Case Study: Identifying an Intermittently Shorted Casing During Indirect Inspections

Abstract Pipeline casings have been used to protect pipelines from additional stress when pipelines are placed under roads, railroads, and other reasons for decades. The interactions between pipelines and casings have thoroughly been discussed in the pipeline integrity industry. The risks associated with metallic shorts and electrolytic couples are well documented and it is commonly understood that a metallically shorted pipeline with a metallic casing will depress cathodic protection (CP) potentials, but what happens when this local depression is not seen on subsequent cathodic protection surveys? This paper will discuss a case study where a transmission pipeline, that parallels and is electrically continuous with another transmission pipeline, was surveyed via an interrupted close interval survey (CIS) and followed by a depolarized close interval survey as well as additional interrupted close interval surveys that had varying results at a cased crossing. This case study explains the test methods and documents reviewed that went into determining the cause of this occurrence.