1. Overview
In modern chemical and process industries, corrosion remains one of the most critical challenges affecting production stability, instrument reliability, and plant safety.
Pipelines, flowmeters, level transmitters, and process sensors are exposed to a wide range of acids, alkalis, solvents, and gas–liquid mixtures, many of which may chemically attack wetted materials.
Understanding the corrosive properties of different media and selecting matching instrument materials are key to extending service life and ensuring measurement accuracy.
2. Corrosion Characteristics of Common Media
Industrial process fluids exhibit widely different corrosion behaviors depending on concentration, temperature, pressure, and impurities.
Typical corrosive categories include:
• Strong acids
Examples: Hydrochloric acid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), phosphoric acid
Severe corrosion to carbon steel
High concentration HCl aggressively attacks stainless steel
Some alloys such as Hastelloy C and titanium offer superior resistance
• Weak acids and organic acids
Examples: Acetic acid, formic acid, citric acid
Moderate corrosion tendency
Stainless steel 316L often acceptable at ambient conditions
Elevated temperature may require PTFE-lined equipment
• Alkaline media
Examples: Sodium hydroxide (NaOH), potassium hydroxide (KOH)
Carbon steel performs well at low temperatures
Stainless steel may suffer stress corrosion cracking in strong alkali
PTFE, PVDF, and rubber-lined materials offer long-term stability
• Salts and brines
Examples: NaCl solutions, seawater, brine slurries
Chloride ions accelerate pitting corrosion
316L > 304 in chloride environments
Duplex or nickel-based alloys preferred for high Cl− concentration
• Organic solvents and hydrocarbons
Examples: fuels, lubricating oils, aromatics, alcohols
Generally mild to stainless steels
Care required for additives, sulfur compounds, and polymer swelling
3. Recommended Material Selection for Process Instruments
Selection depends on fluid properties, temperature, pressure, and expected service life.
Typical wetted material recommendations:
| Process Fluid | Preferred Wetted Material |
|---|---|
| Strong acids (HCl, H₂SO₄) | PTFE / PFA linings, Hastelloy C |
| Weak acids | 316L SS, PTFE/PFA |
| Strong alkali solutions | PTFE / PVDF, lined steel |
| Chloride salt water / brine | 316L SS, duplex stainless steel |
| Organic solvents / hydrocarbons | 304 or 316L stainless steel |
| Slurries containing solids | Rubber-lined steel, stainless steel with hard coatings |
These guidelines apply to flowmeters, level transmitters, valves, and other wetted-surface process instruments.
4. Instrument Selection Considerations
Corrosion resistance is closely tied to instrument type and construction:
Flowmeters
Electromagnetic flowmeters
Best for conductive liquids including acids, alkalis, wastewater
➤ Key materials: PTFE liner, neoprene liner, 316L/Hastelloy electrodesCoriolis mass flowmeters
Suitable for aggressive fluids and high viscosity
➤ Wetted materials: 316L, 904L, duplex steel, or nickel alloys
Level and Pressure Instruments
Radar/ultrasonic level transmitters
Non-contact design ideal for corrosive or volatile liquidsSubmersible pressure transmitters
316L with protective coatings or titanium for seawater and salt brine
5. Conclusion
As chemical processing industries expand and automation levels increase, instrumentation plays a vital role in reliable operation and plant efficiency. Selecting the correct corrosion-resistant materials ensures:
✔ Longer instrument service life
✔ Reduced maintenance costs
✔ Improved measurement accuracy
✔ Higher plant availability and economic benefits
Corrosion cannot be eliminated, but informed material selection and proper product matching significantly minimize failure risk and protect operational investment.