Should I consider Telluric Currents?

A rectifier that reads normal doesn't prove the pipe is protected during a geomagnetic disturbance. Telluric currents, also called geomagnetically induced currents (GIC), flow in the ground and in long buried conductors when the Earth's magnetic field changes. They move the pipe-to-soil potential from the outside. If your line is long, runs through high resistivity soil, or sits at higher latitudes, record potential continuously at your most exposed test stations instead of relying on spot checks.

This isn't a theoretical worry reserved for polar routes. A 2025 study of two Argentine gas pipelines found out-of-range protection readings on quiet days as well as storm days, and that matters for how often you should be looking. The sections below cover what telluric current does to a pipeline, what the research says about corrosion risk, and why the survey schedule most operators follow can miss it.

Telluric currents act on the pipe, not on the power supply

Variations in the Earth's magnetic field generate an electric field at the Earth's surface. Charge flows through the ground and into conductive networks on it, including pipelines, power lines and communication lines. On a pipeline the effect shows up as fluctuations in pipe-to-soil potential (PSP) and induced currents that vary over time. The rectifier is still putting out the same amps and volts. The potential at the steel surface is not the same.

The best-known case is the March 1989 storm that took down Hydro-Quebec's grid. According to Hydro-Quebec, the Earth's magnetic field was fluctuating violently at 2:44 a.m. on March 13, the grid's protection system triggered, and a blackout occurred in less than a minute. The province was without power for more than nine hours. Hydro-Quebec says its grid stays more vulnerable than most because Quebec sits on a large rock shield that keeps current from flowing through the earth, so the electricity finds a less resistant path along the power lines. The grid's very long transmission lines add to the exposure.

That was a power grid event, but the same reasoning applies to a long buried pipe. A long conductor in resistive ground is an attractive path for induced current. The Argentine study lists what governs the size of the effect on a pipeline: its proximity to the magnetic poles, its length, orientation and changes of direction, coating resistance, electrical continuity along the route, soil resistivity, abrupt changes in soil conductivity, and proximity to a marine coast.

The Argentine authors add some history. Telluric effects were long treated as a minor inconvenience in the context of meeting pipeline codes. They say the disturbances have become more evident as pipelines are built at higher latitudes, in higher resistivity soils, and with improved coating materials, and especially during periods of heightened solar activity. Effects have also been observed at lower latitudes, including near the equator. A new line with modern coating through resistive ground fits the profile they describe.

Research shows the corrosion risk is real, and it depends on coating and CP

A 2023 paper in the Journal of Atmospheric and Solar-Terrestrial Physics (Trichtchenko and co-authors) estimated telluric-associated corrosion rates from measured and modelled PSP variations. It used PSP recorded on Australian and European pipelines during two periods of strong geomagnetic activity in 2003 and 2004, plus identical hypothetical pipelines at different latitudes for all of 2004. Without cathodic protection, the estimated corrosion rates exceeded the benchmark values recommended by national and international standards. With cathodic protection, the authors say the acceptable values can still be exceeded in exceptional cases.

Two other results from the abstract are interesting. First, corrosion rates depended on more than geomagnetic activity. They also depended on the pipeline coating, the performance of the CP system and environmental conditions, and for the recorded data the rate for a near-equatorial pipeline in Australia could be higher than for mid-latitude pipelines in Europe. Second, for the identical hypothetical pipelines, corrosion rates rose about five times going from subauroral to auroral latitudes. So latitude matters a great deal, but it is not the only variable, and a southern route is not automatically safe.

Practically, a well coated pipe with healthy CP has more margin, and a pipe with holidays or marginal protection to begin with has less. That is one more reason to fix the ordinary problems first.

Quiet days showed problems too, and spot checks catch only one moment

The Argentine study (Larocca and Arecco, AIMS Geosciences, 2025) examined 2,053 PSP records from two gas pipelines between 2013 and 2018: NEUBA II at mid latitude and San Martin Fueguino at high latitude. It found 172 out-of-range protection records. Of those, 134 occurred during mild or moderate geomagnetic storms and 38 occurred on days without storms, based on the Dst index. The higher latitude pipeline had more out-of-range events, and the authors found that low conductivity soils in Tierra del Fuego appeared to amplify the voltage disturbances.

The authors also report that the rapid magnetic field changes they detected lined up in time with the out-of-range readings on days that the standard global indices called quiet. They conclude that long-term monitoring of PSP is important for building a reliable record of how often and how far potentials swing. The study measured with a copper/copper sulfate reference electrode against a 0.85 V to 1.35 V acceptable range, which is its own framework, so read the results as evidence that quiet days can matter, not as a threshold for your line.

Federal rules for gas pipelines require each rectifier to be inspected six times a year at intervals of no more than 2.5 months, and the CP survey to be done at least once a year at intervals of no more than 15 months (49 CFR 192.465). That is a sound baseline. It also means a disturbance can come and go between any two readings and leave nothing in your records.

Put a recorder on your most exposed test station and let the data decide

A continuous potential recorder at the most exposed test stations closes that gap. A transient shift will show up in the data, and you can compare it against space weather reports. The Argentine authors note that geomagnetic effects can be mitigated by identifying vulnerable segments and installing systems that safely discharge induced currents at specific locations. Designing that kind of mitigation is a job for your CP engineer, and it starts with knowing which segments swing.

Start with one location, not the whole line. Pick the station where your engineer expects the largest effect, based on the factors listed above: long uninterrupted runs, high resistivity soil, abrupt changes in soil conductivity, and changes in pipe direction. Record for a full year. If the data shows swings, you will have numbers to decide whether more recorders or drainage are worth the money. If it shows none, you have spent little to find out. More on pipeline applications is at amcarbon.com/infrastructure.