PetroChina Dushanzi HDPE 5002 is a high-density polyethylene resin grade produced at the Dushanzi Petrochemical Company facility in Xinjiang. The material is positioned in the high-molecular-weight segment of the HDPE family, where melt flow index is intentionally kept low to preserve melt strength, environmental stress cracking resistance, and long-term hydrostatic load capacity. Technical data sheets for the grade typically report a melt flow index in the region of 0.20–0.25 g/10 min under a 5.0 kg load at 190 °C and a density close to 0.950 g/cm³. The grade is supplied as natural or white pellets and is directed toward thick-wall extrusion, blow moulding, and industrial sheet applications rather than thin-wall injection moulding. Because the exact comonomer type, stabiliser package, and release-agent content can vary between production campaigns, converters should request a lot-specific certificate of analysis and not rely solely on generic datasheet values for qualification of pressure-bearing components.

Product Designation and Resin Chemistry

The 5002 designation is a manufacturer-grade code rather than a rheological or density specification. It is produced in a slurry-loop polymerisation process in which ethylene and a small amount of an α-olefin comonomer—most commonly 1-butene or 1-hexene—are polymerised over a Ziegler-Natta catalyst in a hydrocarbon diluent. The comonomer is incorporated as short-chain branches along the polyethylene backbone. These branches reduce crystallite size and increase the concentration of tie molecules connecting adjacent lamellae. The practical consequence is that a density of 0.948–0.952 g/cm³ yields lower stiffness than a homopolymer HDPE of the same nominal density but gives markedly higher slow crack growth resistance. The catalyst system leaves low residual metal content, but the exact specification for titanium, aluminium, and chloride residues is batch-specific. The low melt flow index under 5.0 kg load, typically 0.20–0.25 g/10 min by ISO 1133-1:2022, indicates a high weight-average molecular weight. This molecular architecture creates a broad relaxation spectrum and pronounced die swell; it also increases the energy required for plastication and reduces the output of a given extruder when compared with low-viscosity HDPE grades.

Table 1 provides representative physical, thermal, and chemical resistance data reported for the grade. The values are compiled from public datasheets and polymer database entries; they are not specification limits and should not be used as the sole basis for pressure-pipe design.

Pipe extrusion evaluations of the 5002 grade on grooved-feed single-screw extruders with 30:1 L/D ratios have shown that the resin develops high melt pressure at the breaker plate when melt temperatures are held below 210 °C. In thick-wall pipe tooling, operators often maintain barrel profile temperatures from 180 °C in the first zone to 200–210 °C at the adapter and die, with a gear pump used to damp pressure fluctuations and raise output stability. The processing window is bounded by thermal degradation on the upper side and melt fracture on the lower side. At melt temperatures above 230 °C, the oxidation induction time of the stabilised compound declines and gel formation may appear after prolonged residence time. At melt temperatures below 175 °C, the high-molecular-weight fraction may not fully homogenise, and the extrudate can exhibit shark-skin or melt-fracture defects at line speeds above 0.5 m/min. Pre-drying is generally unnecessary when resin is stored in sealed packaging below 60% relative humidity; bags exposed to humid air should be purged or dried at 80 °C for 2–3 h to avoid surface moisture defects. Pipe processors should not blend 5002 with amine-based processing aids without testing, because the alkaline additives can interfere with phenolic stabiliser systems and reduce OIT. For pipe wall thicknesses above 20 mm, the cooling time is the dominant productivity limitation; quench water temperatures below 20 °C reduce residual stress but increase thermal gradient.

In thick-wall extrusion, processors frequently install breaker plates with screen pack sequences such as 20/40/60 mesh to trap gels and particulate contaminants. Because the 5002 grade has a high melt viscosity, the pressure drop across the screen pack increases more rapidly than with an injection moulding resin. A pressure rise of 5 MPa over the initial set point is commonly used as the trigger for screen replacement. Failure to replace screens can lead to shear overheating, gel re-entrainment, and surface defects on the pipe inner wall. Melt pumps should be operated at suction pressure above 1.5 MPa to avoid cavitation when the melt viscosity is high.

Sheet and geomembrane extrusion trials with Dushanzi HDPE 5002 on flat-die lines equipped with 120-mm grooved-feed extruders and 30:1 L/D screws indicate that melt temperatures of 200–215 °C are sufficient to fill a 3.0–4.0 mm sheet die without surface melt fracture. The melt strength of the grade assists in maintaining web stability between the die and the polishing stack. Chill-roll temperatures in the range of 60–80 °C are used to control cooling rate; lower roll temperatures increase the cooling rate and reduce crystallinity, but can induce excessive curl. For geomembrane applications, the sheet is often evaluated for stress crack resistance according to ASTM D5397-19 single-point notched constant tensile load testing and for oxidation resistance according to ISO 11357-6:2018. For sheet thickness above 2.5 mm, the line speed is usually limited by the cooling capacity of the polishing stack rather than the extruder output. A three-roll stack with roll diameters of 400 mm and water circulation at 50–80 °C provides sufficient contact time for thicknesses up to 4.0 mm. The extruder back pressure should be maintained below 35 MPa to protect the screw thrust bearing.

