What should be noted during trenchless construction of power pipes?
1. Brief Introduction to MPP Pipes
MPP pipes, also known as MPP power cable protection pipes, are divided into trenched and trenchless types. MPP trenchless pipes are also called MPP jacking pipes or MPP pulling pipes. They are made of modified polypropylene as the main raw material and feature high-temperature resistance and external pressure resistance, making them suitable for cable ducting in power transmission lines above 10 kV.
Common specifications range from DN110 mm to DN250 mm, and the pipes are classified into standard and reinforced types. Standard pipes are used for open-cut installation and trenchless crossing projects with a burial depth of less than 4 m, while reinforced pipes are used for trenchless crossing projects with a burial depth greater than 4 m.
2. Scope of Application of MPP Pipes
1) They can be widely used in municipal, telecommunications, power, gas, water supply, and heating pipeline projects.
2) They are suitable for trenchless horizontal directional drilling (HDD) power cable ducting projects in urban and rural areas, as well as open-cut power cable ducting projects.
3)They are suitable for trenchless HDD sewage and drainage pipe projects in urban and rural areas, and industrial wastewater discharge projects.
3. Advantages of MPP Pipes
1)Excellent electrical insulation.
2) High heat deflection temperature and good low-temperature impact resistance.
3) Higher tensile and compressive strength than HDPE.
4) Lightweight, smooth inner wall, low friction, and can be joined by hot-melt welding.
5) Long-term service temperature range from -5 ℃ to 70 ℃.
4. Construction Precautions for MPP Pipes
1) During transportation and construction, the pipes must not be dropped, struck, scratched, or exposed to direct sunlight.
2) During hot-melt butt welding, the axes of the two pipes must be aligned, and the cut ends must be perpendicular and flat.
3) The heating temperature, time, and pressure should be adjusted according to weather conditions.
4) The minimum bending radius of the pipe should be ≥ 75 times the outer diameter.
5. Transportation, Handling, and Storage Precautions for MPP Power Pipes
1) In accordance with national standards and relevant industry or manufacturer standards, the pipes must be handled with care during transportation, loading, unloading, and handling to avoid severe impact. Dropping, throwing, rolling, and exposure to direct sunlight are strictly prohibited. Soft materials should be used to protect the contact area between the ropes and the pipes.
2) The storage area should be flat and well-organized. The stacking height should not exceed 1.5 m, and the distance from heat sources should be at least 5 m. The pipes should not be stored outdoors in direct sunlight; if outdoor storage is unavoidable, they must be covered.
3) The socket ends of the pipes should be stacked in a staggered manner to prevent deformation due to extrusion.
6. Hot-Melt Welding Temperature of MPP Trenchless Pipes
The recommended hot-melt welding temperature is 220 ℃, using the hot-melt butt welding method.
7. Difference Between MPP Trenched Pipes and MPP Trenchless Pipes
Trenched pipes are installed by digging a trench and burying the pipes directly. Trenchless pipes are installed without excavating the road surface, using a jacking machine to bore a hole from one side of the road to the other. Depending on the construction method, they are also called MPP jacking pipes, MPP pulling pipes, or MPP traction pipes.
8. Welding Precautions for MPP Pipes
1) The misalignment of the welded pipe ends should not exceed 10% of the pipe wall thickness.
2) In low-temperature conditions, the heating temperature should be appropriately increased and the heat absorption time should be extended.
3) The heating pressure should be controlled in stages: slightly higher during heating and lower during heat absorption.
4) When the ambient temperature is below -5 ℃ or in windy conditions, insulation and protective measures must be taken; otherwise, the welding quality will be seriously affected.
5) Welding is not allowed in rainy weather.
6) The weld should be cooled naturally; forced cooling will affect the welding quality.
7) The surface of the heating plate and the pipe ends should be cleaned with alcohol regularly to ensure no oil, water, or impurities. The anti-stick coating on the heating plate must not be damaged. Before welding, the pipe ends should be wiped with clean gauze or cloth to remove water, impurities, and soil, ensuring they are clean.
8) If there is moisture on the pipe ends, the ends should be preheated with the heating plate until the moisture is completely evaporated before formal heating.
9) When cleaning the pipe ends, a supervisor should be present to prevent hand injuries from accidental closure of the pipes.
10) For pipes with a wall thickness less than 6 mm, hot-melt butt welding is generally not recommended, as it is difficult to ensure welding quality.
11) All operators must be trained and certified before performing welding work.
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