Stray Current and Segmented Ductile Iron Pipelines

Abstract Stray direct current, commonly called stray current, is an electrolytic process that is typically associated with buried metallic structures. Often, this mechanism of electrochemical action is generated from various sources, such as cathodic protection systems, direct current power trains or street cars, arc-welding equipment, direct current transmission systems, and electrical grounding systems. For underground pipelines, the most frequent source is from an impressed current cathodic protection system. Typically, corrosion engineers deal with stray current corrosion on welded-steel, electrically continuous pipelines. This paper will focus on ductile iron pipelines, which typically are segmented pipelines with electrically discontinuous joints. The idea that segmented pipelines are less inclined to be affected by stray current corrosion has long been known. Often, most of the buried metallic structure installations are quite commonly considered remote from stray current sources; therefore, the dielectric property of polyethylene encasement conforming to ANSI/AWWA C105/A21.5 is adequate to shield against this type of electrolytic activity. However, when the segmented ductile iron pipe is in relatively close proximity to the anode bed of an impressed current cathodic protection system a more far-reaching measure for mitigation might be necessary.