Sample Tubing Materials

When determining the moisture content of gas samples, the materials used to transport the gas samples are extremely important.  As the gas passes through tubing, the polarity of the moisture molecules will cause them to be attracted to the tubing.  Any moisture that remains on the wall of the vessel does not have the opportunity to travel to the sensor, so it will reduce the sensor’s response time.  Also, some tubing materials (rubber, copper, PVC, etc.) are porous enough to allow for moisture penetration directly through the walls of the tubing, even in cases where there is considerable positive pressure.

 

Super Systems, Inc. recommends that only stainless steel is used as the tubing material for measuring low dew points (below -50°F).  It is also important to note that to maintain the integrity of the entire sampling system, all of the necessary valves and fittings, should also be constructed of stainless steel.  These material precautions do not need to be followed “downstream” (after the sensor), since the moisture content of the gas at this point is unimportant.