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Prefabricated Plastic Steel Directly Buried Insulation Pipes Common Problems and Solutions
Plastic-steel thermal insulation pipes have been widely adopted in many developed countries for several decades, delivering excellent energy-saving performance. In recent years, Chinese heating engineers have significantly advanced domestic pipeline technology by studying and integrating this sophisticated method. The directly buried insulation pipe is created by tightly bonding a steel pipe for medium transportation, an outer high-density polyethylene sleeve, and a rigid polyurethane foam insulation layer in between.
However, when using field foaming spray polyurethane, several issues may arise:
First, the polyurethane insulation pipe may start to expand too slowly. This often happens during colder seasons or early mornings due to sudden temperature drops. To resolve this, it's necessary to raise both the ambient temperature and the temperature of the black material. Typically, the black material should be heated to 30–60°C, while the surrounding area should reach 20–30°C.
On the other hand, if the pipe expands too quickly, especially during spring or summer, or during midday construction, it’s usually due to excessive heat. To prevent this, you can cool the black material with cold water or let it cool naturally at night, avoiding direct sunlight exposure.
Another common issue is that the foam inside the insulation pipe has low strength and soft bubbles. This problem is typically caused by an imbalance between the black and white materials. To fix it, you can slightly increase the proportion of the black material (from 1:1 to 1.05). However, be cautious not to overdo it, as an excess of black material can lead to brittle bubbles and negatively affect the overall foam quality.
To avoid these problems and ensure better performance, it's recommended to use the factory-preset method when manufacturing insulation pipes. This involves using a high-pressure foaming machine to inject rigid polyurethane foam liquid into the cavity between the outer sleeves in one go. This approach simplifies the construction process, makes transportation easier, and results in more energy-efficient insulation systems.