What Is Lined Pipe?
Lined pipe is carbon steel pipe with a non-metallic or metallic internal lining that protects the steel from corrosion, erosion, or chemical attack by the process fluid. The carbon steel outer pipe provides structural strength and pressure containment while the lining provides corrosion resistance. This approach is significantly less expensive than manufacturing the entire pipe from a corrosion-resistant alloy.
Non-metallic linings include PTFE (Teflon), rubber, polypropylene (PP), polyethylene (PE), and glass. Metallic linings (CRA liners) are covered in the clad vs. lined pipe comparison. This article focuses on non-metallic linings.
When to Use Lined Pipe
- Strong acids and bases that attack carbon steel and stainless steel
- Highly corrosive chemical plant piping
- Abrasive slurry service (rubber lining)
- Process fluids that contaminate with metal ions (pharmaceutical, food)
- Applications where solid CRA pipe is prohibitively expensive
Lining Material Comparison
| Lining | Max Temp | Chemical Resistance | Abrasion Resistance | Typical Application |
|---|---|---|---|---|
| PTFE (Teflon) | 260°C | Excellent (nearly universal) | Low | Strong acids, HF, chlorine, pharma |
| PFA | 260°C | Excellent | Low-moderate | Similar to PTFE, improved flex life |
| PVDF (Kynar) | 150°C | Good (acids, salts) | Moderate | Acidic water, brine |
| PP (Polypropylene) | 100°C | Good (acids, bases) | Moderate | Acid piping, chemical effluent |
| PE (Polyethylene) | 80°C | Good (acids, bases) | Good | Mining, water treatment |
| Hard rubber | 90°C | Good (dilute acids, bases) | Excellent | Slurry, mining, abrasive fluids |
| Soft rubber | 80°C | Moderate | Good | Abrasive slurry, tailings |
| Glass (borosilicate) | 260°C | Excellent | Low | Pharmaceutical, ultra-pure |
PTFE-Lined Pipe
PTFE (polytetrafluoroethylene) is the most chemically resistant lining material available. It resists virtually all chemicals except molten alkali metals and fluorine gas at high temperature.
| Parameter | PTFE-Lined Pipe |
|---|---|
| Lining thickness | 2-6 mm |
| Max temperature | 260°C (continuous) |
| Max pressure | Limited by steel pipe and vacuum rating |
| Vacuum rating | Full vacuum (with proper design) |
| Size range | NPS 1/2 to NPS 24 |
| Joining | Flanged (PTFE flare over flange face) |
| Standard | ASTM F1545 (lined fittings/pipe) |
| Lining method | Loose-lined (insertion) or molded |
The PTFE liner is typically loose-fitted inside the steel pipe with a flared end that seals over the flange face. This design prevents the process fluid from contacting the steel pipe or the flange gasket surface.
Rubber-Lined Pipe
| Parameter | Rubber-Lined Pipe |
|---|---|
| Lining thickness | 3-12 mm |
| Max temperature | 80-90°C (natural rubber), up to 120°C (special compounds) |
| Rubber types | Natural rubber, chloroprene, butyl, EPDM |
| Size range | NPS 2 to NPS 72 |
| Joining | Flanged |
| Application | Mining slurry, FGD systems, abrasive service |
| Standard | ASTM D1418 (rubber classification) |
| Bonding | Vulcanized bond to steel ID |
Rubber linings excel in abrasive service where the liner absorbs impact energy from solid particles, reducing erosion rates by 5-20x compared to bare steel.
Design Considerations
| Factor | Requirement |
|---|---|
| Vacuum collapse | PTFE liners require anti-collapse design (vented, or supported) |
| Thermal expansion | Non-metallic liners expand more than steel; allowance required |
| Permeation | Some chemicals permeate through thin liners over time |
| Inspection | Spark testing (holiday detection) per NACE SP0188 |
| Repair | Localized repair possible for rubber; PTFE typically requires relining |
| Flange connections | Must seal liner to prevent bypassing at gasket |
For metallic corrosion-resistant linings (CRA materials like Alloy 625 or 316L), see the detailed pipe coating, lining, and cladding article.
Leave a Comment
Have a question or feedback? Send us a message.