Japanese and Foreign Criteria for Cathodic Protection of Steel Pipelines and Structures

摘要

As a result of satisfactory performance, cathodic protection gained worldwide recognition as the most effective and economical method to protect coated steel pipelines, structures, canal gates, condensers, and others against corrosion together with stress corrosion cracking. The effectiveness of cathodic protection in practice can be established in more than one way, and several criteria have been used in the past to prove whether protection is complete. This paper reviews the criteria for cathodic protection of coated steel pipelines and structures in the environments, including seawater, soil, and concrete. As for criteria for cathodic protection of steels in seawater and soil, the action of bacteria is considered. A criterion that indicates degree of protection, including overprotection, is obtained through measuring the potential of the protected structure. The potential of a cathodically protected structure is obtained ideally by placing the reference electrode as close as possible to the structure to avoid an IR drop through coatings and the electrolyte such as soil and concrete. In the case of potential measurement of pipeline, the instant-off method, with steel probes simulating coating defects, is recommended as an effective method to avoid an IR drop. A particular emphasis is placed on the necessity for establishment of the criterion to assess the effect of induced AC voltage on a cathodic protection system for buried pipeline.