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Due to the non conductivity and non magnetism of the PE pipe, it is not possible to track the PE pipe, which will bring inconvenience to future pipeline maintenance. The gas tracing line effectively solves the problem of non-metallic pipelines that cannot be detected using metal pipeline detectors.
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Article 7.2.9 of the "Code for Construction and Acceptance of Urban Gas Transmission and Distribution Engineering" CJJ33-2005 stipulates that when laying polyethylene gas pipelines, tracer lines should be laid at the top of the pipeline along with the pipeline direction, and the joints of the tracer lines should have good conductivity.
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1¡¢ The role of tracer lines
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The "tracer line" is used for detecting, tracking, and locating PE pipelines. The "tracer line" is laid together with the PE pipe; Generally, metal wire cores are used to apply signals to the "metal wire" through detection equipment, and the detection receiver receives the signal to find the accurate position of the tracer line, that is, to synchronously track the specific position of the PE gas pipeline; To facilitate the renovation and maintenance of PE pipelines.
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2¡¢ Development of Tracer Lines
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The first generation tracer line is composed of a matrix of aluminum foil and plastic film. The aluminum foil mainly transmits signals, while the matrix is fixed aluminum foil. The disadvantage of this tracer line is that the strength of aluminum foil is very low, and even during production and transportation, it is easy to break, and the auxiliary equipment is easily damaged. At the same time, the resistance of aluminum foil is very high, and the effective detection distance and depth are limited.
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The second generation tracer line is made by pressing steel wire and plastic film. The tracer line is made of steel wire as the conductor, with high resistance and limited detection distance, making it difficult to meet practical needs.
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The third generation tracer wire: It is composed of a copper clad steel metal wire core and a PE outer protective layer, with a linear appearance.
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3¡¢ Precautions for laying tracer lines
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When burying the trace line, it should be closely attached to the PE pipeline in a straight line shape and located on the top surface of the pipeline. Do not bury PE pipes in a spiral shape, as this may lead to inaccurate detection results.
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A certain length of wire (1m or more is recommended) should be reserved for the tracing line in the inspection well or at the exit point, for the purpose of detecting and applying signals. This can improve detection efficiency and accuracy.
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The connector or branch point of the tracer line must be firmly connected, maintain good conductivity, and be wrapped with insulating tape to prevent corrosion and wire breakage caused by underground moisture, which may interrupt the detection signal. The tracing line at the steel plastic conversion joint of the pipeline can be welded to the flange, and the joint should be treated with anti-corrosion measures to prevent corrosion and wire breakage over time.
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To increase the signal strength of the tracer line and ensure uniform signal distribution, it is necessary to minimize the grounding resistance at the buried end of the tracer line during construction, and take good grounding measures by peeling off the insulation layer and exposing the core wire for 30cm. Especially for the ends of shorter branch pipes, they must be well grounded, otherwise the signal on the branch will be very weak and cannot be detected.
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If the buried length of the pipeline exceeds 1km and there are no inspection wells or other facilities in the middle to reserve tracer heads to meet the detection needs, it is recommended to set up a testing pile at every kilometer and reserve tracer line joints for use during detection.
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In non excavation engineering construction, the tracer line outside the PE pipeline is prone to being torn during the dragging process. A simple method is to choose a larger cross-sectional area and higher strength wire or steel wire rope, or to pre thread a tracer line inside the pipeline to avoid wire breakage. The detection effect is the same as on the outside, but when doing so, it is necessary to handle the problem of connecting the internal tracer line head to the external tracer line.
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In some special cases, it is not possible to apply tracer lines to PE pipelines. In this case, the method of embedding tracer balls can be used to meet future detection and positioning needs.