NORDIPIPE as pull-in version for trenchless rehabilitation of drinking water pipes

In Shumen the Water Supply and Sewerage Company trusted the CIPP technology and instructed the rehabilitation of four sections in its water network. One section was a pilot project: For the rehabilitation of a 328 m long and 920 mm diameter large drinking water pipe the CIPP liner system NORDIPIPE™ was used as pull-in version for the first time.

Shumen is a city in northeastern Bulgaria whose drinking water supply is managed by the Shumen Water Supply and Sewerage Company. The region is supplied by 94 individual and independent water supply systems, covering 8 towns and 143 villages. There are 1,450 km of local distribution pipelines with 56,159 lateral connections. Water is supplied by pumping along 890 km of pipelines to the 72,209 households. Most of them are made of asbestos-cement and were constructed between 1950 and 1970. Others were made of steel that need to be rehabilitated because of leakages to guarantee an immaculate 24-hour drinking water supply for the next decades.

In autumn 2013 the Shumen Water Supply and Sewerage Company commissioned Stroitelna Mehanizatsia, a construction partner of SEKISUI SPR in Europe, with the rehabilitation of a deteriorated steel pipe with a length of around 3000 m and diameters of 544 - 920 mm. The project included four sections, three of them where rehabilitated by trenchless NORDIPIPE™ CIPP technologies of SEKISUI SPR. For the rehabilitation of a 328-metre long drinking water pipe section with diameter of 920 mm, the CIPP liner system NORDIPIPE™ as pull-in version was deemed to be the ideal technological solution.

Open construction would not have been possible due to the challenging construction site conditions. The 920 mm diameter steel pipe lies in an unstable ground with soft, loamy soil which meant limited accessibility, particularly during persistent rainfall. Therefore only a fast trenchless technology solution was considered for which excavation pits as start and end point and less equipment was sufficient. Further difficulties that the technology had to compete with were the high groundwater level, a strong gradient of 6-8%, a 15° bend and an operating pressure of 16 bar.

NORDIPIPE™ pull-in liner and its advantages

NORDIPIPE™ consists of a main hose and a calibration hose whose material combination has been approved in conjunction with NORDIPOX D resin for potable water under various approval schemes in several countries. The main hose is a fiberglass-reinforced needle-felt liner with a number of glass layers, selected according to internal pressure and diameter. Its durable PE outer coating protects the liner from external influences during installation and operation.

The calibration hose, a needle-felt liner with PE coating, raises the main hose into position within the old pipe and provides a smooth surface with increased hydraulic performance compared to the old host pipe.

Both hoses are impregnated with NORDIPOX D, a two-component epoxy resin, to receive a homogenous material combination as well as a consistent liner structure in the cured state. The pull-in version allows an accurate calculation of the resin material and a consistent resin distribution. Its particular material composition of glass-fiber, needle-felt, resin and PE coating makes it a fully structural liner. It can be thus called a "stand-alone pipe" for the purposes of DIN EN ISO 11298 Class A.

The installation process

Three construction pits provided access to the 328 m long pipe section at a depth of 3 m beneath a field alongside a main road. The installation length of 328 m would normally have been no problem. However, due to the poor bearing capacity of the loamy soil, for weight reasons the liner had to be divided into two lengths of 164 m. The impregnation process took place on a road near the construction site. Long distance was needed for laying out the liner while being impregnated by a mobile impregnation setup and directly wound onto a transport spool. The main and calibration hose were impregnated with the specially designed NORDIPOX D epoxy resin at about 4°C.

After pipe cleaning, the main hose was gradually drawn into one of the two 164 m long pipe sections by means of a 20 tonne capacity winch. Afterwards, the calibration hose was inverted with low pressure and a speed of 3–5 m/min by means of a pressure drum to position the main hose in the old pipe. The hoses were steam cured at a laminate temperature of 70°C and a new stand-alone pipe was created within a period of two hours. The insulating PE outer coating of the main hose allowed a reduced curing time despite the challenging construction site conditions and the high water level.

The rehabilitation process was concluded after sealing the four ends of the two 164 m long liner sections within two weeks. Following a pressure test, the pilot project for the NORDIPIPE™ pull-in liner for a 920 mm diameter pipe was successfully completed. The pipe was put back into 24-hour, seven-day operation to supply the city of Shumen safely with drinking water.

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