For the process pumps in a refinery, where high temperature process fluids are used ( 260 deg C and upto 340 Deg C) , one of the pump vendor is requiring LP steam quenching in the stuffing box in their design and claims that this will reduce the heat soak for better life of the mechanical seal and the bearings as these will operate at much lower temperature . But further queried, the vendor says the same pump can also perform without any problem if the purchaser cannot provide steam.
Basically steam is a poor thermal conductivity and i am not convinced with the reply of the vendor.

Other vendors does not say this requirement for the same pump .

Thanks to clarify to have steam quenching design and its advantages and disadvantages.

If you are using a mechanical seal at these temperatures it will most likely be a Metal Bellows seal.  Pipining Plan can be Plan 11+ 62 (LP Steam) or Plan 02 + 62 (LP Steam)
Putting steam into the jacket is rather unusual for this type of application, cooling water is normally used to cool rather than steam.  Stean is used with high viscous product like bitument to keep the product liquid.
As far as the seal is concerned I would recommend no Steam or cooling water to the Jacket.  Make sure that you have a high temperature metal bellows seal with Steam quench.  If steam is not available then use Nitrogen quench.  Plan 62 prevents coking that is why we use it.

The pump manufacturer may claim that warm up piping is not needed. But it is. These streams can set up or become extremely viscous at ambient temperatures.  If you expect the pump to start automatically on loss of the main pump, it must be hot. If you expect operators to be able to start it up within minutes, it must be hot.  And even for an overhung pump, excessive thermal shock can result in rubs, leaks, bearing or seal failures.  I would consider warm up arrangements to be mandatory at these process temperatures.

I am confused about the seal flush plan.  If you are asking if you can use a low temperature seal because you have seal flush that is only ~120 °C, then the answer is no.  If flush is lost, the seal would fail dramatically and catastrophically, which would be guaranteed to start a fire.  Even with flush, you should use a high temperature seal (metal bellows) and a steam quench. 

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