PetroChina Tarim HDPE 5672M enters downstream manufacturing as a high-molecular-weight bimodal ethylene copolymer. The grade is handled throughout the supply chain as a PE 100-type resin when the lot is independently classified under ISO 12162:2009 with an MRS of 10.0 MPa at 20 °C, 50 years. Density is measured according to ISO 1183-1:2019, and melt mass-flow rate is determined according to ISO 1133-1:2022 at 190 °C under 5 kg. Published lot-specific data for 5672M is limited in some downstream configurations; the process windows and acceptance thresholds cited below are representative of PE 100 high-molecular-weight HDPE fabrication practice and must be checked against the released certificate for the actual production lot.

Moisture control is the first boundary condition. In coastal or humid feed-storage areas with ambient relative humidity above 60%, surface condensation on cold pellets introduces polar volatiles that produce micro-voids in the extrudate. Pre-drying in a desiccant hopper dryer at 80 °C for 4 h is required when pellet moisture exceeds 0.1 wt% by weight-loss testing. Regrind of 5672M pipe or sheet is limited to 10 wt% unless the blended lot is re-qualified for slow crack growth under ISO 22088-2:2019, because repeated heat history consumes the primary phenolic antioxidant and narrows the operating window. Blending with PVC regrind must be excluded from the same drying or conveying circuit; thermally released HCl attacks the stabiliser package and creates black specks. The resin must not be combined with amine-based additives without explicit stabiliser interaction analysis, because the resulting acidity shift can accelerate the depletion of the phenolic- phosphite system.

On production-scale grooved-barrel extruders manufacturing potable water pressure pipe, the dominant process conflict appears at the die land rather than at the hopper. A 60 mm single-screw extruder with an L/D ratio of 33:1 and a grooved feed section stabilises output between 300 kg/h and 450 kg/h when die head pressure is held between 250 bar and 380 bar. The barrel profile is set at 190 °C, 200 °C, 205 °C, 210 °C, 210 °C, and melt temperature at the die entry is maintained between 200 °C and 220 °C. If melt temperature drops below 185 °C, thin-wall pipe shows internal melt fracture and helical surface ripples; if it exceeds 230 °C, gel particles accumulate on the 80/120/80 mesh screen pack and create short-period wall thickness variation. The die land ratio is set between 10:1 and 15:1 for SDR 11 and SDR 17.6 dimensions. The finished product is a black PE 100 potable water pipe in SDR 11 or SDR 17.6 according to ISO 4427-2 and EN 12201-2. Natural 5672M is metered with a 40 wt% carbon black masterbatch at 5.0–6.0 wt% addition to achieve a final carbon black content of 2.0–2.5 wt%, providing UV stabilisation without lowering the hydrostatic design stress below 8.0 MPa at 20 °C. The pipe is vacuum-calibrated to an outside diameter tolerance of +0.3% or +0.1 mm, whichever is greater, then cut into 6 m or 12 m lengths. Hydrostatic type testing includes 12.4 MPa at 20 °C for 100 h and 5.4 MPa at 80 °C for 165 h under ISO 1167-2. The operational boundary for this sector is chlorine degradation; network operators with chlorine dioxide residual above 0.25 mg/L must specify a stabiliser package validated by ASTM F2263-14e1 rather than relying on the standard hydrostatic design basis alone.

Unlike the potable water pipe case, gas distribution converts the same bimodal resin into an SDR 11 or SDR 17.6 pipeline whose acceptance route is dominated by rapid crack propagation resistance rather than long-term hydrostatic creep alone. The terminal product for PetroChina Tarim HDPE 5672M in this sector is a yellow or black-with-yellow-stripe PE 100 gas pipe according to ISO 4437-2 and EN 1555-2. The core wall is extruded from black compound using the same carbon black addition as potable water pipe, while a coextruded yellow identification skin contains a 40 wt% yellow pigment masterbatch metered at 4–6 wt%. Skin layer thickness is held below 0.2 mm to avoid altering the overall minimum required strength. Compounding is performed on a co-rotating twin-screw extruder with an L/D of 36:1 and a screw speed of 250 rpm when converting 5672M powder into black or yellow compound. In pipe extrusion, the same grooved-barrel conditions used for water pipe apply, but melt pressure at the die inlet is kept below 350 bar to preserve coextruded skin geometry. Slow crack growth acceptance is verified with the notched pipe test under ISO 13479:2009 at 80 °C and 4.0 MPa, with a required failure time of at least 500 h for PE 100 gas applications.

