HP Steam Turbine Shaft Seals - Shutdown Condition Sealing

If there is no flow under shutdown conditions, then there will be no friction at the boundaries of the control volume with which to create a pressure drop. So the answer in this case is 0.

By definition.

But the question is if there is some amount of above atmospheric pressure on the turbine internal side, what would be the flow out the seals. Conversely, if there in vacuum inside, then the flow in.

Experience preferably, and as a worst case, experimental or analytical approach, used or useful, is what I'm looking for.

"Stopped though still hot"?

The pressure drop can therefore be determined by observing the pressure gauge closest to the equipment in the steam supply line. In comparison with the pressure drop through the turbine when the thing is running, the drop through the turbine itself is negligible with it stationary, nearly all of the drop happening across the seal.

Definitely stopped though still hot, probably complicating things.

I'll look for the nearest gauge. For outleakage, to estimate the flow we'd have the figure out the source free volume and time its pressure decay, probably complicated by some cooling or condensation that is going on. Inleakage has similar issues, since vacuum could be lost in other ways.

Maybe cold condition assessments would be simpler. But it still would be nice to know if anyone has done a simple, cold, controlled experiment or a design analysis for such a seal system.

Maybe a call to a manufacturer would yield something.

I think, but I could certainly be wrong, that during a typical two to four week outage that you will have lost vacuum. And that you would be using mechanical vacuum pumps to re-establish a condenser (and turbine?) vacuum, maybe before introducing heatup steam. Big volume calc here, and the assumption that inleakage to the whole system is from turbine seal inleakage. Of course both HP and LP seals turbines would then be involved at that point.

Definitely agree on issues with respect to labyrinth seal flow orifice equivalencing. I guess that might be what I'm looking to be handed to me from experience or prior analysis..

During a 2-4 week shut down the vacuum would be broken, sealing steam shut off, turbine drains opened, condenser and condensate pumps off and interior would be at atmospheric pressure, hence as the man said before Flow=0.

On start up sealing steam turned on to maintain wisps of OUTWARD flow, warm up steam introduced so it's blowing out any condensate to the turbine drains, steam eductors or vacuum pumps turned on, condenser and condensate pumps turned on. When there is no evidence of moisture from the drains and the vacuum is sufficient the drains can be closed. It is the sealing steam into the labyrinth seals under positive pressure that keeps any inward leakage from occurring. Once the vacuum has been established and the turbines are on line your vacuum system should only be removing minor amounts of air.

Your hypothesis of huge volumes of inward leakage basically surmises that your labyrinths are shot and no amount of sealing steam can keep the air out (or that you have a crack in your condenser or turbine housing) so you're the creek without a paddle anyway. Please do not attempt to start up a plant on the above instructions.