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Electromagnetic Flow Meter for Corrosive Liquids: How to Choose Liner and Electrode Materials
For corrosive liquids, electromagnetic flow meter material selection mainly depends on chemical composition, concentration and temperature. Because the process liquid can be isolated from the metal measuring tube by the liner, electromagnetic flow meters are widely used for many conductive corrosive liquids.
The two wetted parts that need to be checked are the liner and electrodes. They should be evaluated separately because a liner material that is suitable for a chemical does not automatically mean the electrode material is also suitable.
Before selecting materials, the actual process conditions should first be confirmed. A corrosion resistance table can then be used as a practical first reference for screening suitable liner and electrode materials.
Start With the Actual Process Liquid
Descriptions such as “acid,” “alkali” or “chemical wastewater” are usually not specific enough for material selection.
The same material may be suitable at one concentration and temperature but unsuitable under more severe conditions. For mixed liquids, the most aggressive component may determine the material requirement.
For initial selection, confirm:
- the actual chemical or mixture;
- concentration or concentration range;
- maximum operating temperature;
- whether suspended solids, crystals or abrasive particles are present.
These conditions should then be used to check the liner and electrode separately.
How to Select the Liner Material
The liner isolates the process liquid from the metal measuring tube, so its main requirement in corrosive service is chemical compatibility.
For many aggressive chemicals, PTFE and PFA are the main liner materials considered.
PTFE has broad resistance to many acids, alkalis and chemical solutions and is commonly used for general corrosive process applications.
PFA also provides broad chemical resistance and is often considered where higher temperature capability or more demanding process conditions are required.
In many applications, both PTFE and PFA may be suitable. The choice should therefore be based on the specific chemical, concentration, temperature and the operating limits of the meter rather than simply assuming that one material is always superior.
If the liquid contains significant solids or abrasive particles, chemical resistance is not the only requirement. Liner wear also needs to be considered, especially in corrosive wastewater, sludge or slurry service.
How to Select the Electrode Material
Electrode selection is more dependent on the specific chemical environment because the electrodes remain directly exposed to the liquid.
316L stainless steel is commonly used for water and relatively mild process liquids where the medium is not highly aggressive toward stainless steel.
Hastelloy C and similar nickel-based alloys are often considered for more aggressive chemical environments, especially acidic or chloride-containing liquids where 316L may not provide sufficient resistance.
Titanium performs well in certain oxidizing and chloride-containing environments, but it is not universally suitable for reducing acids.
Tantalum offers excellent resistance to many aggressive acids and is mainly used for severe chemical service where this level of corrosion resistance is required.
Platinum-based electrodes are generally reserved for selected highly corrosive applications where their chemical compatibility justifies the higher material cost.
For a broader material comparison, see our liner and electrode selection guide.
The reference table below shows how material ratings vary with the chemical and operating conditions.
Quick Corrosion Resistance Reference
The following examples are selected from the ARTang Electrode & Liner Corrosion Resistance Guide and are intended for preliminary material screening.
Actual suitability may vary with chemical concentration, temperature, impurities and operating conditions. Final liner and electrode selection should be confirmed based on the specific application.
A = suitable
B = usable, but shorter service life
N = not usable
X = corrosion resistant, but not recommended because electrode surface effects may affect measurement.
|
Medium |
Condition |
Stainless Steel |
Hastelloy C |
Titanium |
Tantalum |
Platinum |
PTFE |
PFA |
|---|---|---|---|---|---|---|---|---|
|
Hydrochloric acid |
10–20%, room temp. |
N |
B |
A |
A |
X |
A |
A |
|
Sulfuric acid |
2–5%, room temp. |
N |
X |
X |
A |
A |
A |
A |
|
Nitric acid |
7–65%, room temp. |
X |
X |
X |
A |
A |
A |
A |
|
Phosphoric acid |
1–30%, room temp. |
X |
X |
X |
A |
A |
A |
A |
|
Sodium hydroxide |
10–20%, room temp. |
A |
N |
A |
N |
A |
A |
A |
|
Seawater |
Room temperature |
B |
A |
A |
A |
A |
A |
— |
The table shows why material selection cannot be reduced to statements such as “Hastelloy is better than stainless steel” or “PTFE is suitable for corrosive liquids.”
For example, Hastelloy C is rated differently for hydrochloric acid, sulfuric acid, nitric acid and sodium hydroxide under the listed conditions. The same applies to titanium, tantalum and other electrode materials.
Use the ratings to identify an initial material combination, paying particular attention to X ratings for electrodes, where a material may resist corrosion but still be unsuitable for measurement because of electrode surface effects.
The complete corrosion-resistance guide contains many more chemicals, concentrations, temperatures and liner options.
The selected combination should then be checked against the complete process conditions before final confirmation.
Download Full Electrode & Liner Corrosion Resistance Table →
When Additional Evaluation Is Required
The corrosion resistance table is useful for initial material selection, but some applications require additional evaluation.
Mixed or Changing Chemicals
For mixed chemicals, wastewater or process liquids with changing composition, the material check should consider the most aggressive realistic condition rather than one single sample.
Cleaning chemicals should also be included if they come into contact with the flow meter. A material that is suitable for the normal process liquid may not be suitable for the cleaning stage.
Corrosive Liquids With Solids or Abrasion
If the liquid contains sludge, crystals or abrasive particles, chemical compatibility is only part of the selection.
The liner must also withstand mechanical wear, while electrode coating or abrasion may affect measurement stability.
For these applications, evaluate:
- chemical resistance
- solids concentration
- particle characteristics
- flow velocity
- liner wear resistance
Information to Provide Before Final Material Confirmation
For final liner and electrode confirmation, provide the actual process conditions:
- chemical name or composition;
- concentration or concentration range;
- normal and maximum temperature;
- operating pressure;
- pipe size;
- flow range;
- conductivity, if known;
- presence of solids or contaminants.
For mixed chemicals, include the main aggressive components and any cleaning chemicals that may also contact the flow meter.
Recommended Electromagnetic Flow Meters for Corrosive Liquids
ARTang offers different electromagnetic flow meter configurations for corrosive liquid applications based on the medium, temperature, pressure and required wetted materials.
Aimag-A Electromagnetic Flow Meter
A flexible option for a wide range of chemical, water treatment and corrosive wastewater applications, with liner and electrode materials selected according to the process conditions.
Aimag-C Electromagnetic Flow Meter
Designed for more demanding corrosive applications, especially where higher temperature or pressure conditions need to be considered together with chemical compatibility.
Conclusion
Material compatibility is the key to reliable electromagnetic flow measurement in corrosive liquid applications.
The corrosion-resistance table can be used for preliminary screening, but final material selection should always reflect the actual process conditions, especially for mixed chemicals, elevated temperatures, solids or other demanding applications.
A suitable liner and electrode combination can then be confirmed based on the complete operating requirements.
Not Sure Which Liner and Electrode to Choose?
Send us your process medium, concentration, maximum temperature and flow conditions. ARTang can help review the application and recommend a suitable electromagnetic flow meter configuration.
