Failure in a turbine oil cooler

[maypot]

Hi,

We have a turbine driven generator set and the cooling water for the oil cooler comes from a cooling tower station. However, it could happen that due to clogging of the oil cooler, the cooling pond water pressure might rise to such a point that the cooling water pressure is greater than the oil pressure. In case of failure of a tube in the oil cooler, the consequence might be catastrophic.
Grateful to have advices from the forum members.

Cooling water pressure 2.8 bar
Oil pressure 1.8 bar

Bob

 

[maypot]

The cooling water pressure 1.8 bar
Oil pressure 1.9 bar

 

[MikeHalloran]

Use a water pump that can't generate that much pressure, and rely on the high oil temperature alarm to shut down the turbine?



Mike Halloran
Pembroke Pines, FL, USA

 

[JJPellin]

I assume that this is a common cooling water system and you won't be able to reduce the system pressure. We have this situation in a number of critical pumps. You can either regulate the cooling water pressure down right before the cooler or you can set up a PM strategy to make sure the cooler stays in good order. If the cooling water return pressure is low enough, you can regulate the cooling water supply to just below oil supply pressure. This will also reduce the cooling water flow rate and that could be a problem if the system does not have enough excess capacity. Installation of a larger cooler could get you the same cooling with lower pressure water. Otherwise, we set up a preventive maintenance schedule on the cooler. We open it for inspection every 5 years. We pressure test it on reassembly. We keep a spare in the warehouse and replace it if it shows any deficiency. Is there any possibility of increasing the oil pressure? The machinery manufacturer should have provided a range of acceptable oil pressures. Perhaps 2.0 bar would still be acceptable for the machinery and keep you out of trouble with the water.

 

[turboco1]

install a second cooler, switch over (correctly mind you) and do pm when you know you're dirty... since when does a T-G set have to shutdown for a dirty oil cooler, water or oil side? Most cooling water systems are constant pressure and most oil coolers have a temperature regulating valve on the water exit side to regulate flow based on temperature setting...it is a flow controlled system with constant pressure, usually.

 

[abeltio]

usually in the gas turbine you can adjust the lube oil pressure a bit... without affecting the performance of the system and, most important the safety of the bearings.

from the data supplied seems like the water and oil pressures are too close for comfort.

the L.O. press = 27.6 psig
could you adjust the pressure of the LO to 30.5 psig (2.1 bar)?

also, if you have a pressure regulating valve in the cooling water system could you adjust the pressure to 1.6 bar?

then... is this something you are thinking of like a haz-op scenario?
I had leaky water tubes in lube oil coolers... the first sign is FOAM in the oil and also... the water goes to the bottom of the lube oil tank and the operator should detect the water during the regular checks of the lube oil tank drains, exactly for: water collection.
also, GT manufacturers recommend periodic lube oil analysis, typically once a month, and specifically for water content...
if you have a catastrophic failure because a tube started to leak... that means that some corners were cut in the routine maintenance and monitoring program.

an immediate catastrophic failure will happen if you have a massive tube failure in the lube oil cooler... but that is highly unlikely, unless the poor thing was never maintained.

you could also add another degree of protection with a [Δ]p switch between the water and oil system to monitor that the value of [Δ]p is kept at a certain value when the unit is running... as soon as that value goes to 0 or negative (water press higher than oil pressure)you should drop an alarm to let the operator know of the abnormal situation.


saludos.
a.

 

[FredRosse]

On many of our combined cycle gas turbine installations, the cooling water is typically greater pressure than the oil, but the failure of the cooler is not considered. There is ample margin between the cooler design pressure and the actual pressures. Periodic inspections will reveal heat exchanger tube deterioration.

99 times of 100, heat exchanger tube leaks are at very low flow rates, and are noticed when oil quality is checked.