11182 Cathodic Protection Design Considerations for Buried Nuclear Piping

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Product Number: 51300-11182-SG

ISBN: 11182 2011 CP

Author: Steven F. Daily

Publication Date: 2011

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Degradation of buried metallic piping is a significant issue facing owners and operators of nuclear power plants. The piping at nuclear plants consists of a network of different materials that are interconnected through the station ground to reduce the effects of hazardous voltages associated with lightning and fault currents in the earth. By connecting the metallic piping to the copper grounding grid, corrosion rates can increase on some of the buried piping resulting in loss of metal and reduction in wall thickness. When cathodic protection (CP) is applied at nuclear power plants to control corrosion of the buried piping, much of the current will tend to flow to other metallic structures that are not intended for CP. This will result in a significant increase in the current requirement for cathodic protection. The design of the CP systems is further complicated by the complex configuration of the piping networks, limited space and shielding effects from building foundations and other buried structures. This paper discusses the issues associated with the design and installation of CP systems for buried nuclear piping; taking into account the need for higher current requirements, uniform current distribution, anode bed configuration, test sites and criteria for effective cathodic protection.

Key words: cathodic protection, nuclear power plant, buried nuclear piping, current requirement, current distribution, shielding, dissimilar metal corrosion, coupon test stations, cathodic protection criteria, polarization, over protection.