Grease at Low temperatures

[davejc]

I have experienced the use of a -20deg lithium based grease at low temperatures (about -15deg)and there was evidence of solidification and crytals present. The grease is used to lubriacate seawater seals and led to the seals passing. Does anyone know if the grease expands or contracts at lower temperatures?

The grease properties are as follows:

Drop point 180degC
Base Oil Viscosity 150cSt @ 40degC
Penetration 265-295 (N.L.G.No.2)

 

[TVP]

You need to know what the viscosity is at -15 or -20. Viscosity changes significantly with temperature.

 

[Cockroach]

Yeah DaveJC, the properties of grease change with temperature. In cold weather engineering, "cold" meaning -45C and worse at higher Canadian latitudes, valve applications, these changing properties cause considerable problems for grease seat injection systems.

My valve designs specifically call for a teflon free grease base, lithium is not as bad but is also thermally influenced. I have found that Esso Equilub 80 to be probably the least responsive to temperature, so that it would be my recommendation for seat injection(s). Perhaps this will work for you.

One practice that the industry uses in our winters, is to dehydrate the valves with methanol. Field technicians typically pour significant amounts into the valve cavity. It has been our experience that this is the number one cause of elastomer swelling, methanol is absorbed by the base rubber matrix thus elevating compression. Once this happens, the valves typically hang up. I don't think that there is ANY solution to removing either grease or water in the form of ice from internal components. Some say a nitrogen purge works well, I really don't know since personally I have never used it.

You may want to try blowing out the grease lines with air, basically 78% nitrogen. I would definitely be interested with your experience in this regard.

Hope this helps.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[davejc]

Hi Guys

Thanks for the help, the grease is only used when fitting the seals, although it fills the cavities of the seals. There is no constant grease charging system.
I was interested to know if the grease expands, would this contribute to the seals leaking.
We replaced the grease with lower temperature grease (-40degC) but I am trying to establish the root cause of leakage.
The temperature has now risen and is no longer sub-zero

Thanks

 

[diamondjim]

Sounds like a good question.

I would go to the manufacturer for this
information. Let us know the reply.

 

[Tofflemire]

Hi DaveJC,

Have a look at the forum list, and maybe post your question in one of the other forums.

Tofflemire