Chemical & Corrosive Media
Flow and Level Measurement Solutions for Chemical and Corrosive Media
Measurement Solutions for Chemical and Corrosive Media
Measuring corrosive chemicals requires more than selecting an instrument with an anti-corrosion housing. The wetted lining, electrode, probe, seal, process temperature, pressure, conductivity and hazardous-area classification must all match the actual medium and operating conditions.
Gallop provides flow and level measurement solutions for chemical storage, dosing, transfer and wastewater systems. Depending on the application, the recommended instruments may include an electromagnetic flow meter, vortex flow meter, turbine flow meter, ultrasonic flow meter, radar level transmitter or ultrasonic level transmitter.
Classification and Corrosion Characteristics of Chemical Media
| Media Category | Typical Media | Corrosion Characteristics | Key Selection Considerations |
|---|---|---|---|
| Strongly acidic media | Hydrochloric acid, dilute sulfuric acid, hydrofluoric acid, nitric acid and phosphoric acid | Strong electrochemical corrosion. Hydrofluoric acid can attack ordinary PTFE, while nitric acid causes strong oxidizing corrosion. | Corrosion increases rapidly as the temperature rises. Confirm the exact concentration, temperature and pressure before selecting wetted materials. |
| Weakly acidic media | Acetic acid, citric acid and carbonic acid | Moderate corrosion. 316L stainless steel may be suitable at room temperature, but corrosion becomes more severe at elevated temperatures. | Do not select materials based only on room-temperature performance. |
| Strongly alkaline media | Sodium hydroxide, potassium hydroxide and ammonia solution | High-temperature caustic media can cause severe corrosion and stress-related damage to stainless steel. Ammonia solution can strongly attack copper alloys. | Ordinary 316L should not be used for high-temperature sodium hydroxide without a detailed compatibility review. |
| Salt solutions | Saltwater, sodium hypochlorite, ferric chloride and electroplating wastewater | Pitting corrosion, crevice corrosion and chloride-ion damage to the passive film of stainless steel. | Use 316L with caution when chloride concentration is above 500 ppm. Hastelloy C276 or titanium may be preferred. |
| Organic solvents | Methanol, ethanol, acetone, toluene and xylene | Some solvents swell rubber linings and seals or affect PTFE under specific conditions. | Rubber seals and linings must be checked carefully. Non-conductive solvents cannot be measured by electromagnetic flow meters. |
| Oxidizing media | Sodium hypochlorite, hydrogen peroxide and concentrated nitric acid | Strong oxidation can rapidly age ordinary rubber materials. | Rubber materials should generally be prohibited unless their chemical compatibility has been verified. |
Comparison of Common Wetted Materials for Flow Measurement
| Material | Applicable Media | Media Requiring Caution or Avoidance | Reference Operating Temperature | Remarks |
|---|---|---|---|---|
| 304 stainless steel | Clean water and weakly corrosive aqueous, weak-acid or weak-alkali media at room temperature | Chloride ions, hydrochloric acid, sodium hypochlorite and high-temperature strong alkalis | -20 to 120°C | Suitable for ordinary chemical environments with limited corrosion. |
| 316L stainless steel | Dilute phosphoric acid, acetic acid, general salt solutions and weak bases | Hydrochloric acid, hydrofluoric acid, high chloride concentrations, concentrated nitric acid and high-temperature caustic soda | -20 to 120°C | Common in chemical systems, but not immune to chloride-ion pitting. |
| Hastelloy C276 | Hydrochloric acid, wet chlorine gas, sodium hypochlorite, high-chloride brine and many mixed strong-acid media | Concentrated hot nitric acid | -20 to 150°C | Preferred for strong chlorine corrosion. Commonly used for electromagnetic flow meter electrodes. |
| Titanium alloy | Sodium hypochlorite, wet chlorine gas, nitric acid and organic acids | Hydrofluoric acid and concentrated hydrochloric acid | -20 to 120°C | Excellent resistance to oxidizing media, but unsuitable for some reducing acids. |
| Tantalum | Most strong acids, including hydrochloric, sulfuric and nitric acid | Hydrofluoric acid and strong alkalis | -20 to 150°C | Very high corrosion resistance and very high material cost. |
| PTFE | Strong acids, strong alkalis and many organic solvents | Molten alkali metals and high-temperature chlorine trifluoride. HF requires special temperature and pressure evaluation. | -20 to 120°C as a general reference | A mainstream lining and probe-sheath material. Cold flow and deformation must be considered under high temperature and pressure. |
How to Select Flow Meters for Corrosive Media
1. Electromagnetic Flow Meter
Electromagnetic flow meters are the most common choice for conductive chemical liquids. They have no moving parts and can be configured with corrosion-resistant linings and electrodes to suit different acid, alkali, salt and chemical wastewater conditions.
Important limitation: Electromagnetic flow meters can measure only conductive media. The typical minimum conductivity requirement is ≥5 μS/cm.
Lining: PTFE or PFA is preferred for strong corrosion. Rubber linings should not be selected automatically for strong acids, alkalis or organic solvents.
Electrodes: 316L may be suitable for general weak acids and weak bases. Hastelloy C276 or titanium is preferred for chlorine, sodium hypochlorite and wet chlorine. Tantalum may be considered for selected mixed strong-acid applications.
Temperature: Depending on the lining and construction, PFA can withstand approximately 180 to 200°C, while PTFE is commonly used up to approximately 160°C in suitable designs. Confirm the final limit for the selected model.
Explosion protection: Integral or remote versions can be configured for Ex ia or Ex ib intrinsic safety and used in chemical tank areas and reactor discharge pipelines.
Typical applications: Dilute hydrochloric acid, dilute sulfuric acid, caustic soda, sodium hypochlorite and conductive chemical wastewater.
