Lined piping is commonly employed in the chemical industry. Plastic lined pipes and fittings are available with the following liners :
Types of Liners
| Liner | ASTM spec | Temp Range °C | Availability |
|---|---|---|---|
| PFA | D3307 | -29 to 260 | |
| PTFE | D4894 D4895 |
-29 to 260 | 1" to 12" |
| PVDF | D3222 | -29 to 135 | 1" to 8" |
| PP | D4101 | -29 to 107 | 1" to 12" |
| PP II Copolymer | D2146 |
Applicable Standards
- ASTM F423-82 - PTFE pipes and fittings.
- ASTM F491-77 - PVDF pipes and fittings.
- ASTM F492-85 - Polypropylene pipes and fittings.
- ASTM F1545-95 - All liners (testing).
The plastic liners are available in interference-fit or slip-fit. Interference fits provide good resistance to vacuum. Due to heavy wall thickness of PTFE liners, PTFE lined slip-fit systems are rated to vacuum for most pipe sizes.
PTFE is the most commonly used liner material. It has excellent high temperature resistance to virtually all chemicals except fluorine.
PFA exhibits chemical resistance almost identical to PTFE. PFA has superior creep resistance at high temperatures, excellent low temperature toughness and exceptional flame resistance.
Testing of Lined piping
Pipes and fittings are generally subjected to 10,000 volt non-destructive electrostatic test after lining and machining to detect any pinholes or porosity in the liner. Some manufacturers carry out spark testing at 20,000 volts.
Gaskets in lined piping
Gaskets are generally not required for bolting lined piping except when spools need to be connected and disconnected frequently.
Gaskets must be used when flanging lined items to glass lined, FRP or metal flanges. PTFE enveloped gaskets are recommended for such joints.
Permeation
Plastic lined piping is susceptible to permeation through the liner. Vent holes are provided on the pipe spools to allow permeant vapors to escape. Vent holes provided on lined piping spools should not be plugged. Vent hole extensions are recommended for insulated pipes.
Supporting
Gasket stresses should be limited to 5000 psi for PTFE, 6500 psi for PP and 8000 psi for PVDF. This can be achieved by supporting near concentrated loads such as valves and inline items.
Grounding Issues
Electrical continuity is required across flanged joints to permit grounding of these systems.