With the increasing energy demand pipeline corridors experience more often interference from multiple high voltage powerline systems. The complexity of these co-locations calls for more advanced approaches based on computer aided models that take into account all the details of the pipeline, CP, powerline and soil. Using simple analytical equations often leads to very conservative AC mitigation designs with high material and installation costs.
A computational model approach is proposed whereby dedicated field data is used to build models that become a replica of the real-world situation which ultimately results in cost-effective and safe AC mitigation designs. Digital twin models compute the AC and DC current density required for the assessment of the AC corrosion likelihood according to the NACE SP 21424 or ISO 18086 standard. A field case study will be discussed demonstrating the benefits of the digital twin approach.
According NACE21414 and ISO18086 standards AC corrosion risks on pipelines requires knowledge on the AC and CP current density on a coating defect or coupon. The induced voltage is mainly a result of the pipeline coating properties, connections to grounded structures (anode beds, other pipelines, AC grounding systems, etc.) and the powerline characteristics (AC load, phase arrangement, tower configuration, etc.). A proper mitigation design engineering study should include all these variables. Just installing AC grounding at highest measured AC voltage on the pipe often results in trial and errors and cost-inefficient designs. Small surface areas of e.g. 1 cm2 exhibit a higher risk than larger ones but these small coating holidays are difficult to detect during surveys. Variations in power line load may be significant during a day period or yearly season. These variations are captured by remote monitoring devices, but their installation should be carefully chosen to capture the worst-case events.
A 27 miles long 8" pipeline is in collocation with seven high-voltage AC powerlines. A pipeline stretch of 2 miles is paralleling a 345 kV powerline in the west and a 1-mile stretch is paralleling with a 69kV power line in the east. The length of parallelisms is relatively short. The remaining powerlines are mainly crossing the pipeline at different locations.