SDR and PN appear together on many HDPE pipe schedules, product labels and fittings, but they describe different things. Understanding the distinction helps buyers avoid ordering a matching diameter with the wrong wall or pressure class.
This guide explains the catalogue language used for PE100 products in South Africa. Always confirm the project specification, current manufacturer datasheet and temperature assumptions before purchasing or substituting a pipe class.
What SDR means
SDR is the Standard Dimension Ratio: the pipe outside diameter divided by its nominal wall thickness.
SDR = outside diameter ÷ wall thickness
For the same outside diameter, a lower SDR means a thicker wall. A thicker wall changes the pressure capability, internal bore, mass per metre and handling requirements. That is why OD alone does not fully describe a pressure pipe.
SDR is a dimensional relationship, not a complete design calculation. Material grade, design coefficient, operating temperature, service life, fluid and surge conditions still matter.
What PN means
PN is a nominal pressure designation. In catalogue shorthand, PN16, PN10, PN8 and PN6 refer to pressure classes associated with a defined material and reference conditions.
PN should not be treated as a guarantee for every installation. Elevated temperature, cyclic loading, surge, chemical exposure and a project’s design rules can require derating or a different selection. The engineer’s approved schedule and the manufacturer’s current pressure table take precedence.
Common PE100 catalogue pairings
The HDPE Plumbing & Trading catalogue uses these recurring pairings:
| SDR | Catalogue PN pairing |
|---|---|
| SDR11 | PN16 |
| SDR17 | PN10 |
| SDR21 | PN8 |
| SDR26 | PN6 or PN6.3, depending on the listed fitting family |
Use the table to understand and filter catalogue entries, not to redesign a pipeline. Confirm the exact pipe or fitting datasheet because product families and reference conditions can differ.
How to read a PE100 pipe stamp
A useful pipe stamp or certificate normally gives the information needed to identify the product. Look for:
- manufacturer and product designation;
- material grade, such as PE100 where applicable;
- outside diameter and wall dimension or SDR;
- PN or pressure-class marking;
- manufacturing batch or traceability code;
- referenced product standard;
- date, line or other production identifier.
Photograph enough of the repeating stamp to capture the complete sequence. A close-up showing only “PN16” may omit the OD, material and standard needed to match a fitting.
Why SDR affects more than pressure
Changing SDR also changes internal diameter and the amount of material in each metre. That can affect:
- hydraulic calculations;
- pipe mass and delivery planning;
- lifting and handling;
- bend response and installation method;
- fusion procedure and cooling expectations;
- compatibility with fittings whose approved range is limited.
Do not approve a substitution solely because it has a higher nominal pressure class. The revised bore, weight, joining plan and design basis may still need review.
Match pipe and electrofusion fittings
Electrofusion orders should state OD, SDR and PN together. A coupler may share the correct socket diameter but still need confirmation for the pipe wall and project duty.
Use our electrofusion coupler sizing checklist before sending the take-off. For long straight runs or constrained joint locations, compare electrofusion and butt fusion against the approved WPS.
Temperature and project conditions
Nominal pressure classes are tied to reference conditions. Where operating temperature differs, design pressure cycles are severe or the conveyed medium is not ordinary water, ask the engineer to confirm the applicable derating and material suitability.
Our trade team can help identify catalogue items and obtain available documentation. We do not replace the designer or certify a changed duty.
What to include in a quote request
Send the pipe OD, material grade, SDR, PN, required length, fitting schedule, delivery location and named standard. For a large-bore enquiry, the 355mm HDPE pipe buying guide shows how those details affect a quote.
Contact the Alrode South branch with the approved bill of materials or pipe-stamp photos for current stock, lead times and trade pricing.