Standard dimension ratio, or SDR, is a specified ratio of average outside diameter to minimum wall thickness for outside-diameter-controlled plastic pipe. It is a dimensional designation, not the name of a pipe material or a complete pressure rating. The material, standard and operating conditions still need to be identified.
Standard dimension ratio, or SDR, is a specified ratio of average outside diameter to minimum wall thickness for outside-diameter-controlled plastic pipe. It is a dimensional designation, not the name of a pipe material or a complete pressure rating. The material, standard and operating conditions still need to be identified.
What the ratio tells you
The Plastics Pipe Institute's TR-9 defines DR and the standard SDR series. Charlotte Pipe's manual and pressure catalog identify particular SDR products, dimensions and product standards. Use those published dimensions for the identified product rather than assuming a ratio applies to every plastic pipe.
For comparable products at the same outside diameter, a lower ratio corresponds to a relatively thicker wall. That reduces the inside opening. Comparing ratios across different materials or service standards does not by itself rank one pipe as safer or more suitable. For the distinct material-property label, see tensile modulus. The ratio alone does not supply that value.
You may see DR as well as SDR in material specifications. The exact notation and standard series should be taken from the manufacturer's markings and documentation. They should not be treated as permission to substitute an unlisted product with a similar number.
Dimensions and ratings are separate information
A ratio does not state the resin, pressure classification, temperature limit or allowed use. Manufacturer pressure tables depend on the material and product standard, and any applicable temperature adjustments still matter.
Pressure service and gravity drainage also involve different design questions. A pipe's wall designation does not establish its acceptable load, installation method, joint type or approval for a particular sewer replacement. The pipe stiffness entry explains a separate external load-deflection characteristic and its installation limits.
Our trenchless sewer code guide uses SDR in a specific approved pipe-bursting provision. That requirement belongs to its stated code and method; it is not a blanket rule for every water or sewer line.
Reading a material proposal
Ask for the complete material designation, nominal size, product standard, ratio and intended service. The proposed fittings and joining method must match the product, and the installation design must address the actual site conditions.
Compare pipe schedule, which uses a different wall-dimension series. A useful specification contains enough information to identify the approved pipe and assembly, rather than offering only an SDR number.