TF Gas Transition Fitting (PE–Steel)
A TF gas transition fitting is the critical link between buried polyethylene (PE) pipe and above-ground metallic pipe or equipment in natural-gas networks. As PE use grows across urban and industrial lines, a fully leak-tight, durable hybrid joint matters more than ever. Below are its design details, materials, standards, and engineering notes.
1) Why use TF in gas lines
- Corrosion control: Full isolation of polymer and metal at the transition stops galvanic cells and slows rust.
- Mechanical integrity: Electrofusion on the PE side and welded or threaded joints on the steel side transfer axial and bending loads without stress concentration.
- Ease of installation: All PE fusion happens in the trench; the metallic end can be installed outside the trench under controlled conditions.
- Higher safety: Metal-to-polymer leakage is minimized, turning a typical risk point into one of the safest points on the line.
2) Main components
| Section | Common material | Manufacturing process | Quality control test |
|---|---|---|---|
| Polyethylene | PE100 or PE100-RC | Injection molding + precision machining | Thermal stability (OIT), ring tensile test |
| Metallic | API-grade carbon steel with epoxy or FBE coating | CNC machining; spot welding to the interface bushing | Coating thickness; 1000 h salt-spray |
| Interface bushing | Low-carbon steel or 304 stainless for high-corrosion environments | Friction / interference joining to parent metal | Thread break-torque test |
Different thermal expansion rates are managed with a tapered geometry and anti-slip rings, so seasonal temperature cycles do not overload the fusion joint.
3) Step-by-step installation
- Cut & prepare PE pipe: Square, deburred, and marked.
- Clean & scrape: Remove at least 0.2 mm of oxidized surface with a standard scraper.
- Insert PE spigot of TF: Push to the witness mark on the body.
- Electrofusion: Scanner sets current/time from the product barcode.
- Cooling period: 10–15 minutes minimum; do not move the joint before cooling is complete.
- Connect metallic end: Butt-weld to steel pipe or make up to threaded valve assemblies as designed.
- Pressure test: Hydrostatic/pneumatic at 1.5× the operating pressure after completion.
4) Size range and pressure class
| PE OD (mm) | Steel equivalent (inch) | Pressure class (PN) | Typical use |
|---|---|---|---|
| 25 | ¾″ | 10 | Single-unit residential service |
| 32 | 1″ | 10 | Small commercial service |
| 63 | 2″ | 10 & 16 | Neighborhood mains |
| 90 | 3″ | 10 | PRS/TBS inlet to complexes |
| 125 | 4″ | 10 | City ring mains |
| 160 | 6″ | 10 | Industrial or inter-urban feeds |
| 200–225 | 8–10″ | 10 | Regional medium-pressure lines |
All sizes comply with ISIRI 11233 (national standard) and international GIS/PL3. Each unit is validated by a short-term pressure test at 12 bar and a long-term crack growth test (1000 h).
5) TF for gas vs. brass/polymer TF for water
| Criterion | Gas TF (steel) | Brass/polymer TF (for water) |
|---|---|---|
| Service fluid | Natural gas, LPG | Cold/Hot water, low-risk fluids |
| Sealing method | Electrofusion + steel weld | Electrofusion + threaded seal |
| Impact resistance | Very high (gas surge loads) | Medium |
| Service temperature | −20 °C to +40 °C | 0 °C to +60 °C |
| Reference standard | EN 1555-3 / ISO 4437-3 | EN 12201-3 |
| Example use | From dwelling inlet to TBS (Town Border Station) | Boiler room, water manifold line |
Do not substitute a water-service brass TF for a steel gas TF; material, coating, and safety tests differ and make the swap risky.
6) Standards and mandatory tests
- 100% leak check: Helium scan in a vacuum chamber for every piece.
- Hose/ramp pressure test: 0 → 15 bar in 60 s with no volume loss.
- Thermal stability: 80 °C for 800 h; tensile property change ≤ 20%.
- Ring creep test: 4 MPa for 165 h; fusion seam remains closed.
- Traceability: QR code on body provides batch data (resin lot, EF wire spool number) for inspectors.
7) Field practice & inspection
- Preheat steel welds in cold climates: Up to 60 °C to prevent hot cracking.
- Scheduling: Avoid doing PE fusion and steel welding in one continuous shift to reduce thermal-stress risk.
- Recoat steel weld in field: After pressure test, use two-component epoxy or cold-applied polywrap.
- Structured NDT: MPI on above-trench steel welds; periodic UT on critical lines.
8) Advantages over older methods
- No bolted flanges: Lower weight and less loosening under vibration.
- Faster installation: On a 360 m, 63 mm line, TF cut execution time from 48 h to 18 h.
- Lower maintenance: Replacement cycles ~30 years vs. 10–12 years for threaded metal couplings.
- Smart-grid ready: Space to mount a temperature sensor in the metal cavity for online health monitoring.
TamamBaha supplies a complete range of gas TFs from 25 to 200 mm, with certificates of authenticity and electrofusion machine calibration services—supporting reliable delivery for urban and industrial projects.
