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Production Process of Insulated Steel Pipe
Created on 04.30
Insulated steel pipe is a composite pipeline product widely used for district heating, hot water transmission, and industrial fluid transportation. It combines the structural strength of steel pipe with the thermal insulation performance of polyurethane foam and a protective outer casing, forming a three-layer structure: steel pipe core, insulation layer, and outer protective jacket. The production process directly determines the thermal efficiency, anti-corrosion performance, and service life of the pipeline, which is crucial when choosing a reliable supplier.
1.Steel Pipe Surface Pretreatment
The first step in the production process is the surface preparation of the steel pipe. The pipe is first cleaned to remove oil, grease, rust, scale, and welding slag from the outer surface. Depending on requirements, the pipe may also receive an anti-corrosion primer coating to enhance corrosion resistance before insulation application. This step ensures a clean and suitable surface for the insulation material to adhere properly.
2.Insulation Layer Material Preparation
High-quality polyurethane foam raw materials are prepared for the insulation layer. The polyol and isocyanate components are precisely mixed according to the required density and thermal conductivity specifications. For pre-insulated pipes, the foam is designed to have excellent thermal insulation, low water absorption, and good dimensional stability.
3. Centrifugal or Continuous Foaming Process
The core step of the process is the application of the polyurethane insulation layer:
- Centrifugal Casting: For small to medium-diameter pipes, the steel pipe is centered inside the outer casing, and the mixed foam material is poured into the annular space between the pipe and the casing. The pipe assembly is then rotated at high speed to distribute the foam evenly, forming a uniform, dense insulation layer.
- Continuous Line Foaming: For large-scale production, the steel pipe and outer casing are fed through a continuous line. The foam material is injected between them, and the assembly moves through a curing tunnel to allow the foam to expand and cure in a controlled environment.
The insulation thickness is controlled according to the project’s temperature requirements and heat loss standards.
4.Outer Protective Casing Installation
After the foam has fully cured, the outer protective casing (usually high-density polyethylene or FRP) is installed. For some processes, the casing is already in place during the foaming step. The casing provides mechanical protection against impact, UV rays, and moisture, preventing damage to the insulation layer.
5. Finishing and Quality Inspection
Finished insulated pipes are trimmed at the ends to expose the steel pipe core for connection. Protective caps are installed to keep the pipe ends clean and prevent moisture ingress. Every pipe undergoes comprehensive quality control before delivery:
- Visual Inspection: Check the insulation layer for uniformity, surface defects, and complete coverage.
- Density Test: Verify that the polyurethane foam meets the specified density requirements.
- Thermal Conductivity Test: Sample testing to ensure the insulation meets thermal efficiency standards.
- Adhesion Test: Confirm the bonding strength between the steel pipe, insulation layer, and outer casing.
Only pipes that pass all inspections are marked with specifications, batch numbers, and certification marks, then packaged for delivery. With mature production technology and strict quality control, insulated steel pipe provides a reliable, long-lasting solution for heating and fluid transportation projects worldwide.
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