Suppose there is a turbogen and an emergency diesel generator for a facility.

Now the engine manual provides a calendar-based maintenance schedule for the emergency diesel engine because running infrequently eg during test runs but a running hour-based for an industrial diesel engine which run longer eg on 24 hours basis.

This choice appears to be clearcut at first but when the emergency generator is also used as a back up during the turbogen shutdown which could be to 4 days long, its running hour starts to accumulate very quickly compared to when it's used only to cater for the turbogen trips or when there is another standby turbogen in another facility.

Have anyone faced this scenario before?

Should I switch the PM from recommended calendar based to running hour based because the operating context dictates?

Josh

Now, how many do you have PM program with your emer. generator?

Josh,
The first order of business is to understand how the machne degrades and the factors causing degradation. In an engine operating continuously, wear of piston rings, bearings etc., carbon deposition on valves, pistons and manifolds, fouling of fuel injection nozzles etc. are all significant factors causing degradation. An engine running infrequently on low or no load faces other failure mechanisms, mainly related to cold running. Dominant among these is the heavy carbon deposits on rings, valves, and manifolds. If there is a supercharger, startup lubrication can be an issue.
4 days of running will, if anything, improve the performance of a standby engine, as it will put it on full load and help burn away some of the carbon deposits. I would not add any maintenance tasks on this account. You will need fewer top end overhauls in this case than if the machine were just run for a few hours every month.
The manufacturer will recommend you do more than required, because he has to face the possibility of a wide range of operating scenarios and maintenance skills. Our job is to decide what is right in our case.
Maintenance is all about managing degradation. So we need that understanding first.

Josh
We have also run into this situation. In our case we have the same asset being used differently at various locations around the world. We thought we would end up with different plans for different plants (hour based at some and calendar based at others). We started by looking at the task and the particular failure mode it was intended to address. (As suggested by Vee) When we finished we found that most of the tasks were best performed on a calendar and only a few were based on running hours. We ended up compromising and putting everything on a calendar in order to have a global standard. Some plants are doing a little more PM than they might otherwise but the loss is insignificant.
We also found that in our case we really did not have good historical data in order to optimize the PM interval.

Posted on behalf of Marcelino C. Llamoso

We have the same set up as described below.

This is our PM schedule:
1. Weekly test run for 30 minutes
2. PM/Inspection of battery bank every two months
3. Lubrication/Oil top up every three months
4. Annual change oil

Hello,

I found this which might interest you:

http://www.cumminspower.com/www/literature/technicalpap...ieselMaintenance.pdf

cheers

After so long, this post got attention again.

Vee, I agree with you that we should have the just right maintenance based on the actual degradation as you mentioned above. However, should I base the PM including overhaul such as top end on running hours or calendar?

Btw, I checked NPFA 110 Chapter 8 which can be accessed for free in here:
http://www.nfpa.org/freecodes/free_access_document.asp

quote:

run for 30 minutes

We also have two standby emergency power generators that auto cut-in in case of outage of any of the two gas turbines.

We run them on every thursday and run on load for 30 min. Any leakages in oil fuel circuit are checked. Water hoses are observed. Oil levels made up if required.

Oil change is carrried out on yearly basis.

If we don't run engines on this frequency, we have increase in moisture content of the oil.