When pumping corrosive chemicals, the wetted material is the single most important decision. Two common choices: 316L stainless steel (solid metal) or fluoroplastic-lined (PTFE/PFA on cast iron). Both resist corrosion. But they work differently, cost differently, and fit different chemical services.
This guide compares stainless steel and fluoroplastic pumps so you can choose the right material for your chemical application.
How Each Construction Works
316L stainless steel pump: The entire wetted end (casing, impeller, wear rings) is solid 316L stainless. The metal contacts the chemical directly. No liner, no coating. If the material corrodes, the pump is damaged.
Fluoroplastic-lined pump: The outer casing is cast iron (holds pressure). Inside, a thin PTFE or PFA liner contacts the chemical. The cast iron never touches the fluid. If the liner develops a pinhole, the cast iron corrodes from inside — but this takes years, not months.
The fundamental difference: stainless relies on the metal's own corrosion resistance. Fluoroplastic relies on an inert plastic barrier. Both work — but for different chemicals.
Corrosion Resistance Comparison
| Chemical Service | 316L Stainless | Fluoroplastic Lined |
|---|---|---|
| Dilute sulfuric acid (10%) | ❌ Pits within weeks | ✅ Resists perfectly |
| Concentrated sulfuric acid (98%) | ✅ Resists (passive film) | ✅ Resists perfectly |
| Hydrochloric acid (any concentration) | ❌ Attacked rapidly | ✅ Resists perfectly |
| Nitric acid (70%) | ✅ Resists | ✅ Resists perfectly |
| Organic solvents (acetone, toluene) | ✅ Resists | ⚠️ PTFE swells in some solvents |
| Chloride-containing (seawater, brine) | ❌ Pitting corrosion | ✅ Resists perfectly |
| Strong alkali (50% NaOH) | ✅ Resists | ✅ Resists perfectly |
| Food-grade (milk, beverage) | ✅ Resists + sanitary | ⚠️ Not food-contact certified |
Rule of thumb: For acids (except concentrated sulfuric), fluoroplastic wins. For neutral chemicals, water, and food-grade service, stainless wins. For chlorides, neither 316L nor fluoroplastic is ideal — use duplex stainless or Hastelloy.
Cost Comparison
| Cost Factor | 316L Stainless | Fluoroplastic Lined |
|---|---|---|
| Pump price (same size) | $4,000–$12,000 | $6,000–$15,000 |
| Impeller replacement | $500–$1,000 (stainless impeller) | $300–$600 (PTFE impeller) |
| Casing repair | Can be welded and machined | Cannot repair — liner damaged = new casing |
| Spare parts availability | Standard — available worldwide | Specialized — must order from manufacturer |
Fluoroplastic pumps cost 20–30% more upfront. But they last longer in acid service. Stainless pumps cost less but corrode in acids. Total cost over 10 years depends on the chemical — not just the purchase price.
Mechanical Properties
316L stainless: High strength. Can handle high pressure (up to 40 bar). Can handle high temperature (up to 200°C). Rigid — no flexing under pressure. Can be welded and repaired.
Fluoroplastic lined: The PTFE liner is thin (2–3 mm). The cast iron outer casing holds pressure. Max pressure is 16 bar. Max temperature is 120°C (PTTF softens above this). The liner can delaminate if pressure cycles rapidly.
Key limitation of fluoroplastic: The liner cannot handle vacuum. If the pump loses suction, the PTFE liner collapses inward. The pump is ruined. Always install a vacuum relief valve on fluoroplastic pumps.
When to Choose 316L Stainless
Choose stainless when:
- The fluid is neutral (water, oils, mild chemicals)
- Temperature is above 120°C (PTFE cannot handle it)
- Pressure is above 16 bar (PTFE liner cannot handle it)
- Food or pharmaceutical service (sanitary certification needed)
- You need to repair or weld the pump on site
Typical applications: Clean water transfer, oil circulation, food and beverage, pharmaceutical, high-temperature hot oil.
When to Choose Fluoroplastic Lined
Choose fluoroplastic when:
- The fluid is acidic (HCl, dilute H₂SO₄, HNO₃)
- The fluid contains chlorides (seawater, brine, chloride solution)
- Temperature is below 120°C
- Pressure is below 16 bar
- Zero leakage is required (pair with magnetic drive)
Typical applications: Acid transfer, chemical processing, plating solutions, wastewater treatment, corrosive chemicals.
For zero-leakage acid service, the combination of fluoroplastic magnetic drive pump is the standard choice — PTFE liner handles the acid, magnetic drive eliminates seal leakage.
Common Material Selection Mistakes
Mistake 1: 316L for hydrochloric acid. 316L dissolves in HCl within weeks. PTFE lined pump is the only correct choice. Never use stainless for HCl service.
Mistake 2: PTFE lined pump at 150°C. PTFE softens above 120°C. The liner bulges and delaminates. Use stainless steel for high-temperature acid service (if the acid allows stainless at that temperature).
Mistake 3: PTFE lined pump without vacuum relief. Suction loss collapses the liner. Install a vacuum relief valve on the suction side.
Mistake 4: Ignoring concentration effect. 316L resists 98% sulfuric acid but dissolves in 10% sulfuric acid. Always check corrosion data at your exact concentration and temperature, not just the chemical name.
Material Selection Quick Guide
| If your fluid is... | Choose... |
|---|---|
| Water, oil, neutral | Cast iron or 304 stainless |
| Mild chemical (pH 5–9) | 316L stainless |
| Acid (HCl, dilute H₂SO₄, HNO₃) | Fluoroplastic lined |
| Chloride-containing (seawater, brine) | Duplex stainless or Hastelloy |
| High temperature (>120°C) | 316L stainless or cast steel |
| Food / pharmaceutical | 316L stainless (sanitary grade) |
For material selection by chemical type, our fluoroplastic magnetic drive range handles corrosive acid services. For material compatibility across common chemicals, the material corrosion guide lists wetted material performance. For material recommendation, submit your fluid data — name, concentration, and temperature.