Cathodic Protection for Transmission Pipelines
Overview
The San Francisco Public Utilities Commission (SFPUC) and its contractor (EXARO) are installing new cathodic protection systems for the corrosion protection of several large diameter water transmission pipelines (Bay Division Pipelines and Palo Alto Pipeline), through SFPUC’s Right of Way at various locations in Fremont, Newark, Redwood City, Mountain View, Los Altos and Stanford. The major components of the cathodic protection installation will include a surface mounted rectifier cabinet, underground deep anode well, excavation to the pipeline and connection to the utility power. The project also includes the installation of test stations along the existing pipe appurtenances for future surveying of the pipeline.
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Project Background
Cathodic Protection for Transmission Lines
The SFPUC owns and operates hundreds of miles of steel pipelines that bring drinking water to 2.7 million customers in four Bay Area counties. To protect our transmission pipelines from corrosion, we utilize a common method called cathodic protection. Corrosion can weaken the steel pipelines, resulting in leakage and eventual pipeline failure.
What is cathodic protection?
Metal such as steel that has been extracted from its primary ore has a natural tendency to revert to its original state – via a process called corrosion. Soils create an environment that is conducive to the corrosion process and as a result steel pipelines will corrode when placed into soils unless steps are taken to mitigate this destructive process. Cathodic protection prevents corrosion from happening to a pipeline by applying a protective current from an external DC power source, also known as a rectifier, through a metal rod called an “anode” drilled deep underground. The protective current then passes from the anode to the pipeline. The resulting direct electrical current flow then causes the pipeline to become a “cathode”, thus mitigating the corrosion process. A cathodic protection system is a cost-effective way to protect buried steel pipelines from the corrosive water and soils around it.
Where will the project take place?
There are eleven individual sites in Fremont, Newark, Redwood City, Mountain View, Los Altos and Stanford where we will install new cathodic protection equipment. SFPUC engineers selected these in order to protect the pipelines at key points along their right of way.
East Bay Locations: Sites 1-5
Peninsula Locations: Sites 6-11
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What to Expect During Construction
What to expect at each cathodic protection site:
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Crews will use a drill rig to install the anode column 300 feet underground.
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Crews will use a backhoe with a bucket to dig a trench approximately three feet wide by six feet long.
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They will next dig a small trench to connect a rectifier cabinet to the nearest power source and then backfill the trench.
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The rectifier cabinet installed at each location will measure 40 inches wide 24 inches deep by 50 inches tall.
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Work Hours: 8 a.m. to 5 p.m., weekdays only. No weekend work is anticipated.
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Crews will avoid blocking streets or trails as much as possible.
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Construction will last approximately 3 weeks from start to finish.
When construction is completed:
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Only the rectifier cabinet will be visible.
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When operating, the cathodic protection system does not affect adjacent buildings, fences or other structures and does not pose any danger to people, plants or animals.
Rectifier cabinet
What to expect at each test station site:
Test stations will be installed within existing infrastructure in the pipeline right of way.
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Crews will prepare the site by clearing the structure of any obstructions.
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Installation will typically take 2-4 hours per site and will not involve adding above-ground infrastructure.
Typical test station location
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