In HDPE (high-density polyethylene) pipe systems, SDR (standard dimension ratio) is one of the core parameters that determine pipe performance. SDR 35 and SDR 26 are two common specifications that are suitable for different engineering needs. This article will introduce in detail What is the difference between sdr 35 and sdr 26, and guide how to choose correctly.
SDR (Standard Dimension Ratio) is the ratio of the outer diameter of the pipe to the wall thickness, and the calculation formula is:
SDR = Outer diameter (OD) / Wall thickness (WT)
The smaller the SDR value, the thicker the pipe wall, the stronger the pressure bearing capacity, but the flow rate is relatively reduced; the larger the SDR value, the thinner the pipe wall, the lower the cost, but the pressure bearing capacity is weaker.
|
Comparison Item |
SDR 35 |
SDR 26 |
|
Wall Thickness |
Thinner |
Thicker |
|
Pressure Capacity |
Lower (approx. 0.32 MPa) |
Higher (approx. 0.63 MPa) |
|
Suitable Applications |
Low-pressure drainage, gravity flow systems |
Medium-pressure water supply, pressurized pipelines |
|
Flexibility |
Better, suitable for trenchless installation |
Slightly less, requires more careful installation |
|
Cost |
Lower (less material used) |
Higher (increased wall thickness) |
|
Common Specifications |
Commonly used for drainage pipes below DN300 |
Commonly used for pressurized water pipes |
(1) Situations for choosing SDR 35
Gravity drainage system (such as municipal rainwater pipes, sewage pipes)
Low pressure requirements (such as underground infiltration drainage, farmland irrigation)
Projects with limited budgets (thin wall thickness, low material cost)
Requirement of higher flexibility (such as horizontal directional drilling HDD construction)
(2) Situations for choosing SDR 26
Pressure pipe system (such as water supply network, fire water pipe)
High external load environment (such as deep buried pipes, busy traffic areas)
Requirement of longer service life (thicker wall thickness has better wear resistance)
Transporting corrosive media (such as chemical wastewater, requiring higher safety)
Case 1: Municipal drainage system
SDR 35: A city's rainwater pipe network uses SDR 35 HDPE pipes, saving 15% of material costs, and flexible laying adapts to foundation settlement.
SDR 26: A sewage pressure pipe in an industrial park uses SDR 26 to ensure long-term stable operation under 4 bar pressure.
Case 2: Mine drainage
SDR 35: Suitable for surface drainage ditches, low cost and corrosion resistance.
SDR 26: Used in deep well drainage pumping systems, withstanding higher water pressure and rock loads.
❌ Misunderstanding 1: "The larger the SDR value, the better the quality"
✅ Fact: SDR only reflects the relationship between wall thickness and pressure bearing, and the choice depends on the specific working conditions.
❌ Misunderstanding 2: "SDR 26 can completely replace SDR 35"
✅ Fact: In drainage systems without pressure requirements, using SDR 26 will increase unnecessary costs.
SDR 35 is more suitable for low-pressure, low-cost, high-flexibility drainage applications, while SDR 26 is suitable for medium-high pressure, high-durability pressure pipe systems. Correct selection of SDR level can significantly improve engineering economy and reliability. It is recommended to conduct a comprehensive assessment based on design pressure, construction method and long-term maintenance requirements, and consult a professional pipeline engineer when necessary.
