AC Stray Current Mitigation - A Success Story

Abstract A 20" gasoil pipeline was to be constructed from Sokhna Port to a Terminal at Al-Sadat area on the Suez Hurghada High Way, Arab Republic of Egypt. The 20" pipeline is a 34 Km long pipeline. The 20" pipeline runs parallel to and in close proximity to Over Head Transmission Lines. The location of steel pipelines in the vicinity of AC power transmission facilities has resulted in mutual electrical interference problems that can produce damaging effects on both utilities and an electrical hazard to pipeline personnel. The pervasive use of the utility corridor concept necessitates that the electrical interference aspects be clearly defined and guidelines to minimize the harmful effects be incorporated into pipeline and powerline specifications, designs, and operating procedures. There are three modes of AC interference that can cause damage to pipeline systems and present an electrical shock hazard to pipeline personnel, namely; inductive coupling, resistive (conductive) coupling and capacitive (electrostatic) coupling. This paper highlights the results of the AC interference study, its effects on the pipeline and the operators during the steady state and during fault current conditions. The paper also highlights the results before and after the AC mitigation measures were implemented. Methods The AC interference study together with the mitigation would start with data gathering this include; pipelines alignment sheets, pipeline design bases, Over Head Transmission Lines (OHTL) data both during steady state and fault current, pipeline coating specification and coating materials standard data, pipelines corridor obstacles and ancillary systems. These data were gathered along with some field measurements which included measurement of the soul resistivity at close intervals along the pipeline and OHTL common corridor in addition to field measurement of the steady state induced voltage along the pipeline route. The second step was to calculate the risk of AC interference in terms of; Risk to personnel during construction and operations both in terms of steady state and during fault currents. Risk of pipeline metal arcing. Risk of pipeline coating damage in addition to the risk of AC corrosion. A specialised software was used to calculate the values before and after a proposed mitigation system was done. Furthermore, post field implementation of these mitigation measures were done, results post mitigation between the software results and the actual results were compared. Results The risk of arcing was found acceptable. Damage to coating was also found acceptable. However the risk to personnel during steady state and fault current were found to have exceeded the acceptable limits of 15V AC touch potential suggested by NACE. Furthermore the fault current AC induced voltages reached an estimate of 49000 V AC. Mitigation measures managed to reduce the induced voltages to acceptable levels with a maximum mitigated value of 2.3 V AC. Novel The results obtained before and post implementing the AC interference mitigation measures were compared. Field measurements were also conducted. It was proven that the estimates of the induced vales of AC were found to be accurate with a very minor deviation.