District Heating Insulated Pipe Line DN160-500 mm
Overview
A municipal heating plant is judged on availability, not on peak rate. The utility signs a season-long supply agreement, and a line that stops for a worn haul-off belt in January costs more than a line that runs ten percent slower all year. This configuration is built around scheduled maintenance access: every wear item is reachable without dismantling a neighbouring station. The buyer supplies a city network under a framework contract, runs two or three shifts, and is audited by the utility on batch traceability rather than on price.
Process Flow
Casing runs on a two-shift cycle with maintenance windows planned between campaigns. Steel pipe is inserted and centred, foam is injected against a recorded shot weight, and the pipe cures on racks before trimming. Every length carries a batch number that links back to its casing record, shot weight and cure time for the utility audit.
Key Configuration
Stations are laid out with a 1.2 m maintenance aisle on both sides, and the haul-off, cutter and foam head are mounted on withdrawable frames so a wear part can be changed without cutting the line. Cooling on the DN160-500 mm line is staged from the vacuum tank into spray, which keeps the wall from being quenched from one side. Every pipe carries a batch number that links to its casing extrusion record, its shot weight and its cure time, which is what a utility auditor asks for and what a paper logbook cannot produce reliably.
Applications
Primary and secondary district heating mains; utility-owned pipe stock for repair; network extension programmes; substation connections. The diameter mix is typically 60 percent in the 200 to 350 mm band with the rest split between smaller service sizes and occasional 450 to 500 mm trunk sections.
Standards
GB/T 29047 and CJJ/T 81 for domestic networks, EN 253 where the utility follows European practice. Utility acceptance usually includes a shear test, a closed cell check and a water uptake test on samples cut from production, and the records have to be traceable to the pipe. For the DN160-500 mm line the standard is written into the contract before manufacture, and the test schedule is derived from it.
Service & Support
Two engineers remain on the DN160-500 mm line for 15 to 25 days, through erection, dry running and the first saleable batch. For the DN160-500 mm line the training covers the adjustable parameters only, because a longer course on a shift basis does not survive staff turnover.
Why Huashida
Our equipment operates in more than 40 countries and we run our own pipe processing operations, so we know what a utility audit asks for at the records level and not only at the machine level. The company holds ISO 9001 and ISO 14001, and every line is trial-run on the buyer's pipe size before shipment.
| Item |
Specification |
| Model / Type |
Vacuum sizing and pipe-in-pipe foaming pre-insulated pipe production line, complete line |
| Pipe Diameter Range |
DN160-500 mm |
| Process |
Casing extrusion, polyurethane foaming, end finishing and testing in one continuous flow |
| Insulation Layer |
Rigid polyurethane foam, density 60 to 80 kg/m³, closed cell content 88% or above |
| Thermal Conductivity |
0.033 W/m·K or lower at 50 °C mean temperature |
| Service Temperature |
up to 120 °C continuous, 140 °C peak |
| Line Output |
260 m² of insulated surface per hour at nominal wall |
| Annual Capacity |
sized against the buyer's kilometre target, not a catalogue figure |
| Casing Extruder |
single screw 120 mm, 33:1 L/D |
| Extruder Output |
500 kg/h of HDPE compound |
| Casing Wall Thickness |
4.0 to 6.0 mm, set by diameter and burial load |
| Vacuum Calibration |
stainless calibration sleeve, vacuum held at -0.04 to -0.06 MPa, water ring pump |
| Cooling |
9 m vacuum tank plus spray cooling, water recirculated |
| Haul Off Speed |
1.5 to 2.5 m/min, set by casing wall and diameter |
| Foam Injection |
high pressure machine, 60 kg/min, impingement mixing at 150 to 200 bar |
| Centring |
steel pipe centred inside the casing before injection, spacer set per diameter |
| Curing |
rack curing 24 hours minimum before end finishing |
| Control System |
Industrial PLC and HMI, recipe per diameter, batch record per shift |
| Operators per Shift |
4 to 6 |
| Installed Power |
calculated per configuration, typically 380 to 620 kW |
| Workshop Requirement |
layout drawing issued with the quotation |
| Commissioning |
site supervision by 2 engineers, 15 to 25 days |
| Documentation |
English layout, foundation, electrical, PID and operation manuals |
| Warranty |
12 months machine, 24 months drive train |
| Certification |
ISO 9001 quality system; CE option for EU delivery |
Technical Prameters:
| |
PE-365/760 |
PE-420/960 |
PE-850/1372 |
PE-960/1680 |
| Main extruder |
SJ-90/33 |
SJ-90/33 |
SJ-120/33 |
SJ-150/33 |
| Pipe diameter (mm) |
Φ365-960 |
Φ420-960 |
Φ850-1372 |
Φ960-1680 |
| capacity (kg/h) |
550-700 |
550-700 |
700-900 |
800-1200 |
| Installed power (kw) |
360 |
380 |
440 |
580 |
| Length (m) |
35 |
36 |
40 |
48 |
Features
Stations are spaced with a 1.2 m aisle on both sides and wear items are on withdrawable frames, so a belt or a seal is changed without cutting the line apart.
