I. Introduction to Pre-insulated Steel Pipe for District Heating
Pre-insulated steel pipe for district heating are a highly efficient and energy-efficient pipe structure designed specifically for centralized heating systems, primarily used to transport high-temperature media such as hot water or steam.
The pipe consists of a working steel pipe, an insulation layer, and an outer sheath. The insulation layer is typically made of high-density polyurethane or a composite inorganic insulation material to effectively reduce heat loss. The outer sheath provides corrosion resistance, waterproofing, and mechanical protection, ensuring long-term, stable operation in complex environments.
II. Structural Types of Pre-insulated Steel Pipe for District Heating
i. Polyurethane direct buried insulated steel pipe (plastic sheathed steel structure)
Construction: Working steel pipe + polyurethane foam insulation + high-density polyethylene (HDPE) outer sheath.
Features:
Excellent thermal insulation and low heat loss;
The outer sheath is corrosion-resistant and waterproof, suitable for direct underground burial;
Easy installation and a service life of over 30 years.
Applicable media: Hot water, low-temperature steam (≤150°C).
Applications: Urban central heating mains, residential heating, and industrial circulating hot water systems.
ii. Steel jacketed insulated steel pipe
Structure: Working steel pipe + inorganic insulation layer (glass wool, calcium silicate, etc.) + corrosion-resistant steel casing + support guide ring + sliding bearing.
Features:
Suitable for high-temperature and high-pressure transmission;
High mechanical strength, excellent impact and corrosion resistance;
Insulation layer is heat-resistant (up to 450°C) and resists aging.
Applicable media: High-temperature steam, thermal oil.
Applications: Thermal power plants, high-temperature steam pipeline networks, and chemical heat transmission projects.
III. Implementation Standards for Pre-insulated Steel Pipe for District Heating
| Category | Standard Number | Standard Name | Scope / Description |
|---|---|---|---|
| National Standard | GB/T 29047-2012 | Technical Standard for Pre-fabricated Buried Insulated Pipelines | Specifies design, manufacturing, construction, and acceptance requirements for buried insulated pipelines |
| National Standard | CJ/T 114-2000 | Technical Requirements for Pre-fabricated District Heating Pipes | Design and performance requirements for pre-fabricated insulated pipes in urban heating systems |
| National Standard | GB/T 24593-2009 | Technical Requirements for High-Density Polyethylene Outer Protective Pipes | Applicable to outer protective pipes of polyurethane insulated steel pipes |
| National Standard | GB/T 14902-2011 | Technical Specification for Rigid Polyurethane Foam Insulation | Specifies performance requirements for polyurethane insulation materials |
| National Standard | GB/T 23257-2017 | Technical Standard for Buried Steel Jacketed Steam Insulated Pipelines | Applicable to steel jacket insulation structures for high-temperature steam pipelines |
| National Standard | GB/T 3091-2015 | Low-Pressure Fluid Transport Welded Steel Pipes | Applicable to the manufacturing of working steel pipes |
| National Standard | GB/T 8163-2018 | Seamless Steel Pipes for Fluid Transport | Applicable to working steel pipes under pressure conditions |
| National Standard | GB/T 9711-2021 | Steel Pipes for Oil and Gas Transmission | Applicable for high-pressure or long-distance main heating network pipes |
| National Standard | GB/T 19394-2017 | Technical Specification for Insulation and Protection of Buried Heating Pipelines | Guidelines for design and construction of buried district heating networks |
| International Standard | EN 253:2019 | District Heating Pipes – Preinsulated Bonded Pipe Systems | European standard for pre-fabricated district heating insulated pipe systems |
| International Standard | EN 448:2019 | District Heating Pipes – Fittings | Specification for fittings used in district heating systems |
| International Standard | ISO 15665:2013 | Industrial Piping – Acoustic Insulation | Requirements for industrial piping insulation and thermal/acoustic performance |
| International Standard | ISO 9001:2015 | Quality Management System Standard | Certification for enterprise quality control systems |
| International Standard | ISO 11346:2004 | Long-Term Thermal Aging Performance Test Method | Used to verify the aging resistance of insulation layers |
IV. FAQ on prefabricated insulated steel pipes for district heating
(1) How do I choose the right insulation thickness for my project?
A: Insulation thickness is primarily determined by the working medium temperature, pipe diameter, and allowable heat loss.
Generally, 30-100mm is recommended for hot water pipes (≤120°C), while 50-150mm is recommended for steam pipes (150-250°C).
Large trunk pipes or long, directly buried pipelines should have thicker insulation to minimize heat loss and maximize energy savings.
(2) What media are suitable for insulation pipes of different structures?
A: Polyurethane direct-buried pipe (plastic-jacketed steel): Suitable for hot water and low-temperature steam (≤150°C);
Steel-jacketed steel insulated pipe: Suitable for high-temperature, high-pressure steam or thermal oil;
Composite insulated pipe: Suitable for large temperature fluctuations or special environments;
Vacuum insulated pipe: Suitable for high-end energy-saving projects or long-distance heat transmission networks.
Properly matching the structure and medium can extend service life and ensure safety.
(3) How to determine the design pressure and working pressure of the pipeline?
A: The design pressure is typically 1.5 times higher than the actual operating pressure to ensure safety.
Small hot water networks typically use 1.0 to 2.5 MPa, while large steam networks or industrial heating networks can reach up to 4.0 MPa.
When purchasing, please provide the operating pressure and temperature requirements so that the manufacturer can produce according to these standards.
(4) How to ensure that pipelines are not corroded in underground direct burial environments?
A: The outer sheath is made of high-density polyethylene (HDPE) or corrosion-resistant steel.
The joints are sealed with sleeves and heat-shrinkable.
Before burial, check the soil’s electrochemical corrosion conditions; cathodic protection may be added.
The insulation layer has a density of ≥60 kg/m³ and a water absorption rate of ≤10%, providing effective waterproofing and corrosion resistance.
(5) What are the precautions for pipeline transportation and construction?
Avoid collision, crushing, or dropping during transportation.
Store pipes away from direct rain, horizontally, and with support.
During installation, ensure the integrity of joints and insulation is maintained.
Large-diameter pipes can be transported in sections, with joints welded and insulated on-site.
(6) What is the service life of prefabricated insulated steel pipes for district heating?
Polyurethane direct-buried pipes can last 30 years or longer under normal underground installation conditions.
Steel-jacketed insulated pipes can last 25-30 years or longer under high-temperature and high-pressure conditions.
Regular inspections of pipe joints and the condition of the anti-corrosion coating can extend pipe life and reduce maintenance costs.