Table 1 summarises the compliance matrix for gas-grade PE 100 pipe produced from 5672M.

Rapid crack propagation is assessed by the full-scale S4 test according to ISO 13477:2008 at 0 °C. The critical pressure must exceed the maximum operating pressure of the network; for a 10 bar gas main, the pipe is tested at an internal pressure above 15 bar to satisfy safety factor requirements. If the S4 specimen fails below the design pressure, the processing temperature profile must be lowered by 5 K and the pipe solidification rate at the vacuum calibrator must be reduced to increase the tie-molecule fraction in the amorphous phase. The operational boundary for gas pipe is exposure to methane containing aromatic condensate: 5672M must not be used for wet gas streams containing benzene or toluene at concentrations above 2 wt% because the aromatic species lower the pipe’s long-term stress crack resistance. Site fusion is performed by heated-tool butt welding according to ISO 21307:2017, using a heater plate temperature of 225 °C to 235 °C, bead-up pressure of 0.15 MPa to 0.20 MPa, and a cooling time of 9 min per 10 mm of wall thickness.

What limits chlorinated water resistance in HDPE 5672M extruded pipe?

In public drinking water networks the pipe wall is exposed to free chlorine residuals between 0.2 mg/L and 4.0 mg/L. Chlorine diffuses into the amorphous regions and attacks the tie molecules under tensile stress; the failure mode is brittle cracking that initiates at the inner pipe surface. The terminal product is the same potable water pipe described previously, but the mechanical lifetime is conditional on the stabiliser package and the processing temperature history. For 5672M, extrusion at the upper end of the melt-temperature window can deplete the primary antioxidant before the pipe enters service. Therefore, if the utility uses free chlorine near 4.0 mg/L or chloramine, the pipe is tested according to ASTM F2263-14e1 in an oxidative stress environment. A time-to-failure shorter than 1,000 h under the chosen chlorine concentration and hoop stress indicates that the inner surface has lost oxidative stability and the extrusion line must reduce die temperature by 5 K. The design stress for potable water is 8.0 MPa at 20 °C under ISO 4427, but utilities using chlorine dioxide at residual above 0.25 mg/L may derate the system to 6.4 MPa or specify an SDR 13.6 pipe instead of SDR 17. The finished pipe must also satisfy taste and odour migration requirements under EN 1622 and relevant national approvals for drinking-water contact. Pipe extruded above 220 °C for prolonged die residence shows reduced chlorine resistance even if the MFR and density remain unchanged, because the primary antioxidant is consumed before the pipe is placed underground. In such cases, the inner surface of the pipe must be sampled and tested for OIT retention according to ISO 11357-6:2018; an OIT below 20 min at 200 °C indicates that the processing window was exceeded.

When hydrotransport slurry replaces treated municipal water

In mining and dredging applications, the terminal product is a thick-walled HDPE pipe in SDR 7.4 to SDR 11, intended for abrasive slurries with solids content from 10 wt% to 35 wt%. The governing failure mechanism shifts from slow crack growth to erosion and gouging caused by particle-laden flow. Fine tailings are conveyed at flow velocities up to 3.5 m/s; coarse angular solids are limited to 1.5 m/s to keep the wear rate below 0.5 mm/year on the invert of horizontal runs. The abrasion resistance of 5672M is validated by ISO 4649:2017 Method A, with a mass loss below 120 mm³ for the black compound. The high-molecular-weight bimodal structure alone does not guarantee slurry performance; the pipe must also retain a notched pipe test failure time above 500 h under ISO 13479:2009 at 80 °C and 4.0 MPa. Pipe welding uses heated-tool butt fusion according to ISO 21307:2017, with a heater plate temperature of 225 °C to 235 °C, bead-up pressure of 0.15 MPa to 0.20 MPa, and a cool-down time of at least 10 min for wall thickness above 30 mm. Flange adapters are joined by electrofusion couplers with a fusion time calculated from the pipe diameter and supplier constant. The documented limitation is chemical contact with aromatic hydrocarbons or chlorinated solvents carried by the slurry; such species plasticise the amorphous phase and reduce the available wear depth. For hydrocarbon-contaminated tailings, immersion testing must be performed on site at the actual temperature, and 5672M must not be used without a sacrificial wear layer or alternative liner. Where mine water contains dissolved copper salts below 1,000 mg/L, the pipe remains serviceable, but oxidising agents such as ferric chloride at pH below 2 must be excluded because the resulting surface oxidation reduces abrasion resistance.

