Stray currents for instance caused by DC traction systems can have a harmful effect on the Cathodic Protection system of, for example, a gas pipeline. These stray currents are formed whenever the traction current in a railway system does not flow back to the substation through the track but via the soil. If this is the case, currents use the gas pipe as a conductor. After all, electrical current always seeks the path of least resistance. The stray currents may then disrupt the pipeline potential to such a degree that the CP-system is no longer able to prevent corrosion.
Also, stray currents may influence the soil at railroad crossings. It is remarkable that in winter when the roads are salted, all of a sudden the electrical connection between the track and the soil is very good. When this happens, the soil is affected by the tensions of the track. If there is a pipeline with a Cathodic Protection (CP) system in the vicinity of the railroad crossing, the pipeline potential relative to the soil becomes so small that in specific spots the pipeline is no longer sufficiently protected. As a result, the possibility of corrosion increases. That is why it is very important to conduct influence measurements during different seasons of the year.
Periodic and 24-hour measurement
The owner of the DC-traction system is responsible for the degree of soil influence. If during a periodic measurement it is noted that the pipeline fluctuation is higher than the soil fluctuation (or the other way round), a 24-hour reading must be conducted conform NEN50162. Based on the requirements formulated in this norm, the extent to which this influence is damaging can then be determined.
Korf KB (Cathodic Protection) performs these measurements and can provide an advisory report based on their findings. This report is then sent to the owner of the DC-traction system, who has to take the appropriate action to resolve the issue.
After solving the disruption Korf KB will conduct a second reading to establish whether the undesirable influence levels have been removed. If the problem has been resolved, periodic check-ups will remain necessary to monitor the situation for possible changes. After all, this particular location is a vulnerable spot.
Another phenomenon is AC-influence, which is generally caused by high-voltage grids. The large induction fields around high-voltage networks can induce high AC-potentials on the pipeline. As a result, the pipeline touch safety may be compromised. There is also the risk of AC-corrosion of the pipeline if the potentials exceed 4V. Since the induction levels fluctuate through time and specifically increase whenever the power grid is more heavily burdened, 24-hours measurements are desirable. NEN3654 provides guidelines for AC-infuence.
Korf KB can execute tests to determine the extent to which the pipeline is affected by high-voltage grids, and document its findings in an advisory report. Contact us for a quotation based on your requirements.