Borealis BorSafe HE3490-LS-HW is a black bimodal high-density polyethylene pipe extrusion compound classified within the PE100 hydrostatic design category. The grade is supplied as ready-to-extrude pellets with carbon black and stabilizer additives already dispersed in the polymer matrix. The LS-HW suffix denotes a low-sag melt response combined with improved weldability relative to standard PE100 pipe grades; however, the commercial suffix is not itself a recognized classification and must be read alongside the manufacturer’s release specification and the applicable pipe-system standards. Primary usage includes pressure piping for potable water, wastewater force mains, irrigation networks, and industrial aqueous transfer, with pipe dimensions and operating limits governed by ISO 4427-1, ISO 4427-2, and national installation codes. The material is not formulated for thin-wall injection moulding or film extrusion.

In hydrostatic design, HE3490-LS-HW is assigned a minimum required strength of 10.0 MPa at 20 °C for 50 years according to ISO 9080. This places the product in the PE100 class under ISO 12162. The distinction from PE80 is quantitative: PE80 carries an MRS of 8.0 MPa, so at equal service factors the PE100 grade can achieve an allowable design stress of 8.0 MPa rather than 6.3 MPa. That increase permits thinner walls for a given nominal pressure rating and can lower material consumption per linear metre of pipe. The same strength increase, however, requires tighter thermal control during extrusion because the high-molecular-weight fractions responsible for long-term strength also raise melt viscosity and reduce flow.

What Distinguishes the Low-Sag, High-Weldability Variant From Standard PE100 Grades?

Standard PE100 pipe grades may exhibit satisfactory tensile and hydrostatic properties while still sagging during thick-wall extrusion. HE3490-LS-HW is formulated with a controlled broadening of the molecular weight distribution and a high-molecular-weight tail. This molecular architecture increases melt elasticity and die swell without proportionally increasing shear viscosity. On production-scale grooved-feed single-screw extruders with screw diameters of 90–120 mm and 30:1 to 36:1 L/D, the practical effect is a wider operating window for wall thicknesses above 80 mm. The melt remains geometrically stable between the die and calibration sleeve, reducing gravitational wall thinning compared with standard PE100 lots of equivalent melt flow rate.

Weldability of the high-weldability variant is verified through butt fusion welding according to ISO 21307 and electrofusion welding according to ISO 12176-1. The grade is also positioned for slow crack growth resistance; PE100-RC-type assessments use notched pipe testing based on ISO 13479 and rapid crack propagation testing based on ISO 13477. The LS-HW designation should not be interpreted as automatic certification to every national PE100-RC scheme. Third-party listing and pipe-manufacturer qualification remain the controlling evidence for installation without sand bedding or for aggressive trenchless techniques.

Low-sag behaviour is not solely a function of melt flow rate. It is evaluated by measuring sag of a freely extruded parison or by monitoring wall-thickness eccentricity in the calibration section. The melt strength of a low-sag PE100 may show die swell values 15–25% greater than a reference PE100 under identical shear conditions. This higher die swell requires slightly larger calibration sleeves or reduced haul-off tension. If haul-off tension is too high, the pipe diameter can be drawn below tolerance even though the melt is thermally stable. Conversely, insufficient tension can produce irregular wall thickness as the pipe enters the vacuum tank.

Extrusion processing is typically performed with barrel temperatures from 180 °C to 220 °C and a die-head setpoint of 210 °C to 225 °C. The melt temperature must remain below 230 °C; excursions above that limit can reduce oxidation induction time and create gel defects on the inner wall. Below 190 °C, the high-molecular-weight fraction may not homogenize fully, causing surface roughness or carbon black agglomeration. The resulting process window is therefore narrower than for many general-purpose HDPE grades.

On a 120 mm grooved-feed single-screw extruder running DN 315 SDR 11 pipe, line rates are commonly reported between 400 kg/h and 600 kg/h. The exact rate depends on screw design, die-head pressure, and calibration length. A recurrent failure mode observed on manufacturing lines is an undulating inner wall when the first vacuum tank water temperature falls below 15 °C. Raising the first cooling-zone water temperature to 25–30 °C often restores smooth internal geometry. Inadequate cooling at high line speeds can produce sag and eccentricity even with a low-sag grade, so ultrasonic wall-thickness gauges are used to maintain die centring and minimum wall thickness.

