How diameter, SDR, and pressure relate
Record nominal outside diameter, wall thickness or SDR, tolerances, material grade and governing standard. SDR is the nominal outside-diameter to nominal-wall-thickness ratio. Under the same material and design conditions, a lower SDR means a thicker wall relative to diameter; it does not identify a universal pressure class across different compounds, standards or temperatures.
The PE100+ Association pressure-design guide gives MOP (bar) = 20 × MRS (MPa) / [C × (SDR - 1)], where C is the overall design coefficient. The following calculations assume C = 1.25 and the reference conditions appropriate to the guide. They illustrate the equation, not the approval or pressure marking of a supplied pipe.
| MRS (MPa) | Assumed C | SDR | Calculated MOP (bar) |
|---|---|---|---|
| 10 | 1.25 | 11 | 16 |
| 10 | 1.25 | 17 | 10 |
| 8 | 1.25 | 17 | 8 |
Use the standard's actual nominal dimensions, classes, coefficients and temperature provisions for the proposed product. Confirm applicable transient, installation and service requirements with the designer, and check fittings and joints. The reference design basis is not a warranty that every installed system achieves the same lifetime.
Choose internal bore from the hydraulic duty
Size each section for the zones operating at the same time. Use the actual internal bore, route length, elevation, water properties, fittings and valves, then calculate pressure available at the critical outlets. An outside-diameter category or a crop label does not establish flow capacity. Compare the calculated conditions with the emitter and component requirements.
Sizing to avoid friction loss
Calculate velocity as flow divided by internal cross-sectional area, then calculate losses with an appropriate hydraulic method. For a hypothetical unit-conversion example, a flow of 2 L/s is 0.002 m³/s. With an assumed 50 mm internal diameter, area is approximately 0.0019635 m² and velocity is approximately 1.02 m/s. This is not a recommended velocity limit or an outside-diameter selection. A longer route, elevation change or added fitting still needs a pressure-loss calculation; pressure-compensating emitters do not correct every inadequate supply condition.
PE80 and PE100
PE100 and PE80 have MRS classifications of 10 MPa and 8 MPa respectively in the cited design guide. At equal outside diameter and pressure-design conditions, a qualified higher-strength grade may permit a thinner standard wall and a larger bore. Select from the applicable dimension and pressure tables rather than assuming every PE100 pipe has lower losses than every PE80 pipe.
ISO 4427-1 identifies 20 °C as the reference operating temperature. Use its applicable temperature provisions and the actual product evidence for the intended duty. Material designation does not replace dimensional, joining, pressure and destination requirements.
Confirm before ordering
Request a PE pipe specification comparison. Provide simultaneous flow, section lengths, elevation profile, required outlet pressures, pump and transient data, operating temperatures, standard, proposed grade and joining system. Include quantities and destination so wall dimensions, fittings, documentation and packing can be compared. Use the irrigation-pipe buying checklist to prepare the RFQ.