Piping High Pressure Return into Low Pressure Steam Main

A small 160 psig steam transmission main is being installed through a manufacturing building where currently there is only 30 psig steam for heating and a localized 80 psig system for a particular process (which operates intermittently). Since the 160 psig steam is not used in the building, there are only two drip traps yielding a relatively small flow of high pressure return. Since the total high pressure return flow is less than 2 gpm, and since the plant would like to avoid installing flash system for such a small load, it was suggested that the high pressure return be piped directly into the 30 psig steam main.

It can be assumed that the 30 psig steam will serve a process load in an adjacent building and so will remain operative year-round and the necessary relief valves will be provided should the 30 psig system be shutdown.

I do not have experience doing what has been suggested. One issue I see is linked to trap failure. For the drip service, traps that usually fail open would be employed. This could result in 160 psig steam being bled into the 30 psig main. If demand on the 30 psig steam main is low enough, the pressure relief valves would operate. Another issue might be localized stresses where cooler condensate is being introduced into a hotter pipe. Here, the condensate is hotter (and will flash off into the main) so I don't see this as a concern.

Does anyone have experience, positive or negative, with the practice of piping high pressure return into low pressure steam mains?

Ken A. Nisly-Nagele

[Non-text portions of this message have been removed] Received on Tue Mar 01 08:37:00 2005