Condensate piping is used to remove condensate from steam-heated vessels, ideally for recovery and re-use in boiler feedwater. When hot condensate under pressure is discharged from a steam trap into a low pressure system, the resultant pressure drop causes some of the condensate to flash into steam.
Consequently, the design of condensate piping systems is not as straightforward as that for transporting water, as it must accommodate “two phase” flow. Listed below are five important factors to consider when designing condensate piping systems.
1. Pipe Sizing and Design Code
Pipe sizing has to take into account the volume of flash steam created. This is a function of the pressure drop across the steam trap and condensate flow rate. Flash steam can cause very high velocities if the return line is not sized correctly, causing back pressure in the system and reducing steam trap performance. It is recommended that piping be designed according to the ASME B31.1 Power Piping Code.
Condensate piping systems are vulnerable to carbonic acid corrosion. For this reason, stainless steel is recommended to prolong system life but cost implications might preclude this as a material of construction. If carbon steel is used instead, schedule 80 pipe is recommended because of its larger wall thickness.
3. Piping Connection
Condensate piping undergoes expansion and contraction. Threaded connections don’t have the capacity to withstand this thermal cycling and are also a prime target for acid corrosion. Ideally, pipes should be welded or tube connectors employed to minimize leaks.
4. Connection to the Condensate Header
Condensate headers should be horizontally aligned, with condensate lines connected to the top. Headers aligned vertically, or those with bottom or side entries can cause hydraulic shock.
All components of a condensate piping system must be designed and installed for ease of maintenance. Lack of regular maintenance will lead to poor system performance, and inevitably, structural failure.