EC-3-6 Determine the Effectiveness of the -850 mV On-Potential Criterion for Cathodic Protection

The NACE Standard for cathodic protection (CP) applied to steel pipelines is RP0169-2002, “Control of External Corrosion on Underground or Submerged Metallic Piping Systems.” There has been a long-term, on-going, industry discussion on the application of the primary criterion, i.e. -0.85 V potential criterion. The primary issue of debate is whether the criterion should be applied with the CP current on (on-potential criterion) or as a polarized potential, which is typically measured upon interruption of the CP current (off-potential criterion). The objectives of this project were to:

Evaluate the effectiveness and applicability of the -0.85 V on-potential criterion for the protection of buried pipelines
Establish the conditions for which the -0.85V on-potential criterion is applicable
Establish any complimentary methodologies that should be utilized in conjunction with the -0.85V on-potential criterion to ensure its effectiveness

Research will continue in 2012 to assess the effectiveness of each of the standard CP criteria for a variety of soil and coating combinations. The effort will expand on the previous comparison by repeating the analysis with additional ILI and CP data that are of high quality and accuracy.

Key Results

The general scope of this project was to review the literature and to utilize existing operator data for analysis of proposed methodologies. Multiple ILI data and corresponding CIS potential data were available for two pipelines, each approximately 50 miles in length. To achieve the above objectives, the following was performed:

Data for two pipelines were analyzed and the effectiveness of the on-potential criterion was compared to that for the off-potential criterion for those pipelines.
Review of the literature for conditions where the on-potential criterion is applicable resulted in a discussion of the complexities of applying on-potential and off-potential criteria, including situations for which the on-potential and off-potential may not provide accurate measurements.
The majority of the effort was placed on establishing a methodology to be used in conjunction with the on-potential criterion to verify its effectiveness.