Comprehensive guide to pressure sensors for aggressive gases

Pressure sensors play a crucial role in modern industry, especially in environments where aggressive gases are processed, transported or stored. These sensors must not only withstand extreme conditions, but also resist the corrosive effects of the gases to ensure accurate and reliable measurements. This guide provides a comprehensive overview of the selection and application of pressure sensors for aggressive gases, with a particular focus on material selection for durability and safety.

Importance of pressure sensors in the handling of aggressive gases

Pressure sensors are essential for monitoring and controlling processes that use aggressive gases. They help to ensure the safety of equipment by continuously monitoring pressure to warn of potential leaks or dangerous pressure rises. In critical applications, such as chemical processing or gas extraction, these sensors can mean the difference between safe operation and a dangerous incident.

Criteria for the selection of pressure sensors

When selecting a pressure sensor for use with aggressive gases, several factors must be taken into account:

• Material resistance: The sensor housing and diaphragm must be made of materials that are resistant to the specific aggressive gas. Stainless steels such as 1.4404 (316L) or specialized alloys such as Hastelloy are often the preferred choice due to their high corrosion resistance.
• Temperature and pressure ranges: The sensor must be suitable for the specific temperature and pressure ranges that occur in the application.
• Certifications and industry standards: The selection can also be based on relevant certifications and standards to be met, such as ATEX for potentially explosive atmospheres.

Stainless steels and their resistance

Stainless steel is a commonly used material for pressure sensors, but not all stainless steels are created equal. Here’s a look at some common types:

• 1.4301 (304): A basic stainless steel suitable for less aggressive environments. Its use should be avoided in applications with high corrosion requirements.
• 1.4401 (316): Provides improved corrosion resistance, ideal for use with a variety of aggressive gases. Its molybdenum composition improves resistance to chlorides and acids.
• 1.4404 (316L): Similar to 316, but with even higher corrosion resistance, ideal for extremely aggressive environments.
• 1.4539 (904L): A high-alloy variant known for its exceptional resistance to highly corrosive conditions. It is particularly suitable for difficult industrial applications.

Recommendations for practice

To maximize the longevity and reliability of the pressure sensors, the following practices should be observed:

• Installation: It must be ensured that the sensor is installed correctly and that the ambient conditions meet the specifications.
• Wartung: Regular inspections and maintenance are essential to maintain the functionality and accuracy of the sensors.
• Prüfung: Regular calibrations must be carried out to ensure that the sensors are operating within their specified parameters.

Resistance of various stainless steels to aggressive gases and hydrogen

* DDM Standard

Explanations of the materials / steels:

• 1.4301 (304): Well suited for less aggressive applications; limited resistance to chlorine and sulphur dioxide.
• 1.4401 (316): Provides improved resistance to chlorine and excellent resistance to ammonia; suitable for a wide range of applications.
• 1.4404 (316L): Similar to 316 but with better resistance to sulphur dioxide and hydrogen chloride; ideal for more difficult conditions.
• 1.4539 (904L): Excellent resistance in almost all aggressive environments; the best choice for extremely corrosive conditions.

Additions to resistance to hydrogen:

• Hydrogen: Considered a relatively inert gas, but hydrogen embrittlement can occur under certain conditions (especially at high pressures and in the presence of catalysts). This table reflects the general resistance of the above stainless steels to hydrogen under standard conditions.
  • 1.4301 (304): Shows good resistance to hydrogen under most conditions. However, embrittlement may occur in highly corrosive environments or at extremely high pressures.
  • 1.4401 (316) and 1.4404 (316L): These alloys offer very high resistance to hydrogen embrittlement thanks to their higher molybdenum content, which improves corrosion resistance.
  • 1.4539 (904L): Although highly resistant to many aggressive media, resistance to hydrogen may vary depending on specific operating conditions. In general, 904L performs well, but should be carefully evaluated under extreme conditions.

Specific product information on pressure sensors for aggressive gases

Product overview

Our range of pressure sensors is specially designed for use in environments with aggressive gases. With advanced materials and innovative technology, our sensors offer maximum reliability and performance. Below we present three of our top products:

1. Pressure sensor model PX25H:

• Material of the wetted parts: 1.4404 (316L) Stainless steel, for outstanding corrosion resistance to a wide range of aggressive gases, including chlorine, ammonia and hydrogen
• Sealing-free construction: All wetted parts are welded without seals and are subjected to a 100% helium leak test.
• Measuring ranges: 0-100 mbar to 0-150 bar, with an accuracy of ±0.1% v.MB (of measuring range)
• Temperature range: -20 °C to +80 °C, ideal for demanding industrial applications
• Applications: Chemical processing, petrochemicals, gas extraction

2. Pressure sensor model PV22H₂:

• Material of the wetted parts: 1.4404 (316L) Stainless steel, for outstanding resistance to hydrogen
• Sealing-free construction: All wetted parts are welded without seals and are subjected to a 100% helium leak test.
• Measuring ranges: 0 to 4 bar, with an accuracy of ±0.25% v.MB (of the measuring range), for precise measurements on fuel cells
• Temperature range: -40 °C to +125 °C, ensures reliable measurement even at extreme temperatures
• Certifications: Hydrogen suitability
• Applications: Fuel cell

3. Differential pressure sensor model PV2722:

• Material of the wetted parts: 1.4404 (316L) Stainless steel, for outstanding corrosion resistance to a wide range of aggressive gases, including chlorine, ammonia and hydrogen
• Sealing-free construction: All wetted parts are welded without seals and are subjected to a 100% helium leak test.
• Measuring ranges: 0-100 mbar to 0-3.5 bar differential pressure, with an accuracy of ±0.5% v.MB (of measuring range)
• Temperature range: -40 °C to +125 °C, ensures reliable measurement even at extreme temperatures
• Applications: Differential pressure measurement on filter elements or heat exchangers

Technological advantages:

DDM pressure sensors are equipped with the latest sensor technology including the following:

• Analog signal processing for excellent accuracy, high resolution and outstanding long-term stability.
• Temperature compensation: All sensors have integrated, active temperature compensation, which ensures accuracy over the entire operating temperature range.
• Customizable outputs: Analog 4-20 mA, 1-6 V, 0-10 V and customer-specific digital interfaces to enable seamless integration into existing systems.

Service and support in selecting the right sensor:

• Technical advice: Our team of experts provides support in selecting the ideal sensor for each specific application.
• Customized solutions: We offer tailor-made adaptations to meet special requirements.
• After-sales support: A comprehensive warranty and technical support after the purchase are included with DDM.

Resistance of 1.4401 (316L) to aggressive gases

The wetted parts of the pressure sensors presented are made of the material 1.4404 (316L). The following table shows their resistance to various aggressive gases – general corrosion resistance data was used to create this table. It should be noted that the actual resistance may depend on many factors such as concentration, temperature, pressure and the presence of other chemicals. The classification into “medium”, “high” and “very high” is a simplified representation and should be verified by specific tests or technical data sheets for each application.

Explanations:

• Medium: Acceptable resistance to these gases under certain conditions, but may be susceptible to corrosion at higher concentrations, temperatures or in the presence of moisture.
• High: generally has good resistance to these gases, but does not offer absolute protection under extreme conditions.
• Very high: offers excellent resistance to these gases and is recommended for applications where high reliability is required.

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