Steel Jacketed Pre-insulated Pipe

I. What Is Steel Jacketed Pre-Insulated Pipe?

A Steel Jacketed Pre-Insulated Pipe (often structurally referred to as a "steel-in-steel" system) is a highly durable, multi-layered piping system designed to transport high-temperature or high-pressure fluids while minimizing heat loss.

Unlike standard pre-insulated pipes that use a plastic outer casing (like HDPE), this system utilizes a secondary outer steel pipe as a protective protective shield. This makes it exceptionally strong and uniquely suited for harsh environments, such as underground networks with high water tables or overhead steam distribution lines.

II. Steel-jacketed insulated pipe structure composition

1. Working Steel Pipe (Inner Pipe)

The working steel pipe is the pipeline that directly transports the medium, mainly used for transporting:

Steam

• High-temperature hot water

• Heat transfer oil

• Chemical media

  
  

Commonly used materials

Common types:

• Seamless steel pipe

• Straight seam welded pipe

• Spiral steel pipe

2. Insulation Layer

The insulation layer is located between the inner pipe and the outer steel pipe, and is used to reduce heat loss.

Common Insulation Materials

Functions of the insulation layer:

• Reduce heat loss

• Improve conveying efficiency

• Prevent medium temperature drop

• Save energy costs

3. Outer Steel Pipe (Steel Sleeve)

The outer layer uses a steel pipe as a protective layer, forming a robust mechanical protection structure.

Functions of the Outer Steel Pipe:

• Prevents external impact

• Improves pressure resistance

• Prevents groundwater erosion

• Extends pipeline lifespan

Common corrosion protection methods

III. Two typical structures of steel-jacketed insulated pipes

1. Inner Sliding Structure

Features:

• The working steel pipe can slide due to thermal expansion.

• The insulation layer is fixed inside the outer protective steel pipe.

• Suitable for high-temperature steam transportation.

Advantages:

• Strong thermal compensation capacity.

• Long service life.

• Suitable for long-distance pipeline networks.

2. Outer Sliding Structure

Features:

• The working steel pipe and insulation layer move as a whole.

• The outer protective steel pipe is fixed.

Advantages:

• Relatively simple structure

• Easy construction

• Lower cost

IV. Working Principle of Steam Pipeline Insulation

During steam transportation, temperatures can typically range from 150°C to over 350°C. Without effective pipeline insulation, heat continuously escapes into the surrounding air, soil, or environment. This constant thermal dissipation leads to massive energy waste, accompanied by a severe drop in both steam temperature and pressure, ultimately compromising overall system efficiency.

To mitigate these losses and maximize transportation efficiency, steam pipelines must utilize high-performance insulation systems designed to minimize heat transfer.

1. Heat Loss Issues in Steam Transportation

Heat loss includes:

• Pipe wall heat conduction loss

• Air convection heat loss

• External radiation heat loss

• Heat loss due to damp underground environments

If the transportation distance is long and the insulation is poor, the following will occur:

• Lower steam temperature

• Insufficient end-point heating

• Increased energy consumption

• Higher boiler operating costs

• Condensation buildup in pipelines

This is a key reason why long-distance steam pipeline networks must use professionally insulated pipes.

2. How does insulation reduce heat loss?

Steel-jacketed insulated pipes fill the space between the working steel pipe and the outer protective steel pipe with insulation materials such as rock wool, aluminum silicate, or polyurethane.

These insulation materials have low thermal conductivity, effectively preventing heat transfer outwards.

Their working principle mainly includes:

• Reducing the rate of heat conduction

• Reducing convective heat loss due to airflow

• Reducing heat radiation loss

• Maintaining stable internal pipe temperature

High-quality insulation can significantly reduce heat loss, improve steam transport efficiency, and thus reduce overall operating costs.

3. How does a steel-cased steel structure improve insulation performance?

Its structure includes:

• Inner working steel pipe: responsible for transporting steam

• Middle insulation layer: reduces heat loss

• Outer protective steel pipe: protects the insulation layer and enhances overall strength

Compared to ordinary insulation pipes, this structure has superior:

• Waterproof performance

• Pressure resistance

• Mechanical impact resistance

• Service life

Especially in underground direct burial projects, the outer protective steel pipe can effectively prevent groundwater from seeping into the insulation layer, avoiding moisture damage and insulation material failure.

4.  Advantages of long-distance steam transportation

V. Production Process of Steel Jacketed Insulated Pipe

Raw material preparation → Inspection of working steel pipes → Rust removal of working steel pipes → Corrosion protection treatment of working steel pipes → Installation of supports and sliding devices → Filling with insulation layer → Outer steel pipe assembly → Welding and sealing → Corrosion protection treatment of outer steel pipes → Finished product inspection → Packaging and warehousing

Process Flow Description

1. Raw Material Preparation

Prepare the working steel pipe, outer protective steel pipe, insulation material, and anti-corrosion material.

2. Working Steel Pipe Inspection

Inspect the outer diameter, wall thickness, material, and surface quality of the steel pipe.

3. Working Steel Pipe Rust Removal

Remove rust and impurities from the steel pipe surface using sandblasting or shot blasting.

4. Working Steel Pipe Anti-corrosion Treatment

Apply an anti-corrosion coating to the inner working steel pipe to improve its corrosion resistance.

