Case Study 1: The Classical Interference Problem.
Corrosion Engineering International, LLC was called upon in 2016 to provide a series of tests to evaluate abnormal conditions that were reported to one gas distribution operator regarding a crossing with a foreign line. These conditions centered upon a crossing of a pair of high-pressure natural gas pipelines owned by two separate operators taking custody at a shared regulator station from a transmission operator in the region. Corrosion Engineering International, LLC was tasked by Operator A to provide insight as to the cause of the abnormal condition reported to Operator B. Our objective was to validate the findings reported to Operator B and ensure any negative effects attributable to the presence of Operator A’s Cathodic Protection devices were properly mitigated.
Corrosion Engineering International, LLC was able to identify a classic interference condition with negative impacts demonstrated upon Operator B. This was found to be created by the close proximity of the two pipelines and deteriorated coatings present on Operator A’s assets in the vicinity of the crossing. A series of prototype solutions were evaluated for effectiveness in accordance with industry best practices as supported by materials published through NACE International. The most appropriate solutions involved recoating several thousand feet of steel pipeline and possibly implementing a ground bed for the stray current drain. However, a more expedient measure was sought in the meanwhile to limit the continued negative effects known to exist. With a “Time is of the essence” mentality, CEI developed a prototype solution utilizing a temporary bond installed between adjacent test points on each system and a diode to control current direction.
The provided configuration demonstrates a traditional solution with increased cathodic protection current through non-conventional means. The diode, in this case, acted as a half-wave rectifier acting upon a natively present alternating current (AC) induced upon Operator B’s line. The solution arrived upon directed a portion of the AC signal previously discharged through the coating to instead divert to ground through the bond to Operator A. The observed effect was a more electronegative shift in the average potential for Operator B, as well as a reduction in AC discharge observed throughout the line. The impact to Operator A owned assets was shown to be negligible as a result.
It was the recommendation of Corrosion Engineering International, LLC that the bond solution outlined above be pursued through the installation of a set of test leads at the crossing, which was not previously installed. The 010 test point owned by Operator B was located directly over the crossing of the two lines which was intended to host the new leads and bond solution outlined herein. The bond condition will stand as a temporary solution as Operator A has scheduled a partial pipeline replacement of the area in question early in 2017. Following this installation, Operator B’s line requires a full inspection with an interrupt to ensure the resulting status does not elevate protection levels into ranges encouraging hydrogen evolution. Such a condition is cautioned as it could prove detrimental to the Fusion Bonded Epoxy coating type employed.