Shorted Cased Crossing Disrupts the Cathodic Protection of Three Operators
While conducting a scheduled compliance test point survey, data collected highlighted some significant changes from the years prior. With further data review, JRGO identified a large LPA (low potential area) with the epicenter being shorted cased crossing that was not there during the previous monitoring. This change in the cathodic protection circuit (CP) had severely diminished potentials for miles up and down stream totaling 8 affected miles of pipeline. This did not only affect the asset of the operator, but also the two other foreign operators in the area. The foreign operators that where affected by this had been in the middle of devising plans to add additional impressed current anode beds in the area to correct the low ‘’off’’ reads. Once the problem was pointed out, additional work was put on hold until JRGO finished their investigation.
Over the life of the system (installed in the mid 70’s) and some recent heavy construction that had taken place in the roadway, the casing had become shorted to the carrier pipe. A simple short can cause major issues for an operator and in this case foreign operators as well. This casing was located under a stretch of state highway that served as a main backbone for local traffic and rerouting would be unfavorable. Overhead and underground utilities in the area would prove to make excavating a challenge as well. Planning began to address the problem and the challenges involved.
Please refer to the following graphical presentation of the pipeline potentials created by the shorted casing, and how the system reacted once the short was repaired.
1. Green Lines – ON and Instant Off Before Remediation
2. Blue Lines – ON and Instant Off After Remediation.
A direct metallic short is classified by PHMSA guidelines as an immediate condition. JRGO put together a plan and budget to excavate each end of the casing. With the plan and budget approved by the operator, JRGO’s Integrity Services Division put the plan into motion. The south end of the casing had two foreign line crossings that needed additional observation from the foreign operators in order to excavate. The north end of the casing was excavated first. Shoring was used to secure and allow for safe entry at a depth of 12 feet. Upon removing the casing boot, the casing and closest spacer were inspected. It was documented that the two halves of the spacer at the end of the casing were not fastened together, which allowed it to shift inside the casing. The spacer could not simply be removed due to the downforce of the carrier pipe. The decision was made to cut the casing back far enough to remove the spacer. Before the removal, pipe-to-soil reading were taken from the casing, carrier pipe, and foreign lines. After removing a 14’’ section of the casing and one spacer, post readings were taken.
Upon removing the casing spacer, it was inspected for any sign of a metallic short. It was noted that the rubber lining of the spacer had been damaged which exposed the metal banding that made up the spacer. In the location that the metal banding was exposed, the extruded coating had a flaw as well. Although small, you could clearly see the area where current was being discharged. By removing the damaged spacer, the short was cleared and compliant CP levels stabilized. Although not all shorts can be cleared by investigating the ends of casing, in certain scenarios it pays off to investigate as option #1. Organizing additional testing and communication between operators will, in most cases, result in cost savings for everyone involved.