Case study - Dallas Water Utilities - Leak Detection


Courtesy of Pure Technologies - a Xylem brand

Service: Sahara Leak Detection
Client: Dallas Water Utilities (DWU)
Department of Public Works
Type of Pipeline: Raw Water Transmission Main
Diameter: 108-inch
Pipe Material: PCCP
Length: 7.3 miles

The City of Dallas Water Utilities (DALW) currently draws its raw water from six sources: the Elm Fork of the Trinity River and Lakes Ray Roberts, Lewisville, Grapevine, Ray Hubbard and Tawakoni. Due to population growth in the Dallas-Ft. Worth Metroplex, DALW is bringing additional water sources on-line. One of these sources is Lake Fork.

When the Lake Fork Raw Water Transmission Main is completed, it will be used to replenish Lake Tawakoni’s water supply. DALW is currently constructing Phase III of this main, which is composed of 108' Prestressed Concrete Cylinder Pressure Pipe (PCCP). Phase I of this line had been previously installed, but had failed a series of hydrostatic pressure tests. The failure of the pipeline to hold pressure above 190 psi suggested the presence of high pressure leak(s).

Operators attempted to locate these leaks using a variety of methods including: visual inspection (internal and external), leaknoise correlators and excavation. None of these methods proved universally effective.

In April 2004, Pure Technologies launched the Sahara leak detection system. Normally used as a condition assessment tool that identifies leaks in in-service pipelines of any material construction type, Sahara was adapted to pinpoint the leaks in uncommissioned pipelines. In August 2004 Wiss, Janney, Elstner Associates, Inc. (WJE), the forensic engineers contracted to assist in remediation of the pipeline, contracted with Pure Technologies to inspect Phase I of the Lake Fork Raw Water Transmission Main using the modified Sahara system.

As this section of the pipeline was not in service, the requisite flow required to perform a typical under pressure insertion did not exist. Therefore, the pipeline was dewatered, a dragline was installed inside the pipe, and the line was repressurized.

A number of modifications were made to insert the system into the pipe, including the installation of a hydraulic winch attached on top of the insertion tube and cable drum. On the receiving end, a hydraulic capstan, spooler, pit rollers, generator and hydraulic power pack were used to pull the Sahara system through the pipe. This 'pull-through' method required the winch and capstan operators to synchronize the deployment and retrieval of the cable.

Data was collected between STA 2280+50 and 1893+75 of this line, spanning a distance of approximately 38,675 feet or 7.3 miles. Two substantial leaks were detected.

Subsequently, WJE and a contractor repaired the indicated leak locations by welding the bell & spigot joints. Phase I of the Lake Fork Raw Water Transmission Main passed its pressure test on October 22, 2004.

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