The purpose of this NACE International technical report is to provide basic information regarding the mechanisms involved with cathodic protection (CP) shielding for external coatings applied to carbon steel pipelines, and the manner in which the breakdown of coating systems may or may not contribute to CP shielding. It is intended to be a basic reference from which the tendency of a coating system to fail and shield CP may be understood on a conceptual basis. Non-corrosion-related pipeline protection systems, including concrete weight coating, polyethylene encasement, insulation, and mechanical pipeline protection systems, are outside the scope of this report. End users of this report may include pipeline designers, corrosion engineers, integrity management specialists, regulators, CP service providers, coating suppliers, coating service providers, equipment suppliers, and pipeline/facility owners.

Revised in 2020!  Assessment of corrosion in the field is complex because of the variety of applications, process conditions, and fluid phases that exist in industrial plants where corrosion occurs.  A wide range of direct and indirect measurement techniques is available, but each technique has its strengths and weaknesses.  In some applications, certain techniques cannot be used.  Some techniques can be used online, while others are used off-line.  Commonly, more than one technique is used so the weaknesses of one are compensated for by the strengths of another.  In other cases, a combination of different techniques can be synergistic, such as process sampling along with detection of corrosion upset.

The purpose of this technical committee report is to analyze the various techniques with respect to their benefits and limitations across the broad spectrum of industries in which they are used.

This revision incorporates Guided Wave Monitoring (GWM), On-Line Gas Chromatography (GC), and Acoustic Solid Detection (ASD) techniques and updates references to NACE standards.