Bearing Temperature Trip and Time Delay

 

Hello members, 

I'd like to hear from you about your protection philosophy of critical machinery on bearing temperatures. Do you use bearing temperatures as an ESD input to automatically shutdown your machines? If yes, does the temperature protection logic involve any time delay? If yes, how much is it?

At the place where I work, currently we use bearing temperatures as shutdown points with 0 seconds time delay and considering relaxing this a bit.

 

Please share your thoughts. 

Regards- Ali M. Al-Shurafa 

Original Post

I think you need to define what you feel is critical machinery and in particular does the machine meet API 670.  API 670 for instance requires two temperature measurement devices per radial bearing.  What I would recommend in that instance would likely be much different than if only one device was employed.  Also, for temperature, are we using imbedded devices, drainback or a combination?  Do we do something different for a thrust bearing vs. radial, tilt pad vs. sleeve, gearbox vs. steam turbine vs. motor...

As I hope you can see, just too many variables to reach a recommendation. 

John from PA posted:

define what you feel is critical machinery: major equipment that can slow down production in case of failure.

does the machine meet API 670: some of them were built on APIs but most of them are older than the recent editions of the APIs

 API 670 for instance requires two temperature measurement devices per radial bearing.  What I would recommend in that instance would likely be much different than if only one device was employed: Most of the machines in my review have a single temperature element.

 Also, for temperature, are we using imbedded devices, drainback or a combination?  Do we do something different for a thrust bearing vs. radial, tilt pad vs. sleeve, gearbox vs. steam turbine vs. motor... : These machines are mostly horizontal (motors , turbines, gearboxes pumps and compressors) mounted on journal bearings and the sensors are embedded. I'm asking about both radial and thrust

As I hope you can see, just too many variables to reach a recommendation. I thought at least with respect to the time delay with the above the details, there would be a general practice where you used to work.

William_C._Foiles posted:

Other considerations:

  • Where do you set the alarms?  In BN racks.
  • Do you have trouble cooling the oil given your location? No. We try to avoid spurious alarms.
  • What is the oil viscosity?  Higher viscosity lube oil will have higher temperatures. The issue is not a high temperature that need a troubleshooting. I'm try to see what others do as a general philosophy.
  • The type of machine plays a part.  Turbines, motors, gearboxes, pumps and compressors: 500-30,000 hp, mostly 1200-9000 rpm 

Regards- Ali M. Al-Shurafa

Whether you have alarms, trips, or none is a value decision per company.  

Better question that Where alarms are set would be 'What level' is used for alarms and trips?'  

If you use cooling water for the lube system, then you may be able to achieve reasonable inlet oil temperatures at your location.  Air coolers can be limited in hot climates.  These other questions can help determine reasonable values for alarms.  OEMs do not always account for site conditions very well.

 

The potential issue with time delays is that the bearing will be severely damaged before the shutdown. This will result in greater damage or damage to the rotating and stationary parts other than the bearing, which takes longer to repair.  Another issue with simple delays is that spiking signals are not always mitigated by just a time delay.

Of course much depends upon the alarm levels.   The bearing loading affects bearing failure along with temperature.  

 

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