How Does 5002 Differ from Lower-Molecular-Weight Injection Moulding Grades?

The principal difference is observed in the melt flow index. Dushanzi HDPE 5002 is specified in the 0.20–0.25 g/10 min range under 5.0 kg load, whereas a standard injection moulding HDPE grade often has a melt flow rate of 4–20 g/10 min under 2.16 kg. The lower flow index corresponds to higher melt viscosity, greater die swell, and longer relaxation times. In thin-wall injection moulding, this viscosity level produces flow hesitation, weld-line weakness, and the need for high clamp force; therefore the 5002 grade is not interchangeable with high-flow grades used for caps, closures, or thin-wall containers. The trade-off is beneficial for extruded products: the high-molecular-weight distribution resists parison sag in blow moulding, and the slow crack growth resistance of the resin exceeds that of many lower-molecular-weight grades. The comparison must be made at equal density and comonomer content, because density changes of 0.002 g/cm³ can shift flexural modulus by 30–50 MPa. In injection moulding machinery, the 5002 resin would require a barrel capacity of at least 1.5–2.0 times the shot weight and injection pressures that may exceed 140 MPa; it is therefore normally avoided for parts with wall sections below 2.0 mm.

Table 2 summarises the typical property contrast between the 5002 grade and a generic high-flow injection moulding HDPE. The comparator range is deliberately broad because injection moulding grades span multiple melt flow classes and comonomer levels.

For blow moulding, the difference is equally important: a grade with 4–20 g/10 min MFR cannot sustain heavy parisons for 200-L drums without excessive sag, whereas the 5002 grade maintains melt strength at take-off weights above 3 kg. This distinction derives from the molecular weight distribution, not merely from density. Grades with similar density but lower molecular weight may match stiffness but fail ESCR tests at 50 °C in Igepal solutions.

Accumulator-head machines running 200-L drum tooling have been used to evaluate the 5002 grade in large-part extrusion blow moulding. The resin’s high melt strength reduces parison sag at take-off weights above 3 kg; parison programming and die gap adjustments are required to compensate for die swell of 20–35%. For a nominal wall thickness of 5–6 mm, mould cooling water at 10–15 °C and blow air pressure of 6–8 bar have been reported in plant trials. The cooling phase is the productivity constraint: demoulding at surface temperatures above 65 °C can cause post-moulding distortion. Unlike lower-viscosity HDPE, the 5002 grade may require higher melt temperature set points to prevent melt fracture, but the set point should not exceed 220 °C for extended cycles. Accumulator-head tooling should be sized to avoid excessive residence time; residence times beyond 10–15 min at high melt temperature can reduce OIT and generate gels. Pin and bushing die gaps are normally set 20–40% wider than the target wall thickness to account for die swell and parison weight. Post-moulding shrinkage of the 5002 grade in heavy-wall sections is anisotropic and can range from 1.5% to 2.5% depending on cooling rate and mould temperature.

When Long-Term Hydrostatic Strength Governs Material Selection

Specification for pressure-pipe compounds requires more than a density and MFR check. A resin used for water and gas distribution must be evaluated as a compound under ISO 9080:2022 hydrostatic strength testing and classified according to ISO 12162:2009. Dushanzi HDPE 5002 is often screened for PE100-type service because its high ESCR and moderate density are consistent with the requirements, but no resin can be declared PE100 on the basis of resin properties alone. Compound formulation, extrusion processing, and long-term testing of the finished pipe determine the final classification. The grade’s slow crack growth resistance, measured as F50 in a 10% Igepal solution at 50 °C per ASTM D1693-15 Method B, is a useful comparator for applications exposed to aggressive soil surfactants or constant internal pressure. However, the test result is not a direct predictor of service life; design stress must be derived from the material’s regression curve. In applications involving chlorinated water, residual chlorine can reduce slow crack growth resistance; validation under ASTM F2263-14 or equivalent oxidative stress methods may be required.

Long-term hydrostatic strength testing is time-consuming; minimum testing durations for PE100 evaluation can exceed 10,000 h at multiple temperatures. Designers should not interpolate from short-term tensile creep data. The ISO 9080 regression curve uses failure data from pipe specimens tested at 20 °C, 60 °C, and 80 °C, with the lower confidence limit at 50 years as the design basis. Processors should also observe the following operational limits: avoid blending with amine-based polymer processing aids without stabiliser testing; avoid sustained exposure to melt temperatures above 230 °C; and store unopened bags below 60% relative humidity to prevent surface moisture defects. The grade is not intended for use as a food-contact material unless a specific lot is accompanied by certification meeting EU Regulation No 10/2011 or 21 CFR 177.1520. Published data for the effect of recycled-content blending on ESCR of Dushanzi HDPE 5002 is limited; fabricators should qualify any post-consumer recyclate addition above 10 wt% by lot-specific ESCR and OIT testing. Equipment used for pressure-pipe production should include mass-pressure and melt-temperature sensors at the die entry, and the extrusion record should be retained for each production lot to support ISO 9080 regression analysis.