High Pressure Steam Leak Dripping Water

[Mikegt98]

Question for the group. I found this forum and decided to post the following question. There is a steam leak coming out of a flange to an HP Turbine. The steam is 959# and 540 deg F. The leak is barely noticable, mostly by the water dripping from the flange. The question is about the water dripping from the flange. I am curious as to why the water is not evaporating from the flange. The flange is about 450-475 deg F. The only thing that I can think of is that more water is being condensed from the steam leak than can be evaporated by the flange. Scratching my head on this one.

 

[Montemayor]

Mikegt98:

Is your observation based on theory or on actual, real fact?

Go to:

http://webbook.nist.gov/chemistry/fluid/

And you will find that at 975 psia and 540 oF, your system is composed of liquid water, not steam. Therefore, your description of the leaking fluid is misleading and confusing.

Are you trying to say that you are leaking condensate that you expect to be evaporated (or flashed) due to the 450 oF pipe flange temperature?

You’re going to have to better define what you have or are trying to describe. Are you familiar with the thermodynamic T-S (or Mollier Diagram) for steam? In what area are you working on? Is your steam supposed to be saturated? Superheated? supercritical?

 

[rmw]

First, I suspect that this is a flange in a line coming from a HP turbine, not 'to' it. Sounds like a cold reheat line to me, based on the temp and press.

Second, saturation temp for 959 psig or psia is 541F or 539F respectively (give or take a few truncated decimals). Doubtful that plant instrumentation is going to measure accurately enough to know the exact temperature, but we can work in the neighborhood.

Therefore your steam is either right at saturation, or possibly even less than 100% quality, (not good) explaining where the moisture is coming from, and yes, if there is free liquid along the bottom of the line, and it is leaking out in sufficient quantities, then all of it cannot be vaporized by the sensible temperature of the flange, and you get the liquid indication of the leak. Very explainable.

rmw

 

[rmw]

I'll widen my postulation that the line might even be 'from' the turbine 'to' the first point HP feed water heater, which still would indicate that is is cold reheat to me.

rmw

 

[itdepends]

What about the sensible heat in the liquid (not just the flange).

A liquid at that temperature should flash when exposed to atmospheric pressure- there should still be steam present at the leak point.

Mike- is the water coming from the flange itself or is it coming out of the insulation on the pipe (I'm assuming the pipe is insulated).

If it's coming out of the insulation your leak may be further up the pipe and the flashed steam I am referring to above would be condensing as it cools during its' path through the insulation.

P.S.- if you do have a leak under the insulation you are going to end up with a corrosion problem unless you find and rectify it.

Cheers

 

[Mikegt98]

Sorry for evidently posting a misleading question. The leak is coming from the inlet flange to a High Pressure Turbine. The properties are correct and the steam is mechanically dried to a quality of 99.99. So yes it is right on the Saturation-Vapor line. This was not the intent of the question. The intent of the question is why doesn't the steam leak flash once it leaks out of the flange.

The insulation was removed from the flange and water is still dripping. There is no noticable steam, only the condensation dripping from a 450-500 degree flange face.

Also as "itdepends" posted, any water in the steam should flash when it goes from High Pressure to Atmoshphere.

 

[JimCasey]

Not all the water flashes to steam. From your conditions you'll only get 36.8% flash. (assumed adiabatic, Isenthalpic expansion to standard atmosphere)

STEAM is an invisible gas. IF it stays concentrated enough as it cools to form a cloud of droplets, you may see it. If there is adequate ventilation and low humidity, the steam may disperse enough not to condense into droplets, and would never be seen. Meanwhile, the 65.2% that remains liquid drips out of the flange joint.

 

[25362]

Please forgive me for trying to do a little lateral thinking. Mikegt98 said the leak is barely noticeable, and if the drops are initially small enough any cooling by a vaporizing film wouldn't be visually apparent.

It also appears as if cooling resulting from a (leaking) steam expansion is followed by an effect similar to a kind of thermostatic trap set to release condensate at lower temperatures. Would the impregnated gasket material act as such or could it enhance vaporization and cooling ?