Executive Summary
“DN100” is not a physical measurement. Depending on applicable standards, DN100 may correspond to 108 mm, 110 mm or 114.3 mm outside diameter (OD). A gap up to 6.3 mm cannot be compensated by any gasket. This guide compares IPS, ISOmetric and Chinese GB pipesizing systems, highlights common specification traps, and provides a practical fiveitem checklist for ordering couplings. Shandong GOLDDRILL supplies grooved and mechanical couplings covering IPS, ISO dn, Chinese GB Series I and Series II pipe dimensions. Contact our sales team to confirm correct part numbers for your project.
1. The problem starts with one letter: DN
Most onsite coupling failures stem from specification errors, not mechanical defects. Buyers and suppliers both reference nominal DN labels, yet actual pipe outer diameters mismatch on arrival.
Per ISO 6708 and GB/T 1047, DN is only a dimensionless reference designation, not a realworld dimension. DN100 does not mean a pipe outer diameter of 100 mm. When working on crossborder mining or industrial projects, three sizing systems often coexist on one billofmaterials:
IPS / ASTM: inchbased outer diameters widely used in global mining HDPE piping
ISOmetric dn system: dominant across Europe, Middle East, Africa and Latin America
Chinese GB: DN as nominal label with two separate steelpipe outerdiameter series underneath
The biggest pitfall: identical DN markings can represent two completely different steelpipe ODs under Chinese standards, neither guaranteed to match IPS or ISO dimensions.
2. The three systems at a glance
|
System |
Governing standard |
Core rule |
Example |
|
IPS (inch) |
ASTM D3035 / F714 |
Nominal inch size; OD is fixed reference |
4" HDPE =114.3 mm OD |
|
ISO metric |
ISO 4427 2 |
dn equals actual outer diameter in mm |
dn110 =110 mm OD |
|
Chinese GB |
GB/T 1047 + GB/T 28708 |
DN is label; OD from Series I or Series II |
DN100 =114.3 mm or 108 mm |
Two critical notes:
ISO dn numbers equal real measured outer diameter; no conversion required.
IPS nominal inch sizes map to fixed millimeter OD values; wallthickness is expressed as DR (dimension ratio = OD ÷ wall thickness).
3. IPS: the inchorigin dimension set
IPS outerdiameter values derive from imperial inch measurements converted into millimetres, not rounded metric figures.
|
IPS size |
OD(inch) |
OD(mm) |
|
2" |
2.375 |
60.3 |
|
3" |
3.500 |
88.9 |
|
4" |
4.500 |
114.3 |
|
6" |
6.625 |
168.3 |
|
8" |
8.625 |
219.1 |
When ordering couplings for IPSspec pipe, always select products qualified for the exact OD and tolerance band. Common HDPE DR classes include DR 7, DR 9, DR 11, DR 13.5.
Shandong GOLDDRILL offers fullrange grooved and mechanical couplings for IPSdimension mining HDPE pipes.
4. ISO metric: the dn series
ISO 44272 defines metric PE pipe dimensions, where dn directly denotes pipe outer diameter. Typical sizes: dn 63, 75, 90, 110, 125, 160, 200, 250, 315 mm etc. Wallthickness uses SDR (standard dimension ratio) notation.
Do not assume IPS and ISO sizes are approximate equivalents. 6inch IPS pipe measures 168.3 mm OD, while ISO dn160 pipe measures exactly 160 mm — an 8.3 mm gap that prevents interchangeability.
GOLDDRILL mechanical couplings support standard ISO dn HDPE pipe series for mining watersupply and slurry transport.
