I came across CP guidelines which mention that -0.85V pipe to soil potential is required for effective ICCP protection. Just curious to know if this threshold only true to a pipe which is mostly coated and have occasional small defects only i.e. pipe which has known max defect sizes?
What happens suppose if I do not have a coating at all? Will -0.85V be enough now?
My understanding is that it won't be sufficient, as now we will need more current to protect.
In addition, why does the pipe to soil potential change in close interval inspetions when the inspector is on the top of defect?
Its an open ended discussion, feel free to add your answers.
A bare pipe would indeed require a different approach to CP, potentially needing a higher driving voltage or more anodes to maintain adequate protection. The -0.85V threshold is usually referenced in the context of coated pipelines with minor defects, where it serves as a general guideline for effective CP.
for more answer to your question you can read my scientific article, I have carried out experiments on carbon steel samples with optimal cathodic protection and on other sample with overprotection.
Article Application of Electrochemical Impedance Spectroscopy as An ...
The -0.85V criterion is mainly applied to pipelines with a good quality coating. An effective, intact coating covers most of the surface, which means only a small percentage of the steel needs direct cathodic protection. As a result, the amount of electrical current required to achieve the desired protective potential is significantly lower compared to uncoated or poorly coated pipelines. This synergy between a high-performance coating and cathodic protection not only improves corrosion control but also makes the cathodic protection system more efficient and cost-effective.
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