Pipe fittings are indispensable connection parts in the pipeline system, which directly affect the sealing, durability and installation efficiency of the system. Under the metric standard, HDPE (high-density polyethylene) and PVC (polyvinyl chloride) are the two most commonly used materials, each with its own advantages and applicable scenarios. This article will explore the metric plumbing fittings of these two materials in depth to help you make a reasonable choice.
Overview of metric plumbing fittings
Metric plumbing fittings are measured in millimeters (mm). Compared with imperial (inch) fittings, they are more precise in size and widely used in Europe, Asia and other regions. The main types include:
Coupling
Elbow (45°/90°)
Tee
Reducer
Flange
Cap
Comparison of HDPE and PVC pipe fittings
(1) Material characteristics
| Property | HDPE Fittings | PVC Fittings |
| Chemical Resistance | Excellent (resists acids, alkalis and solvents) | Good (not resistant to some organic solvents) |
| Flexibility | High (bendable, impact-resistant) | Low (rigid, prone to cracking) |
| Temperature Range | -50°C ~ 60°C | 0°C ~ 60°C |
| Connection Methods | Heat fusion, electrofusion welding | Solvent cementing, threaded connections |
| Pressure Rating | Medium-high pressure (PN6-PN16) | Medium-low pressure (PN6-PN10) |
| Environmental Impact | Recyclable, non-toxic | Non-recyclable, releases toxic gases when burned |
(2) Common metric sizes
HDPE fittings: DN20 (20mm), DN32 (32mm), DN50 (50mm), DN100 (100mm)
PVC fittings: DN16 (16mm), DN25 (25mm), DN40 (40mm), DN75 (75mm)
Note: DN (Diameter Nominal) indicates the nominal diameter, which may differ slightly from the actual size.
Application and advantages of HDPE accessories
(1) Main applications
Water supply system: resistant to high pressure, pollution-free, suitable for municipal water supply.
Gas pipeline: anti-permeability, anti-corrosion.
Industrial pipeline: transport of chemicals, wastewater treatment.
Underground laying: resistant to ground pressure, resistant to soil corrosion.
(2) Core advantages
Hot-melt connection: seamless welding, eliminating the risk of leakage.
Long life: underground use can reach more than 50 years.
Environmentally friendly and safe: in line with drinking water standards (such as ISO 4427).
How to choose metric plumbing fittings?
(1) Select materials according to the purpose
Water supply/gas/chemical industry → HDPE (pressure resistance and corrosion resistance) is preferred.
Drainage/electrical/temporary engineering → PVC (economical and easy to install).
(2) Pay attention to certification standards
HDPE: must comply with ISO 4427 (water supply) and EN 1555 (gas).
PVC: must comply with GB/T 5836 (building drainage) and UL 94 (flame retardant).
(3) Match the pipeline system
Ensure that the DN size of the fitting is consistent with the pipeline (such as DN32 pipe with DN32 joint).
For high-pressure scenarios, choose thickened type (such as HDPE PN16 grade).
Installation precautions
(1) Installation of HDPE fittings
Hot melt welding:
Clean the pipe mouth and use a special hot melt machine to heat to 210°C~230°C.
Cool under pressure after docking to avoid cold welding.
Electrofusion connection:
Applicable to narrow spaces, and the built-in resistance wire is melted by electricity.
(2) Installation of PVC accessories
Adhesive connection:
Apply PVC special glue, quickly insert and rotate 90° to ensure fit.
Threaded connection:
Wrap the raw tape to avoid over-tightening and causing pipe cracking.
FAQ
Q1: Can HDPE and PVC fittings be mixed?
A: No! The two materials are not compatible, and a transition joint (such as HDPE-PVC flange adapter) is required for connection.
Q2: Which material is more suitable for low temperature environments?
A: HDPE (resistant to -50°C), PVC is brittle at low temperatures.
Q3: Can metric fittings be connected to imperial pipes?
A: Yes, but a conversion joint (such as DN20 to 3/4 inch) is required.
HDPE and PVC metric fittings have their own advantages:
HDPE: Suitable for high-pressure, corrosion-resistant, long-life projects (such as municipal water supply).
PVC: Suitable for low-cost, fast installation scenarios (such as building drainage).
