What are the technical requirements for insulated pipes in municipal engineering?

Municipal centralized heating, centralized cooling and thermal pipe networks in utility tunnels constitute vital components of urban infrastructure. The quality and technical parameters of insulated pipes are directly related to transmission efficiency, operational safety and service life of pipe networks. As public livelihood‑oriented projects, municipal works impose strict and unified industrial technical standards for insulated pipes, with clear specifications covering material performance, temperature‑resistance parameters, structural design as well as construction and acceptance. Based on current national and industrial standards, this paper sorts out core technical requirements for insulated pipes in municipal engineering in detail, providing compliance references for the design, material selection and construction of municipal pipe networks.

Technical requirements for material performance form the fundamental core of municipal insulated pipes. Prefabricated directly‑buried insulated pipes commonly adopted in municipal pipe networks shall comply with national standards such as GB/T 29047‑2021. Rigid polyurethane foam is the preferred insulation material thanks to its low thermal conductivity and high closed‑cell rate, suitable for working conditions of municipal hot‑water pipe networks. For organic insulation materials under normal operating conditions, thermal conductivity at an average temperature of 50 ℃ shall be kept within specified limits. For inorganic insulation materials, thermal conductivity at 25 ℃ ambient temperature shall not exceed 0.08 W/(m·K) to guarantee basic thermal‑insulation performance. Meanwhile, materials shall feature favorable hydrophobicity and stability. The closed‑cell structure can effectively block the infiltration of underground water and water vapor and prevent damp‑induced failure of insulation layers, adapting to various municipal construction scenarios including underground direct burial and utility‑tunnel laying.

Technical requirements for temperature and pressure resistance shall match operating conditions of municipal pipe networks. Conventional municipal hot‑water heating pipe networks operate at a long‑term temperature ≤ 120 ℃, which can be sustained by polyurethane‑insulated pipes, while short‑term peak temperature resistance shall reach 130‑140 ℃. For high‑temperature thermal pipe networks, composite insulation structures combined with inorganic insulation materials such as aluminium silicate and aerogel blankets shall be adopted to accommodate higher‑temperature working conditions. In terms of pressure, the design pressure of thermal pipes inside municipal utility tunnels generally shall not exceed 1.6 MPa. The overall pipe structure shall remain stable under rated pressure‑temperature conditions without deformation, damage or accelerated ageing to satisfy requirements for long‑term continuous operation.

Technical requirements for structure, appearance and dimensions shall conform to municipal construction standards. Standard municipal insulated pipes adopt a three‑layer composite structure: service steel pipe + insulation layer + polyethylene outer casing. The insulation layer shall have uniform thickness free of defects such as hollowing, voids, delamination and shrinkage cracking, ensuring uniform overall thermal insulation and eliminating thermal‑cold bridge effects. Outer casings shall be made of high‑density polyethylene with uniform wall thickness and smooth surface, featuring good impact resistance, ageing resistance and corrosion resistance against soil compression and outdoor environmental erosion. Pipe fittings and special‑shaped components such as elbows and tees shall adopt insulation structures consistent with main pipes to maintain continuous insulation across the whole pipe network.

Technical requirements for construction and sealing constitute key control points in municipal engineering. Joint treatment for municipal insulated pipes shall be implemented in strict accordance with specifications. Joint sections shall be densely filled with special foaming materials and sealing components, and fitted with accessories such as waterproof end‑caps and electro‑fusion sleeves for sealing protection to block water‑vapor ingress. Laying of directly‑buried pipes shall meet specified backfill depth requirements to avoid damage to pipe insulation structures caused by ground load compression. For insulated pipes laid inside utility tunnels, the calculated outer‑surface temperature shall not exceed 50 ℃ to effectively prevent scald injuries to operation‑and‑maintenance personnel, control pipe‑network temperature loss and ensure qualified transmission efficiency.

Technical requirements for safety and acceptance guarantee long‑term stable operation of municipal pipe networks. Municipal insulated pipes shall possess good thermal‑cycling stability; their insulation performance and structural form shall show no obvious changes after repeated heating‑and‑cooling cycles, adapting to seasonal temperature fluctuations of urban pipe networks. In addition, they shall be flame‑retardant, ageing‑resistant and corrosion‑resistant for complex outdoor and underground humid environments. During project acceptance, core indicators including insulation‑layer thickness, thermal conductivity, sealing performance and outer‑casing integrity shall be emphatically checked. Pipes can be put into service only after all parameters satisfy industrial specifications such as CJJ/T81 and CJJ28.

To sum up, technical requirements for insulated pipes in municipal engineering cover the full dimensions of materials, temperature resistance, structure, construction, safety and acceptance. All indicators are formulated around core demands for safe, energy‑saving and long‑term operation of municipal pipe networks. Strict compliance with industrial standards for material selection and construction can effectively reduce pipe‑network energy consumption, cut operation‑and‑maintenance failures, extend pipe‑network service life and ensure stable and efficient operation of urban heating and cooling pipe‑network systems.