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.  

The column on the right is NOT from the DSD table but provides designers with the equivalent BS EN 1092-1 Flange connection sizes to connect to.  *In some cases, there is more than one flange connection option available so the engineer may select the Flange Adaptor / DN from the table that is the best fit for the selected pipes inside diameter, for example:

  • 450 OD SDR17 PN10 PE pipe has an ID of 395mm, so DN400 (450OD/DN400 Full Face Straight adaptor) is the best choice 
  • 450 OD SDR9 PN20 PE pipe has an ID of 345mm, so DN350 (450OD/DN350 Full Face Stepped adaptor) is the best choice
  • 560 OD SDR17 PN10 PE pipe has an ID of 492mm, so DN500 (560OD/DN500 Full Face Straight adaptor) is the best choice
  • 560 OD SDR11 PN16 PE pipe has an ID of 455mm, so DN450 (560OD/DN450 Full Face Stepped adaptor) is the best choice

Click here for Wastewater pressure Flange Adaptor assemblies, 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.

PE Nominal Size (DN/OD)/Nominal Outside Diameter (dn)

(Outside diameter of PE Pipes/Fittings)

Equivalent Size in DN / ID

(DSD nominated matching size DN)

BS EN 1092 Flange DN

(For pressure connections)

110

100

100

160

150

150

225

200

200

250

225

200

280

250

250

355

300

300

400

375

350

450

400

350/400*

500

450

400/450*

560

500

450/500*

630

525

600

710

600

600

800

675

700

900

825

800

1000

900

900

1200

1050

1000

1400

1200

1200

1600

1350

1400

1800

1650

1600

2000

1800

1800

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)

DSD PE OD DN Conversion Table Page