What is SDR Pipe?
Pipe SDR stands for Standard Dimension Ratio – also referred to as the standard dimensional ratio. Pipe SDR(Standard Dimension Ratio) is defined as the ratio of the nominal outside diameter to the nominal wall thickness of the pipe of PE, PVC, UPVC, PPR, etc. It is a measurement and method often used by pipe or pipe fittings manufacturers to rate the working pressure capacity of a pipe.
The SDR pipe formula as below:
SDR = D / T
where
D = pipe outside diameter (mm, in)
T = pipe wall thickness (mm, in)
Definition of SDR with an example
SDR for a 10 inches ASTM D2241 – PVC Pipe with an outside diameter of 10.750 inches and wall thickness of 0.168 inches can be calculated as
SDR = (10.750 in) / (0.168 in)
= 64
An SDR 64 means that the outside diameter of the pipe is 64 times the thickness 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 higher SDR indicates a thinner-walled pipe at any given diameter and has a low-pressure rating. As an example, SDR17 has a thinner wall and lower pressure class than an SDR 11. Knowing and understanding this value is essential for many applications, including, but not limited to, the following:
• When calculating the internal pressure inside of a pipe system
• When inserting objects into a pipe system such as ID stiffeners for compression fittings
• When determining the tensile strength of a pipe under high stress
• When assessing the compressive strength of a pipeline undergoing burial
The relationship between the SDR and the pressure rating is given by the Lames formula for the hoop stress in thick-wall cylinders:
s = P(D – T) / 2T
This can be rearranged as;
s = P (SDR – 1)/2
Where is the maximum hoop stress P is the internal pipe pressure.
The hoop stress is the design stress for the material, which is the (MRS) divided by the overall service (design) coefficient C.
MRS/C = P (SDR – 1)/2
or rearranging;
P = 2 MRS / C(SDR-1)
This pressure ‘P’ is then defined as the ‘Maximum Operating Pressure’ MOP or the pressure rating of the pipe.
MOP = 2 MRS / C(SDR-1)
Where MRS and MOP are in MPa
Or
MOP = 20 MRS / C (SDR – 1)
Where MRS is in MPa and MOP is in bar.
Example: What is the MOP or pressure rating of an SDR11 PE100 water pipe?
For PE100 the MRS = 10 MPa. For water applications, the minimum recommended service design coefficient ‘C’ is 1.25.
Hence :
MOP = 20 * 10 / 1.25 (11 – 1)
MOP = 16 bar
SDR Pipe Chart
SDR Pipe Specifications
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