball bearing with grease lubrication, thrust bearing is toward non drive end [discharge end] bearing is angular contact single tow pair mounting."

So the thrust bearing is not covered by condensate but by air like any standard 'Between Bearings - Pump'.

my dear you are quiet right about my subscription

hey hi friend, i thnk the problem is with the balancing of the pump, thrust load is damaging the bearings, no problem wheather it is grease or oil lubricated. Try to find following points checked.

1- Check for all impeller installation, they are in proper sequence as per the manual.(The design of 1st stage and last stage is diff from other impellers, try to find out the same)carefull in impeller installation.

2- check for impeller direction of vanes , vane direction is important in closed impellers.

3- check for damage in balacing disc or balacing drum, is balancing path cleared na.

4- check for balancing line choking.

5-you can go for taper roller also as thrust bearings.

Dear Mr. ARSHAD BBC,

The Bearing Manufacturers clearly mention the clearances as C1 or C2 etc. If this is not properly followed, in course of time it will develop problem, in your case it is with in 3 to 4 Hours

The Selection of Bearings are based on certain parameters given by the Bearing Manufacturers and if not followed properly, then the problem will start.

You have mentioned that you have 6 pumps. If other pumps are working alright and only this particular pump creates problem means either thrust balance is not taken care or dynamic balancing is exceeded the permissible limits. Pl. examine these issues.

Pl. post the information after solving your problem and what you have done so that CR4 Members also get informed.

Thanks,

DHAYANANDHAN.S, INDIA

<...What could be the causes of failure?...>

A reluctance to discuss the problem with the <...Boiler Feed Water Pump...> manufacturer and follow that body's advice must be among the possibilities.