Continuous Verification Monitoring at AC Mitigation Stations

Keywords:

Induced AC, AC Corrosion, AC Current Density, AC Mitigation, Fusion Bond Coating, Remote Monitoring, Cathodic Protection

 Abstract:

The introduction of high performance, fusion bond coatings provide pipeline structures with unprecedented isolative characteristics.  These high performance coatings are of great benefit to the industry as they maximize the efficiency and performance of cathodic protection systems.  They also hold induced AC on the pipeline and the subsequent discharge to ground tends to occur at small holidays in the coating, at higher than expected current discharge levels.  With increased points of AC induction from the expanding electric power infrastructure and other sources, pipelines can experience sustained AC corrosion current densities in excess of 100A/m², a level at which corrosion is known to occur.  On the pipeline under study, Enbridge has a goal of mitigation to a constant level of <20 A/m².  Induced AC by its nature is transient and volatile, and even mitigated values can fluctuate considerably.  Methods of tracking these levels through periodic measurements or data logging at test-point sites provide an incomplete picture and data retrieved after the fact rather than real time.  For this pipeline, "AC Mitigation/Monitor Stations" were designed combining solid-state decoupling mitigation devices and AC discharge current monitoring devices to reduce the AC to acceptable levels and capture the fluctuations in real-time. This allows for immediate notification of out-of-range levels, as well as continual logging of the readings in the internal memory for upload retrieval over the web at user defined intervals.  The conclusion is this method of benchmarking and verification of AC mitigation performance provides superior information through the transmission of actionable alarm data and increased frequency of logged data retrieval.  This method is designed to provide permanent, ongoing verification of mitigation system effectiveness as the influences contributing to AC induction continually change.