SDR (Standard Dimension Ratio) and S Pipe Series

Standard Dimensions Ratio - SDR

Many plastic pipe manufacturers use the "Standard Dimension Ratio" - SDR - method of rating pressure piping. The SDR is the ratio of pipe diameter to wall thickness and the SDR can be expressed as

SDR = D / s                                 (1)

where

D = pipe outside diameter (mm, in)

s = pipe wall thickness (mm, in)  

Example - SDR

SDR for a 10 inches ASTM D2241 - PVC Pipe with outside diameter 10.750 inches and wall thickness 0.168 inches can be calculated as

SDR = (10.750 in) / (0.168 in)

      = 64

A SDR 64 means that the outside diameter - D - of the pipe is 64 times the thickness - s - of the wall.

• with a high SDR ratio the pipe wall is thin compared to the pipe diameter
• with a low SDR ratio the pipe wall is thick compared to the pipe diameter

As a consequence a high SDR pipe has a low-pressure rating and low SDR pipe has a high-pressure rating.

Pipe Series - S

Pipe series - S - is a dimensionless number related to the nominal outside diameter and wall thickness of a pipe. The pipe series - S - can be calculated as

S = (SDR - 1) / 2                        (2)

where

S = pipe series