Technology Insights: UV-CIPP (Ultraviolet Light Cured-in-Place Pipe) Lining Technology

In the trenchless pipeline rehabilitation industry, Ultraviolet Light Cured-in-Place Pipe (UV-CIPP) lining technology is widely recognized as one of the most efficient and environmentally friendly methods available. Put simply, it acts as a "minimally invasive surgery" for urban underground infrastructure, creating a brand-new, high-strength pipe directly inside an old, damaged, or aging pipeline without the need for disruptive excavation.

The core of this technology lies in a pre-fabricated composite liner. During manufacturing, fiberglass strands, which possess exceptional tensile strength, are woven into a flexible tube and thoroughly impregnated with a light-curing resin. At this stage, the liner behaves like a soft, uncured "plastic sleeve." It is tightly enclosed by inner and outer protective films to prevent the resin from wearing off during transit and to block out ambient light, which would otherwise trigger premature curing.

The onsite installation process follows a strict engineering workflow, divided into five distinct phases:

First is Site Preparation. Because the new liner relies entirely on the shape of the existing host pipe to form its structure, any significant buildup of silt, scale, or root intrusion will prevent the liner from expanding properly. Therefore, engineers must first use high-pressure jetting vehicles to thoroughly flush, clean, and clear the pipeline.

Next comes the Liner Insertion. To prevent the heavy liner from tearing against the rough bottom of the old pipe, crew members pull a tough, smooth gliding foil into the pipeline first. Given that typical manhole diameters are only 600 mm to 700 mm, introducing a large pipe directly is impossible. Engineers use a specialized folding rack to fold the liner, feeding it slowly into the manhole. The pulling speed must be strictly controlled under 5 m/min to ensure the liner lays perfectly flat and smooth along the bottom of the host pipe without any longitudinal bunching.

The third step is End Packer Installation. Once the liner is fully in place, specialized sealing packers are attached to both ends and secured tightly with at least three heavy-duty fastening straps. This creates a completely airtight chamber within the liner, preparing it for inflation and equipment insertion.

The fourth step is the technical core of the process: Inflation and UV Curing. Air compressors are engaged to pump air into the liner. As the pressure slowly builds, the folded liner expands like a long balloon until it presses firmly against the inner wall of the host pipe. Once the pressure stabilizes, a "UV light train"—equipped with high-output UV lamps and high-definition cameras—is introduced through an air-lock system and pulled to the opposite end of the pipe. The UV lamps are then ignited sequentially, and the train is pulled back at a constant speed of approximately 1 m/min. The UV light triggers a rapid polymerization reaction, hardening the resin in a remarkably short time. Throughout this process, the internal temperature must be maintained above 80°C to ensure an optimal cure, which engineers monitor in real time from a control vehicle via cameras and temperature sensors.

The final phase is End Treatment. Once the resin has fully cured and cooled down, the crew depressurizes the system, removes the packers, and pulls out the inner protective film. What was once a soft fabric sleeve is now a structural, high-strength composite pipe with an elastic modulus of up to 20,000 MPa. Technicians then use specialized cutting tools to trim away the excess liner extending into the manholes, ensuring the new edge sits perfectly flush with the original pipe profile, and cut open the sections blocking intermediate manholes to restore full access.

Compared to traditional thermal curing methods that rely on hot water or steam, UV-CIPP offers overwhelming engineering advantages. Its curing speed is exceptionally fast, it generates zero toxic industrial wastewater during construction, and it reduces the internal friction coefficient of the pipe to around 0.009. This allows engineers to solve structural defects using a significantly thinner wall thickness without sacrificing—and often even improving—the flow capacity of the network, making it a truly green, highly efficient, and reliable solution.