Connection Method with Heat-Shrinkable Sleeve/Belt for Steel Belt Reinforced Pipes
2020/04/02
This connection method adopted by steel belt pipe manufacturers uses fiber-reinforced polyethylene heat-shrinkable belt as the inner layer and heat-shrinkable sleeve as the outer layer. The inner wall of the heat-shrinkable sleeve is coated with hot-melt adhesive. After heating, it closely fits and fastens adjacent pipe ends to form an integrated joint.
Heat-shrinkable sleeve connection is generally applicable to steel belt reinforced polyethylene spiral corrugated pipes with diameter below 1200mm. For pipes larger than DN1200, users shall wrap two layers of fiber-reinforced polyethylene heat-shrinkable belts around the joint and fasten with clamps additionally.
All operations must be conducted in strict accordance with construction specifications. Firstly, polish and clean the outer pipe wall of connecting sections for surface treatment. Then slide the heat-shrinkable sleeve over the two pipe ends to be connected, and heat the sleeve to bond its inner wall tightly with the pipe outer wall. A steady clamping force will be formed after cooling to meet pipe connection standards. When aligning pipes, keep pipe ends closely matched with minimal gaps.
Control the flame temperature properly during heating. Heat gradually from the middle to both ends or from one end to the other. Fully expel all air between the sleeve and pipes for complete fitting, and ensure hot-melt adhesive oozes out from sleeve ends.
The applicable ambient construction temperature ranges from -20℃ to 60℃. Thermal insulation measures shall be taken if the temperature is below 0℃.
Standard Operating Procedures
- Inspect the flatness of butted pipe ends. The local gap after assembly shall be within specified limit. On-site trimming is required if failing to meet the standard.
- Suspend the pipe ends properly to reserve sufficient space for circumferential heating operation.
- Slide the heat-shrinkable sleeve onto one pipe end and move it over 500mm away from the joint. Keep the protective inner film intact to prevent dust, dirt and water from contamination.
- Polish the outer cylindrical surface within 120mm from the pipe end, including crests and troughs of corrugations. Polish at least three and a half corrugation sections with steel brushes matched to pipe profiles.
- Wipe the polished pipe ends thoroughly with clean cloth.
- Align and fix the two pipe ends accurately without misalignment.
- Use PE welding rods matching pipe material to make no less than four evenly distributed circumferential welding spots to fix the joint preliminarily.
- Preheat the circumferential surface within three corrugations from pipe ends to 40℃-50℃, which shall be over 15℃ lower than the softening point of hot-melt adhesive. Use surface thermometer for temperature monitoring.
- Wind and bake reinforced fiber heat-shrinkable belts at joints for full circumferential wrapping and firm overlapping.
- Preheat both pipe ends within the polished area to 40℃-50℃.
- Shift the heat-shrinkable sleeve to the polished section, with the initial heating position about one-third of the sleeve length away from the joint. Remove the inner protective film and avoid foreign matter adhesion. Use wedge-shaped supports to keep the sleeve concentric with the pipe for uniform circumferential gap.
- Heating construction: Heat evenly around the circumference from one end with red flame or professional ring heater. Avoid longitudinal flame movement and local overheating. Press the shrunk part gently with matched rolling tools or heat-resistant gloves to exhaust residual air and fit closely with corrugations without damaging pipes. When approaching 5cm away from pipe ends, heat the inner hot-melt adhesive first then the outer layer. Finally conduct overall mild heating until hot-melt adhesive overflows fully from sleeve ends.
It is critical to control heating temperature accurately. Excessively high temperature will damage PE pipe surfaces and crack heat-shrinkable sleeves, while insufficient heat leads to incomplete adhesive melting, poor bonding effect and failure to reach required peel strength.
Qualified construction tools are essential for qualified connection work. Available heat sources include portable liquefied gas tanks, natural gas burners and blowtorches equipped with matched nozzles. Specialized automatic heating equipment is highly recommended to greatly improve overall connection quality.
