Pipelines long-line currents

Although iron pipes suffer from the same corrosion risk as steel pipelines, associated with the generation of a galvanic cell with a small anode and a large cathode, the risk is mitigated for iron pipelines because the electrical continuity is broken at every pipe joint. For this reason long-line currents are uncommon in iron lines and cathodic protection is rarely necessary. It also accounts for the ability to protect iron lines by the application of nonadherent polyethylene sleeving . 

On bare or ineffectively coated pipelines where long-line corrosion activity is of primary concern, the measurement of a net protective current at predetermined current discharge points from the electrolyte to the pipe surface, as measured by an earth current technique, may be sufficient. 

The first anode installation for the cathodic protection of gas pipelines in New Orleans consisted of a 5-m-long horizontal cast-iron tube. Later old tramway lines were used. Since in downtown New Orleans there was no suitable place to install impressed current anodes and to avoid detrimental effects on other pipelines, Kuhn recommended the use of deep anodes which were first installed in 1952 at a depth... 

With long-term interference from operational currents of high-voltage power lines or railway power and supply lines, the contact voltage must not exceed 65 V [9]. The relevant operational current has to be stated by the operator responsible for the basic calculation. If the calculated pipeline potentials are above 65 V, connection with grounds is always necessary. 

Materials that are currently being transported over long distances by pipelines include coal, iron ore, limestone and copper concentrates. For hydraulic transportation over long distances to be economic, it is necessary that solids are reduced to an optimum size. To keep solids in suspension, a certain minimum velocity must be maintained. This velocity increases with the size of the particle. The increased velocity has a bearing on the wear life of the rubber lining. Wear in a slurry pipe line system increases with the cube of the velocity as well as increasing directly with the particle size. 

Zinc has long been used in the form of cells and electrodes in pipeline systems subject to severe electrical fault currents as from lightning or from induced ac from overhead electrical transmission systems. Since gas piping in an industrial complex often does not have cathodic protection, the underground gas pipe system may have flanges or couplings to provide electrical insulation at the property line of an industrial gas consumer. 

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