When selecting materials for acid and alkali-resistant flow meters, it’s important to consider factors such as the material of the measuring tube, electrodes, lining, and the properties of the acidic or alkaline medium, including concentration and temperature. Below is an overview of suitable materials based on these criteria.
Measuring Tube Materials:
Hastelloy: Known for its excellent corrosion resistance, Hastelloy is highly resistant to strong acids like concentrated sulfuric acid and hydrochloric acid. It is often used in chemical processing and other high-corrosion environments.
316L Stainless Steel: This material is well-suited for environments with mild acids or alkalis. It offers good corrosion resistance to weaker acidic and alkaline media, making it a popular choice for less corrosive applications.
Tantalum: Tantalum has exceptional corrosion resistance. It can withstand almost all strong acids and alkalis, except for hydrofluoric acid. While expensive, it is often used in high-precision and high-corrosion scenarios.
Electrode Materials:
Tantalum or Platinum Electrodes: These materials are ideal for measuring acidic solutions. Their excellent resistance to acid corrosion ensures stable measurement signals.
316L Stainless Steel Electrodes or Gold-Plated Electrodes: For alkaline solutions, 316L stainless steel is suitable for typical alkaline media, while gold-plated electrodes provide enhanced resistance for more aggressive alkaline environments.
Lining Materials:
PTFE (Polytetrafluoroethylene): PTFE is highly resistant to both strong acids and alkalis, as well as organic solvents. It can operate in temperatures ranging from -200°C to +260°C, making it perfect for applications in chemical, pharmaceutical, and other industries dealing with highly corrosive liquids.
Rubber Lining: Chloroprene rubber linings provide good resistance to low-concentration acids, alkalis, and salts, making them ideal for municipal water treatment or industrial wastewater applications with neutral or mildly corrosive media.
Fluoroelastomers: These materials combine high-temperature resistance with excellent corrosion resistance, making them suitable for more demanding conditions, particularly for measuring corrosive media at higher temperatures.
PFA (Perfluoroalkoxy): PFA offers corrosion resistance similar to PTFE but has a higher mechanical strength at high temperatures—up to twice that of PTFE. This makes it suitable for high-temperature, highly corrosive environments, and it is commonly used in the food and pharmaceutical industries, especially where steam sterilization is required.
Other Materials:
PVDF (Polyvinylidene Fluoride): PVDF offers excellent resistance to 98% concentrated sulfuric acid, 40% hydrofluoric acid, and concentrated nitric acid. It is effective across a pH range of 1–14 and can maintain stability in temperatures between -5°C and 120°C. PVDF is commonly used in glass rotor flow meters and other similar applications.
Conclusion:
Choosing the correct material for a flow meter depends on the specific requirements of the application, such as the nature of the medium, temperature, and environmental factors. Hastelloy, tantalum, and PTFE are ideal for high-corrosion environments, while materials like 316L stainless steel and PVDF offer good performance for less aggressive conditions. Always consider the operational demands and cost-effectiveness when selecting the appropriate material for your flow meter.