Buried HDPE Electrofusion Fittings Series for Gas

Buried Polyethylene HDPE Electrofusion Fitting Series

Connection Precautions

1. Before pipeline connection, pipes, fittings, ancillary equipment, valves, and instruments should be checked according to design requirements, and visual inspection should be conducted at the construction site. Only those meeting standards can be used.
2. The same manufacturer's pipes and fittings should be used for connection. If pipes and fittings from different manufacturers (brands) must be connected, their reliability should be verified through testing before use.
3. After each connection is completed, visual quality inspection should be conducted. Those not meeting requirements must be reworked.
4. Construction personnel should undergo on-the-job training.
5. After each construction, pipe ends should be temporarily sealed.
6. When performing connection operations in cold weather (below -5°C) and windy environments, protective measures should be taken or construction process parameters should be adjusted.

Transportation and Storage

1. During pipe transportation, scratching, throwing, violent impact, exposure to sunlight, rain, oil contamination, and chemical contamination are prohibited.
2. Pipes should be stored in warehouses with flat ground and good ventilation. Outdoor stacking should have covering to avoid exposure to sunlight and rain.
3. Pipe stacking height should not exceed 1.5 meters.

Construction Standards

General Provisions

(For specific construction standards, please refer to relevant national standards for gas pipeline construction)
1. Polyethylene gas pipelines should undergo visual inspection before connection. Only those meeting requirements can be used. Any damage exceeding 10% of wall thickness should be cut off.
2. Polyethylene gas pipeline connections should adopt electrofusion or heat fusion connections. Threaded connections and bonding are not allowed. Connection between polyethylene gas pipelines and metal pipelines must use steel-plastic transition joints.
3. Different connection methods for polyethylene gas pipelines should use corresponding connection tools. Open flame heating is prohibited during connection.
4. Polyethylene gas pipeline connections should use pipes and fittings of the same material. In special cases, products of different grades with similar performance may be used, but must be tested to ensure connection quality before proceeding.
5. When performing connection operations in cold weather (below -5°C) or windy environments, protective measures should be taken or high-speed connection processes should be used.
6. When there is a large temperature difference between pipe/fitting storage location and construction site, pipes and fittings should be placed at the construction site for a certain period before connection to allow their temperature to approach the construction site temperature.
7. During pipeline connection, the inside and outside of pipe ends should be clean, free of foreign matter and oil. After each work session, pipe ends should be temporarily sealed.
8. After pipeline connection is completed, joint visual quality inspection should be conducted. Those not meeting requirements must be reworked. After rework, joint visual quality inspection should be conducted again.

Electrofusion Connection

1. Electrofusion connection should select electrofusion connection machines and clamping tools compatible with the electrofusion fittings. During connection, the voltage and heating time should comply with the specifications of the electrofusion connection machine and electrofusion fitting manufacturer.
2. During electrofusion connection cooling period, the connection piece should not be moved or subjected to any external force.
3. Electrofusion connection should also comply with the following provisions:
The pipe connection end should be cut vertically. Use clean cotton cloth to wipe dirt from the pipe and fitting connection surfaces. Mark the insertion depth, and uniformly scrape the surface skin. Before electrofusion connection, use special clamps to straighten two or three corresponding connection pieces on the clamping tool, keeping them on the same axis.
4. Electrofusion saddle connection should also comply with the following provisions:
· The pipe section below the main pipe connection should be supported with special brackets and fixed firmly.
· Before electrofusion saddle connection, use clean cotton cloth to wipe dirt from the connection surface, and use scrapers or coarse sandpaper to remove the outer skin from the main pipe connection area.
· The main pipe section at the electrofusion saddle fitting connection should be flat. Saddle fittings should not be installed at the natural bend of the main pipe to ensure good fit between the pipe outer surface and the saddle inner surface.
· During drilling operations, drilling depth should be closely monitored. For gas-tapping drilling, all branch pipes must be completely sealed before drilling operations can proceed.

