Corrosive service is where most valve selection mistakes happen. A valve that performs well on water can fail within months on hydrochloric acid, hypochlorite or caustic, and the failure is usually in the body bore rather than the seat. This guide explains what a PTFE lined butterfly valve protects and which fields to confirm before specifying one.
What the Lining Has to Protect
PTFE — polytetrafluoroethylene, often called by its trade name Teflon — is chemically inert against a very wide range of aggressive media, including mineral acids, caustics and most solvents. A few media are exceptions, notably molten alkali metals and elemental fluorine, so compatibility must always be checked at the actual concentration and temperature.
In a butterfly valve the medium does not only touch the seat. It contacts the disc, the disc edge and the body bore, and those surfaces stay exposed when the valve is open, closed or partly open. If only the seat is PTFE and the body is bare metal, the corrosive medium still reaches the body. That is the central fact behind lining selection.
Fully Lined Body vs Seat-Only PTFE
Three configurations are in common supply, and the price difference reflects how much surface is protected:
- Fully lined — the body bore and flange faces are lined and the disc is encapsulated, so every wetted surface is fluoropolymer. The choice for continuous acid transfer, dosing lines and any service where a leak would be a safety event.
- Seat-only PTFE — a standard ductile iron or carbon steel body with a PTFE seat. Lower cost and straightforward to actuate, but the body bore stays exposed, so it suits mildly corrosive or intermittent service.
- PFA or modified PTFE — used where higher temperature or better permeation resistance is needed, at higher cost.
Chemical Compatibility Comes Before Price
Start with the medium, not the valve. For each line, record the chemical name, the concentration as actually run in the plant rather than the nominal figure in the process description, any trace contaminants, and the maximum temperature that can occur. A few cases show how much the answer moves. Concentrated sulphuric acid is normally handled with PTFE or PFA lining, while dilute acid is often acceptable in an all-stainless valve. Sodium hypochlorite is a frequent exception to the "PTFE handles everything" assumption, because permeation and gasket choice matter as much as the liner. Caustic soda at high concentration and temperature also puts gaskets and packing under review.
Ask the supplier for the liner grade and the basis of the compatibility recommendation — an answer stated as a range of concentrations and temperatures is workable, a one-word answer is not.
Temperature and Pressure Limits
Standard PTFE lining is generally limited to roughly 200 °C in continuous service. As temperature rises toward that ceiling the liner softens, relies more on support from the body, and allows more permeation. In cryogenic service the position reverses: PTFE stays usable where elastomers become brittle, but the body material then sets the practical limit.
PTFE lined butterfly valves are most often supplied with PN10 and PN16 bodies. The liner is usually the limiting component, so design against the pressure–temperature rating of the assembly rather than the flange marking alone. If the process runs hot, ask for the derating curve for the specific liner and body combination.
End Connections, Discs and Gaskets
Lining changes how a valve is installed. Wafer bodies fit between flanges and are the most common choice at lower classes; lug bodies allow bolting to one flange at a time, which helps on pump isolation. The flange gaskets carry the same chemical duty as the valve, so select them together. The disc is usually stainless steel encapsulated in PTFE, so tell the supplier if the medium carries solids — a soft encapsulated edge can be damaged by abrasive particles.
Actuation and Operating Practice
Quarter-turn actuators suit manual and automated lined valves, but the valve should never be forced. The liner is the weakest structural element in the assembly, and an oversized or badly set actuator can deform it at the end of travel. When automating, specify stroke limits and confirm the actuator is sized for the torque the valve actually needs.
Two habits extend liner life. Avoid throttling continuously: high-velocity corrosive flow across a partly open disc erodes the liner edge. And avoid sudden decompression, which can pull the liner away from the body wall once gas has permeated into the material.
Testing, Documentation and RFQ Fields
Shell and seat pressure testing is commonly specified to API 598, so include that reference in the enquiry. Lined valves also justify a few additional checks: liner thickness measured at defined points on a report, a spark or holiday test on the finished lining to detect pinholes, confirmation that hydrotest water has been drained and the valve dried, and material certificates for body, disc and stem together with the liner grade.
Reguvale holds ISO 9001 quality-system certification and SGS-CSTC factory audit reports. Where a project requires NSF/ANSI 61, WRAS or other potable-water approval, or additional third-party inspection, treat that as a project requirement and request it for qualified orders — state it in the RFQ so the offer and the documentation match the specification.
Send these fields and a supplier can quote the right product without rounds of clarification:
- Size in DN and inch, with the flange standard and drilling.
- Medium, concentration, and whether solids are present.
- Maximum and normal operating temperature and pressure, including upsets.
- Lining type: fully lined, seat-only PTFE, or PFA.
- End connection: wafer, lug, or double flanged.
- Actuation, fail position, test standard and documentation required.
For the product range itself, see PTFE lined butterfly valves and the wider butterfly valve family. Where the medium is clean and non-corrosive, a standard stainless steel butterfly valve is usually the more economical answer.
Frequently Asked Questions
What temperature can a PTFE lined butterfly valve handle?
Standard PTFE lining is generally limited to roughly 200 °C in continuous service, and permeation and liner stiffness both change as that ceiling approaches. The practical limit for a given line depends on the medium, the concentration and the body material, so confirm it for the actual duty.
Is a fully lined body necessary, or is a PTFE seat enough?
It depends on how aggressive the medium is. A seat-only design leaves the body bore, disc edge and flange faces in contact with the medium, so for continuous acid or caustic duty a fully lined body is normally the safer specification. For mildly corrosive or intermittent service, seat-only PTFE is often adequate and costs less.
Does PTFE resist all chemicals?
No. PTFE resists a very wide range of acids, bases, solvents and oxidisers, but a small group of media such as molten alkali metals and elemental fluorine attack it, and some services depend as much on gasket and packing selection as on the liner.
Which pressure rating should a lined butterfly valve have?
PTFE lined butterfly valves are commonly supplied as PN10 and PN16. Because the liner is usually the limiting component, design against the pressure–temperature rating of the complete assembly rather than the flange marking alone, and ask for the derating curve when the process runs hot.
Can a PTFE lined valve be throttled?
It is not recommended. Continuous throttling pushes high-velocity corrosive medium across a partly open disc and erodes the liner edge, and that damage is not repairable in place. Use the lined butterfly valve for isolation and a separate control valve for regulation.
If you are specifying a lined valve for an aggressive medium, send the chemical, concentration and temperature with the line size and flange standard. Reguvale can confirm the lining type that fits the duty and quote against your documentation requirements. Start at request a quotation, or use contact to send a piping specification directly.