No-Dig Winners

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Stroitelna Mehaniztsia

Category: Project Rehabilitation

Country: Bulgaria

Large Diameter Pipe Rehabilitation using CIPPin Zhezkazgan


One of two parallel pipelines for discharge cooling water from the turbines of the electric generators were rehabbed using the cured in place pipeline (CIPP) method. The steel pipelines diameters range from 1220 mm to 2220 mm.The different pipe diameters are connected with short taper sections. The pipelines operate both as a gravity sewer (half full) and a pressure line depending on the operation of the turbines. The pipes are more than 60 years old and lie partially under plant surface structures. The owner could not replace the leaky pipe using conventional dig-out and replace techniques for the sections located along the building and side connections. Rehabilitation of the pipe using CIPP was the preferred solution but presented major challenges: (1) the design and production of the liners had to be relatively lightweight and yet capable of standing the buckling loads during gravity operations and 2 bar working pressure loads during pressure operations; (2) the logistical complexities of transporting supplies and equipment from Western European countries to Bulgaria through and to Central Asian countries for installation; (3) the site’s physical restrictions, safety hazards and harsh weather; and (4) the weight and size of the liner material to be installed. The first liner proved particularly challenging to install. The inversion had to be done so that the liner taper fit exactly in the taper of the host pipe and conformed to the two elbows in the middle and end of the inversion. In addition, there was not enough space to open an exit shaft, so the inversion had to stop just short of an existing hatch. The liner was hot-water cured taking 72 hours of almost continuous efforts. After this inversion was completed, another liner was installed from the other end of the pipeline until it overlapped with the end of the first liner, the joint was sealed manually with glass matt and resin. The second liner required 48 hours to cure because of the huge volume of water required and a total of 96 hour to install.

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