Boiler Feed Water Pumps oil cooler issue.

[Daren Samy]

We have experienced increased water content in lube oil of main feed water pump. This lube oil is supplied by shaft mounted main oil pump from lube oil tank to bearings of main boiler feed water pump and main boiler feed water booster pump. Both pump are coupled in series by motor and reduction gear.In lube oil tank, heater remains off and there is no provision of silica jel damp removers. During first operation, water contents remain with in range. But when it is taken out of service, water contents start to build up. Consequently, I have to remove oil cooler to perform hydrostatic rest. Hydrostatic test is qualified. I am clueless about water ingress. What can be reason ?

Daren!

 

[LittleInch]

I would assume your seal between shaft and pump is letting water by. If this is a mechanical seal they usually need to have rotation to work correctly. If the pump stops it should not be pressurised waiting to start otherwise your seal will leak.

Other option is whether there is condensation coming in from the outside air via the tank breather pipe?

but pump seals sounds like the most obvious to me. Can you post more details of the pump and its seal arrangement?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Oil cooler leak would be my guess, since hydrotest fails with cooler inline ( higher pressure water leaks into zero pressure oil when oil pump is not running).

 

[TugboatEng]

Hydro test is qualified means it was tested and did not leak?

 

[Daren Samy]

1. Leakage from mechanical seal is minimum. There is leakage detection line attached to drain cavity if water leakes from mechanical seal. So, water ingress from mechanical seal is no option and it is quite obvious.

2. Hydrostatic test of cooler always qualifies at room temperature (even of dismounted/removed cooler). There is serrated gasket at sealing surface of cooler. We are using 56KR Klingret gasket. There is no problem with oil when if pump remains operational for the first time. When it is downed and taken into service again, oil shows water contents.

Daren!

 

[LittleInch]

Daren, we can't see what you can so it would be good to post the P &ID of the lube oil system and also the section details of the pump.
Where is this drain cavity? That's why we need to see a drawing.

When you say "taken out of service" or the pump is "down" what do you mean?

Just turned off? Or isolated and drained ? Or ??

Is there a breather on the oil tank?
Does it go through a desiccant?

What is used to cool the oil? water? what does this cooler look like?

Why do you have to remove it each time?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Daren Samy]

Water cools the oil.
Pump down means that pump is taken out of service as per operation requirement to take stand by operation in service
Pump remains in stand-by mode.
There is no breather on tank
There are heaters in tank but they are not taken in service as temperature remains in acceptable range.
Is is barrel type four stage pump. I have no sectional diagram at present. But I try to explain.
From free end to drive end arrangement.
Thrust bearing, journal bearings with lybrith seals on both side, mechanical seal , cooling water jacket, balance drum, 4 stage impeller, mechanical seal, cooling water jacket, journal bearing with lybrith seals on both ends.
Designer has provided 5mm cavity between lybrith seal and mechanical seal on DE and NDE side. If oil leaks from lybrinth seal, it is collected in cavity and if water leaks from mechanical seal, it goes into cavity. Then through cavity, this oil/water drains through drain pipe into trench.

Daren!

 

[LittleInch]

What do you mean by no breather on the lube oil tank? There is no filter or no breather?

Doesn't make sense to have no breather.

But if not humid air getting in then where? We need to see some sort of diagram or photo or details of this oil cooler to try and help.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

That raises a question, is the oil being cooled to a point that causes condensation? Is cooling water flow being maintained through the cooler while the unit is in standby? What is the temperature of the sump when the unit is idle?

 

[LittleInch]

Also what are the operating pressures of the water and oil in person and standby mode?

Operating temperature?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Is this oil cooler a plate frame heat exchanger ? - notorious for inter stream leaks.

 

[TugboatEng]

Plate and frame exchangers are not notorious for interstream leaks. The fluids are typically air gapped with external leakage routes.