Case study - Hetch Hetchy Water and Power Project (SFPUC)


Courtesy of Pure Technologies - a Xylem brand

Service: Magnetic Flux Leakage (MFL)
Client: San Francisco Public Utilities Commission (SFPUC)
Project Date: 2007 to 2010
Location: California, USA
Type of Pipeline: Water Transmission Main
Diameter: 56-inch to 72-inch
Pipe Material: Steel

San Francisco Public Utilities Commission (SFPUC) operates three parallel cement mortar-lined steel pipelines 47.5 miles long, otherwise known as the San Joaquin Pipelines, which range in size from 56- to 78-inches in diameter. Some have been in service for nearly 80 years, prompting the utility to seek an advanced method of condition assessment to find potential corrosion damage, third party damage and to assess joint integrity to prepare a replacement or repair plan should the need arise.

In 2008, the utility contracted Electromechanical Technologies, Inc. (EMTEK), now a wholly-owned subsidiary of Pure Technologies Ltd., to perform the in-line “smart pigging” inspection of the lines utilizing advanced MFL technology. The project was conducted over a three-year period and included the development of a customized MFL tool, caliper tool, and propulsion equipment to conduct full-scale field inspections.

The customized MFL tool, owned by SFPUC, detected the exact positions of pipe wall loss and hidden pitting in the line not visible through an external assessment. Results were validated by internal inspections of damaged pipe sections, providing a comprehensive understanding of the pipeline location, full circumference and length, establishing locations of weak points for repair and mitigation, and ultimately saving millions of dollars in unnecessary replacement.

Magnetic Flux Leakage

Magnetic flux leakage (MFL) is an electromagnetic method of nondestructive testing that is used to detect corrosion, pitting and wall loss in lined and unlined metallic pipelines.

With MFL technology, permanent magnets are used to temporarily magnetize the steel pipe and the magnetic field changes are recorded and analyzed. The magnetic flux is uniform if there are no flaws in the wall of the pipe. If internal or external flaws are present, such as pitting, corrosion or other forms of damage, the magnetic flux is distorted beyond the wall of the pipe, and this distortion or ‘leakage’ is measured by Hall Effect sensors.

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