The lap length of the outer protective pipe at the insulation pipe patch is not arbitrarily fixed; the standard clearly stipulates it. This length directly determines the sealing effect at the patch.
According to GB/T 50538-2020 "Technical Standard for Anti-corrosion and Insulation Layers of Buried Steel Pipelines," when repairing the protective layer, if the end has no waterproof cap structure, the overlap between the heat shrink tape and the insulation pipe protective layer should not be less than 100mm; When the end has a waterproof cap structure, the heat shrink tape should cover the cap, and the overlap with the insulation pipe protective layer should not be less than 80mm. The circumferential overlap should be located at the top area of the pipeline, with an overlap width not less than 80mm.
The overlap between the patch mold and the protective layer also has requirements, which should not be less than 100mm. If an electric hot-melt sleeve patch is used, the overlap width with the insulation pipe protective layer should not be less than 100mm. These regulations are not arbitrary-if the overlap is too short, the sealing area is insufficient, making cracking and water ingress more likely; If the overlap is too long, it increases material costs and construction difficulty. The values of 100mm and 80mm are reasonable values verified by engineering practice.
The significance of lap length is to ensure sealing reliability. The lap joint between the heat-shrink tape or electric melt sleeve and the outer protective pipe is the key part of the patch seal. If the lap length is insufficient, the heat-shrink tape is prone to detachment due to thermal expansion and contraction during pipe operation, allowing groundwater to seep in through the overlap seam. The longer the overlap surface, the more reliable the seal and the stronger the resistance to thermal displacement.
The control of lap length during construction mainly depends on two aspects: first, selecting heat shrink tape or electric heat melt sleeve specifications that match the outer diameter of the outer protective tube; second, ensuring uniform shrinkage of the heat shrink tape and uniform melt overflow at the edges during construction. The standard includes lap length in the clause to provide a basis for this key parameter.