Key technical points of HDPE pipeline construction
HDPE (high-density polyethylene) pipelines have become the preferred pipe material in municipal engineering, water supply and drainage systems, gas transmission and other fields due to their excellent corrosion resistance, flexibility and long life. However, to ensure the long-term stable operation of the pipeline system, standardized construction technology is essential. This article will introduce in detail the key technical points of HDPE pipeline construction, covering the core content of the whole process such as material acceptance, welding process, laying and installation, quality inspection, etc.
Preparation work before construction
1. Material acceptance and storage
Pipe inspection:
Check product certificates and test reports (comply with GB/T 13663, ISO 4427 and other standards)
Check the appearance of the pipe: no bubbles, cracks, depressions or impurities, the port is flat and burr-free
Measure wall thickness and diameter deviation (≤±1.5%)
Preparation of pipe fittings and welding machines:
Matching flanges, elbows, tees, etc. must be made of the same material as the pipe (PE100/PE80)
The hot melt welding machine needs to be calibrated for temperature (210±10?) and pressure parameters
Storage requirements:
Avoid direct sunlight, stacking height ≤1.5 meters, and support with wooden squares at the bottom
2. Site survey and design
Confirm the pipeline direction, elevation, and slope (≥0.5%) according to the construction drawings
Check underground obstacles (cables, other pipelines) and mark them
Plan welding pits (width ≥ pipe diameter + 1m, length ≥2m)
Key points of HDPE pipe connection technology
1. Butt fusion
Applicable scenarios: pipes with DN ≥ 90 mm
Construction process:
End milling: use a milling cutter to cut the pipe end to a flat surface with a gap of ≤ 0.3 mm
Heating with a heating plate: the temperature is controlled at 200-220°C, and the heating time is adjusted according to the wall thickness (refer to the table below)
|
Pipe Wall Thickness (mm) |
Heating Time (sec) |
Changeover Time (sec) |
Cooling Time (min) |
|
4-10 |
30-50 |
≤5 |
6-8 |
|
10-20 |
50-80 |
≤6 |
8-10 |
|
>20 |
80-120 |
≤8 |
10-15 |
Butt pressurization: pressure is controlled in stages (absorption pressure 0.15MPa, welding pressure 0.2MPa)
Cooling and shaping: It is forbidden to move the pipeline during natural cooling
Key control points:
Even welding flange (height ≈ 1/3 of the pipe wall thickness)
No cold weld, carbonization or impurities in the weld
2. Electrofusion
Applicable scenarios: small pipe diameter (DN≤315mm) or repair work
Operation points:
Scrape off the oxide layer at the pipe mouth (length ≥ socket depth of electrofusion sleeve)
Use a barcode scanner to check the electrofusion sleeve parameters (voltage, time)
No water injection or pressurization during cooling
Pipeline laying and backfilling specifications
1. Trench excavation and foundation treatment
Trench bottom width: D (pipe diameter) + 0.5m (DN ≤ 500mm)
Foundation cushion:
General soil: Lay 10cm sand cushion
Soft soil foundation: Replace 30cm gravel + geogrid reinforcement
Slope control: Use laser level to check, deviation ≤ ± 0.1%
2. Pipeline installation
Pipe lowering method: Flexible sling lifting (wire rope is prohibited from directly contacting the pipe)
Bending radius: ≥ 25 times the pipe diameter (avoid stress concentration)
Pier setting: Pour concrete at the valve and tee to fix
3. Backfill technical requirements
|
Backfilling Layer |
Material Requirements |
Compaction Requirement |
|
Pipe bottom to 30cm above pipe |
Fine sand or gravel ≤10mm in diameter |
≥90% |
|
Within 50cm above pipe |
Native soil (remove rocks & frozen soil) |
≥85% |
|
More than 50cm above pipe |
Compacted in layers |
≥95% |
Notes:
When backfilling, the internal pressure of the pipeline must be maintained at 0.05MPa to prevent deformation
Test the compaction degree layer by layer (ring knife method test)
Quality inspection and acceptance standards
1. Non-destructive testing
Appearance inspection: symmetrical weld flanges and no cracks
Ultrasonic testing: spot check the internal fusion of the weld (≥10% ratio)
Air pressure test:
Strength test: 1.5 times the working pressure, stable pressure for 1h without leakage
Tightness test: 1.15 times the working pressure, 24h pressure drop ≤1%
2. Common problem handling
|
Problem Phenomenon |
Root Cause Analysis |
Solution |
|
Uneven weld bead |
Uneven heating plate temperature |
Replace heating plate, re-weld |
|
Local pipe depression |
Insufficient backfill compaction |
Excavate and re-compact |
|
Joint leakage |
Incorrect electrofusion parameters |
Cut out section, use repair coupler |
Safety and civilized construction requirements
1. Welding operation area: set up cordons and equip fire-fighting equipment
2. Groove protection: install warning lights at night, and the slope gradient is ≤1:0.5
3. Environmental protection measures: waste welding shavings are classified and recycled to avoid soil pollution
The construction quality of HDPE pipelines is directly related to the life of the system, and the three core links of material selection, welding process, and backfill compaction must be strictly controlled.
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