Pipeline electrochemical methods

Cathodic protection is an electrochemical method of corrosion control that has found widespread application in the protection of carbon steel underground structures such as pipelines and tanks from soil corrosion. The process equipment metal surface is made as the cathode in an electrolytic circuit to prevent metal wastage. 

The effectiveness of cathodic protection can be accomphshed by monitoring the pipeline potential using the close interval potential survey (CIPS) method or by using direct current voltage gradient (DCVG) or IR coupon techniques. Also, physical and electrochemical methods can be used to estimate the corrosion rates of a cathodicaUy protected system. 

Considering the good decontamination results achieved by the above mentioned equipments the development of the electrochemical method has been extended for the decontamination of the main pipeline. 

While the anodic oxidation of the zinc coating gives some protection to steel structures, the problems arising from the rusting of steel which is in prolonged contact with seawater are serious. A successful protective measure is to attach metal blocks to, for example, undersea pipelines, the metal being chosen so as to function as an anode in an electrochemical cell in which the seawater is the electrolyte and the Fe of the pipeline is forced to be the cathode. This method of protection (known as cathodic protection) is... 

One method of getting around these problems is to use a small working electrode coupon connected to the pipe. The size of the electrode is based on a reasonable estimate of the holiday sizes on the pipe. The polarization curve is obtained by observing the potential on the known electrode. Such data must be evaluated carefully, since it represents only one point. On a long pipeline, several test locations should be evaluated. For more details on electrochemical polarization, the reader is advised to consult Refs 39 to 41 and 42. 

Cathodic protection is widely used in classic and atomic power plants, oil refineries, chemical works, and for the protection of gas and water pipelines and other metal structures. Excellent results are obtained by this method during anticorrosion electrochemical protection of reactors, tanks, pipelines (external and internal surfaces), pumps, coolers, heat exchangers, etc. Con-... 

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