Borealis HDPE HE3494-LS-H is a black bimodal high-density polyethylene compound supplied for pressure pipe extrusion and classified as PE100 under ISO 12162. The compound is characterized by a density of 0.959 g/cm³ when tested to ISO 1183-1 and a melt mass-flow rate of 0.23 g/10 min at 190 °C and 5 kg to ISO 1133-1. The designation PE100 corresponds to a minimum required strength of 10.0 MPa at 20 °C for 50 years derived from ISO 9080 regression analysis. As a carbon black-filled, low-sag compound, the product is directed at drinking water, wastewater, and industrial pressure piping systems where long-term hydrostatic strength, slow crack growth resistance, and outdoor handling stability are specified by design codes such as ISO 4427 and EN 12201-2.

HE3494-LS-H is produced as a pelletized black compound based on a bimodal molecular weight distribution formed in a cascade polymerization process. The high molecular weight fraction carries the slow crack growth resistance, while the low molecular weight fraction provides processing fluidity. α-olefin comonomer incorporation in the high molecular weight fraction reduces crystallite thickness and increases the number of effective tie molecules bridging adjacent lamellae. This microstructural base is what allows the compound to meet ISO 12162 PE100 requirements while retaining extrudability on conventional single-screw grooved-feed lines.

Material Classification and Standardized Property Profile

The classification of HE3494-LS-H as PE100 is not a single-point yield value; it is based on the lower confidence limit of long-term hydrostatic strength determined by multi-temperature pipe testing. The property set shown in the table is measured on compression-moulded specimens or extruded pipe according to the cited methods. Density of the black compound is higher than that of the unpigmented base resin because of the 2.2 % carbon black dispersion required for UV stabilization and pipe marking. Melt flow at 190 °C/5 kg is low, consistent with a high-molecular-weight tail; this imposes melt-pressure demands but supports sag resistance and slow crack growth performance.

Batch-to-batch melt flow variation is typically held within ±0.02 g/10 min. In production terms this is sufficient to require feed-throat temperature and screw-speed compensation on grooved-feed single-screw extruders. The carbon black dispersion level is controlled to ≤3 under ISO 18553; larger agglomerates can act as stress concentrators in slow crack growth testing, even if short-term tensile values remain unchanged.

Because the material is fully compounded, the reported density includes carbon black. This differs from natural PE100 grades, where density is typically 0.950 g/cm³. Users should not compare black-compound density with base-resin density when calculating pipe mass; the 0.959 g/cm³ value should be used for finished pipe mass calculations.

In pressure pipe design, the long-term strength of PE100 compounds is converted to wall thickness through the MRS of 10.0 MPa and the applicable service coefficient. For water at 20 °C and 50 years, the design stress is typically 8.0 MPa when a service coefficient of 1.25 is applied. The same nominal pressure rating therefore requires a thinner wall than a PE80 system with an MRS of 8.0 MPa, reducing pipe mass and hydraulic friction losses. Rapid crack propagation resistance must also be verified for pressurized systems; the relevant test is ISO 13477, with arrest behaviour dependent on pipe diameter, wall thickness, and test temperature. Because the failure mode shifts from ductile to brittle with increasing stress and temperature, long-term tests are run at 20 °C, 60 °C, and 80 °C to construct the ISO 9080 regression line. The use of a service coefficient is not a material property; it is a system-design selection that accounts for installation damage, surge pressure, and operational variability.

What Limits Long-Term Hydrostatic Design Basis in PE100 Systems?

The main constraints on hydrostatic design are the ductile-to-brittle transition and slow crack growth propagation. In a bimodal PE100 compound, the low-molecular-weight fraction reduces melt viscosity and improves processability, while the high-molecular-weight fraction increases the number of tie molecules bridging adjacent crystalline lamellae. Tie molecules are the primary microstructural feature resisting crazing and crack propagation under sustained stress. Under ISO 9080 testing, failure times at 80 °C are extrapolated to 20 °C using an Arrhenius shift; the slope change associated with the ductile-brittle transition is explicitly handled in the standard's regression model. HE3494-LS-H is positioned for applications where the operating hoop stress remains below the knee of the stress-rupture curve at the design temperature. Slow crack growth screening for pipe grades is commonly carried out by the notched pipe test to ISO 13479; acceptance thresholds are stipulated in national specifications and vary by pipe class, but tests are typically conducted at 80 °C under a defined hoop stress. Chemical environments that reduce surface energy can accelerate slow crack growth; design for such service should use ISO/TR 10358.

Rapid crack propagation is a separate low-temperature failure mechanism in which a brittle crack travels faster than the energy release rate can be dissipated. The ISO 13477 small-scale steady-state test measures critical pressure and crack arrest length; the result is geometry-dependent and must be reported with pipe diameter, wall thickness, and test temperature. In practice, PE100 grades are selected over PE80 for water and industrial mains specifically because their higher MRS and higher crack arrest thresholds reduce the risk of long-running fractures at temperatures near 0 °C. Published data for this specific configuration is limited, so pipe producers validate the final pipe geometry on their own extrusion lines.

