SDR 21 vs SDR-26

Sarah
DeGuzman

SDR 21 and SDR 26 are both under the SDR rating system for the pipe. SDR 21 has a 200 psi rating, vs SDR 26 which has a 160 psi rating at @73°F.

The SDR (standard dimension ratio) is a pressure pipe rating method. The SDR increases as the pressure rating decreases. D stands for pipe exterior diameter (mm, in), and S stands for pipe wall thickness (mm or in). SDR provides excellent tensile and impact strength.

In this article, you will learn about SDR 21 pipe and SDR 26 pipe and compare SDR 21 vs SDR 26 properties.

SDR 21 Overview

Charlotte Pipe PVC 1120 SDR-21 PR 200
Courtesy: Lowe’s

SDR 21 means that the outside diameter is 21 times the wall thickness. The pipe’s outer diameter equals the minimum wall thickness multiplied by the SDR.

SDR 21 sees common use in:

  • Potable water supply lines
  • Transmission mains
  • Sewage force mains
  • Golf courses
  • Other irrigation systems
  • Oilfield saltwater disposal
  • Stormwater disposal

Water reclamation and sewer projects provide the most frequent application. Typically engineers specify the standard schedule series for pressure piping.

SDR 26 Overview

Sewer Pipe, 18 in, 14 ft L, PVC SDR26
Courtesy: Pace Supply

The number “26” denotes that the outside diameter is 26 times the wall thickness. The pipe’s outer diameter equals the minimum wall thickness multiplied by the SDR. All PVC pipe is classified as Class 160 and meets or exceeds the standards of ASTM Specification D2241.

SDR 26 generally does not meet pressure piping requirements brought on by ASME B 31.1 and ASME B 31.3. It also should not be buried deeper than 13 feet. 

SDR 26 vs SDR 21 Pipe Properties

Material Type

Polyvinyl Chloride (PVC) is commonly used for both SDR 26 and SDR 21. PVC is a high-strength thermoplastic material widely utilized in pipelines, medical equipment, wire and cable insulation, and other applications. In fact, it is the world’s third-most produced synthetic plastic polymer.

Despite these benefits, PVC is not heat resistant. As a result, PVC should only be utilized in non-potable water applications and never for air inhalation.

HDPE (High-Density Polyethylene) is also commonly used. HDPE provides better dampening and shock absorption than PVC and as such provides a superior choice in most industrial applications.

SDR 21 vs SDR 26 Wall Thickness

The wall thickness of the SDR 21 vs. SDR 26 for various sizes is as follows:

Nominal
Pipe Size
Pipe ODSDR 21 Wall
Thickness (in)
SDR 26 Wall
Thickness (in)
1.5”1.900”0.0900.073
2”2.375”0.1130.091
2.5”2.875”0.1370.11
3”3.500”0.1670.135
4”4.500”0.2140.173
5”5.563”0.2650.214
6”6.625”0.3160.255
8”8.625”0.4100.332
10”10.750”0.5110.413
12”12.750”0.6060.490
SDR 21 vs SDR 26 Properties

SDR 26 wall thickness ranges from 0.073-0.490 while SDR 21 ranges from 0.090 to 0.606 wall thickness. Exact specifications vary by manufacturer.

Corrosion Resistance

SDR 21 and SDR 26 are unaffected by electrolytic and galvanic corrosion and any other known corrosive soil or water condition. Corrosion resistance is influenced by pipe material, process media, and the surrounding environment.

Because the SDR 26 and SDR 21 are usually made of PVC or HDPE, neither corrodes by soil or water. These plastic components provide unique physical properties that protect them from corrosion and chemical attack from acids, alkalies, salt solutions, and other chemicals. Polar solvents, such as ketones and aromatics, destroy plastic pipes quickly.

Flexibility Strength

The SDR (standard dimension ratio) was designed to be more versatile than schedule pipe. The flexibility of SDR comes at the sacrifice of structural integrity. When pipes are buried, they are exposed to irregular and unpredictable forces. SDR pipe provides some advantages, including the ability to be trenched or directionally drilled. This eliminates bends or elbows and increases availability via large master reels. Ultimately the assembly of fewer joints results in increased integrity.