MATCOR’s Ted Huck presented a virtual keynote at CORCON 2021. Over 300 corrosion industry professionals connected at the NACE Gateway India Section’s 2021 Virtual CorCon Conference. The primary discussion was around the impact of AC Corrosion Mitigation criteria on the design and operation of cathodic protection systems.
Historically, DC cathodic protection systems are designed to meet specific polarization requirements. The CP system delivers sufficient current to assure that the entire length of the pipeline meets the polarization levels required. Little consideration is given to DC current density, other than to provide a guideline for sizing the CP system.
The actual operation of the CP system is dictated by the amount of current required to polarize the pipeline.
In practice, this often results in operating the CP system by pushing enough current to properly polarize the pipeline to the farthest distance possible from the CP station. Testing is entirely based on these polarization levels. This includes confirmation testing via close interval potential surveys (CIS).
However, the latest NACE specifications on AC Interference and Mitigation (SP 21424-2018) incorporates DC current density as a key parameter. Historically this was not a consideration for the operation of a pipeline’s cathodic protection system.
The AC Mitigation criteria has a stringent requirement if the system’s DC current density is not monitored and controlled. However, if the pipeline’s CP system current density is both monitored and controlled, the requirement is less stringent.
This linking of AC Mitigation Criteria to a DC current density value (that historically has never held any significance) represents a significant change in how CP systems must be designed, monitored, and controlled.
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