Installation precautions for HDPE pipes in municipal engineering
In municipal engineering, the installation of HDPE (high-density polyethylene) pipes must follow strict specifications to ensure their durability, sealing and safety. The following are key precautions:
Preliminary preparation
Material acceptance
Check the quality certification documents of pipes and fittings (such as certificates of conformity, test reports) to ensure compliance with national standards such as GB/T 19472.2.
Appearance inspection: no cracks, scratches, depressions or bubbles, and the port is flat and burr-free.
Check whether the specifications (such as SDR value, ring stiffness grade) are consistent with the design requirements.
Trench excavation
Trench bottom width: When the pipe diameter is ≤DN500, the trench width is ≥ the outer diameter of the pipe + 0.5m; when the pipe diameter is larger, sufficient operating space must be reserved.
Slope and base: Slope according to design requirements (such as 1:0.33), the base must be flat and free of gravel and hard objects, and the over-excavated part should be backfilled and compacted with sand and soil.
Groundwater level: If groundwater is encountered, it is necessary to take precipitation measures or replace the gravel layer with anti-floating pipes.
Pipeline installation
Connection method
Hot-melt butt welding (applicable to large-diameter pipes):
Clean the heating plate, control the temperature (200~220℃), and perform the welding pressure and time according to the manufacturer's parameters.
Check the uniformity of the flange after butt welding to avoid false welding.
Electrofusion connection (with socket pipe fittings):
Ensure that the oxide layer is scraped off the pipe end, the insertion depth is clearly marked, and the power-on time/voltage meets the requirements of the pipe fittings.
Mechanical connection (flange or clamp): Check whether the sealing ring is installed in place and the bolts are tightened symmetrically.
Main points for laying
Flexible foundation: Lay a 10~15cm medium-coarse sand cushion layer, and fully support the 120° range below the pipe.
Bending radius: Cold bending is allowed, but the curvature radius ≥ 25 times the pipe diameter (such as DN400 pipe requires R ≥ 10m).
Snake laying: When the temperature changes greatly, reserve 2%~3% of the expansion and contraction to avoid thermal expansion and deformation of the straight line.
Backfill requirements
Backfill in layers
Backfill on the pipe side: use sand or fine soil with a particle size of ≤10mm, symmetrically compact in layers (each layer ≤20cm), and the compaction degree ≥90%.
50cm above the top of the pipe: direct mechanical rolling is prohibited, and manual compaction is adopted.
Upper backfill: compact in layers according to the requirements of roads or greening to avoid settlement.
Special area treatment
Add steel casing protection when crossing the road, and seal and prevent seepage at both ends of the casing.
Soft soil foundation needs to be replaced or reinforced with gravel piles to prevent uneven settlement of the pipeline.
Quality and safety control
Testing items
Pressure test: inject water to stabilize the pressure for 1h, and the pressure drop is ≤0.05MPa to be qualified (refer to GB 50268).
Water-tight test: non-pressure pipelines are tested in sections according to the specifications, and the allowable water seepage is ≤Q=0.0046Di (m³/24h·km).
Electrofusion joint inspection: Detect the fusion quality by X-ray or ultrasonic.
Safety measures
Groove support: set baffles or slopes when the depth is ≥1.2m, and set warning lights at night.
Lifting operation: use nylon slings to avoid scratches on pipes, and keep personnel away from the radius of the boom.
Prevention of common problems
Leakage: strictly check the quality of the interface to avoid socket failure or incorrect welding parameters.
Deformation: control the compaction degree during backfilling to avoid overloaded vehicles rolling over inadequate backfill sections.
Through standardized construction and full-process quality control, HDPE pipes can give full play to their advantages of corrosion resistance, good flexibility, and long life (more than 50 years), and are suitable for municipal scenarios such as water supply and drainage, rainwater and sewage pipe networks.
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