Pre Insulated Steel Pipe

Published:2025-06-19 | Last Updated: 2026-04-24    Views: 157

I. Overview of Pre-insulated Steel Pipes

Pre-insulated steel pipes are composite pipes that integrate the working steel pipe, insulation layer, and outer protective layer into one unit in a factory. They are mainly used in centralized heating, cooling, and oil and gas transportation, and have significant advantages such as low heat loss, fast construction, and strong corrosion resistance.

i. Composed of a three-layer structure

Pre-insulated steel pipes are often referred to as "pipe-in-pipe" structures, consisting of three parts from the inside out:

Working Steel Pipe:

• Function: Transporting media (such as hot water, steam, crude oil).

• Material: Commonly used seamless steel pipe (ASTM A106/API 5L), spiral submerged arc welded pipe (SSAW), or straight seam steel pipe (ERW).

Insulation Layer:

• Material: Usually rigid polyurethane foam (PU).

• Features: Extremely low thermal conductivity (approximately 0.013-0.03 W/m·K), effectively reducing energy loss; also has good adhesion, ensuring a tight bond between the inner pipe and the outer shell.

Outer Sheath:

• Material: High-density polyethylene (HDPE) or fiberglass reinforced plastic (FRP).

• Function: Protects the insulation layer from mechanical damage, groundwater erosion, and ultraviolet radiation, ensuring a service life of 30-50 years for the pipe.

  
  

ii. Main performance parameters

II. Pre-insulated steel pipe specification parameter table

These specifications are applicable to conventional polyurethane pre-insulated steel pipe systems. Specific parameters can be customized according to engineering design requirements, such as pressure rating, insulation thickness, and outer protective layer structure.

III. Application areas and applicable working conditions

Pre-insulated steel pipes are mainly used in engineering systems requiring long-distance transportation of hot water or heat media, and demanding low heat loss and direct burial installation. Different application scenarios require different temperatures, pressures, and structural configurations. The following are common applications and simplified selection guidelines:

1. District Heating System

Applicable Operating Conditions:

• Medium-to-low temperature hot water transportation (typically 70°C – 120°C)

• Direct underground burial in urban areas or industrial parks

• Long-distance continuous operation

Selection Recommendations:

• Standard PU polyurethane insulation layer is sufficient.

• HDPE is preferred for the outer sheath.

• Standard pressure rating ≤ 2.5 MPa

Typical Applications: Urban heating networks, residential heating systems

2. Industrial Hot Water and Heat Energy Transmission

Applicable Operating Conditions:

• Factory circulating hot water system

• Medium-high temperature media (100°C – 150°C)

• Intermittent or continuous operation

Selection Recommendations:

• Choose high-density PU insulation layer (improves heat resistance)

• Increase insulation thickness appropriately (reduces heat loss)

• Increase steel pipe wall thickness appropriately according to pressure

Typical Applications: Chemical plants, food processing, pharmaceutical industry

3. Oil and Chemical Pipeline Systems

Applicable Operating Conditions:

• Including the transport of hot media or requiring insulation

• Some corrosive environments

• Projects with high safety requirements

Selection Recommendations:

• Outer sheath must have stronger corrosion resistance

• Preferably use high-standard steel grades (API 5L X52 and above)

• Reinforced insulation structure (can withstand temperatures above 150°C)

Typical Applications: Oil refineries, chemical industrial parks, energy transmission systems

4. Underground Direct Burial Transmission Project

Applicable Working Conditions:

• Direct underground installation without pipe racks

• Long-term underground operation (over 30 years)

• Complex soil moisture or corrosive environment

Selection Recommendations:

• HDPE outer sheath structure must be used

• Water absorption rate controlled ≤ 10%

• Select integral foaming molding process

Typical Applications: Urban underground pipe networks, inter-regional heating pipelines

• Excellent thermal insulation: Low thermal conductivity (≤0.033 W/m·K), minimal heat loss, and significant energy-saving effect.

• Long service life: Stable overall structure, designed lifespan of 30–50 years.

• Strong corrosion resistance: HDPE outer sheath effectively resists soil and environmental corrosion.

• Suitable for direct burial: Can be directly laid underground, convenient and efficient construction.

• High strength and good safety: Strong pressure-bearing capacity of the steel pipe, stable and reliable operation.

• Low maintenance cost: Minimal maintenance required during operation.

V. Pre Insulated Steel Pipe Standards

VI. Comparison of Main Alternatives to Pre-insulated Steel Pipes

VII. Common specifications and models of polyurethane thermal insulation steel pipes

VIII. FAQ

Q1. What is the difference between Pre Insulated Steel Pipe and Polyurethane Insulated Steel Pipe?

Pre Insulated Steel Pipe is a general term for factory-made insulated piping systems, while Polyurethane Insulated Steel Pipe specifically refers to the use of PU foam as the insulation layer.

PU insulation provides low thermal conductivity (≤0.033 W/m·K), better energy efficiency, and longer service life, making it the most widely used insulation material in modern district heating systems.

Q2. When should I choose Direct Buried Insulated Pipe instead of traditional pipeline systems?

Direct Buried Insulated Pipe is suitable when the pipeline needs to be installed directly underground without a pipe trench system.

It is the best choice for urban heating networks because it reduces construction cost, shortens installation time, and minimizes long-term maintenance compared to traditional on-site insulated pipelines.

Q3. Is Pre Insulated Pipe Manufacturer selection important for project quality?

Yes, choosing a reliable Pre Insulated Pipe Manufacturer is critical.

A qualified manufacturer ensures:

Stable insulation quality (factory-controlled PU foaming)

Compliance with standards like EN 253

Accurate welding and joint systems

Poor manufacturers may cause heat loss, water ingress, and reduced service life.

Q4. Can District Heating Pipe System be designed with different temperature levels?

Yes. District Heating Pipe Systems can be customized according to temperature requirements.

Typical ranges:

Low temperature: 70–90°C (residential heating)

Medium temperature: 90–120°C (urban networks)

High temperature: up to 150°C or higher (industrial systems)

Proper insulation thickness must be selected based on heat load and distance.

Q5. What are the advantages of Underground Heating Pipeline using pre insulated pipes?

An Underground Heating Pipeline using pre insulated pipes offers:

Reduced heat loss during long-distance transmission

No need for external insulation after installation

Better protection against soil moisture and corrosion

It is the most efficient solution for modern city heating infrastructure.

Q6. How do I choose between Thermal Insulation Steel Pipe types for different projects?

Thermal Insulation Steel Pipe selection depends on temperature, pressure, and environment:

Standard PU type → for district heating and hot water systems

Reinforced insulation → for higher temperature or long-distance pipelines

High corrosion environments → require HDPE outer jacket or enhanced protection

The correct selection directly affects energy efficiency and system lifespan (30–50 years).