DSD Polyethylene Outside Diameter (OD) conversion to Nominal Diameter (DN)

The Hong Kong Drainage Services Department (DSD) publishes a conversion table in PS Appendix, Clause 1.5, to ensure proper ID alignment when connecting Polyethylene pipes with other pipe materials in its pressure and drainage network. PS Appendix 5A

PE pipe size is defined by its outside diameter (DN/OD for pipes and dn for fittings), whereas Ductile Iron and other pressure wastewater pipe materials are defined by their nominal Bore (DN). There are several standard OD sizes for PE pipes that are not included in the DSD conversion table, these are the common WSD water pipe sizes (DN/OD 90, 125, 180, 315). These sizes are not standard for DSD, however are sometimes used in sewer rising mains, where the engineer has to match head-loss and flow to an existing pump curve.

It should be noted that PE pipes internal dimension varies depending on the pipes wall thickness (PN / SDR Rating). The two columns on the left side of the table provide the official DSD PE OD to DN conversions, as given in DSD PS Appendix 5A, for both pressure and gravity drainage.  

Click here for selecting Flange assemblies for wastewater pipes. Designers can select either Full Face Straight, Full Face Stepped or standard Flange Adaptor assemblies by comparing column: 'd3' for the Flange Adaptor with their selected pipe ID from the pipe tables to determine the best fit flange to match the pipe and equipment. All dimensions are given in mm.

Note: Larger sizes are not stipulated in Appendix 5A, but are available up to DN/OD 2800 in PN8 SDR21.

Page from DSD PS Appendix 5A (for reference)