PE100 Pipe SDR and PN Rating Explained

Short answer: In the PE100 SDR PN rating system, SDR (Standard Dimension Ratio) is the outside diameter of a pipe divided by its wall thickness — SDR = OD ÷ t. A lower SDR means a thicker wall and a higher pressure rating. PN (Pressure Nominal) is the pipe’s rated working pressure in bar. For PE100 at 20 °C with a design factor of 1.25, the relationship is P = (20 × MRS) ÷ [C × (SDR − 1)], which gives SDR 11 = PN16, SDR 17 = PN10, SDR 26 = PN6.3, SDR 9 = PN20, and SDR 7.4 = PN25. Always confirm both the SDR and the PN on the pipe marking, because the same SDR can yield different pressure ratings in different materials.

1. What SDR Actually Measures

SDR is a pure geometry ratio. It contains no information about the material at all.

SDR = OD ÷ t
where OD = outside diameter (mm), t = wall thickness (mm)

Because it is a ratio, SDR lets you compare wall thickness across different diameters. A DN110 SDR17 pipe and a DN400 SDR17 pipe have very different wall thicknesses in millimetres — but the same ratio of diameter to wall, and therefore (in the same material) the same pressure rating.

SDR Wall thickness relationship Relative stiffness Relative bore
SDR 7.4 Thick wall Highest Smallest
SDR 9 Thick wall Ma'olunga Small
SDR 11 Medium-thick Lotolotonga-ma'olunga Lotoloto
SDR 17 Lotoloto Lotoloto Medium-large
SDR 26 Thin wall Ma'olalo Largest

The trade-off is unavoidable: thicker wall means more pressure capacity but less internal bore for the same outside diameter, plus more material weight and cost per metre.

2. The PE100 SDR PN Rating Table

For PE100 (MRS 100 = 10.0 MPa) at 20 °C water service, using the standard design factor C = 1.25:

SDR PN (pā) PN (MPa) Common application
SDR 7.4 PN 25 2.5 MPa High-pressure industrial, keli
SDR 9 PN 20 2.0 MPa High-pressure mains
SDR 11 PN 16 1.6 MPa Standard pressure water mains
SDR 13.6 PN 12.5 1.25 MPa Medium-pressure distribution
SDR 17 PN 10 1.0 MPa General water supply, irrigation mains
SDR 21 PN 8 0.8 MPa Low-pressure distribution
SDR 26 PN 6.3 0.63 MPa Gravity/low-head lines, fakatafe vai
SDR 33 PN 5 0.5 MPa Very low pressure, non-pressure

3. The Governing Formula

The pressure rating of any thermoplastic pressure pipe comes from one equation, derived from the ISO 161-1 / EN ISO 15494 framework:

P = (20 × MRS) ÷ [C × (SDR − 1)]

  • P = allowable working pressure (MPa)
  • MRS = Minimum Required Strength of the material (MPa) — 10.0 for PE100, 8.0 for PE80, 6.3 for PE63
  • C = overall service (design) coefficient — typically 1.25 for PE water pipe
  • SDR = dimension ratio (OD ÷ t)

Worked example for PE100, SDR 17, C = 1.25:

P = (20 × 10) ÷ [1.25 × (17 − 1)] = 200 ÷ 20 = 10 bar = PN10 ✓

And for PE100, SDR 11, C = 1.25:

P = (20 × 10) ÷ [1.25 × (11 − 1)] = 200 ÷ 12.5 = 16 bar = PN16 ✓

4. Why the Same SDR Gives a Different PN in Other Materials

Because MRS and C change, SDR alone never determines pressure. Compare SDR 17 across three materials:

Naunau MRS (MPa) C SDR 17 → PN
PE63 6.3 1.25 PN 6.3
PE80 8.0 1.25 PN 8
PE100 10.0 1.25 PN 10
PVC-U 25.0 2.5 PN 10
PVC-O 50.0 1.6 PN 15.6 (rounded PN 16)

Note how PE100 and PVC-U both land on PN10 at SDR 17 — but for opposite reasons. PE100 has low MRS and a low design factor; PVC-U has high MRS and a high design factor because it is brittle. The pipe marking must always state the material grade, the SDR, and the PN together. A “SDR 17” stencil on its own is not a pressure rating.

5. Design Factor C: The Hidden Variable

The design factor is the safety margin applied to the material’s long-term strength. It accounts for:

  • Long-term creep behaviour — thermoplastics lose strength over decades under sustained load
  • Service temperature — above 20 °C, strength falls
  • Pressure surges — water hammer adds transient load
  • Installation damage risk — surface scratches, point loads
  • Consequence of failure — mains under roads justify a higher margin
Application context Typical C for PE100
Buried water mains, standard service 1.25
Non-buried / above-ground exposed 1.5–2.0
Aggressive chemicals or elevated temperature 2.0+
High surge risk / critical infrastructure 2.0+

This is why two suppliers can quote “the same pipe” at different pressure ratings — they assumed different C values. Always ask which design factor a quoted PN is based on.

