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A Right Way To Calculate Pipe CP Potential Attenuation

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Shown on Figure 1 is a typical impressed current CP diagram. When the rectifier is first turned on, i.e. time t=0, there is no polarization yet. At that moment, the applied DC voltage is fully consumed by IR drops at anode (IRa0) and cathode (IRc0), plus original potential difference between anode and pipe (Eoca- Eocc). When t=0, the current is at the greatest value. Over time when polarization kicks in, due to adding polarization resistance, the current is gradually reduced.

Product Number: 51322-17599-SG
Author: John Yang, Jiulong Liang
Publication Date: 2022
Industries: Corrosion Monitoring and Control , Coatings
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Pipeline polarized potential attenuation is supposed to be IR-free pipe-to-soil potential distribution along a pipeline. Currently, most of the potential attenuation calculations in published documents or in CP training manuals are either a pure IR drop attenuation or attenuation that contains IR drop. Polarization and IR drop are caused by applying current to the pipe surfaces. When current density distribution along a pipeline is determined, the attenuation of cathodic polarization (IR free potential
shift) can be established. Current density is restrained by both pipe to soil resistance and pipe polarization resistance. This article uses current density attenuation and polarization resistance to determine the polarization (IR-free potential shift) attenuation.

Pipeline polarized potential attenuation is supposed to be IR-free pipe-to-soil potential distribution along a pipeline. Currently, most of the potential attenuation calculations in published documents or in CP training manuals are either a pure IR drop attenuation or attenuation that contains IR drop. Polarization and IR drop are caused by applying current to the pipe surfaces. When current density distribution along a pipeline is determined, the attenuation of cathodic polarization (IR free potential
shift) can be established. Current density is restrained by both pipe to soil resistance and pipe polarization resistance. This article uses current density attenuation and polarization resistance to determine the polarization (IR-free potential shift) attenuation.

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