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Polyurethane Foam Pre-insulated Steel Pipe

Published:2025-04-12 | Last Updated: 2025-06-12    Views: 28

Polyurethane Foam Pre-insulated Steel Pipe


I. Analysis of the structure of polyurethane foam pre-insulated steel pipe


i. What is polyurethane foam pre-insulated steel pipe?

Polyurethane foam pre-insulated steel pipe (referred to as insulated steel pipe or prefabricated insulated pipe) is an industrial-grade composite pipe.

It uses high-performance polyether polyol and polymethyl polyphenyl polyisocyanate as raw materials and is foamed on-site through chemical reaction.


ii. Core structural features

a. Working steel pipe pressure bearing:

The inner layer adopts pressure bearing steel pipe (such as LSAW Steel Pipes seamless steel pipes, etc.) to transport high temperature fluid or chemical medium.

b. Polyurethane foam insulation layer:

Foaming is injected between the working steel pipe and the outer sheath at one time to form a hard closed-cell foam.

This layer is the insulation core of the polyurethane foam insulation pipe.

c. HDPE outer sheath protection:

The outer layer is covered with high-density polyethylene (HDPE) to resist mechanical damage and corrosion.


iii. Six core advantages

a. Lightweight and high strength:

30% lighter than traditional insulation pipes, compressive strength ≥200kPa.

b. High-efficiency thermal insulation:

Thermal conductivity ≤0.033W/(m·K), reducing heat loss by 40%.

c. Safety protection:

Flame retardant (B1 grade) + cold resistance (-50℃) + corrosion resistance.

d. Waterproof and sealed:

The water absorption rate of the closed-cell structure is <3%, eliminating leakage.

e. Convenient construction:

Prefabricated insulation pipes are ready for use after leaving the factory, shortening the construction period by 50%.

f. Long-lasting and durable:

The underground direct burial life is over 30 years, maintenance-free.


iv. Application areas

This type of direct buried polyurethane insulated steel pipe has become a rigid demand product in five major industries:

a. Petrochemical: transporting high-temperature oil and gas media

b. Central heating: urban underground hot water pipeline network

c. Power engineering: steam pipeline insulation

d. Building HVAC: central air conditioning hot and cold pipelines

e. Transportation energy: airport/high-speed rail station thermal energy system


Polyurethane Foam Pre-insulated Steel Pipe


II. Structure of polyurethane foam pre-insulated steel pipe 


(1) Working steel pipe layer 

Material selection: seamless steel pipe spiral seam steel pipe or straight seam steel pipe.

Surface treatment: through the process of descaling by shot blasting, the descaling grade reaches the Sa2 level of GB8923-1988 standard, and the surface roughness is R=12.5 microns.

(2) Polyurethane foam insulation layer 

Molding process: adopting “pipe-in-pipe foaming” technology, injecting polyurethane rigid foam into the cavity between the steel pipe and the outer protection layer through high-pressure foaming machine.

Core function: waterproofing, heat preservation and supporting the self-weight of the pipe network.

Temperature Adaptation: It is suitable for medium transportation of -50℃~120℃, and can resist temperature up to 180℃ through modification.

(3) High-density polyethylene outer sheath 

Material Characteristics: Prefabricated black or yellow polyethylene pipe with low-temperature resistance (-70℃~100℃), acid and alkali corrosion resistance.

Surface treatment: corona treatment of the inner wall of the outer pipe to enhance the adhesive properties with the insulation layer.

Main function: mechanical protection (impact resistance, anti-hard object damage) and anti-corrosion waterproof dual function.

Polyurethane foam pre-insulation steel pipe is a combination of high-function polyether polyol and many times methyl polyphenyl polyisocyanate as raw materials by chemical reaction foaming. 

high density polyurethane foam steel pipe insulation has light weight, high strength, adiabatic, sound insulation, flame retardant, cold-resistant, anticorrosive, non-absorbent, easy and fast construction and other excellent features, has become an indispensable product for the petroleum, chemical, electric power, construction, transportation, refrigeration and other industrial sectors such as adiabatic insulation, waterproofing leakage plugging, sealing and other indispensable products.