6. Temperature Derating

All pressure ratings above are for water at 20 °C. Above that, capacity falls. Typical PE100 derating factors:

Water temperature Derating factor PN16 becomes
20 °C 1.00 PN 16.0
30 °C 0.87 PN 13.9
40 °C 0.74 PN 11.8
50 °C 0.62 PN 9.9
60 °C 0.50 PN 8.0

At 60 °C, an SDR 11 PE100 pipe that is PN16 at 20 °C is only good for about PN8. Never specify PE100 for continuous service above 60 °C — use PP-R, PE-RT, or CPVC instead.

7. PE100 vs PE100-RC

PE100-RC (“Resistant to Crack”) is an enhanced PE100 grade designed for installation methods that damage the pipe surface — trenchless techniques, rocky backfill, and recycled or rough soils. Its MRS is the same 10.0 MPa, so the SDR/PN table is unchanged. What differs is the material’s resistance to slow crack growth mo e point load damage.

Api Standard PE100 PE100-RC
MRS 10.0 MPa 10.0 MPa
SDR/PN table Unchanged Unchanged
Slow crack growth resistance Standard Substantially higher
Point load resistance Standard Substantially higher
Indicated for HDD / pa 'a e paipa With care Yes — preferred grade
Relative cost Baseline Higher

If your installation involves horizontal directional drilling, pa 'a e paipa, or sharp-edged backfill, PE100-RC pays for itself in reduced failure risk. For standard open-trench burial in selected sand bedding, standard PE100 is entirely adequate.

8. Reading a Pipe Marking

A correctly marked PE100 pressure pipe should show, at minimum:

  • Material grade — e.g. “PE100” or “PE100-RC”
  • Outside diameter — e.g. “dn110” or “OD 110”
  • SDR — e.g. “SDR 17”
  • Pressure rating — e.g. “PN10”
  • Standard — e.g. “ISO 4427” or “GB/T 13663”
  • Manufacturer and production date/batch

If any of the first five are missing, treat the pipe as unverified. A missing material grade is the most common gap on cheap pipe, and it is the single most important piece of information — because MRS drives everything downstream.

9. Ngaahi Fehuʻi ʻoku Faʻa ʻEke

What does SDR mean in HDPE pipe?

SDR stands for Standard Dimension Ratio. It is the outside diameter divided by the wall thickness. A lower SDR number means a thicker wall and a higher pressure rating; a higher SDR means a thinner wall, larger bore, and lower pressure rating.

Is SDR 11 stronger than SDR 17?

ʻIo. SDR 11 has a thicker wall than SDR 17 in the same diameter, so it carries a higher pressure rating (PN16 vs PN10 for PE100). The trade-off is reduced internal bore and higher material weight per metre.

What is the difference between PN10 and PN16?

PN10 means the pipe is rated for a working pressure of 10 pā (1.0 MPa), and PN16 for 16 pā (1.6 MPa). In PE100, PN10 corresponds to SDR 17 and PN16 to SDR 11. Both ratings assume 20 °C water service and a design factor of 1.25.

Can I use SDR 26 for a pressure main?

ʻIo, at low pressure. PE100 SDR 26 is rated PN6.3 — suitable for gravity-fed and low-head distribution, and for drainage and non-pressure service. It is not appropriate for a pumped transmission main requiring PN10 or above.

How do I calculate the pressure rating of a PE pipe?

Use P = (20 × MRS) ÷ [C × (SDR − 1)]. For PE100, MRS is 10.0 MPa and the standard design factor C is 1.25. This gives the working pressure in MPa; multiply by 10 for bar. Remember to apply a temperature derating factor if the service temperature exceeds 20 °C.

Does a thicker wall always mean a better pipe?

ʻIkai. A thicker wall raises pressure capacity but reduces the internal bore for the same outside diameter, which lowers flow capacity and raises pumping energy. It also costs more and weighs more. The correct specification is the lowest SDR that safely meets your pressure and surge requirement — not the thickest available.

Is PE100 the same as HDPE?

HDPE (polietileni maʻolunga-maʻolunga) is the generic polymer family. PE100 is a specific grade within it with a Minimum Required Strength of 10.0 MPa, defined by ISO 12162. Older grades PE63 and PE80 are also HDPE but with lower strength. Specifying “HDPE” alone is incomplete — always specify the grade.

10. Quick Reference Summary

Question Answer
How is SDR calculated? OD ÷ wall thickness
Does lower SDR mean higher pressure? ʻIo
PE100 MRS? 10.0 MPa
Standard design factor C for PE100 water pipe? 1.25
PE100 SDR 11 pressure? PN16
PE100 SDR 17 pressure? PN10
PE100 SDR 26 pressure? PN6.3
Max continuous service temperature? 60 °C (with derating)
Grade for trenchless installation? PE100-RC

Need help matching an SDR and PN to your project pressure? Send your working pressure, surge allowance, service temperature, and diameter to sean@siuhepipe.com or WhatsApp +86 19539065330, and we’ll confirm the right specification.

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