Hydrostatic test programs for PE100 classification use pipe specimens with a defined standard dimension ratio and internal pressure at multiple temperatures. The failure mode is identified by visual observation and time-to-failure. The ISO 9080 standard requires at least three temperatures and data points arranged to define ductile and brittle branches. For PE100 grades, the ductile branch is generally correlated with tensile yield and molecular weight, while the brittle branch is sensitive to comonomer distribution, tie-molecule density, and stabilizer package. Melt flow rate alone cannot predict the brittle branch; a pipe grade with a lower melt flow may still fail earlier under slow crack growth if the comonomer distribution is non-uniform or if carbon black dispersion is poor.

When Low-Sag Performance Governs Large-Diameter Pipe Extrusion

Pipe wall thickness for large diameters and high pressure ratings creates a molten tube that must resist gravity-driven sag before cooling. The high molecular weight tail and shear-thinning character of HE3494-LS-H are formulated to limit sag. On production lines using 45D single-screw extruders with grooved feed zones, melt temperatures at the die head are maintained between 200 °C and 220 °C. Lower temperatures reduce sag but increase head pressure and motor load; higher temperatures reduce melt viscosity but can accelerate thermo-oxidative degradation if residence time exceeds the antioxidant protection window. Extrusion trials indicate that wall-thickness eccentricity is more sensitive to axial melt temperature uniformity than to short-term melt-flow variation; die-head setpoints varying by more than ±5 °C across the circumference produce measurable thickness shifts in pipes above 800 mm diameter. Pre-drying is not required for sealed packaging; if sacks are exposed to relative humidity above 60 %, surface moisture can produce surface defects and should be removed with a dry-air hopper dryer at 70 °C to 80 °C for 2 h to 4 h.

The melt flow at 190 °C/5 kg is intentionally low; it is not an indicator of poor processability because the bimodal distribution creates shear-thinning behaviour at extrusion shear rates between 10 s⁻¹ and 1000 s⁻¹. On a 45D extruder with a grooved feed section, stable output is more dependent on temperature uniformity than on the absolute melt flow value. Production-scale equipment behaviour differs from laboratory data because shear heating in the screw increases melt temperature by 5 °C to 15 °C above set-point depending on screw speed and barrel configuration. A 45D grooved-feed extruder running at high throughput can move the effective melt temperature toward the upper end of the processing window, which consumes antioxidants faster. Operators compensate by reducing barrel temperatures or adjusting screw oil temperature, but these changes affect melt pressure and output. The grade is less sensitive to moisture than polar pipe resins; however, surface moisture at load hoppers remains a common cause of surface roughness in thick-wall pipe.

How Does HE3494-LS-H Differ from PE80 and Standard PE100 Compounds?

The primary difference is MRS: PE80 has 8.0 MPa, whereas PE100 has 10.0 MPa. This permits thinner wall sections and lower mass per metre for identical nominal pressure. For a 10 bar water main at 20 °C, the PE100 design stress of 8.0 MPa produces a standard dimension ratio of 17, whereas a PE80 design stress of 6.3 MPa produces an SDR of 13.6. The higher SDR corresponds to a thinner wall and lower hydraulic friction loss, but it also increases pipe flexibility and requires attention to bedding stiffness.

Compared with standard unimodal HDPE pipe grades, the bimodal distribution shifts the molecular weight distribution to higher molecular weight fractions without eliminating the low-molecular-weight lubricating fraction. The result is a more pronounced shear-thinning response, allowing extrusion at higher throughputs than unimodal resins of similar melt flow. Differences from other PE100 compounds are formulation-specific: the low-sag character of HE3494-LS-H becomes measurable in thick-wall pipe production, while some standard PE100 grades may show equal slow crack growth resistance but lower sag resistance. The carbon black dispersion and UV stabilizer package distinguish it from unpigmented PE100 grades intended for indoor industrial piping. Under ISO 13479, notched pipe test failure times are used as a comparative indicator; values are strongly dependent on pipe diameter, wall thickness, and test stress, so direct comparison between grades requires identical specimen geometry.

In potable water service, national approvals are application-specific. The base polyethylene belongs to olefin polymers potentially covered by FDA 21 CFR 177.1520 and EU Regulation 10/2011 for food-contact use, but the black compound must be evaluated under the relevant national drinking water scheme before installation. Exposure to strong oxidizers, aromatic hydrocarbons, or fuel fractions can swell or oxidize the polymer, reducing design life; chemical resistance should be checked to ISO/TR 10358. Processors should not exceed a melt temperature of 240 °C for extended periods, and the use of post-consumer recyclate in pressure pipes requires revalidation to ISO 13479 because the slow crack growth performance of PE100 is sensitive to molecular weight distribution and tramp contamination.