Geothermal ground-loop pipe made from 5672M is installed in horizontal directional drilling paths where the coil must resist kinking and must not suffer environmental stress cracking when backfilled with wet bentonite. The terminal product is a U-bend header fusion-welded to SDR 11 pipe in lengths up to 150 m, pressure-tested with compressed dry air or water to 4.5 bar for 30 min before insertion. Process temperatures for this application are calculated at -5 °C to 45 °C, which is within the embrittlement limit and above the lowest installation temperature permitted by the coiling specification. Coil loops produced on a turntable winder require the melt temperature to be held at 205 °C to 215 °C and the vacuum calibration tank water temperature at 35 °C to 40 °C to minimise frozen-in stress. A process conflict arises when the winder speed exceeds 12 m/min for pipe diameters above 40 mm: the residual ovality exceeds 3% and the pipe fails insertion into the borehole. The insertion itself requires a pulling force below the pipe’s maximum allowable pull force, calculated as 0.5 × σ_s × π × (D² − d²) using the design stress σ_s from ISO 4427. Geothermal system thermal performance is validated by ISO 13256 for ground-source heat pumps, but the pipe itself relies on the PE 100 hydrostatic type tests under ISO 4427 and a minimum slow crack growth test under ISO 13479. The limitation is that 5672M must not be used for direct steam or superheated water above 60 °C because the hoop stress resistance drops below the heat pump loop assumption. Coils stored outdoors before installation must be protected from direct sunlight with an opaque cover; extended UV exposure without carbon black protection lowers the outer surface molecular weight and creates a brittle skin that is invisible to pressure testing.

Thermomechanical limits in thick sheet extrusion for chemical containment

In chemical containment and tank lining, 5672M is extruded into black or grey sheet with thickness from 3 mm to 15 mm on a single-screw extruder with a slit die and a three-roll polishing stack. The terminal product is a weldable liner panel cut to geometric shell sizes, joined by extrusion welding with a 4 mm or 5 mm HDPE welding rod. The key processing conflict is plate-out and thermal degradation in the slit die because the low melt flow rate of the resin increases residence time at the die lips. Die temperature is maintained at 210 °C; melt pressure at the die inlet is held between 160 bar and 220 bar to prevent melt surging. The polishing roll temperatures are staggered at 70 °C, 80 °C, and 60 °C to reduce warpage. Chemical resistance of the finished liner is evaluated by immersion testing according to ISO 175:2010, with mass change below 0.5% after 7 days at 23 °C for inorganic acids up to 30 wt%. The documented limitation for HDPE is unacceptable swelling in aromatic and chlorinated hydrocarbons; therefore, 5672M is restricted to aqueous inorganic media and selected polar solvents. Contact with food, pharmaceutical, or potable water requires a separate migration compliance review under EU 10/2011 or FDA 21 CFR 177.1520 depending on the market. Butt-welding of sheet edges uses a manual extrusion gun with preheated air at 300 °C and a polytetrafluoroethylene nozzle to limit oxidation; welding speed is held between 150 mm/min and 250 mm/min for 4 mm rod. A bend test on the welded seam is carried out according to DVS 2203-4 to detect weak fusion along tank corners. Sheet thickness tolerances are held to ±0.2 mm for liners up to 6 mm and to ±0.5 mm above 6 mm, because local thinning changes the diffusion path for permeating acids.

For trenchless rehabilitation of gravity sewers, the governing process conflict is not melt fracture but the retention of slow crack growth resistance after surface scoring during pull-in. The finished product is a close-fit or slip-lining pipe segment, typically PE 100 SDR 17.6 or SDR 26, produced from 5672M and pulled through an existing host pipe. Surface scratches deeper than 0.5 mm become initiation points for slow crack growth when the pipe operates with intermittent sewage head and temperature excursions above 40 °C. The pipe is therefore specified with a minimum notched pipe test failure time under ISO 13479:2009 of 500 h at 80 °C and 4.0 MPa, although published data specific to 5672M in this configuration is limited. The structural design method uses the semi-probabilistic approach of ISO 11298-1 or ISO 11299-1, with a long-term ring flexural modulus measured according to ISO 9969. Insertion lubricant selection is restricted to bentonite-based or water-soluble polymers that do not contain aromatic hydrocarbon carriers. A terminal acceptance pressure test for the rehabilitated line is carried out with air at 1.0 bar to 1.5 bar for 15 min, followed by CCTV inspection and a visual weld bead examination under ISO 21307:2017. The pipe must not be re-rounded with an open flame; heat-based re-rounding above 120 °C on the surface can destroy the crystalline tie-molecule network and create a low-cycle fatigue crack path.