How to measure Dew Point in ultra-high-pressure Gas

Although some applications measure humidity at atmospheric pressure, there are many more industrial processes that require measurements of humidity, trace moisture and dew point at line pressure. Compressed air is usually at around 7 barg (100 psig), but there are some applications where pressures are much higher.

Why is it important to monitor the dew point of air or other gases under pressure?

The main reason to measure the dew point of gas under pressure is to avoid the risk of condensation forming in the system, which can lead to bacterial growth or corrosion of valves. Condensation becomes a risk when gas is pressurized because the dew point of air or gas rises with pressure. This makes drying the air especially crucial and monitoring the dew point of the dry gas not only helps control drying cost but also provides quality checks on the high-pressure air or gas. Our article ‘How to calculate pressure dew points (PDP) accurately’ explains the physics that causes this.

What are the main applications where you would need to measure dew point at pressures over 100 barg?

In industrial applications, pressures from 20 to 450 barg (290 to 6527 psig) are referred to as ‘ultra-high pressures’. Typical applications for ultra-high-pressure air include:

  • Breathing air tanks. Tanks of breathing air are used for diving, firefighting and working with hazardous materials. To keep the tanks small, the air may be pressurised up to 380 bar (5500 psig) and control of moisture is important to avoid bacterial growth or damage to valves.
  • Read more about the critical measurements in breathing air.

  • Hydrogen refuelling stations. These may operate at 350 bar (5076 psig) through to 700 bar (10,153 psig) so as to supply the fuel quickly. Dry gas is important to avoid the risk of damaging the engine as well as to avoid the risk of icing up in cold weather.

  • Marine. High pressure air is used in marine and military applications for breathing and instrument air, as described above. Because of the extra force it provides, it is often used for clearing submarine ballast tanks for ascent to the surface. The high pressure allows the tanks to be cleared quickly and gives the crew a greater level of control and responsiveness.
  • Avoiding excess moisture is vital in marine applications because of the risk of freezing. Reducing the pressure of a gas has a cooling effect, and this, coupled with the already low temperatures below sea, could easily lead to ice forming in air lines and disable the submarine.

    Why ceramic metal oxide moisture sensors are recommended for measuring dew point in high pressure air or gas

    Metal oxide moisture sensors directly measure the partial pressure of water vapor. For any given partial pressure of water vapour there is only one corresponding dew point. This means that as the partial pressure of water vapour increases with total pressure, the measurement performance remains valid and directly related to its factory calibration.

    The Michell Ceramic Metal Oxide moisture sensor has been designed with high-pressure applications in mind, providing excellent performance when compared to the performance of alternative polymer-sensor products.

    What are the options for measuring trace moisture in ultra-high-pressure gas?

    In-line measurements.

    The sensor is placed directly in the gas line and measures at line pressure.

  • Pros – this produces reliable results. The sensors are small and easy to install and maintain – especially with the Michell Instruments Sensor Exchange Program, which ensures minimal fuss and virtually no downtime.
  • Cons – the choice of sensors is limited to metal oxide. Although easy to install, it is important to have reliable seals.

  • Spot checks using a portable hygrometer.

  • Pros – portables can be used to make spot checks on various parts of the system as a backup to online measurements, for example to find the exact location of leaks.
  • Cons – it is not possible to use portables for inline measurements on ultra-high-pressure systems. Above 100 barg, extractive sampling is needed.

  • Extractive sampling.

    A sample of gas is removed from the system and moisture is measured at a lower pressure.

  • Pros – it is possible to use any moisture sensing technology.
  • Cons – this technique requires a full sample conditioning system, which is larger and more expensive than an in-line dew-point transmitter.
  • Recommended products

    We have a wide choice of dew-point transmitters and portable hygrometers that are capable of measuring dew point and trace moisture in gases at various pressures.

    Measure trace moisture in pressures from 100 barg/1450 psig up to 138 barg/2002 psig

    SF82 | Dew Point Control | Compressed Air Dryers ( - 100 barg/1450 psig

    Portable Fast-Response Hygrometer - Michell MDM50
    Caption: Portable Fast-Response Hygrometer - Michell MDM50

    Portable Fast-Response Hygrometer - Michell MDM50 ( High-pressure version (HP): 100 barg/1450 psig

    Process Moisture Analyzer - Michell Promet EExd ( - 30 to 138 barg /435 to 2002 psig

    Moisture in Natural Gas Analyzer - Michell OptiPEAK TDL600 ( - inlet pressure max 100 barg/1450 psig

    Hydrocarbon Dew-Point Analyzer | Automatic On-line Analysis ( for water dew point at 138 barg/2002 psig

    Measure trace moisture at pressures up to 350 barg

    Portable Dew-Point Hygrometer - Michell MDM300 Series
    Caption: Portable Dew-Point Hygrometer - Michell MDM300 Series
    MDM300 Sampling Options
    Caption: MDM300 Sampling Options

    Portable Dew-Point Hygrometer - Michell MDM300 Series ( 350 barg/5076 psig With optional sampling system

    Measure trace moisture at pressures up to 450 barg/6527 psig:

    Dew-Point Transmitter - Michell Easidew EA2
    Caption: Dew-Point Transmitter - Michell Easidew EA2

    Michell Easidew EA2 | Moisture Meter ( - up to 450 barg/6527 psig For in-line measurements in ultra-high-pressure air. A hazardous area version is available for measurements in flammable gases, such as natural gas or biomethane.

    Process Moisture Analyzer - Michell Promet I.S ( up to 450 barg/6527 psig A complete sampling system for measurements in natural gas or other flammable gases.

    Measure trace moisture in air or gas up to 900 barg/10,153 psig

    Moisture measurements in these pressures are possible with the Michell Ceramic Metal Oxide Moisture Sensor and Michell Easidew Dew-Point Transmitters range. Contact us to get expert advice for your project.

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