DC- or AC-tension fields in the proximity of pipelines can be highly disadvantageous for the functioning of Cathodic Protection systems. Whenever these types of tension areas are observed, immediate measurements and in some cases more extensive problem analyses have to be executed. Korf KB can take care of these activities.
DC-influenceStray currents caused by, among other factors, DC traction systems can have a highly negative effect on the Cathodic Protection system of, for example, a gas pipeline. Stray currents can be formed, for example, whenever the traction current in a railway system does not flow back to the substation via the track but via the soil. If this is the case, the currents will tend to use the gas pipe as their 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.
Apart from the scenario depicted above, stray currents may also influence the soil at railroad crossings. It is striking that in winter, after salt spreading activities, the electrical connection between the track and the soil is all of a sudden remarkably good. When this happens, the soil is influenced 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 potential may become so small that locally the pipeline is no longer sufficiently protected. As a result, the chances of corrosion increase. It is therefore highly important that influence measurements are conducted during different seasons.
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 observed that the pipeline fluctuation is higher than the soil fluctuation (or the other way round), a 24-hours measurement 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) executes these measurements and can provide an advisory report on the basis of the findings. This report is then sent to the owner of the DC-traction system, who has to take the appropriate action to solve the problem.
After solving the malfunction Korf KB will conduct a second measurement to establish whether the undesirable influence levels have been removed. If the problem has been solved, periodic check-ups will remain necessary to monitor whether the situation has not changed again. 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. Furthermore, there is 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 in this respect.