Industrial Control Valve
Control Valve Material Selection for Chemical Service: PTFE/PFA Lining, Hastelloy and Beyond
Corrosion failures are expensive because they are rarely gradual in appearance and always gradual in mechanism — the valve that passed hydrotest fails eight months later at the weld or behind the lining. Material selection for chemical service is about the combination of chemistry, temperature, pressure and mechanical duty, not about a single corrosion table.
The four families
| Option | Typical envelope | Strengths | Limitations |
|---|---|---|---|
| Fluoropolymer-lined (PTFE, PFA, FEP, PO) on a ductile-iron or carbon-steel body | −29 to +200 °C (PTFE), to 230 °C (PFA); up to Class 150/300 | Broadest chemical resistance at the lowest cost; handles HCl, H₂SO₄, wet Cl₂, most solvents | Permeation, vacuum collapse of the liner, thermal cycling, poor abrasion resistance |
| Solid stainless (316L, 904L, duplex 2205/2507) | −196 to +600 °C (alloy dependent) | Mechanical strength, vacuum rated, good general resistance | Chloride pitting / SCC; not for HCl, hot H₂SO₄ |
| High-nickel alloys (Hastelloy C276 / C22, Monel 400, Inconel 625) | −198 to +400 °C (C276 to ~1040 °C in dry service) | Excellent reducing-acid and chloride resistance; handles wet chlorine and hypochlorite | High cost, long lead time, specialist welding |
| Reactive metals / ceramics (titanium, zirconium, tantalum, SiC, Al₂O₃) | Application-specific | Titanium for oxidising media and chlor-alkali; ceramics for extreme abrasion | Titanium is attacked by dry chlorine and reducing acids; ceramics are brittle |
Lined valves: the caveats that matter
- Permeation. Fluoropolymers are not impermeable; small molecules (chlorine, bromine, HF, some solvents) diffuse through over time and attack the metal shell. PFA and a thicker lining reduce it; for severe permeators, specify a higher alloy body or solid construction.
- Vacuum. A liner is a plastic sleeve inside a metal shell. Under vacuum or with a flashing fluid, the liner can collapse. Lined valves need vacuum-rated designs (anchored liner, vacuum rings) or an explicit vacuum limitation.
- Thermal cycling. The liner and shell expand at very different rates. Repeated cycling from ambient to 180 °C fatigues the bond. Ask for the manufacturer's permitted cycle count.
- Abrasion. Slurries will cut through a PTFE lining quickly. Use a rubber-lined or ceramic trim design instead.
- Electrostatic. Non-conductive linings require antistatic grade material where a flammable atmosphere or a low-conductivity solvent is present.
Practical selection matrix
| Medium | Common concentration / temperature | Recommended wetted materials |
|---|---|---|
| Sulphuric acid | 93–98%, ambient | Carbon steel (passivated) or PTFE-lined; 316L only in narrow ranges |
| Sulphuric acid | <70%, elevated | PTFE/PFA-lined, or Hastelloy C276 |
| Hydrochloric acid | Any strength | PTFE/PFA-lined or Hastelloy C276 — never standard stainless |
| Caustic soda (NaOH) | 50%, 80–120 °C | Nickel, Monel, or 316L with caution above 50 °C (caustic SCC) |
| Wet chlorine / hypochlorite | Ambient | Titanium (wet Cl₂), PTFE/PFA-lined, or Hastelloy C276 |
| Seawater / brine | Ambient | Duplex 2205 / 2507, Monel, or lined |
| Nitric acid | 65%, ambient–80 °C | 304L / 310S stainless — titanium is unsuitable |
| HF (hydrofluoric acid) | Anhydrous and aqueous | Monel 400, PTFE-lined (with permeation review) — never glass |
Documentation for chemical service
Specify and request: full material certificates to EN 10204 3.1 (3.2 for critical service), positive material identification (PMI) on alloy trim, a lining spark test at a defined kV, and — for lined valves — a documented hydrostatic and vacuum test after lining. For regulated industries, the elastomer and fluoropolymer should carry FDA, USP Class VI or EC 1935/2004 declarations as applicable.
Browse the plastic and lined valve range or send your chemical, concentration and temperature for a material recommendation.
Frequently Asked Questions
When should I use a PTFE-lined valve instead of stainless steel?
Use a lined valve when the fluid attacks stainless steel, as hydrochloric acid, wet chlorine and most concentrations of sulphuric acid do, and when the temperature is below roughly 200 degrees Celsius for PTFE or 230 degrees for PFA. Where pressure, vacuum or abrasion is severe, or the temperature is higher, a high-nickel alloy or another solid material is usually the better choice.
Can lined valves be used under vacuum?
Standard lined valves have a limited vacuum capability because the fluoropolymer liner can collapse away from the shell. Vacuum-rated designs use an anchored or locked liner and sometimes vacuum rings. Always state the minimum absolute pressure in the specification.
What is permeation and why does it matter?
Permeation is the slow diffusion of small molecules such as chlorine, bromine or hydrogen fluoride through the fluoropolymer lining. Over time the permeated species reaches the metal shell and corrodes it from behind, causing liner blistering and shell failure. Thicker PFA linings and higher-alloy shells reduce the risk.
Is Hastelloy C276 always the safest choice?
C276 has outstanding resistance to both oxidising and reducing media and to chloride pitting, but it is expensive and is not universal - it is not the best choice for hot concentrated caustic, for example, where nickel or Monel performs better. Material selection should always be made against the specific chemical, concentration and temperature.
Send us the process data — fluid, inlet pressure, differential pressure, temperature, required flow and pipe size — and our engineers will return a sized selection with Cv calculation, leakage class and material recommendation, plus documentation packs for FAT / IQ-OQ.
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