PTFE and PFA-Lined Valves for Corrosive Service: Selection Guide

Some chemical services defeat metals. Wet chlorine, hydrochloric acid, hydrofluoric acid, sodium hypochlorite, and hot concentrated sulphuric acid attack stainless steels and even many nickel alloys, and where an alloy would survive it is often prohibitively expensive. Lined valves solve this by lining a standard, strong ductile-iron or carbon-steel body with an inert fluoropolymer, so the metal provides the pressure boundary and mechanical strength while the plastic liner provides the corrosion resistance. The fluid only ever touches the liner.

Why Lined Valves

The economic and technical case for lined valves is straightforward: a fluoropolymer such as PTFE is chemically inert to almost all industrial chemicals, so a lined valve gives near-universal corrosion resistance at a fraction of the cost of a solid exotic-alloy valve. The liner also provides a smooth, non-stick, non-contaminating wetted surface, which matters for high-purity and colour-sensitive products. The trade-offs are temperature and pressure limits, sensitivity to abrasion and thermal cycling, and the need to avoid full vacuum unless the liner is vacuum-rated.

Lining Materials

The common fluoropolymer and plastic linings differ in temperature capability and how they are applied:

Lined Valve Types

• Lined ball valves - PTFE/PFA-lined body with a PFA-encapsulated ball; full quarter-turn isolation for acids and chlorine.
• Lined butterfly valves - the disc and body are fully lined/encapsulated; economical for larger sizes and moderate pressure.
• Lined diaphragm valves - a PTFE or elastomer diaphragm isolates the bonnet; excellent for slurries, and for services where a crevice-free wetted path is needed.
• Lined plug valves - a PTFE-sleeved or fully-lined plug for tight shutoff in aggressive chemical duty.
• Lined check valves - swing or dual-plate designs with fully lined wetted parts for backflow prevention in corrosive lines.

Design Limits and Cautions

Lined valves must be applied within their limits or the liner fails:

1. 1Respect the pressure-temperature envelope - liner strength falls as temperature rises, so the valve's P/T rating is lower than the bare body would suggest.
2. 2Avoid full vacuum unless the liner is specifically vacuum-rated - vacuum can collapse or lift a liner off the body.
3. 3Limit rapid thermal cycling - differential expansion between the liner and steel body can cause the liner to cold-flow, wrinkle, or debond over time.
4. 4Watch abrasion - PTFE and PFA are soft; for abrasive slurries choose PVDF, a reinforced liner, or a lined diaphragm/pinch design.
5. 5Provide permeation venting where required - some gases slowly permeate the liner, and body vent holes prevent pressure building behind the liner.
6. 6Protect from freezing and mechanical impact, and always install with matched lined flanges and correct gaskets to avoid liner damage at the joint.

Selection and Standards

Select the lining from the specific chemical, concentration, and temperature - PTFE or PFA for the broadest acid and chlorine resistance, PFA where higher temperature or high purity is needed, and PVDF where abrasion resistance matters more than maximum chemical range. Confirm the pressure-temperature rating, vacuum service, and any solids/abrasion in the stream. Lined valve bodies are typically ductile iron or carbon steel to ASME B16.34 ratings, with face-to-face to ASME B16.10 and flanges to ASME B16.5. Vajra Industrial Solutions supplies PTFE, PFA, FEP, and PVDF-lined ball, butterfly, diaphragm, plug, and check valves selected against your chemical service data, within the correct pressure-temperature envelope, with material and lining certification.