Flash Steam is a consistent occurrence in a steam system. Whenever condensate is being released from a higher pressure steam line to a lower pressure it occurs. For example, a steam line operating at 100 psig will have a saturation temperature of 338oF. When the condensate that is formed in this steam line is discharged to the atmosphere, the condensate temperature at atmospheric conditions can not be more than 212oF. This change in energy must be converted and that is accomplished by flashing some of the condensate into steam. Keep in mind that when the condensate is flashed back into steam, the steam takes up a much larger volume and this volume needs to be accounted for when sizing condensate return lines. The amount of flash steam that is going to be produced can be calculated and should be done when designing a condensate return line, however utilizing a Flash Steam Chart can also provide a quick reference tool to help calculate the amount of flash steam that will occur. When designing condensate return lines for condensate/flash steam flow the line velocity should not exceed 4500 feet per minute. Velocities above this rate can cause water hammer issues in your return line.

For additional information of Flash Steam and Condensate Return lines refer to the following Best Practices from Swagelok Energy (www.swagelokenergy.com):

Swagelok Energy Best Practices No.7 – Flash Steam
Swagelok Energy Best Practices No 14 – Condensate Return

It is helpful to remind ourselves the substantial benefits of insulating steam piping.  Huge amounts of energy is put into producing steam and yet as we transport it from point A to point B we often allow large energy losses to radiate freely into the ambient air.  Heat energy as we know moves from a higher temperature to a lower temperature and the rate of this transfer is proportional to the temperature differential and the surface area of the pipe (other factors do impact the losses such as wind speed, surface emittance, and thermal conductivity of the pipe material). 

For example 100 psi steam is 338 F and if the ambient temperature is 60F, that is a  278F incentive for the heat to radiate out of the piping.  Now if we use 3″ piping that is also lots of opportunity for the heat to escape.  So, for every foot of 3″ piping carrying 100 psi steam and exposed to 60F ambient temperature, 778 BTUs per hour are lost.  That is nearly 6.5 million BTUs or the equivalent of 21,000 lbs of steam per year lost for each foot of piping.

All steam lines need to have adequate condensate removal from the steam line on a continuous bases. No matter how well the steam line is insulated; the heat energy will be transferred from steam into the atmosphere, and the steam in the steam line will change state (latent energy is released); thus condensate will form in the steam line. The condensate volume will depend on the steam line insulation, steam pressure, and steam line length. The condensate will flow with the steam at the bottom of the steam line in a swaying motion (not a straight line); thus the steam line “drip pocket must be large” (drip pocket is the name of the branch line extending down).

Read the Best Practices:  http://www.plantsupport.com/download/PSE_BP_1.pdf

All steam lines need to have adequate condensate removal from the steam line on a continuous bases. No matter how well the steam line is insulated; the heat energy will be transferred from steam into the atmosphere, and the steam in the steam line will change state (latent energy is released); thus condensate will form in the steam line.

 The condensate volume will depend on the steam line insulation, steam pressure, and steam line length. The condensate will flow with the steam at the bottom of the steam line in a swaying motion (not a straight line); thus the steam line “drip pocket must be large” (drip pocket is the name of the branch line extending down).

www.swagelokenergy.com     Best Practices

Many years ago it was “in vogue”  for almost every steam facility to have a steam turbine.  There were many lower pressure steam turbines for pumps, fan drives, etc.  I believe that most were taken out and pressure reducing valves were installed for steam pressure reduction.  Are there any low pressure steam turbines that have a real payback vs. steam pressure reducing stations?  Has the technology improved?  Is there payback for this?

What type of steam control will provide the highest turndown for a process application?

What type of steam trap do you recommended for heat transfer applications?

Maria Delgado
Industrial Engineer

We are looking for specific design information for the length and material selection for steam pressure gauge pigtails to release the heat from the steam.