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Instant-Off Potentials Underestimate Cathodic Protection Levels on Pipelines

Picture for Instant-Off Potentials Underestimate Cathodic Protection Levels on Pipelines
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Cathodic protection (CP) is used to prevent external corrosion on underground pipelines. The effectiveness of CP is commonly evaluated by measuring the DC potential (voltage) of the pipeline with respect to a reference electrode located on the surface of the earth above the pipeline. Criteria used to interpret pipeline potential measurements are given by Section 6 of NACE SP-0169-2013 “Control of External Corrosion on Underground or Submerged Metallic Piping Systems.

Product Number: 51323-19083-SG
Author: Peter Haas
Publication Date: 2023
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$20.00
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The criteria and methods given by AMPP/NACE SP0169 and TM0497 rely heavily on the use of Instant-Off potential measurements to assess cathodic protection levels on pipelines. Despite wide acceptance of these standards, there is little or no data to demonstrate that an Instant-Off potential accurately represents the polarized potential that exists across the metal/electrolyte interface of a pipeline under normal operating conditions. This paper summarizes laboratory testing that was conducted to demonstrate the accuracy of Instant-Off potentials. Test results show that Instant-Off potentials significantly underestimate pipeline polarized potentials. Examples are given where the reliance on Instant-Off potentials can lead to pipeline damage.

The criteria and methods given by AMPP/NACE SP0169 and TM0497 rely heavily on the use of Instant-Off potential measurements to assess cathodic protection levels on pipelines. Despite wide acceptance of these standards, there is little or no data to demonstrate that an Instant-Off potential accurately represents the polarized potential that exists across the metal/electrolyte interface of a pipeline under normal operating conditions. This paper summarizes laboratory testing that was conducted to demonstrate the accuracy of Instant-Off potentials. Test results show that Instant-Off potentials significantly underestimate pipeline polarized potentials. Examples are given where the reliance on Instant-Off potentials can lead to pipeline damage.

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