Diaphragm material for pressure transmitters should be selected according to the medium, temperature, corrosion condition, and process connection. The diaphragm is the part that directly receives pressure from the process medium. If the material is wrong, the transmitter may corrode, leak, drift, or fail even when the pressure range and output signal are correct.
Many buyers ask for “anti-corrosion material” without specifying the medium. This is risky. No single diaphragm material is suitable for all corrosive applications. Material selection must be based on the actual chemical condition.
Start With the Medium
The first step is to identify the medium clearly. The supplier needs to know whether it is clean water, wastewater, acid, alkali, solvent, slurry, steam, hydrogen, or another process fluid. If it is a chemical liquid, the concentration and temperature should also be provided.
The most important information includes:
- Medium name
- Concentration
- Working temperature
- Whether chloride or fluoride is present
- Whether the medium is acidic or alkaline
- Whether the medium contains solids or crystals
Without this information, material selection becomes guesswork.
Common Diaphragm Materials
Different diaphragm materials are used for different applications. The following are common options, but final selection should always be checked against the actual medium.
- 316L stainless steel
Commonly used for water, air, oil, and many general industrial liquids. It is economical and widely available, but it is not suitable for all corrosive media. - Hastelloy C276
Often used when 316L is not enough. It has better corrosion resistance in many chemical applications, but it is still not a universal solution. - Tantalum
Suitable for some strong acid applications. However, tantalum is not suitable for alkali and should not be selected only because it is expensive. - Monel
Used in certain special chemical media. It may be considered for some fluoride-related applications, depending on the actual condition. - Titanium
Used in some oxidizing or chloride-related conditions, but its suitability must be checked according to the medium. - Gold-plated diaphragm
Often used in hydrogen service to help reduce hydrogen permeation risks. - PTFE lining or coating
Used when metal materials are not suitable or when broad chemical resistance is needed.
Do Not Only Look at the Diaphragm
In real applications, the diaphragm may not be the only wetted part. The process connection, flange, gasket, seal ring, and lining may also contact the medium. If these parts are not compatible, the transmitter can still fail.
For corrosive service, confirm:
- Diaphragm material
- Process connection material
- Flange material
- Gasket or seal material
- PTFE lining, if required
This is especially important for diaphragm seal pressure transmitters, where the flange and diaphragm are part of the same wetted structure.
Consider Temperature and Cleaning
Material compatibility can change with temperature. A material that works at room temperature may not be suitable at higher process temperature. Cleaning chemicals can also affect material choice, especially in food, pharmaceutical, or batch chemical processes.
If the process includes cleaning, flushing, steam sterilization, or chemical washing, these conditions should be included in the selection.
When PTFE Lining Is More Practical
In some corrosive applications, using a PTFE-lined structure may be more practical than using an expensive metal diaphragm alone. PTFE lining can help isolate metal parts from the medium, especially for certain acid or alkali applications.
However, PTFE lining also has limits. Temperature, pressure, vacuum, mechanical strength, and installation condition must be considered. It is not only a material choice, but also a structure choice.
Conclusion
Choosing diaphragm material for pressure transmitters requires more than selecting the most expensive alloy. The correct choice depends on medium composition, concentration, temperature, corrosion behavior, and all wetted parts.
SIY Electric can help check diaphragm materials such as 316L, Hastelloy, tantalum, Monel, titanium, gold-plated diaphragm, and PTFE-lined structures according to the actual working condition.
