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Recent Results
Development of a Variable Cathodic Protection Criteria
The CP criteria for buried piping systems are not consistent in different global CP standards. For instance, the standard of the International Standard Organization (ISO) and the European standard (EN) offer more specific CP criteria with respect to environmental conditions such as soil resistivity, aeration, presence of bacteria, pipe temperature and overprotection. However, they do not have the -850 mV on-potential criterion contained in the NACE Standard SP 0169-2007. The Australian National Standard (SAA) recommends the use of coupons or an electrical resistance (ER) probe in conjunction with the -850 mV off-potential or the 100 mV polarization criterion, which was not included in the above standards.
Based on operators’ experience, the current CP criteria in the NACE Standard SP 169-2007 may not always assure that pipes are effectively protected and some pipe/soil environments may require alternative criteria such as those in other global standards. This effort aimed to collect and analyze available global CP criteria and data to better understand why and when the NACE Standard SP0169 criteria are effective.
Key Results
By compiling and reviewing global CP criteria along with field and laboratory data, the report provides recommendations on evaluation of the -850 mV on-potential criterion, the -850 mV off-potential criterion, the potential criteria in high resistivity soils, the 100 mV polarization criterion, and CP criteria with elevated temperatures and bacteria. It also discusses how the joint use of monitoring and inspection devices with the effective use of CP criteria may affect how appreciate the significance of CP criteria in pipeline external corrosion control and the overall pipeline integrity management.
Significant research is still needed to understand the effectiveness of CP criteria from a fundamental perspective. Mathematical modeling of a pipeline CP system with consideration of both the temporal and spatial variations of the pipe potential and corrosion rate and solution chemistry near the pipe surface should be performed. This would provide a broad understanding of the effectiveness of CP criteria from both macro and micro scales.