EVOH for Industrial Fluid Pipe

EVOH for industrial fluid pipe is specified as a buried semicrystalline barrier core inside coextruded multilayer pipe and is not supplied as a single-layer pressure pipe. Pipe-grade EVOH is differentiated by ethylene comonomer molar content rather than a single commercial designation. Common specifications include ethylene contents of 27 mol%, 32 mol%, 38 mol%, and 44 mol%; melt mass-flow rate of 1.8–4.5 g/10 min at 190 °C with 2.16 kg load per ISO 1133-1:2022; density of 1.12–1.20 g/cm³ per ISO 1183-1; and tensile yield stress of 45–70 MPa per ISO 527-2 when measured on dry compression-moulded film. Model configurations are described by layer sequence: PE/tie/EVOH/tie/PE, PE-RT/tie/EVOH/tie/PE-RT, PP-RCT/tie/EVOH/tie/PP-RCT, PA12/tie/EVOH/tie/PA12, or PVDF/tie/EVOH/tie/PVDF. The EVOH core commonly occupies 5–15 wt% of the pipe wall. For hydronic oxygen-barrier pipe of outside diameter 16–63 mm and SDR 7.4–11 per ISO 4065, the EVOH layer is 0.10–0.20 mm thick. For hydrocarbon or volatile-solvent retention, the EVOH layer is increased to 0.15–0.30 mm. Dry oxygen permeability of a 15 µm cast film at 23 °C and 0% RH under ASTM D3985 is 0.16–0.60 cm³·mm/(m²·day·atm) depending on ethylene content, but moisture and temperature increase this value sharply.

The product is supplied as cylindrical pellets of 2.5–4.0 mm diameter and 2.0–3.5 mm length, packaged in 25 kg moisture-barrier polyethylene bags inside corrugated boxes or octabins. Bulk transfer of pipe-grade EVOH is less common because moisture uptake during transfer can exceed 0.10 wt% within 1–2 h in humid ambient air. Pellets exposed to ambient air above 60% RH for more than 12 h require redrying before coextrusion. Pipe-grade EVOH is available in standard and high-flow variants; high-flow variants with melt mass-flow rate up to 4.5 g/10 min improve distribution at low layer thickness but may have slightly higher oxygen permeability than low-flow grades of the same ethylene content.

What Limits Continuous Service Temperature in EVOH Core Layers?

Continuous service temperature for the EVOH barrier core is limited by moisture-induced plasticization rather than melting. The melting endotherm of pipe-grade EVOH is 162–191 °C by differential scanning calorimetry at 10 K/min; the dry glass transition is 48–72 °C, but at 80% RH the glass transition can fall below 35 °C. Oxygen permeability increases by a factor of 5–20 between 0% RH and 85% RH. In hydronic systems, DIN 4726 requires oxygen diffusion no greater than 0.1 g/(m³·d) at 40 °C. A 0.10–0.20 mm core of 27 mol% or 32 mol% ethylene normally satisfies this limit, but at 60 °C and 85% RH the same layer may exceed the limit unless thickness is increased or a lower-ethylene grade is used. Published data for continuous operation above 60 °C in high-moisture industrial fluid streams is limited.

Processing places a separate boundary on the service window. Pipe-grade EVOH is predried in desiccant dryers with dew point ≤ −40 °C to a residual moisture content of 0.02–0.10 wt% as determined by ISO 15512:2019; typical drying conditions are 90–105 °C for 4–6 h. Wet pellets produce acetic acid, gel particles, and layer-thickness variation above ±8% on production lines. Single-screw extruders with L/D 28:1–32:1 and grooved feed sections are used, with barrel zone set points of 180 °C, 195 °C, 210 °C, and 220 °C, die temperature 225 °C, and melt temperature 218–230 °C. Residence time is kept below 8 min; melt exposure above 240 °C accelerates vinyl-alcohol degradation and increases gel counts. Running below 175 °C melt temperature causes layer-thickness nonuniformity and excessive die-head pressure, typically above 120–160 bar on a 65 mm barrier-layer extruder. The EVOH melt stream is coextruded into a feedback or spiral mandrel die with melt-temperature variation maintained within ±2 K to keep layer distribution within ±5% of nominal.

On production lines, the EVOH layer is not exposed to the pipe bore or the outer environment. The inner polyolefin layer typically provides at least 1.5 mm of fluid-contact thickness, and the outer layer provides weathering and mechanical protection. Interfacial tie layers based on maleic anhydride grafted polyethylene or polypropylene must have peel adhesion above 3 N/15 mm per ISO 8510-2 at 23 °C. The EVOH core contributes less than 5% of axial tensile strength at SDR 9; hydrostatic pressure rating is carried by the substrate layers and is evaluated by ISO 9080 regression on the complete pipe construction.

