Case Studies

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Remote Monitoring Improves Performance-article link to July/August 2009 Integrated Solutions Magazine featuring NTG.

 

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Proactive AC Mitigation Monitoring Increases Safety and Pipeline Integrity

Underground pipelines are prone to corroding, leaking, rusting and other damage, which can potentially cause dangerous oil or gas leaks. To prevent this, Cathodic Protection (CP) rectifiers are installed at various points along a pipeline. The CP rectifier delivers an electrical current to keep the metal from migrating into the soil. Pipeline technicians are dispatched every 60 days to check the CP rectifiers to verify proper operation. However, if something happened to a rectifier immediately after an inspection, no one would know there was a problem until the next inspection, two months later. This poses a huge risk such as dangerous leaks that could cause environmental catastrophes as well as costly fines that could quickly escalate into the millions of dollars.

Problem
Problem Using Elecsys Pipeline Watchdog remote monitors, a major pipeline company has been continously verifying the operation of AC mitigation systems on pipelines throughout the Chicago, IL region for several years. While troubleshooting erratic readings at some of the test stations, it was discovered that the AC mitigation on the pipeline had failed and that excessive AC voltage was affecting the measurements at the stations. In addition, there was growing concern about corrosion due to AC current density levels.

Solution
To resolve the issue, the pipeline company requested that Elecsys add the capability to measure induced AC voltage to the remote monitoring equipment in the field. Test sites were set up in locations known to have excessive induced AC voltage levels. Mitigation systems were already in place at the sites selected, and induced voltage levels were reduced to below 15 volts AC. The Elecsys P2S-AC monitoring/data-logger systems were installed along with dual coupon test stations to measure induced AC voltage potential and AC current density. Typical test point measurements, including DC coupon to soil potential, instant off potential, and native coupon potential were also measured. The monitoring systems were configured to log all test site values at one minute intervals. Data was stored on 2GB cards inside the devices. Every three hours readings were transmitted via GSM cellular telemetry to the secure Pipeline Watchdog web site. Additionally, any out-of-range alarm readings were transmitted to the website for immediate notification to the pipeline technician. The pipeline company requires mitigation to be below the NACE (National Association of Corrosion Engineers)15 volts safe touch standard, and AC current density below 20A/m². Using the graphing tool on the website, the technician was able to verify over time whether the mitigation was consistently reducing the AC voltage and current to acceptable levels. To test a mitigation failure, the system was disconnected at one site location for a two day period. The graphs in Figures 2 and 3 are screen shots from the Pipeline Watchdog one-click graphing tool. These graphs clearly show the changes in induced voltage and current density resulting from this failure simulation. Of particular note is the daily fluctuation seen in the readings.

The unmitigated voltage readings shown in Figure 1 were often below the safe touch standard of 15 volts during the test period, yet were also frequently in the danger zone. Periodic measurements by field technicians, depending on the time of day made, may fail to detect frequent unsafe conditions. Additionally, AC current densities displayed in Figure 2 remained above the desired maximum level of 20A/m² even when the induced voltage level was in the safe range.

Conclusions

Conclusions A wide range of variables affect the AC voltage and current levels on pipelines co-located with high voltage transmission lines. This combined with the occasional failure of AC mitigation systems present significant challenges to the pipeline operator. The continual monitoring of induced AC voltage potential and AC corrosion current density in this field study provided an accurate view of the AC mitigation system effectiveness. Immediate notification of out-of-normal values provided the pipeline operator with the necessary information to respond quickly to system anomalies. The perpetual data record allows the operator to review and graph data to identify trends over time. The capability of the system to store all readings in memory for retrieval over the web gives the pipeline technician a complete profile of the induced AC at test locations. Data trends are easily produced so proactive responses to changes can be planned and instituted. Continual potentials and AC corrosion current density monitoring of both induced AC voltage should be an integral part of any comprehensive AC mitigation system design. To learn more about the Elecsys Pipeline Watchdog P2S-AC Remote Monitoring System or other remote monitoring devices, contact us at 913-888-5222 or visit us on line at www.elecsyscorp.com.

Copyright 2010 Elecsys Corporation