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Corrosion And Corrosion Protection Of Water Wells

The subject wells are part of a project by San Francisco Public Utilities Commission (SFPUC) to
develop a groundwater supply in the South Westside Basin of San Francisco for use during
drought conditions for Daly City, San Bruno, and the South San Francisco District. The project
includes 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 corrosion
was observed on the pump columns and on the stainless steel pump shaft.

Product Number: 51322-17631-SG
Author: Elmer Cheung,
Publication Date: 2022
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During routine maintenance inspection of some of the water wells owned/operated by San
Francisco Public Utilities Commission, severe corrosion was observed on the pump columns and
on the stainless-steel pump shafts. Due to a phenomenon known as ennoblement of stainless
steel 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 potential
profiles of the wells were conducted. Our results showed that this ennoblement was occurring in
eight out of 13 of the well locations. Ennoblement can cause galvanic corrosion of the pump
column if it is electrically connected to the stainless steel casing. Cathodic protection of the pump
column and the well casing was considered a feasible option to mitigate galvanic corrosion as
well as MIC. Cathodic protection (CP) has subsequently been installed on some of the wells. The
corrosion analysis, design considerations and results of the CP survey are included in this paper.

During routine maintenance inspection of some of the water wells owned/operated by San
Francisco Public Utilities Commission, severe corrosion was observed on the pump columns and
on the stainless-steel pump shafts. Due to a phenomenon known as ennoblement of stainless
steel 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 potential
profiles of the wells were conducted. Our results showed that this ennoblement was occurring in
eight out of 13 of the well locations. Ennoblement can cause galvanic corrosion of the pump
column if it is electrically connected to the stainless steel casing. Cathodic protection of the pump
column and the well casing was considered a feasible option to mitigate galvanic corrosion as
well as MIC. Cathodic protection (CP) has subsequently been installed on some of the wells. The
corrosion analysis, design considerations and results of the CP survey are included in this paper.

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