Fluorine-lined Pipe Fittings Materials And Core Design

A lined pipe combines a metal outer shell with a fluoropolymer inner layer to convey corrosive fluids safely. The metal shell provides mechanical strength and pressure containment. The fluoropolymer liner isolates the fluid from the metal, preventing chemical attack. PTFE lined pipe handles continuous service from -29°C to 260°C (ASTM F423). PFA lined pipe serves -29°C to 260°C with lower permeability.

How to select a lined pipe using design standards?

1. Choose pressure class: PN 10/16/25 for GB, Class 150/300 for ASTM.

2. Select liner material: PTFE for standard acids ≤120°C, PFA for high-purity/oxidizing >120°C, FEP for steam ≤150°C.

3. Verify temperature derating: PTFE/PFA derate approximately 25% at 150°C.

4. Confirm mechanical locking features for vacuum service.

Common Design Pitfalls – What to Avoid

• ❌ Mixing standards: GB flanges with ASME piping require adapters.

• ❌ Ignoring temperature derating: Check P-T curve for hot services.

• ❌ Skipping vacuum-rated design: Mechanical locking prevents liner collapse.

• ❌ Wrong liner extension: Liner must extend to flange face.

Core Design Standards

GB/T 26500-2025

• Covers DN 15 to DN 1200, pressure classes PN 10/16/25

• Unifies N-series and W-series dimensional requirements

• Flanges per GB/T 9119

ASTM F1545

• Covers plastic-lined ferrous metal pipe, fittings, and flanges

• Class 150 (1.9 MPa) and Class 300 (5.1 MPa)

• ASTM F423 for PTFE-lined pipe, ASTM F781 for PFA-lined

• Flanges per ASME B16.5

Liner Material Selection

PTFE

• -29°C to 260°C per ASTM F423

• Resists all chemicals except molten alkali metals

• Standard for hydrochloric acid, sulfuric acid (≤98%), caustic soda

• A teflon lined pipe uses the same material

PFA

• -29°C to 260°C per ASTM F781

• Lower permeability, smoother surface than PTFE

• Specified for high-purity chemicals, hot acids, oxidizing media

• Base resin per ASTM D3307

FEP

• Up to 150°C, cost-effective for steam and hot water

Dimensional and Pressure Limitations

GB/T 26500-2025: DN 15 to DN 1200, PN 10/16/25.

ASTM-based: Class 150 (1.9 MPa) and Class 300 (5.1 MPa).

Flange dimensions: GB/T 9119 or ASME B16.5.

Temperature derating:

• PTFE/PFA maintain full pressure at ambient

• Derate approximately 25% at 150°C

• At 260°C, limitations by mutual agreement

• Below -29°C, consult manufacturer

A ptfe lined carbon steel pipe with Class 150 may be limited to 1.0 MPa at 200°C. A pfa lined pipe maintains lower permeability at elevated temperatures.

Liner Retention and Design Features

Retention methods:

• Mechanical locking: dovetail grooves or perforations

• Flare processing at pipe ends

• Flange-facing extension: liner extends 5-10 mm past flange face

• Vacuum-rated designs: support rings prevent collapse

For ptfe hose pipe applications, lining principles apply to flexible connections. Pressure ratings are typically lower than rigid pipe.

Design Checklist

1. Define process conditions: media, temperature, pressure, vacuum requirement.

2. Choose liner:

   • Standard acids ≤120°C → PTFE

   • Hot acids >120°C or oxidizers → PFA (ASTM D3307 resin)

   • Steam ≤150°C → FEP

3. Verify flange standard: GB/T 9119 or ASME B16.5.

4. Verify pressure-temperature rating:

   • If service >120°C, obtain P-T curve

   • Class 150 PTFE at 200°C may be limited to 1.0 MPa

5. Specify liner retention:

   • Vacuum service → dovetail grooves or support rings

   • Confirm liner extends 5-10 mm past flange face

General acid service ≤120°C: A ptfe lined pipe with carbon steel shell (ptfe lined carbon steel pipe) and Class 150/PN 16 flanges provides reliable service per ASTM F423 or GB/T 26500.

Hot acid, oxidizing, or high-purity service: A pfa lined pipe is required. ASTM F781 provides governing specification, with base resin per ASTM D3307.

Steam and utility service: FEP offers a cost-effective option where temperature is ≤150°C.

After selecting the liner and standard, confirm P-T rating against maximum surge pressure. Verify flange dimensions and liner extension (5-10 mm past flange face). For vacuum service, specify mechanical locking (dovetail grooves or support rings). 

FVF PTFE Lined Pipe

• FVF PTFE lined pipes with shortest lengths are around 100mm depending upon nominal bore and the longest lengths is 6 meters for up to DN150 and 3 meters above this. Generally constructed from carbon steel pipe, and stainless steel is also popular for dangerous access area where there is the potential for external corrosion.
• Its working temperature is high at the range of -29°C-180°C; except the molten alkali metals, element fluorine and aromatic hydrocarbon, lined products can be used in any chemical medium.
• Vacuum resistance. In the range of -29°C-150°C, it is applicable for vacuum condition. In chemical production, the vacuum condition occurs due to cooling, longitudinal emissions, or medium backflow. 
• It is high-pressure resistant . Within temperature working condition, it can sustain the working pressure of 3.0MPa.
• It is penetration Resistant.It has excellent antiosmosis by adapting the high-quality PTFE and making it of high density and enough thickness after advanced lining processing.
• PTFE advanced lining molding process achieved the status of syn chronous hot expansion or cold shrinkage for steel components and fluorine plastic. 

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