[Haichuan Pipeline Construction] Case: In-situ thermoplastic forming method for trenchless repair of drainage pipes
Thread Content
In November, a thermoplastic molding process was used to perform trenchless repairs on DN400 drainage pipes in Chongqing. A "wonderful reaction" of steam and pressure was underway. The in-place thermoplastic forming method, known as formed-in place pipe (FIPP) in English, originated in the United States. This process uses a new type of polymer thermoplastic material that has the characteristics of heating, softening and cooling. The lining pipe is pre-made into an "I" shape or a "C" shape in the factory, and then rolled onto a reel and transported to the construction site.
After the lining pipe reaches the set temperature, increase the internal pressure of the hose to stretch and expand the lining pipe until it closely fits the original pipe. Then, keep the pressure constant and inject cold air to cool down, so that the lining material cools and hardens to form a new lining pipe that is close to the pipe wall, thus realizing the overall repair of the pipeline.
The biggest feature of this process is that the repair materials are prefabricated and produced in the factory. It is similar to the traditional pipelines buried through excavation. The mechanical properties, chemical corrosion resistance, pipe wall thickness and other performance indicators of the lining material are "guaranteed after leaving the factory." The shape of the pipe is only changed on-site through the physical effects of heat and pressure, which does not cause changes in material properties. It is one of the quicker of the many types of lining repairs. If the time for dredging pre-treatment and hose pre-heating is not included, the process from pipe removal to repair is often completed within 1 to 2 hours and water flow can be restored. Pipes with a diameter less than DN300mm can even be completed within 30 minutes.
Limited by the size of the drainage inspection wellhead, the diameter of the general drainage pipeline repair range is DN100-DN900mm. Repairing larger diameter pipes requires digging expansion inspection wells. In addition, due to the factor of temperature decreasing with the length of the pipeline, the length of a single repair is limited. When the distance of a single repair is too long, it may be difficult for the end of the lining pipe to reach the temperature required for material softening, resulting in the end being unable to fully fit and quality accidents occurring.
Since the repair material has good thermoplastic properties, this process can be used to repair slightly misaligned, reduced diameter, special-shaped, and curved pipes. For example, special-shaped pipes with various cross-sectional shapes such as oval, horseshoe, rectangular, etc. ； For example, DN400 variable diameter pipes may have DN360 or DN450 pipe diameters partially in the middle, but the pipe diameter change range should not be too large, otherwise the lining pipe will not be able to fully open the circle, or excessive expansion will cause the wall thickness to thin or even break. ； For example, if a pipe with misaligned interfaces is repaired, although the misalignment cannot be eliminated, it will make the misalignment smoother, thereby reducing the flow resistance and increasing the flow efficiency. ； In addition, it can also be applied to the repair of bends with a certain included angle. In practice, bent pipes with an included angle of less than 30° are often repaired.
Environmentally friendly and economical FIPP repair material is modified PVC material, which is acid and alkali resistant, corrosion resistant, aging resistant, etc., and is suitable for the transportation of various media including sewage. After repair, the design service life is up to 50 years, and defects such as corrosion and scaling will not occur later. At the same time, the surface roughness coefficient of the inner wall of the lining pipe is small (the inner surface roughness coefficient after repair is 0.009). Although the flow cross-section is slightly reduced after repair, the flow efficiency is actually greatly improved.
During the construction process, steam and pressure are mainly used, which does not produce any pollutants and gas pollution, and is in line with the current green and environmentally friendly technical requirements. In addition, because the liner material has good toughness and other properties after being heated and softened, when there are problems with on-site installation or quality defects after inspection and repair, the liner can be reheated and extracted after softening, so it can * * Reduce the risk of restoration project failure and the cost of rework.