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The subject wells are part of a project by San Francisco Public Utilities Commission (SFPUC) todevelop a groundwater supply in the South Westside Basin of San Francisco for use duringdrought conditions for Daly City, San Bruno, and the South San Francisco District. The projectincludes construction of 13 groundwater wells with a total capacity of 7.2 million gallons per day(mgd). During routine maintenance inspection of two of the wells in Daly City, severe corrosionwas observed on the pump columns and on the stainless steel pump shaft.
During routine maintenance inspection of some of the water wells owned/operated by SanFrancisco Public Utilities Commission, severe corrosion was observed on the pump columns andon the stainless-steel pump shafts. Due to a phenomenon known as ennoblement of stainlesssteel the potential of stainless steel in water can become positive, in the range of +300 mV (CSE)which can result in serious galvanic corrosion of the pump column. Casing-to-water potentialprofiles of the wells were conducted. Our results showed that this ennoblement was occurring ineight out of 13 of the well locations. Ennoblement can cause galvanic corrosion of the pumpcolumn if it is electrically connected to the stainless steel casing. Cathodic protection of the pumpcolumn and the well casing was considered a feasible option to mitigate galvanic corrosion aswell as MIC. Cathodic protection (CP) has subsequently been installed on some of the wells. Thecorrosion analysis, design considerations and results of the CP survey are included in this paper.
There are several ways to validate the performance of a cathodic protection (CP) system for buried pipelines. Over the years, pipeline networks and their corrosion challenges have become increasingly complicated, not least due to the many sources of both AC and DC interference that affects CP operation. Also, the various measurement techniques that can be applied to test CP effectiveness has increased over the years. Finally, the sheer number of buried pipeline miles has been constantly increasing.
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In 2002 NACE International published a cost of corrosion study backed by the U. S. Federal Highway and Safety Administration estimating the annual cost of corrosion in the U. S. to be $276 billion. In the more detailed breakdown of these costs by industry/market segment the cost associated with the water and wastewater utilities segment in the “Utilities” category was estimated at $36 billion. The water and wastewater utilities segment represented the single largest cost segment in the study. The $36 billion estimate for this single segment of the Utilities category represented more cost than any of the other four categories: Transportation, Infrastructure, Government, and Manufacturing & Production.
Several well casings were selected as candidates for down hole inspection logs to determine if cathodic protection could be a solution to the external corrosion problem. "Test" cathodic protection systems were installed. Based on logging results and economic evaluation, implementation of a cathodic protection pilot project commenced.