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Cathodic Protect Area Of Influence Study

Picture for Cathodic Protect Area Of Influence Study
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Product Number: 51321-16877-SG
Author: Jared Pannell; Naga Vijayasankaran; Elens van Roggen Corrpro
Publication Date: 2021
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$20.00
$20.00

As Cathodic Protection (CP) becomes more and more of a common practice to reduce the risk of external corrosion, areas are becoming congested with CP systems. This is seen predominantly in shared right-of-ways and in plant facilities. In a plant facility, every underground asset can be tied together through piping and electrical grounding. If test point locations do not meet criteria it can be challenging to determine which CP system should be adjusted to provide proper cathodic protection, without negatively impacting other adjacent continuous sub-surface assets. Area of influence testing is a way to identify the amount of IR (voltage drop) from a single CP system that most affects the sub-surface asset. This test can only be performed if the soil is considered homogeneous in resistivity, so R (resistance due to soil resistivity) becomes a constant. This is
where an area of influence study can benefit the owner/operator of the assets.
Testing is done by turning all rectifiers Off and allowing the area to depolarize. Then a single rectifier is cycled On and Off, so that the area cannot polarize, and the IR drop can be recorded accurately at every test point in the area. The step is repeated for every rectifier one by one for the areal extent of the study.
Readings taken at every test point location indicate the magnitude of influence of the individual CP system that is interrupted at that geographic location. Using Geographic Information System (GIS) technology, discrete test point readings are converted to a continuous interpolated surface using spatial interpolation algorithms such as Inverse Distance Weighted interpolation and Kriging which can be overlaid on imagery. This visual representation allows engineers to investigate the geographical extent and variance of the CP system influence on underground assets. Cumulative effects of multiple rectifiers in any given region can also be visualized in a similar fashion.
In plant facilities where there are hundreds of CP units, area of influence maps can highlight areas of concern and aids the decision-making process to balance potentials as required to meet criteria.

As Cathodic Protection (CP) becomes more and more of a common practice to reduce the risk of external corrosion, areas are becoming congested with CP systems. This is seen predominantly in shared right-of-ways and in plant facilities. In a plant facility, every underground asset can be tied together through piping and electrical grounding. If test point locations do not meet criteria it can be challenging to determine which CP system should be adjusted to provide proper cathodic protection, without negatively impacting other adjacent continuous sub-surface assets. Area of influence testing is a way to identify the amount of IR (voltage drop) from a single CP system that most affects the sub-surface asset. This test can only be performed if the soil is considered homogeneous in resistivity, so R (resistance due to soil resistivity) becomes a constant. This is
where an area of influence study can benefit the owner/operator of the assets.
Testing is done by turning all rectifiers Off and allowing the area to depolarize. Then a single rectifier is cycled On and Off, so that the area cannot polarize, and the IR drop can be recorded accurately at every test point in the area. The step is repeated for every rectifier one by one for the areal extent of the study.
Readings taken at every test point location indicate the magnitude of influence of the individual CP system that is interrupted at that geographic location. Using Geographic Information System (GIS) technology, discrete test point readings are converted to a continuous interpolated surface using spatial interpolation algorithms such as Inverse Distance Weighted interpolation and Kriging which can be overlaid on imagery. This visual representation allows engineers to investigate the geographical extent and variance of the CP system influence on underground assets. Cumulative effects of multiple rectifiers in any given region can also be visualized in a similar fashion.
In plant facilities where there are hundreds of CP units, area of influence maps can highlight areas of concern and aids the decision-making process to balance potentials as required to meet criteria.

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