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Application of Insulated Steel Pipes in District Heating Projects

Number of visits：65 seconds Update time：2025-11-17

In urban and industrial park heating projects insulated steel pipes are increasingly being utilized. Due to their ability to provide efficient and reliable thermal energy transmission, insulated steel pipes have gained widespread application in heating systems.

This article introduces the types, advantages, and selection criteria of insulated steel pipes, aiming to provide valuable guidance.

I. Main Types and Insulation Structures of Insulated Steel Pipes

i. Classified by Construction Method

Type	Description	Insulation Structure
Pre-insulated Direct-buried Steel Pipe	Suitable for directly buried heating networks	Inner steel pipe → Polyurethane (PU) foam insulation → HDPE outer jacket
Above-ground Insulated Steel Pipe	Pipes exposed indoors or outdoors	Inner steel pipe → Polyurethane / rock wool insulation → Aluminum or steel protective jacket
Steam-dedicated Insulated Steel Pipe	High-temperature steam transmission pipeline	Inner steel pipe → High-temperature refractory rock wool or glass wool → Steel or aluminum protective jacket

ii. Classified by Steel Pipe Type

Type	Description	Insulation Structure
LSAW Longitudinal-seam Insulated Steel Pipe	Large-diameter, longitudinal-welded steel pipe for long-distance high-pressure pipelines	Inner steel pipe → Polyurethane foam or rock wool → PE/HDPE outer jacket
SSAW Spiral-seam Insulated Steel Pipe	Medium- and small-diameter, spiral-welded steel pipe for long-distance hot-water transmission	Inner steel pipe → Polyurethane foam or rock wool → PE/HDPE outer jacket
Seamless Insulated Steel Pipe	For special high-temperature and high-pressure service	Inner steel pipe → Polyurethane foam or glass wool → PE/HDPE or aluminum jacket

iii. Classified by Insulation Material

Insulation Material	Features	Typical Structure
Polyurethane Foam (PU)	High thermal efficiency, light weight	Inner steel pipe → PU foam → HDPE jacket
Rock Wool	Excellent fire resistance, high-temperature tolerant	Inner steel pipe → Rock wool → Aluminum or steel jacket
Glass Wool	High-temperature resistant, corrosion resistant	Inner steel pipe → Glass wool → Aluminum or steel jacket

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II. Advantages of Insulated Steel Pipes

i. Cost and Economic Efficiency

Energy Conservation and Consumption Reduction: High-quality insulated steel pipes significantly reduce heat loss, lowering operational energy costs.

High Long-Term Investment Return: With a lifespan exceeding 30 years, they reduce replacement frequency and minimize long-term procurement and maintenance expenses.

Controllable Material and Construction Costs: Prefabricated pipes for direct burial simplify on-site construction and reduce labor expenses.

ii. Procurement and Supply Convenience

Standardized Production: Standardized pipe specifications, lengths, and materials simplify procurement and acceptance.

Multiple Specifications Available: Meets diverse project requirements for diameter, pressure, and temperature, minimizing secondary procurement risks.

Flexible Stock and Customization: Suppliers offer both stock items and project-specific customization to ensure project timelines.

iii. Project Risk Control

Reliable Quality: Steel pipes withstand high pressure and corrosion, while the insulation layer provides excellent sealing, reducing risks of pipeline leakage and heat loss.

Low Construction Risk: Prefabricated insulated pipes minimize on-site insulation work, lowering the likelihood of construction errors and rework.

Strong Compliance: Meets domestic and international standards (GB, EN, ASTM, API), facilitating acceptance inspections and compliant procurement.

iv. Maintenance and Operational Advantages

Low Maintenance Costs: The integrity of the pipe body and corrosion-resistant outer jacket minimize routine maintenance and repair expenditures.

Extended Service Life: The combination of high-quality steel pipe, insulation layer, and protective jacket prolongs pipeline lifespan, reducing long-term procurement frequency.

Versatile Application: Suitable for high-temperature, steam, and long-distance hot water transportation projects, mitigating operational risks.

v. Comparative Table of Advantages and Disadvantages for Various Types of Insulated Steel Pipes