III. Polyurethane foam pre-insulated steel pipe detailed specification model list



Nominal Diameter(DN)

OD(mm)

WTmm)

Outer diameter of outer protection tubemm)

Wall thickness of outer protection tube(mm)

Insulation thickness(mm)

20

27

3.0

95

2.5

31.5

25

32

3.0

100

2.5

31.5

32

38

3.0

110

2.5

33.5

40

48

3.0

125

3.0

35.5

50

57

3.5

125

3.0

31.0

70

76

4.0

142

3.0

30.0

80

89

4.0

155

3.0

30.0

100

108

4.0

170

3.0

30.5

125

133

4.0

200

3.2

30.0

150

159

4.5

238

3.0

36.5

200

219

6.0

310

4.9

40.6

250

273

7.0

365

5.6

40.4

300

325

8.0

420

5.6

41.9

350

377

9.0

475

7.8

41.2

400

426

10.0

530

8.8

43.2

450

478

10.0

587

8.8

45.7

500

529

10.0

655

9.8

53.2

600

630

10.0

760

11.1

53.9

700

720

10.0

850

12.0

53.0

800

820

10.0

960

14.0

56.0

900

920

10.0

1054

14.0

53.0

1000

1020

10.0

1155

14.0

54.0

1200

1220

10.0

1380

15.0

65.0

1400

1420

10.0

1580

16.0

64.0


Polyurethane Foam Pre-insulated Steel Pipe


IV. Polyurethane insulated steel pipe production process


Polyurethane Insulated Steel Pipe Production Process

StepOperation ContentNotes
Steel Pipe CuttingCut seamless steel pipes, straight seam steel pipes, or spiral steel pipes to the required length according to design requirements.Ensure precise dimensions to meet design requirements.
Steel Pipe Rust RemovalTreat the surface of the steel pipe with shot blasting or sandblasting to achieve Sa2 rust removal standard.Improve surface roughness of the steel pipe to enhance adhesion of the insulation layer.
Outer Sheath PreparationSelect high-density polyethylene outer sheaths of appropriate specifications and treat them with corona discharge to enhance adhesion.Ensure tight bonding between the outer sheath and the insulation layer.
Support InstallationInstall central control supports on the steel pipe to maintain concentricity and support the pipe structure.Ensure stability of the polyurethane foam insulated steel pipe during the foaming process.
Positioning and AssemblyPlace the steel pipe inside the polyethylene outer sheath, adjust the position, and seal both ends.Ensure uniform clearance between the steel pipe and the outer sheath.
Foam InjectionUse a high-pressure foaming machine to inject polyurethane raw materials into the gap between the steel pipe and the outer sheath.Ensure uniform foaming and fill all gaps.
Foam CuringLeave undisturbed for a period of time to allow the polyurethane foam to react and fully cure.Curing time is adjusted according to ambient temperature and foaming agent characteristics.
Cutting and TrimmingCut and grind the pipe ends to ensure smooth joints for subsequent welding or connection.Ensure joint quality for easy on-site installation.
Inspection and TestingCheck the dimensions of the steel pipe, insulation layer thickness, adhesion effect, and appearance quality to ensure compliance with standards.Includes dimensional inspection, insulation layer thickness testing, adhesion strength testing, etc.
Finished Product StoragePackage and store qualified products in the warehouse, awaiting shipment or on-site installation.Ensure the integrity of the polyurethane insulated pipes during transportation and storage.



V. Application of Polyurethane Foam Pre-Insulated Steel Pipe


i. Centralized heating and cooling system 

Widely used in town centralized heating and district cooling projects.

Conveying medium: hot water (≤120℃) or cold water 

Core advantage: reduce heat loss by 40%, support direct burial laying 

Typical scenario: residential heating, commercial complex air conditioning circulatory system 

ii. Oil and gas transportation 

Covering onshore pipelines, submarine pipelines and energy facilities.

Pressure-resistant and anti-corrosion: can withstand high pressure gas transportation (≤150℃) 

Special treatment: can adapt to extreme temperatures of -50℃~180℃ through modification 

Safety protection: the outer layer of polyethylene prevents chemical corrosion and mechanical damages 

iii. Water Transmission Project in High Alpine Areas 

Specially designed for tundra environment.

Anti-freezing performance: maintain the structural integrity of the pipe at -70℃ low temperature 

Direct burial advantage: no pipe trench required, burial depth 0.6-1.2 meters tundra 

Application cases: Arctic Circle water pipeline network, drinking water system in plateau area 

iv. Industrial special pipeline 

Meet the complex needs of multiple industries.

Chemical industry: conveying acid and alkali media (PH 3-11 corrosion resistance) 

Pharmaceutical industry: thermostatic drug/pure water conveyance in clean environment 

Municipal engineering: leakage prevention of sewage network, steam piping in industrial parks 

v. Supporting engineering services 

Adapt to diversified construction scenarios.

Prefabricated pipe fittings: insulation elbows, tees and other shaped parts 

Intelligent monitoring: built-in leakage alarm system 

Special specifications: support DN15~DN3000 pipe diameter customization


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