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PLATTLINE Zinc Ribbon Anodes

Technical Articles

Technical Article #3 - A.C. Mitigation Installation

It is common for a pipeline and an existing powerline touse the same right of way area to minimize land use, reducedamage to the environment and to help reduce installed costs. Alternating Current, power arching and stray currents maydevelop due to the proximity of the pipeline to the power line.This, in turn, is hazardous to personnel constructing, operatingand maintaining both systems, as well as possible minor tosevere damage to the pipeline itself.

ANR Pipeline Company, located in Detroit, Michigan, hassuccessfully designed the use of PlattlineT Zinc RibbonAnodes for Mitigation of Alternative Currents between a 24"pipeline and two 345kv transmission lines operated by theNew York Power Authority. The above two systems areapproximately 80 feet apart throughout the 154 miles fromNiagara to Syracuse, New York. Studies performed for theEmpire State Pipeline determined that the transmission linescan attain maximum values on the order of 200 to 250 volts inat least three locations if no mitigative measures were present.With the following mitigative designs, the maximum predictedmagnetically induced pipeline potential is reduced to 70 voltsand less than 44 volts along approximately 98% of the rightof way. The touch and step voltages do not exceed 15 voltsat any location during worst case steady state conditions,meeting ANSI/IEEE Standard 80 safety criteria.

According to NACE Standard RP0177-83, RecommendedPractice in Mitigation of Alternating Current & LightningEffects on Metallic Structure and Corrosion Control Systems, 4.2.1. 30 volts ac (RMS) open circuit or a sourcecurrent capacity of 5 mA or more, through 1500 ohms, will beconsidered to constitute an anticipated shock hazard.

Pipeline Application

A pair of Plattline Standard, Type II Zinc Ribbon Anodes were buried 6' deep and 38" apart; one on either side of the pipeline. See Diagram 1. At two specific sites where there were "hot spot" from soil resistivity testing, vertical rods were connected to the ribbon anodes. These 30 foot, 3/4" diameter galvanized steel rods were connected in an alternating pattern. See Diagram 2.

Gradient Control Grid Application

The second phase of safety control was the construction of 3 types of gradient control grids which reduces the touch and step voltages that occur at main line valve stations. These stations are the only locations where exposed pipeline metal exists. The main grid conductor is made of cut lengths of Plattline Standard Type II Zinc Ribbon Anode and crimped either with copper rings or cad welded in place. This grid is then buried approximately 1.5 feet from the surface with a layer of crushed stone (6 inches thick) over the entire grid for maximum drainage and personnel protection. A fence is then constructed around each grid. See Diagram 3.