5. Install Supports and Sliding Devices

Install guide supports and sliding supports to reduce thermal expansion stress.

6. Fill the Insulation Layer

Fill the space between the inner pipe and the outer protective steel pipe with insulation material to reduce heat loss.

7. Outer Protective Steel Pipe Fitting

Fit the outer protective steel pipe to the outside of the insulation layer, forming a steel-clad steel structure.

8. Welding and Sealing

Weld and seal the joints to prevent moisture from entering the insulation layer.

9. Corrosion Protection Treatment of Outer Steel Pipe

Apply corrosion protection to the outer steel pipe to extend its service life.

10. Finished Product Inspection

Inspect the dimensions, welds, insulation layer, and pressure resistance to ensure they meet the required standards.

11. Packaging and Warehousing

Number and package the finished products for storage or shipment.

VI. Application areas of steel-jacketed insulated steel pipes

1. Urban Central Heating and Combined Heat and Power (CHP)

High-Pressure Steam Pipeline: In urban central heating and long-distance district heating networks, the temperature of saturated or superheated steam transported from power plants is typically 150°C to 350°C, or even higher. Ordinary high-density polyethylene (HDPE) outer sheaths cannot withstand such high temperatures, necessitating the use of steel-cased steel systems.

High-Temperature Hot Water Main Pipelines: Some heating systems use ultra-high temperature water (e.g., 130°C to 150°C) as the heat transfer medium. Their main pipelines and large-diameter inter-regional pipelines generally employ steel-cased steel structures to ensure system lifespan.

2. Industrial Park "Heat Sharing" and High-Energy-Consuming Industries

Industrial Centralized Heating: Industries such as textile printing and dyeing, papermaking, shipbuilding, rubber, and food processing require large amounts of steam in their production processes. Through steel-jacketed pipelines, the park's thermal power plant can safely transport steam across several kilometers to various enterprises.

Large Chemical Plants and Refineries: Petrochemical enterprises have intricate process pipelines that transport various high-temperature heavy oils, cracking media, chemical raw materials, or high-temperature by-product steam. Steel-jacketed pipelines provide an extremely high safety barrier, preventing chemical leaks and maintaining the temperature of the media.

3. Laying in Harsh and Special Geological Environments

High Groundwater Levels and Water-Rich Areas: In southern my country, coastal areas, and riverine regions, groundwater levels are high and soil is moist. The steel-clad steel outer sheath uses a fully welded seal, capable of withstanding the seepage pressure of groundwater and ensuring the internal insulation layer remains "absolutely dry," preventing water immersion failure.

High Traffic Load Areas (Crossing Roads): When pipelines need to be directly buried across main roads, railways, airport runways, or areas frequently traversed by heavy trucks, the excellent compressive strength and settlement resistance of the outer sheath protect the internal working pipe from compression and deformation.

Deep Burial Environments: In projects requiring deep burial (e.g., more than 3 meters underground) or tunneling through obstacles using pipe jacking, the outer sheath can withstand enormous deep soil lateral pressure.

4. Oil and Gas Extraction and Transportation

Heavy Oil Thermal Recovery (Steam Injection Pipeline): In oil extraction, some crude oils have extremely high viscosity and cannot be pumped directly. High-pressure steam at temperatures as high as 300°C to 350°C needs to be injected from the surface into the well to "melt" the crude oil. Steel-jacketed insulated pipes are commonly used for the surface transportation pipeline from the steam generator to the wellhead.

Long-Distance Crude Oil Transportation: Some crude oils easily solidify at room temperature. To maintain their fluidity, long-distance oil transportation pipelines require heating and efficient insulation. Steel-jacketed pipelines can ensure temperature stability during long-distance transportation.

VII. Common problems with steel-jacketed insulated steel pipes

Q1: What types of projects are steel-jacketed insulated steel pipes mainly suitable for?

Steel-jacketed insulated steel pipes are mainly used in high-temperature steam, hot water, and heat energy transmission projects, and are particularly suitable for:

• Urban centralized heating

• Steam pipeline networks

• Power plants

• Petrochemical plants

• Industrial park heating systems

Q2: What is the difference between steel-jacketed insulated steel pipes and polyurethane insulated pipes?

Q3: How to choose insulation materials for steel-jacketed insulated steel pipes?

Q4: Can steel-jacketed insulated steel pipes be directly buried?

Yes.

Steel-jacketed insulated steel pipes have strong compressive strength and waterproof capabilities, making them very suitable for direct underground burial.

However, in actual projects, the following factors need to be considered:

• Groundwater environment

• Soil corrosivity

• Outer steel pipe corrosion resistance level

• Thermal expansion compensation design

In humid areas, a 3PE reinforced anti-corrosion structure is generally recommended.

Q5: What is the typical service life of steel-jacketed insulated steel pipes?

Under normal circumstances, the designed service life of steel-jacketed insulated steel pipes can reach over 30 years.

The main factors affecting service life include:

• Corrosion protection quality

• Insulation material quality

• Operating temperature

• Installation and construction quality

• Underground environment

If corrosion protection and sealing are inadequate, groundwater entering the insulation layer may shorten the service life.

Q6: What are the most important parameters when selecting steel-jacketed insulated steel pipes?