Heat Fusion Connection

1. Before and after heat fusion connection, dirt on the heating plate of the connection tool should be wiped clean with clean cotton cloth.
2. Heat fusion connection heating time, heating temperature, fusion pressure, holding pressure, and cooling time should comply with pipe and fitting manufacturer specifications. During holding pressure and cooling periods, the connection piece should not be moved or subjected to any external force.
3. Heat fusion connection should also comply with the following provisions: Before connection, both pipe ends should extend a certain free length from the clamps, and corresponding connection pieces should be straightened to keep them on the same axis, with misalignment not exceeding 10% of wall thickness.
4. Dirt on pipe or fitting connection surfaces should be wiped clean with clean cloth. The connection surface should be milled to be perpendicular to the axis and match the corresponding connection surface. The end surface to be connected should be heated with an electric heating plate. After heating is complete, the connection piece should be quickly removed from the heating plate. Use uniform external force to make complete contact, gradually increasing pressure to form uniform double flanges.

Pipeline Installation

Buried Pipeline Installation

1. For open trench installation of pipelines (excluding pipe-jacking method), pipelines can only be installed after trench bottom elevation and pipe foundation quality inspection are qualified.
2. During pipeline lowering, metal materials should not be used to directly tie and hoist pipelines. Scratching, twisting, or excessive pulling and bending of pipelines should be prevented.
3. Polyethylene pipelines should be laid in a serpentine pattern and can be bent with the terrain. Pipeline bending radius should comply with the provisions of this manual. Mechanical or heating methods should not be used to bend pipelines.
4. The horizontal and vertical clearances between pipelines and thermal pipelines should not be less than the provisions in Table 6 and Table 7, and the soil temperature around gas pipelines should not exceed 40°C. The horizontal and vertical clearances between pipelines and buildings, structures, or other adjacent pipelines should comply with the current national standard "Urban Gas Design Code" GB50028. When directly buried steam thermal pipeline insulation layer outer wall temperature does not exceed 60°C, horizontal clearance can be halved.

Horizontal Clearance Between Buried Polyethylene (HDPE) Pipeline and Thermal Pipeline (m)

Vertical Clearance Between Buried Polyethylene (HDPE) Pipeline and Thermal Pipeline (m)

5. Minimum cover thickness for pipeline burial should comply with the following provisions:
(1) Buried under vehicle lanes, not less than 0.9m;
(2) Buried under non-vehicle lanes (including sidewalks), not less than 0.6m;
(3) Buried where motor vehicles cannot reach, not less than 0.5m;
(4) Buried under paddy fields, not less than 0.8m.
6. During pipeline installation, metal tracer wires (bands), warning tapes, or other markers should be buried along the pipeline. Tracer wires (bands) should be laid close to the pipe and should have good conductivity, effective electrical connection, and signal source wells. Warning tape installation should comply with the following provisions:
(1) Warning tapes should be installed 300-500mm above the pipe top, but should not be installed in roadbeds or road surfaces;
(2) For pipes with diameter not exceeding 400mm, one warning tape can be installed directly above the pipeline. For pipes with diameter exceeding 400mm, two warning tapes should be installed parallel above the pipeline with horizontal clearance of 100-200mm;
(3) Warning tapes should be made of polyethylene or non-degradable materials, and the color should be yellow. The warning tape should have conspicuous, permanent warning text.
7. When polyethylene coiled pipes or straight pipes limited by construction conditions are installed using pipe-jacking method, during pipe dragging, the trench bottom should not have stones or sharp protrusions that may damage the pipe surface. The dragging length should not exceed 300mm.
Maximum dragging force for polyethylene pipelines should be calculated as follows: 15DN²
F= SDR Where: F-Maximum dragging force (N); DN-Nominal outer diameter of pipe (mm); SDR-Standard dimension ratio.
8. When polyethylene coiled pipes are installed using pipe-jacking method, warning tape installation should comply with the provisions of this manual and be fed into the trench simultaneously with the pipeline. Pipeline bending radius should comply with the relevant provisions of this manual.

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