Moisture in your gas stream: how it damages your sensors and what it costs you
Moisture in a gas stream is one of the most common, and most underestimated, causes of sensor failures and measurement errors. From electrochemical sensors to infrared detectors: condensation is their greatest enemy.
⏱ approx. 4 minutes reading time
Why moisture is so destructive to gas sensors
Gas saturated with water vapour appears to behave normally, until it touches a colder surface. At that point, the moisture condenses and liquid water forms in the system. That moment, when the gas stream reaches its dew point, is the beginning of problems.
Most gas sensors are designed for dry or slightly humid gas streams. Condensation in or on the sensor leads to a series of problems that sometimes appear immediately and sometimes develop gradually.
- Short circuits and corrosion: Liquid water on electrochemical sensors (e.g. O₂, CO₂ or H₂ sensors) causes short circuits between electrodes. With repeated humidity cycles, oxidative corrosion of the internal contacts occurs.
- Membrane blockage: Sensors with a gas-permeable membrane (e.g. galvanic cells) become blocked by a film of water. The gas no longer reaches the active sensor surface, resulting in under-reading or failure.
- Optical contamination: In NDIR (infrared) and UV sensors, moisture deposits on the optical windows and lenses. This permanently weakens the signal and results in systematically low concentration readings.
- Drift and calibration errors: Even without visible condensation, at relative humidity above ~80% RH, the dielectric constant of the gas around the sensor changes. This causes measurement drift without any visible alarm.
The dew point is the critical limit
As soon as the gas temperature falls below the dew point, even locally at a cold fitting or wall, moisture condenses immediately. In outdoor applications or at varying temperatures, this risk is always present, even if the gas seemed relatively dry at the source.
The hidden costs of moisture problems
Sensor damage caused by moisture is rarely a one-off incident. The pattern we see at customers: sensors fail regularly, are replaced, and fail again, without the cause being addressed. This results in the following:
- Sensor replacement €150–800 per sensor depending on the type
- Unplanned downtime leading to loss of production
- Incorrect measurements
Add to this the technician's time to replace the sensor, the calibration procedure that has to be repeated, and the uncertainty about the reliability of measurements in the meantime, and it quickly becomes clear that a small investment in gas conditioning soon pays for itself.
Case study: Wet methane stream damages measurement sensors in a natural gas application
A customer monitoring the methane concentration in a natural gas stream was faced with recurring sensor failures. The natural gas from the grid contained enough moisture to locally exceed the dew point at the prevailing process temperatures. The result: condensation directly on and in the measurement sensors. Sensors failed regularly and had to be replaced and recalibrated. The cause was not the sensor itself, but the condition of the gas stream upstream of it.
After analysing the problem, we recommended installing a Perma Pure BE-Series Braided Exchanger directly upstream of the measurement step. The Nafion membrane dryer brings the moisture content of the gas stream into equilibrium with the ambient humidity, without power consumption, without purge gas and without loss of measurable gas components such as methane. In practice, the relative humidity of the gas stream dropped to approximately 60% RH, well below the condensation point. Condensation in the system became a thing of the past.
When is the BE-Series the right choice?
The BE-Series is ideal for applications in which the gas stream must be dried to ambient humidity without losing analytes. Typical applications: outdoor air quality monitoring, mobile gas measurement equipment, industrial emission monitoring and medical gas analysis.
