Overall decision-making principle:
Safety first: Regardless of the method used, it is necessary to ensure reliable support for the work pit and standardized electrical operation.
Permanent priority: As long as conditions permit, priority should be given to solutions such as electric melting and flanges that can form permanent connections. Although the initial time may be slightly longer, it is a one-time solution to avoid secondary repairs.
Temporary backup: The mechanical connection method is a valuable emergency measure, but it must be included in the planning and management to clarify the subsequent replacement time.
Tailored to local conditions: The final decision should comprehensively consider the impact of water outage, damage form, on-site resources, and long-term operational safety.
Mastering these methods and being able to flexibly apply them is necessary to remain calm in the event of a pipeline emergency, and to restore water supply safety with minimal cost and fastest speed.

 

 

Guidelines for Systematic Construction of PE Water Supply and Drainage Pipelines: From Excavation of Pipe Trenches to Backfilling Protection
The construction of PE water supply and drainage pipelines is an interconnected system engineering, and its long-term reliability and safety depend entirely on the meticulous control of each link during the construction process. The following will provide you with comprehensive construction guidance from excavation of pipe trenches to backfilling protection.
1、 Excavation of pipe trench and foundation treatment
The pipe trench is the"foundation"of the pipeline, and its quality directly affects the laying quality and long-term deformation of the pipeline.
Precise excavation and size control
Line shape and width: The pipe groove should be kept as straight as possible to ensure even stress distribution on the pipeline. The width of the groove bottom is usually the outer diameter (DN) of the pipeline plus 0.30m, which provides the necessary working surface for pipeline installation and initial backfilling. If pipeline connections (such as hot melt butt joints) need to be made in the groove, the width of the groove bottom at the interface should be increased to DN+0.50m or more to ensure sufficient operating space for the welding machine.
Burial depth requirement: The minimum depth of soil cover on the top of the pipe is the key to protecting the pipeline from external load impact.
Under the roadway: it should not be less than 0.80m. If this depth cannot be reached due to objective conditions, protective measures must be taken. The most effective method is to lay steel sleeves and thread PE pipes inside the sleeves, with the sleeves bearing the main load.
Under the sidewalk: should not be less than 0.60m.
Turning treatment: When turning the pipeline, it should be achieved through standardized elbow fittings, and the support pier at the elbow should be ensured to be stable. For small-diameter PE pipes, elastic laying can be carried out due to their flexibility, but the bending radius (R) must strictly comply with the specifications to prevent stress concentration or flattening of the pipeline. For example, for a DN160 pipeline, the minimum bending radius R ≥ 50 × 160=8000mm.
Bottom foundation treatment - the cornerstone of quality
The bottom of the groove must be flat, continuous, and supported firmly. When excavating manually, the last 20cm layer of civil engineering should be cleared manually to avoid mechanical disturbance to the original foundation.
There should be no sharp stones, bricks or other hard objects at the bottom of the groove to avoid damaging the pipe wall. For rocks or hard soil layers, a layer of sand or fine soil with a thickness of not less than 10cm should be laid at the bottom of the trench as a buffer protection layer.
If over excavation occurs, it is strictly prohibited to use the original soil for backfilling or simple virtual paving. Good graded sand and gravel materials must be used for backfilling, and compacted layer by layer to achieve a density similar to that of the original foundation.
Entry inspection of materials and equipment
All PE pipes and fittings must be checked for their specifications, SDR series (wall thickness), production license, and product qualification certificate before entering the site. Conduct a visual inspection on site to ensure that there are no serious scratches, dents, bubbles, or uneven colors.
Construction equipment should be complete and in good condition, especially hot melt welding machines (butt welding machines, socket welding machines) and electric fusion welding machines, which should be calibrated to ensure accurate and reliable heating plate temperature and welding parameters.
2、 Pipeline connection and installation: control of core processes
Pipeline connection is the most critical link in construction, and its quality determines the sealing and strength of the entire pipeline system.
Pipeline cutting and preparation
A specialized pipe cutter must be used to ensure that the cut is level and perpendicular to the pipe axis, which is a prerequisite for ensuring complete adhesion of the subsequent hot melt joint surface.
Hot melt connection (butt welding)
Standardization process:
Clamping and milling: Securely clamp the pipe onto the welding machine and mill the end face with a milling cutter until continuous and smooth chips are obtained.
Heating: Remove the milling cutter and move the heating plate (temperature strictly controlled at 200 ± 10 ℃) between the pipe end faces, applying the specified heat absorption pressure until the flange reaches the specified height.
Switching and docking: Quickly remove the heating plate, dock the two tube end faces within the specified time, and increase the welding pressure to the specified level.
Cooling: Maintain pressure to fully cool the interface in its natural state. During the cooling period, it is strictly prohibited to move the pipeline or apply any external force.
Quality criteria:
Appearance: The weld should form a uniform and full flange, with consistent height and shape. The lowest point of the flange shall not be lower than the surface of the pipe. Check for any false welding or burnt marks on the inner and outer edges.
Back bending test (sampling): On site, the welded joint can be processed into a test piece for reverse bending test to observe whether there are cracking defects in the welded joint.
Electric fusion connection
Key steps:
Scraping the oxide layer: Use a specialized scraper for the electric fusion connection area to thoroughly scrape off the oxide layer on the outer surface of the pipe, exposing fresh material. This is fundamental to ensuring conductivity and fusion effect.
Cleaning and positioning: Clean the scraping area with alcohol and install the electrofusion fittings in place.
Stable welding: Connect the welding machine to the pipe fittings to ensure stable input voltage, and strictly follow the welding time (t) and cooling time marked on the pipe fittings or provided by the manufacturer to perform the welding procedure. During welding, it is not allowed to move the pipe with electricity.
Quality criterion: Observe whether the observation hole (indicator post) on the electric fusion pipe is protruding normally, which is an important visual indicator to determine whether the internal fusion is sufficient.
Mechanical connection
Suitable for parts that require frequent disassembly or connection with pipes of different materials. During installation, it is necessary to ensure that the sealing ring is clean, accurately positioned, and free from distortion. When tightening bolts, it is necessary to use diagonal alternating and staggered tightening methods to ensure uniform force distribution and prevent leakage caused by unilateral compression.
Installation of special parts and accessories
Support pier setting: In areas such as bends, tees, pipe end sealing plates, valves, and fire hydrants that generate thrust or stress, concrete thrust piers with a strength of C20 or higher must be installed to effectively transmit the thrust to the undisturbed soil. The support pier should be tightly attached to the fittings, and the contact surface should be chiseled before pouring to enhance the bonding.
Transition connection: When connecting PE pipes with metal valves or equipment, specialized steel plastic transition joints or flange connections must be used, and it is strictly prohibited to directly thread on the PE pipe.
Exhaust and Drainage: Automatic exhaust valves must be installed at the starting point of the pipeline to eliminate accumulated air and prevent air resistance and water hammer; Consider installing a drain valve at the low point to facilitate system drainage and maintenance.
3、 Backfilling and protection: constructing permanent barriers for pipelines
Backfilling is not only about restoring the terrain, but also providing a uniform and stable supporting environment for the pipeline.
Prevent pipeline floating: Before backfilling, confirm that there is no accumulated water in the trench. Especially in rainy seasons or areas with high groundwater levels, once there is water accumulation in the tank, the empty pipe is easily displaced or even damaged due to buoyancy.
Special section treatment: In areas with rock or mixed soil and rock, in order to prevent sharp stones from directly contacting and damaging the pipe wall, clay or sand should be used to backfill 20-30cm above the pipe top, carefully compacted to form an initial protective layer, and then backfilled with the original excavated material.
Symmetric backfilling and layered compaction: Backfilling must be carried out simultaneously and symmetrically from both sides of the pipeline to avoid displacement of the pipeline due to unilateral pressure. The thickness of each layer of backfill should not exceed 20-30cm, and a small compactor should be used to compact the layers in layers to ensure that the compactness meets the standard.
Backfilling before pressure test: Before the pipeline pressure test, the backfill soil should cover the top of the pipe and the thickness should not be less than 50cm. This is to prevent the pipeline from moving due to internal pressure during the pressure test process, and to provide an external constraint to ensure the safety of the test.
Final backfilling timing: It is recommended to carry out the final large-scale backfilling when the pipeline is filled with water. The weight of water can offset some of the load of backfill soil and prevent the pipeline from deforming due to soil pressure in a long-term empty state. After the pipeline is laid, it should be brought into a water state as soon as possible to avoid being left vacant for a long time.
4、 Other key control points
Personnel qualifications: All welders must hold certificates and undergo regular skill assessments.
Environmental adaptability: PE pipes will become brittle at low temperatures (usually<5 ℃), and insulation measures should be taken during welding (such as building insulation sheds, preheating pipes), and welding parameters should be adjusted appropriately. Effective protective measures must be taken during welding in strong winds, rainy and snowy weather to ensure that the welding area is clean and dry.
Pipeline support: For long-distance or sloping installations, pipeline supports, brackets, or anchorages should be set up according to calculations to prevent the pipeline from sliding down.
Pressure testing: After installation, it is necessary to strictly follow the specifications (such as the"Code for Construction and Acceptance of Water Supply and Drainage Pipeline Engineering"GB 50268) for strength testing and tightness testing. This is the final checkpoint to verify the safety of the entire system.
Timely backfilling and data archiving: After the acceptance of concealed works is qualified, backfilling should be organized immediately to reduce the risk of pipeline exposure. At the same time, all construction records, welding parameters, inspection reports, etc. should be organized and archived to form a complete engineering quality traceability chain.
The core of the construction quality of PE water supply and drainage pipelines lies in the precise control of the three major elements of"materials, connections, and backfilling". Only by strictly following design specifications and process flow, and treating every detail with a rigorous attitude, can a safe, durable, and reliable water supply and drainage system be constructed.