Modeling Pipe to Soil Potentials From Geomagnetic Storms in Gas Pipelines in New Zealand

Gas pipelines can experience elevated pipe to soil potentials (PSPs) during geomagnetic disturbances due to the induced geoelectric field. Gas pipeline operators use cathodic protection to keep PSPs between -0.85 and -1.2 V to prevent corrosion of the steel pipes and disbondment of the protective coating from the pipes. We have developed a model of the gas pipelines in the North Island of New Zealand to identify whether a hazard exists to these pipelines and how big this hazard is. We used a transmission line representation to model the pipelines and a nodal admittance matrix method to calculate the PSPs at nodes up to 5 km apart along the pipelines. We used this model to calculate PSPs resulting from an idealized 100 mVkm-1 electric field, initially to the north and east. The calculated PSPs are highest are at the ends of the pipelines in the direction of the applied electric field vector. The calculated PSP follows a characteristic curve along the length of the pipelines that matches theory, with deviations due to branchlines and changes in pipeline direction. The modeling shows that the PSP magnitudes are sensitive to the branchline coating conductance with higher coating conductances decreasing the PSPs at most locations. Enhanced PSPs produce the highest risk of disbondment and corrosion occurring, and hence this modeling provides insights into the network locations most at risk. Steel pipelines are used to transport natural gas across long distances. These pipes are covered in an insulating coating to protect them from corrosion. During a geomagnetic storm, there are rapid changes in Earth's magnetic and electric fields. These changes cause electrical currents to flow through breaks in the insulating coating and on and off the pipelines, resulting in a voltage between Earth and the pipe. Over time the currents can cause corrosion and the voltages can lead to the coating separating from the pipe, resulting in further corrosion. We have developed a model of New Zealand's gas pipeline network and used it to calculate the voltages in the pipelines in New Zealand's North Island during a simplified geomagnetic storm. This model will help us understand where the greatest risk of corrosion is and how widespread the risk is. The highest risk is at the ends of the pipeline, aligned with the direction of the imposed electric field. Branchlines and changes in direction of the pipeline change the local voltages. We modeled New Zealand's gas pipeline network to calculate pipe to soil potentials due to uniform electric fields of 100 mV/kmPotentials are greatest at ends of pipelines, following theoretical curves with variations due to branches and changes in directionThe lower coating conductance of the branchlines leads to higher potentials on both that line and connected lines