2. Vortex Flow Meter
The corrosion resistance of a vortex flow meter is mainly determined by the material of the measuring body and probe. A 316L construction may be suitable for some corrosive process gases, vapors and less aggressive liquids, but it is not the first choice for strongly corrosive liquids without further material verification.
3. Turbine Flow Meter
Turbine flow meters can use 316L or PTFE impellers, but the medium should be clean and free of solid particles. They may be used for clean corrosive solvents and conductive or non-conductive liquids. Impurities can quickly wear the impeller, so turbine flow meters are less commonly selected for demanding chemical corrosion applications.
4. Ultrasonic Flow Meter
Ultrasonic flow meters are available in pipe-section and external clamp-on configurations.
Pipe-section type: The wetted pipe body can be lined with PTFE or PFA for corrosive liquids.
External clamp-on type: The pipe wall must be compatible with the medium, but the instrument does not contact the chemical. This can be useful for strong corrosion and retrofit projects.
Limitations: Bubbles, deposits and scale on the pipe wall can weaken the ultrasonic signal and reduce measurement stability.
Liquid Level Measurement for Corrosive Media
1. Radar Level Transmitter
A radar level transmitter with a PTFE-coated or PTFE-wrapped antenna is suitable for strong acids, strong alkalis, solvents, crystallizing media and volatile chemical tanks. Non-contact radar measurement keeps the electronics away from the liquid and is a preferred option for many aggressive chemical storage applications.
For hazardous areas, an intrinsically safe configuration such as Ex ia IIC T6 can be selected when it matches the project requirements and safety-barrier arrangement.
2. Ultrasonic Level Meter
Ultrasonic level meters are non-contact instruments, but they are not recommended for strongly corrosive tanks with heavy volatilization. Corrosive vapors may attack the transducer, while acid mist can crystallize and accumulate on the probe, eventually causing measurement failure. They are more suitable for wastewater or chemical tanks without a large amount of corrosive vapor.
3. Input-Type Hydrostatic Level Transmitter
For static-pressure level measurement, the diaphragm may be specified in 316L, Hastelloy C or titanium. The vented cable should have a PFA sheath when it is exposed to corrosive media.
Risk to consider: If the cable sheath is damaged during immersion, the corrosive liquid can reach the instrument and cause direct damage. This type is suitable for open corrosive tanks, but it is generally not recommended for closed pressure reactors without a suitable engineered installation.
Explosion Protection, Temperature, Pressure and Safety Requirements
Hazardous areas: Chemical tank areas, reaction vessels and organic-solvent storage tanks may fall under Ex IIC T4/T6 requirements. Ex ia IIC T6 intrinsically safe instruments are often preferred, but the safety barrier and complete system must be matched. Ex d may suit some conditions, although the enclosure can be more vulnerable to corrosion in aggressive environments.
Temperature: Temperature can accelerate corrosion and change the compatibility of linings, seals and electrodes. Select materials according to the highest actual working temperature, not the normal room temperature.
Pressure: PTFE linings may deform or delaminate under unsuitable high-temperature and high-pressure conditions. Confirm the lining grade, pressure rating and installation conditions before approval.
Certification: Explosion protection and corrosion resistance are separate requirements. Verify both the explosion-proof certificate and the material or wetted-parts certificate.
Project Cases
Case 1: Hydrochloric Acid Storage Tank and Discharge Pipeline
Operating conditions: 15% dilute hydrochloric acid; 25 to 45°C; 0.4 MPa; conductive medium.
Measurement points: Tank liquid level and discharge-pipeline flow rate.
Flow measurement: DN200 split-type electromagnetic flow meter with PTFE lining, Hastelloy C electrode and 4-20 mA output.
Level measurement: 80 GHz non-contact radar level meter with PTFE-coated antenna and Ex ia IIC T6 configuration.
Operating result: Continuous operation for 32 months without corrosion leakage or electrode corrosion, with stable data transmission to the DCS.
Case 2: Ultra-Pure Water Delivery Pipeline
Operating conditions: Ultra-pure water with low conductivity; 40°C; 0.5 MPa. An electromagnetic flow meter was not suitable because the medium was non-conductive.
Measurement point: Pipeline flow rate.
Selected instrument: External clamp-on ultrasonic flow meter.
Operating result: Stable operation for 20 months. The external clamp-on arrangement avoided contact between the instrument and the medium and provided a hygienic retrofit solution.
Summary and Common Selection Pitfalls
Do not select materials according to room-temperature conditions only. Check the highest operating temperature because corrosion can increase significantly as temperature rises.
Housing protection is not the same as wetted-parts corrosion resistance. The housing protects the electronics from the surrounding environment; the lining, electrodes, diaphragms and probes determine compatibility with the measured medium.
For organic solvents, check all linings, seals and gaskets for swelling or dissolution. Non-conductive organic solvents cannot be measured by electromagnetic flow meters.
For chloride-containing media, use 316L with caution. Hastelloy C276 or titanium may be more suitable for preventing pitting and perforation.
Explosion protection and corrosion resistance are independent specifications. Both certificates and the actual wetted-material configuration must be verified.
For highly corrosive and volatile liquids, avoid ultrasonic level measurement where acid mist or corrosive vapor can coat the probe. Radar level measurement should generally be evaluated first.
Choose the Right Chemical Measurement Configuration
Before selecting a flow meter or level transmitter, provide the medium name, concentration, conductivity, temperature range, pressure, flow or level range, pipe size, tank structure, hazardous-area classification and required output signal. Gallop can recommend a suitable lining, electrode, antenna, probe and communication configuration for chemical processing, storage, transfer and wastewater measurement projects.
Contact Gallop for a chemical and corrosive media measurement solution.
