PE-Xa/EVOH and PE-Xb/EVOH pipes are made from cross-linked high-density polyethylene. The modification of the polyethylene is a chemical process in which two-dimensional hydrocarbon molecular chains are joined to one another by cross-links, forming a strong three-dimensional network.
Flexibility, strength and abrasion resistance
Thanks to this structure, PE-Xa and PE-Xb pipes offer increased flexibility and strength, together with high resistance to abrasion even under demanding service conditions.
The oxygen-protection EVOH layer
The outer barrier (oxygen-protection) layer is a thin sheath of EVOH that practically prevents oxygen from the surrounding air diffusing into the medium carried through the pipeline. To ensure a reliable bond between the outer and barrier layers, an adhesive layer is applied between them.
PE-Xa vs PE-Xb — what differs
Both are cross-linked polyethylene with a co-extruded EVOH barrier; they differ in cross-linking method and on-site handling. The comparison below summarises the difference.
| Property | PE-Xa | PE-Xb |
|---|---|---|
| Cross-linking method | Peroxide (Engel) | Silane (moisture) |
| Degree of cross-linking | ≈ 85 % | ≈ 65–70 % |
| Flexibility on site | Supple, "memory effect", hand-bent with a tool | Stiffer, holds its shape, needs a pipe bender |
| Jointing | Press fittings / sliding sleeve (no fusion) | Press fittings / sliding sleeve (no fusion) |
| EVOH barrier | To DIN 4726 — for closed circuits | To DIN 4726 — for closed circuits |
| Standard and duty | EN ISO 15875 · GOST R 52134; up to 95 °C, up to 10 bar | EN ISO 15875 · GOST R 52134; up to 95 °C, up to 10 bar |