Plastic pipe is the most valuable thing a settlement can make from plastic because it is corrosion-proof, light and easy to join, and PE or PVC suits water, drainage and irrigation. Use only plastic whose history you know for drinking water, join it by the method its plastic needs, and pressure-test every length at 1.5 times its working pressure before burying it.
Part of Plastics and Polymers
Plastic pipes and containers are extruded or molded vessels that carry or store water, drainage and other liquids.
Why Pipe Comes First
Plastics Manufacturing ranks water pipe first among applications: it is corrosion-proof, lightweight and easy to join, with PE or PVC as the suitable plastics. Containers come next: watertight, lighter than ceramic and unbreakable, in PE or PP. For the water network that uses the pipe, see Water Systems.
Salvage Pipe Before Making It
Existing pipe is the quickest supply. The corpus’s Salvaged Modern Pipe says salvaged PVC, PE and copper make the best water pipe, but to reject lead, asbestos-cement and anything that carried fuel or chemicals, and to test at 1.5 times. Salvaged drainage pipe is thin-walled and has no pressure rating, so use it only for gravity drains.
Pick The Plastic By The Job
| Need | Plastic | Why |
|---|---|---|
| Flexible main line, buried or surface | HDPE | Flexible, UV-resistant when black; see HDPE Pipe |
| Rigid distribution run, buried | PVC | Strong solvent-welded joints; see PVC Pipe |
| Irrigation, low pressure | PE | Cheap, forgiving |
| Storage drums and jugs | PE or PP | Tough, waterproof |
Do not weld or cement mixed plastics, because joints depend on the plastics fusing or dissolving. PVC pipe joins by solvent cement; polyethylene does not accept it, and joins by barbed fittings and clamps or by fusion. Fusion joining is from general knowledge, not the corpus.
Containers: Storage Is Safe, Contents Matter
A container that held fuel, solvent or chemicals can retain them in the wall, so keep it out of food and drinking-water service. For cisterns, the corpus’s Plastic Liner advice is to use only plastic whose history you know for drinking water. Keep stored water out of sunlight, since light degrades some plastics and grows algae. For blow-moulded bottles see Plastic Blow Molding.
Worked Example: What Pressure Can A Pipe Carry?
For a thin-walled pipe the hoop stress is σ = P × D / (2t), so the safe pressure is P = 2 × σ × t / D. Take a pipe of outside diameter D = 50 mm and wall t = 3 mm, and assume a design stress of σ = 5 MPa for the plastic (an assumption: the corpus gives no figure, so measure or look up the one for your plastic).
P = 2 × 5 MPa × 3 mm / 50 mm = 0.6 MPa = 6 bar.
If you rate the line at 6 bar, the 1.5-times test is 1.5 × 6 = 9 bar. Whether a pipe survives that depends on its short-term strength, which a design stress does not tell you, so burst-test a sample length before committing to a design. Rating a pipe from a remembered figure is dangerous. The method rests on the standard thin-wall hoop-stress formula, from general knowledge.
Common Mistakes
- Using drainage pipe for pressure — it has thin walls and no rating.
- Burying PVC without protecting the above-ground end — sunlight degrades it.
- Using a fuel drum for drinking water — the wall retains the contents.
- Skipping the pressure test — a joint that fails after burial means digging it up.
Pressure, fumes and solvent cement
A pipe that bursts under test throws fragments, so test with the line anchored, people clear of the line and water, not air, as the test fluid. Solvent cement is flammable and its vapour harmful: use it with ventilation and no flame. Never heat unidentified plastic to bend or weld it.
What’s Next
- Learn next: Insulation and Tools — the other high-value uses
- Combine with: Extrusion Products — making the pipe