Every pipe carries a batch number linking casing record, shot weight and cure time, which is the form a utility auditor actually asks for.
The line is specified for sustained two-shift running rather than for a peak figure, so the drive train and cooling circuit are sized with margin.
Changeover between the three main diameters is a recipe recall and a sleeve change, planned between campaigns rather than inside a shift.
On the DN160-500 mm range the sleeve sets the diameter while the wall is still molten, which is what keeps ovality inside the foaming station's limit.
HDPE Jacket Process Flow:
- Vacuum Feeding of PE Granules: The raw PE granules are automatically fed into the system via vacuum suction.
- Hot Air Drying: The granules are dried using hot air to remove moisture, ensuring optimal extrusion quality.
- Extrusion Plasticizing: The dried granules are plasticized through the extruder, heated and mixed to form a molten plastic mass.
- Mold Shaping: The molten plastic is shaped into the desired pipe profile by passing through the extrusion die.
- Vacuum Sizing: The pipe is then subjected to vacuum sizing, adjusting its dimensions to precise specifications.
- Water Cooling: The pipe is cooled rapidly by immersion in a water tank to solidify its shape and structure.
- Pulling Out: The solidified pipe is pulled out of the cooling tank at a controlled speed.
- Cutting: The pipe is cut to the desired length using a precision cutting machine.
- Carrier Laying-off: The cut pipes are then neatly laid off onto a carrier for further handling or packaging
Composition of Equipments:
- Hopper Dryer
- Single Screw Extruder
- Extrusion Mould Die
- Head Bracket
- Vacuum Calibration Device
- Water Cooling Tank
- Haul-off Unit
- Planetary Cutting Machine
- Pipe Bracket
- Loader
- PLC (Programmable Logic Controller)
The production steps of the insulation layer for a pre-insulated pipe, specifically focusing on the polyurethane (PU) foam insulation, are outlined below in detail:
- Formation of the Casing Structure:
- The steel pipe is first inserted into the high-density polyethylene (HDPE) outer protection pipe, creating a casing structure.
- Supports are evenly arranged in the annular space between the steel pipe and the HDPE outer pipe to maintain a uniform distance and prevent the two pipes from touching directly.
- The two ends of the casing are sealed with flanges to ensure that the polyurethane foaming material will be contained within the space during the injection process.
- Preparation of the Steel Pipe Surface:
- Prior to the injection of the insulation material, the surface of the steel pipe undergoes pre-treatment such as shot blasting or blast cleaning. This step removes any impurities, rust, or scale, providing a clean and suitable surface for optimal adhesion of the polyurethane insulation.
- Additionally, corona treatment of the polyethylene pipe shell's surface may also be performed to enhance its adhesion properties.
- Injection of Polyurethane Foaming Material:
- The casing structure is hoisted onto a foaming platform specifically designed for this purpose.
- A high-pressure foaming machine is used to inject the polyurethane foaming material into the casing. The material expands and fills the entire annular space between the steel pipe and the HDPE outer pipe.
---FAQ---
Q: What availability can the line hold over a season?
A: Above 92 percent with scheduled maintenance, which is what a framework supply contract assumes. The figure depends more on spare parts held on site than on the machine, which is why we quote a first-year spares list with the line.
Q: How is batch traceability handled?
A: Each pipe is recorded against its casing extrusion batch, shot weight, cure time and operator, and the record is exportable. Utility audits in our experience ask for that link rather than for a certificate alone.
Q: What decides the casing outside diameter tolerance?
A: For the DN160-500 mm range diameter is a sleeve-and-vacuum setting, and confusing it with haul-off speed is the usual cause of scrap.
Q: How is the steel pipe kept concentric inside the casing?
A: Spacers cut to the annulus hold the steel concentric on a DN160-500 mm pipe, at both ends and at intervals along the run.
Q: Why is rack curing specified rather than immediate trimming?
A: For DN160-500 mm trimming before the core hardens tears the cells rather than cutting them, so the end face becomes a path for groundwater.
Q: What foam density does the line hold?
A: On the DN160-500 mm line a density outside 60 to 80 kg/m3 appears in the shear test before it appears in service.
Q: What is the delivery time for a complete line?
A: The DN160-500 mm line ships 90 to 120 days after deposit, or 150 for the largest build in a busy period.
Q: How many containers does the line need?
A: The DN160-500 mm line loads into six to eight 40HQ containers, and the plan shows every module.
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