In closed-loop hydronic distribution and compressed-air piping, the EVOH layer is positioned between the inner fluid-contact polymer and the outer protective polymer. The inner layer is selected for pressure rating and compatibility with the process fluid; the outer layer is selected for UV, impact, and abrasion resistance; the EVOH core suppresses oxygen ingress that can corrode carbon-steel pump internals, valve seats, and storage vessels. Pipe outside diameters from 16 mm to 63 mm are supplied as coils or straight lengths. Oxygen diffusion through the complete pipe is verified by ISO 17455. Batch-to-batch repeatability is controlled by specifying EVOH layer thickness variation not exceeding ±5% of nominal. Calibration records typically report oxygen permeation at 40 °C and 60 °C. For compressed-air lines, oil mist and condensed water do not directly contact the EVOH core, but prolonged saturation of the inner polyolefin layer above 80% RH can still reduce barrier performance; therefore, the inner layer is specified at no less than 1.5 mm in condensing conditions.

For industrial chilled-water lines, the barrier requirement is directed primarily at preventing oxygen ingress rather than product loss. Without an EVOH layer, oxygen ingress through monolithic PE-RT pipe can exceed the DIN 4726 limit by an order of magnitude under the same test conditions. Specifiers should verify that the complete pipe certification covers the intended temperature and pressure envelope; a barrier pipe qualified at 70 °C and 8 bar does not automatically satisfy 90 °C service with the same SDR. The EVOH core may survive short-term excursions to 95 °C during system commissioning, but cyclic exposure above 70 °C increases the risk of tie-layer creep and layer disbonding.

When an Oxygen Barrier Core Must Outperform PVDF and PA6 in Hydrocarbon Retention

Where the pipe carries fuel, aromatic solvents, or volatile organic condensate, EVOH is selected for lower oxygen and hydrocarbon permeation than PVDF and PA6 at low humidity. At 23 °C and 50% RH, published resin supplier data place EVOH 32 mol% oxygen permeability at 0.5–2.0 cm³·mm/(m²·day·atm) under ASTM D3985, PA6 at 10–20 cm³·mm/(m²·day·atm), and PVDF at 15–40 cm³·mm/(m²·day·atm). The advantage narrows above 80% RH and above 60 °C. For hydrocarbon retention, an EVOH core of 0.15–0.30 mm reduces permeation below many buried fuel-piping thresholds, but the pipe construction must prevent direct contact between EVOH and aromatic neat liquids. Immersion in toluene or xylene can swell EVOH and initiate tie-layer delamination.

Compared with monolithic PVDF pipe, EVOH barrier pipe has lower oxygen and hydrocarbon permeation at 23 °C and 50% RH but cannot be exposed to hot strong oxidizers or high-water polar solvents. Compared with PVDC, EVOH does not release chlorinated decomposition products during purge cycles and can be reground into selected noncritical middle layers, but its oxygen barrier is more moisture-sensitive. Compared with PA12 pipe, EVOH multilayer pipe requires tie layers and coextrusion yet may reduce oxygen permeation by 10–50× under the same conditions. In dry-gas service above 80 °C, monolithic PA12 or PVDF pipe may be preferred because the EVOH barrier advantage is reduced and differential thermal expansion between layers increases residual stress.

Multilayer pipe with an aluminum core provides very low oxygen permeation and lower thermal expansion, but it is heavier, retains less coil flexibility, and can corrode at exposed cut ends if not sealed. EVOH-based fully polymeric barrier pipe is coilable in smaller diameters and has no metallic corrosion path, but its oxygen barrier is slightly more sensitive to high humidity than an intact aluminium core. Specifiers choosing between aluminium-barrier and EVOH-barrier pipe should compare the complete pipe permeation certificate under ISO 17455 at the maximum intended service temperature rather than at ambient temperature alone.

For industrial waste-gas condensate and mild solvent transfer lines, EVOH is specified only when the inner layer keeps the EVOH core below 60 °C and 80% RH. Concentrated sulfuric acid, aqueous ammonia, phenol, dimethyl sulfoxide, and high-water polar solvents are incompatible because they disrupt hydrogen bonding in the vinyl-alcohol phase. The EVOH layer is not used as the fluid-contact layer. Field failures commonly appear as delamination at the tie-layer interface; peel adhesion below 3 N/15 mm per ISO 8510-2 is associated with layer separation during burst testing at 23 °C. In butt fusion joining of multilayer pipe, the EVOH and tie layers are removed from the fusion zone with a peeling tool to avoid contamination of the polyethylene weld; incomplete removal reduces weld elongation at break below 200% under ISO 13953. Hydrostatic pressure ratings are assigned to the complete multilayer pipe by ISO 9080 regression, not to the EVOH core alone. Published data for EVOH core performance in continuous high-temperature organic solvent mixtures above 60 °C is limited.