Computer modelling is a common approach used to understand personnel safety and pipeline integrity risks impacting pipelines near high voltage AC power lines. A modelling approach often relies on the timely availability of accurate power line data from electric utilities to incorporate into simulation software. Long lead times for power line information requests, however, can often leave operators with assets in a prolonged high-risk state. This paper presents an AC mitigation case study wherein generic; shovel-ready AC mitigation grounding and corrosion monitoring systems were applied across a large pipeline system in Alberta, Canada. These systems were installed wherever AC pipe-to-soil potentials were encountered above a set threshold. A computer model was later developed to look for possible performance gaps and identify areas for mitigation supplementation. The case study demonstrates that a correctly deployed direct-to-install approach can be highly effective at reducing steady-state interference risks but can leave gaps due to the limitations of what can be measured in a field setting. Computer modelling is shown to be an effective means of bridging these gaps to ensure that all personnel safety and pipeline integrity risks are mitigated.
A large diameter, 1067 mm (42 in) and 914 mm (36 in), high pressure gas mainline, and four (4) smaller diameter lateral pipelines, between 406 mm (16 in) and 610 mm (24 in), were constructed in Alberta, Canada, between 1999 and 2000. At the time of construction, the pipelines were built in proximity to several high voltage alternating current (HVAC) transmission lines. In subsequent years, additional transmission lines were built near the pipeline system, bringing the total number of lines with significant proximity to eight (8). A diagram illustrating the alignment of the pipeline system and nearby transmission lines is shown in Figure 1.
As a result of continued additions and upgrades to the nearby transmission line system, the pipeline system was subject to an ever-changing profile of AC interference peaks and valleys. A traditional AC mitigation approach would begin with a detailed engineering study. The study would rely heavily on the electric utility to provide accurate transmission line physical and electrical parameters in a timely manner. This data gathering process can often take many months and would leave the subject pipelines in an indefinite high-risk state. To expedite an AC interference solution, immediate and direct measures were taken to reduce AC interference levels whenever specific criteria were exceeded. Mitigation systems were installed when field measurements confirmed that one or more of the following criteria were exceeded:
