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The electromagnetic interference effects on buried pipelines induced by geomagnetic field are monitored for the first time in China, including geomagnetically induced current (GIC) and pipe-to-soil potential (PSP). It is of great significance for studying the influence of geomagnetic storms on pipeline corrosion and protection in mid-low latitudes. In order to monitor the GIC and PSP simultaneously, a monitoring experimental scheme is proposed. The monitoring data are obtained at Changyi oil transportation station (36 • 30 N, 119 • 30 E) and Xiligu cathodic protection station (36 • 42 N, 119 • 12 E). For comparison, the geoelectric field data are acquired from the geomagnetic observatory near the monitoring stations. Based on the monitoring result and theoretical consideration, the effectiveness of potentiostat and the influence of GIC on the pipeline is evaluated by analyzing the correlation between the monitoring data and the geoelectric field data. The monitoring data show that the pipeline GIC maximum is 7.88 A caused by the magnetic storm commencing suddenly and the PSP positive offset of the two monitoring points exceeds the limit required by relevant standards. The GIC maximum is 3.98 A caused by the magnetic storm commencing gradually, and the PSP offset exceeds the standard when the potentiostat is cut off. The results of our research indicate that the geomagnetic storms can also cause serious corrosion of pipelines in the middle and low latitudes; the larger the distance between insulating flanges is, the stronger the corrosion situation of pipelines will be; the greater the variation rate of geomagnetic disturbance is, the more serious the corrosion of pipelines will be. Because the protection range of the cathodic protection station is limited and the response performance of the potentiostats is varied in different areas, medium or small geomagnetic storms can also cause serious corrosion even if the pipeline is protected by the potentiostat.

In order to research the electromagnetic interference in buried oil and gas pipelines generated by the grounding current of a grounding electrode of Ultra High Voltage Direct Current (UHVDC) system, observation experiments of stray current and pipe-to-soil potential (PSP) in the pipeline were carried out. Monitoring devices were installed at two sites of the Dong-Huang oil pipeline before the commissioning of the Zalute–Qingzhou and Shanghaimiao–Shandong ±800 kV UHVDC projects. Monitoring data on the stray current and PSP of the two monitoring sites were obtained when the two UHVDC projects were operated in monopolar mode on 24 December 2017 and 2 January 2019 and the grounding current reached 6250 A. The amplitude characteristics of the stray current and PSP at different distances from the grounding electrode and the effects of the magnitude of the stray current and PSP on the cathodic protection system are analyzed herein. The results show that the effects of the grounding current on pipeline corrosion are not only closely related to the distance between the grounding electrode and the pipeline but are also related to the running state of the potentiostats of pipelines and the distance between insulation flanges. Optimizing the performance of potentiostats and the distribution of insulation flanges can reduce the effects of UHVDC grounding current on pipeline corrosion.

Compared with the investigation of geomagnetically induced currents (GIC) in power grids, there is less study about the effect of geomagnetic disturbance (GMD) on buried oil and gas pipelines in mid-low latitude areas, which includes GIC and pipe-to-soil potentials (PSP) effects. Therefore, it is of great significance to research the GMD effect in the mid-low latitudes. For this purpose, we performed the observation experiments on GMD influencing the GIC and PSP in China's oil and gas pipelines. The data of GIC and PSP in the pipelines are obtained, which do not pertain to the characteristics of the geomagnetic storms caused by solar activity, as well as the GIC and PSP monitoring data deriving from geomagnetic storm on May 21, 2016. By analyzing the characteristics of waveform, frequency and phase of the geoelectric fields data from Lingyang Geomagnetic Observatory (35 • 32 N, 118 • 52 E) 60 km away in northeast from the pipeline observation site, the study corroborated that GIC and PSP variations are driven by tidal geoelectric fields (TGF) during the geomagnetic quiet days in this paper. The mechanism of GIC generated by tidal geoelectric field is analyzed. Likewise, an analysis of GMD data from the Maling Mountain Geomagnetic Observatory (34 • 42 N, 118 • 27 E), the GIC and the PSP have been done, it is illustrated that the GIC and PSP effects are caused by TGF and geomagnetic storm induced geoelectric field together during a geomagnetic storm. The results demonstrated that, near large areas of water, the effect of tidal geoelectric field on pipeline corrosion is persistent and serious. TGF impacts the calculation accuracy of GIC in pipelines and PSP. Therefore, we should account for the errors caused by TGF when calculating GIC and PSP in pipelines near seashores and a large body of water.

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