SDR 26 and SDR 35 both categorize under the SDR rating system for pipe. At 5% deflection, the SDR 26 pipe can undergo pressurization of 115psi vs the SDR 35 pipe’s rating of 46psi. Despite that, neither pipe is pressure rated as applications should be restricted to drainage.
The SDR (standard dimension ratio) is a rating system for pressure pipework. The lower the pressure rating, the greater the SDR. While D means pipe outside diameter (mm, in) and S is the pipe wall thickness in the unit of mm or in. SDR is highly resilient, with high-tensile and high-impact strength.
In this article, you will learn about SDR-26 pipe, SDR 35 pipe, and compare each pipe’s properties.
SDR-26 has a 160 psi rating at @73°F. The “26” indicates that the outside diameter is 26 times the thickness of the wall. The minimum wall thickness times the SDR is the outer diameter of the pipe. All polyvinyl chloride (PVC) pipe registers as Class 160 and meets or exceeds all ASTM Specification D2241 requirements.
SDR-26 is commonly used in sewer applications. Specific applications include gravity and non-pressure drainage of sewer and surface water where extra heavy wall SDR-26 is specified. However, it is not to be used in wellfield protection areas and at depths greater than 13 feet.
SDR 35 provides a PVC pipe material with a standard dimension ratio (pipe diameter/wall thickness) equal to 35. It fashions from rigid PVC (polyvinyl chloride) vinyl compounds with a cell class of 12364, as identified in ASTM D 1784. The intent of this specification is to provide pipe suitable for non-pressure drainage and surface water. Also, SDR 35, from a strength classification requirement for PVC pipe, requires a minimum pipe stiffness of 46 psi at 5% deflection.
SDR 35 is a medium-strength pipe between Schedule 20 and Schedule 40 PVC. In addition, it is commonly used mainly in stormwater and drainage applications.
In the SDR family, SDR 35 provides a mid-range strength offering. Stronger pipes include SDR 13.5, SDR 17, SDR 21, SDR 26, and SDR 32.5. Weaker offerings include SDR 41 and SDR 64.
SDR 26 vs. SDR 35 Pipe Properties
Both pipes typically fashion from Polyvinyl Chloride (PVC). PVC is a high-strength thermoplastic material widely used in applications, including pipelines, medical equipment, wire, and cable insulation. In fact, it’s the third-most-produced synthetic plastic polymer on the planet.
Despite these advantages, PVC doesn’t handle high heat. Due to this, PVC should be limited to non-potable water applications and not used to provide breathing air.
The wall thickness of the SDR 35 vs SDR 26 for various sizes is as follows:
|SDR 26 |
|SDR 35 |
Wall Thickness (in)
The 4-inch size has a 4.215-inch outside diameter, while the 6-inch is 6.275 inches, the 8-inch is 8.4 inches, the 10-inch is 10.5 inches, the 12-inch is 12.5 inches, and the 15-inch is 15.3 inches in diameter. The minimum thickness of the walls varies between 0.12 and 0.437 inches.
While SDR-26 wall thickness ranges from 0.173-0.775 with 4.500 inches (4-inch size), 6.625 inches for 6-inch, 8.625 inches for 8-inch size, 10.750 inches for the 10-inch size, 12.750 for the 12-inch length, and 18.673 for the 18-inch size.
Since SDR-26 and SDR 35 both fashion from PVC, neither sees any corrosive impact from soil or water. PVC provides unique physical qualities that make it resistant to corrosion and chemical assault from acids, alkalies, salt solutions, and a wide range of other substances. However, polar solvents such as ketones and aromatics quickly degrade the PVC.
PVC pipe is classified as a flexible conduit as it deflects at least 2% without any signs of rupture or cracking. Because of this flexibility, PVC pipes can be installed at burial depths of more than 50 feet. The flexibility of SDR surpasses the strength of Schedule 40 in these types of installs. SDR flexes as the world shifts and settles and under the weight of fill material. As such, the SDR design results in fewer breaks with a greater flex tolerance.