Batch-to-batch melt flow rate variation should be monitored with an online rheometer or by sampling every 4 h according to ISO 1133-1:2022. Variations exceeding ±15% from the reference lot may require adjustment of screw speed or barrel profile. Quality control on incoming lots should include density, melt flow rate, carbon black dispersion, and oxidative stability. Carbon black dispersion is assessed by ISO 18553, and a significant change in oxidation induction time below 15 min may indicate stabilizer under-dosage or thermal abuse during compounding and should lead to quarantine.

Material Data, Pipe Classification, and Compliance Matrix

The following table lists typical physical and mechanical values published for HE3490-LS-HW. The values are not batch-release limits; specification values must be obtained from the current supplier certificate because manufacturing tolerances and additive packages can shift within the approved range.

Thermal conductivity is approximately 0.38 W/(m·K) at 23 °C when measured by transient plane source methods. Heat capacity and thermal diffusivity should be used in cooling-length calculations for thick-wall extrusion. The carbon black loading of 2.0–2.5% by mass provides long-term ultraviolet stabilization for above-ground temporary storage, but buried installation remains the intended service environment.

The primary use of HE3490-LS-HW is extruded pressure pipe produced to ISO 4427 dimensional series. Potable water pipes are typically installed as butt-fused strings with fusion parameters from ISO 21307. When local codes permit trenchless installation without sand bedding, slow crack growth resistance becomes the controlling material property. Point loads from stones and backfill can initiate cracks in lower-resistance PE100 grades but are better accommodated by PE100-RC-qualified materials. The product has been reported in large-diameter water mains; published data for extreme diameters is limited and should be confirmed through pipe-manufacturer qualification and third-party certification.

Compliance Markings and Third-Party Verification

Compliance for pressure-pipe service is demonstrated through material classification, pipe testing, and installation jointing standards. The following table identifies the principal standards and verification functions associated with the grade when used in water piping systems.

When Long-Term Hydrostatic Strength Governs Pipe Wall Design

The hoop stress for a thin-walled pipe under internal pressure is calculated as σ = P × (SDR − 1) / 2, where P is internal pressure, SDR is the ratio of outer diameter to wall thickness, and σ is wall stress. For PE100 with a design stress of 8.0 MPa derived from MRS 10.0 MPa and a service factor of 1.25, SDR 11 corresponds to a pressure rating of 16 bar at 20 °C for water. SDR 17 corresponds to 10 bar. These ratings fall as temperature increases; at 40 °C, the allowable design stress must be reduced using the derating factors given in the applicable pipe standard.

For pipe diameters above DN 500, the low-sag characteristic has a direct effect on wall-thickness tolerance. A standard PE100 melt may produce eccentricity of 2–3% in SDR 17 wall thickness after calibration, whereas a low-sag grade can hold the same within approximately 1% when cooling is optimized. Because hydrostatic resistance is governed by minimum wall thickness, improved concentricity translates into less material consumed to meet the same pressure rating. The relationship is not linear; at SDR 11, even a 1% reduction in minimum wall thickness can reduce the design margin by a measurable but code-compliant amount.

For no-dig installation, slow crack growth resistance is the differentiator. In pipe bursting and directional drilling, external scratches from rock or tooling can initiate cracks if the pipe is dragged under high tensile load. PE100-RC formulations are designed to resist crack propagation from such point loads. The notched pipe test of ISO 13479 uses a circumferential external notch and an elevated-temperature internal pressure; a PE100-RC material must exceed the standard PE100 threshold by a substantial margin. The exact threshold for HE3490-LS-HW must be taken from the certification body because national schemes differ in test stress and acceptance criteria.

Operational boundaries must be observed. The material should not be processed at melt temperatures above 230 °C or with prolonged hold-up at high temperature; oxidative degradation reduces long-term hydrostatic strength and can lower oxidation induction time below 20 min. Avoid contact with strong oxidizing agents, aromatic hydrocarbons, and chlorinated solvents because these media accelerate environmental stress cracking. Regrind use should be restricted to clean, unpigmented process scrap from the same grade, and its proportion in the blend should be validated by slow crack growth testing when national pipe standards require full notch-pipe re-qualification. Pipe sections stored outdoors for more than 12 months should be assessed for surface oxidation before butt fusion welding.