Steam velocity under vacuum

[McCormick93]

I have a situation where vacuum will be pulled on a steam line, creating lower density and higher velocity steam than the pipe was originally designed for.

Many publications list 12,000 ft/min as a maximum velocity for steam in a process plant environment.

Does anyone know what happens when when this velocity is exceeded? Can a vacuum condition be treated differently than positive pressure when considering velocity?

 

[katmar]

Some guidelines and references for this type of problem were given by Art Montemayor in thread378-71486

Basically, you have three factors to consider.

1. Under vacuum conditions pressure drop can be important because it becomes a higher fraction of the available driving force.

2. High velocities can be noisy. I seem to remember a value of 0.7 Mach being recommended to avoid excessive noise.

3. If your steam is wet you could get erosion and the allowable velocities would have to kept well below the values recommended for dry steam.

regards
Harvey

 

[dicksewerrat]

What happen when the pump shuts down? or a valve closes on
12,000 ft.min pipe? pressure wave, big one.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[katmar]

Richard,

Depending on the degree of vacuum, the kinetic energy in the steam at 12000 ft/min is roughly equivalent to that in water at 120 ft/min (2 ft/sec). You don't want to slam your valves shut, but with a bit of care it is quite safe.

Harvey