Type	Advantages	Disadvantages	Applications
Direct-buried Pre-insulated Pipe (LSAW longitudinal-welded)	• Ideal for large-diameter, long-distance transport • High insulation, low heat loss • Service life > 30 years	• Higher manufacturing & transport cost • Strict requirements on terrain	District heating, long-distance hot-water networks, industrial park steam/hot-water lines
Direct-buried Pre-insulated Pipe (SSAW spiral-welded)	• Lower cost for medium/small diameters • Easy to install • Stable thermal performance	• Pressure rating slightly lower than LSAW • Not suitable for very large diameters	Medium- & small-diameter hot-water lines, underground distribution networks
Direct-buried Pre-insulated Pipe (seamless)	• Withstands high temp. & pressure • Excellent corrosion resistance • Suited for critical duties	• High cost • Long-distance transport difficult	High-temperature steam lines, special industrial process piping
Above-ground Insulated Pipe (LSAW or SSAW)	• Easy to install and maintain • Fire-resistant & weather-proof (Al or steel jacket)	• Appearance vulnerable to environment • Slightly higher heat loss than buried	Indoor exposed piping, outdoor overhead lines
Steam-dedicated Insulated Pipe (seamless + rock-/glass-wool)	• High temp./pressure capability, fire-safe • Superior insulation performance	• High material cost • Complex outer-jacket installation	High-temperature steam distribution, industrial process piping

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III. Recommendations for Selecting Insulated Steel Pipes

When selecting insulated steel pipes, we should comprehensively consider the pipeline application, conveyed medium, temperature and pressure conditions, construction environment, and economic factors to ensure the project's safe and efficient operation.

The following are directly applicable selection recommendations:

i. Determine Pipe Type

Direct Burial Pipe: Suitable for long-distance underground transportation of hot water or steam, offering excellent thermal insulation.

Exposed Pipe: Suitable for indoor or overhead installation, featuring easy construction and maintenance.

Steam-Specific Pipe: Suitable for high-temperature steam or high-pressure conditions, requiring high-temperature resistance, pressure resistance, and flame retardancy.

ii. Selecting Steel Pipe Material and Welding Method

LSAW (Longitudinal Submerged Arc Welded) Pipe: Large diameter, high pressure-bearing capacity, suitable for long-distance pipelines.

SSAW (Spiral Submerged Arc Welded) Pipe: Medium to small diameter, low cost, suitable for hot water networks.

Seamless Steel Pipe: Mandatory for high-temperature/high-pressure conditions, excellent corrosion resistance.

iii. Determining Insulation Materials

Polyurethane Foam (PU): Excellent thermal insulation, lightweight, suitable for hot water and low-temperature steam.

Rock Wool: High-temperature resistant, flame-retardant, suitable for steam and exposed outdoor piping.

Glass Wool: High-temperature resistant, corrosion-resistant, suitable for high-temperature steam pipelines.

iv. Outer Sheath Selection

HDPE/PE Sheath: Suitable for direct burial underground pipes, offering waterproofing, corrosion resistance, and protection against mechanical damage.

Aluminum/Steel Sheath: Suitable for exposed installations or high-temperature steam pipelines, providing fire resistance and corrosion protection.

v. Additional Selection Considerations

Ensure pipe diameter, wall thickness, and length match design specifications.

Account for installation environment: underground burial, overhead, or exposed installation.

Verify standards and certifications: compliance with GB, EN, ASTM, API, and other relevant standards.

Evaluate cost-effectiveness: select appropriate material and insulation thickness based on project budget.

vi. Insulated Steel Pipe Selection Checklist

Option Category	Available Types	Application	Features & Remarks
Pipe Type	Direct-buried pipe	Long-distance underground hot-water/steam	Excellent insulation, low heat loss
	Above-ground pipe	Indoor or overhead installation	Easy to install & maintain
	Steam-specific pipe	High-temperature steam lines	High temp./pressure resistant, fire-safe
Steel Material	LSAW longitudinal-welded	Large-diameter long-distance	High pressure rating, suited for long runs
	SSAW spiral-welded	Medium- & small-diameter lines	Low cost, easy construction
	Seamless pipe	High temp. & high pressure	Corrosion resistant, withstands high pressure
Insulation Material	Polyurethane foam (PU)	Hot water, low-temp. steam	Best thermal performance, lightweight
	Rock wool	Steam, high-temp. above-ground	Fire-proof & high-temp. tolerant, heavier
	Glass wool	High-temp. steam lines	Corrosion resistant, suits high temperatures
Outer Jacket	HDPE / PE	Direct-buried lines	Water-proof, corrosion-proof, mechanical impact resistant
Outer Jacket	Aluminum / Steel jacket	Above-ground & high-temp. steam	Fire-, corrosion- & high-temp. resistant
Standard Certification	GB / EN / ASTM / API	All pipelines	Ensure code compliance & reliable quality
Diameter & Wall Thickness	Per design requirements	All pipelines	Meet flow, pressure & heat-load demands
Installation Environment	Underground / Overhead / Exposed	All pipelines	Select suitable pipe type & jacket for environment
Economy	Budget-optimised	All pipelines	Balance material, installation & maintenance costs

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