5. China: one DN label, two OD series
GB/T 28708 defines two independent steelpipe outerdiameter series:
Series I: international inchderived outer diameters (matches IPS)
Series II: traditional domestic metric steelpipe sizes, common within Chinese domestic projects
|
DN |
GB Series I(mm) |
GB Series II(mm) |
IPS HDPE(mm) |
ISO dn(mm) |
|
DN50 |
60.3 |
57 |
60.3 |
63 |
|
DN100 |
114.3 |
108 |
114.3 |
110 |
|
DN150 |
168.3 |
159 |
168.3 |
160 |
Series I and Series II sometimes coincide numerically, yet diverge drastically on many sizes; there is no fixed offset between them.
Important exception: Chinese HDPE watersupply pipe (GB/T 13663.2) follows ISO 44272 dnSDR system, so Chinese ISOspec PE pipe shares identical outer dimensions with international ISO PE pipe.
Shandong GOLDDRILL manufactures couplings for both GB Series I and Series II steel pipe as well as GBcompliant HDPE pipe. If you are unsure which series your project adopts, send pipe OD, material and standard information to our sales team for model confirmation.
6. Pressure ratings: labels cannot be directly transferred
DR (IPSASTM) and SDR (ISO) share identical mathematical calculation (OD / wallthickness), yet preferred values and published pressure ratings differ. System maximum working pressure is always limited by the weaker component of pipeandcoupling assembly. Never convert pressure classes purely by nominal labels.
7. Four installationbreaking traps
Order only by DN: DN100 covers three different ODs; gaskets cannot absorb severalmillimetre mismatch.
Treat IPSISO nearvalues as interchangeable: small numerical similarity does not guarantee fit.
Rely only on nominal size instead of datasheet OD range: always verify manufacturer documented OD coverage.
Confuse Chinese steelpipe Series I / II with Chinese HDPE dimensions: steelpipe DN does not equal HDPE dn dimension.
8. Fiveitem specification checklist
Include this checklist in every RFQ to avoid costly sizing errors:
Pipe outer diameter in millimetres (measured or specified OD, reject nominalonly DN)
Wallthickness ratio: DR or SDR plus target pressure rating
Governing standard: ASTM, ISO 44272, GB/T 28708 Series I / II, GB/T 13663.2 etc.
Pipe material: HDPE, carbon steel, stainless steel, linedcoated pipe; determines coupling type and gasket compound
Pipe tolerance and maximum ovality class
Add one mandatory sentence for every enquiry: “Please confirm pipe outer diameter in mm and SDR / DR for supplied pipe.”
Before quotation, you may send these five parameters to Shandong GOLDDRILL sales engineers, we will recommend suitable groovedclamp or mechanicalcoupling models matching your exact conditions.
9. FAQ
Q: Is DN100 equal to 4inch pipe? A: No. 4inch IPS OD=114.3 mm. Chinese DN100 steelpipe can be 114.3 mm (Series I) or 108 mm (Series II); nearby ISO PE pipe is dn110 (110 mm). One DN label, three distinct physical sizes.
Q: Can I select couplings only with DN plus pressure rating? A: No. DN is a reference symbol, not dimension. Always provide OD, SDR/DR, standard and pipe material.
Q: Will GOLDDRILL couplings cover IPS, ISO and Chinese GB pipe? A: Yes. Shandong GOLDDRILL develops dedicated coupling ranges for IPS inchbased, ISO dn metric, Chinese GB Series I and Series II steel & HDPE piping. Please contact sales to confirm exact part numbers against your pipe actual dimensions.
10. What to do next
Review existing BOM: flag any coupling lineitems specified only by DN or inch nominal size without OD data as highrisk items.
Standardise RFQ template using the fiveitem specification checklist.
Confirm product applicability with manufacturer before purchase.
About Shandong GOLDDRILL Shandong GOLDDRILL manufactures miningoriented pipeline products including grooved couplings, ring clamps, shoulder clamps, HDPEpipe matching clamps, pipe fittings, composite steel pipes, HDPE pipes and industrial valves. Our product portfolio covers IPS, ISOmetric and Chinese GB pipe standards. For dimensional review and model recommendation, send your pipe OD, SDR and applicable standard to our sales team.
