In-Service Degradation of the Pipe Steel of Grounding Anodes
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IN-SERVICE DEGRADATION OF THE PIPE STEEL OF GROUNDING ANODES О. H. Arkhypov,1 D. О. Koval’ov,1, 2 D. І. Usov,3 О. V. Lyubymova-Zinchenko,1 and Т. P. Venhrynyuk4
UDC 17620 178.620.181
We analyze the regularities of changes in the mechanical and electrochemical characteristics of steel grounding anodes in the installations of cathodic protection of pipelines for 20 yr of operation. The grounding anodes were made of Du159 pipes (20 steel) after their operation for 20.5 yr as a part of a pipeline. The obtained results are important for understanding the degradation processes running in pipe steels during their long-term operation. Noticeable changes in the electrochemical properties were not discovered, which is important from the viewpoint of stability of the functional characteristics of anodes. Keywords: anode, degradation, long-term operation, strength characteristics, impact toughness.
The reliability of the branched system of oil-and-gas mains in Ukraine depends, to a great extent, on the efficiency of their electrochemical protection against soil corrosion in complex with insulating coatings. The most dangerous manifestation of this type of corrosion is the initiation and propagation of stress-corrosion cracks, which can be difficultly detected and monitored. It is also known that the long-term operation of structural steels causes the degradation of the metal, which manifests itself in deterioration of its mechanical properties [1–7]. Cyclic loads accelerate this process and the characteristics of cyclic corrosion crack resistance are especially sensitive to the in-service degradation of pipe steels [8, 9]. Special installations are used for the purposes of cathodic protection. The grounding anode is one of the main elements of these installations. The choice of this anode and the method of its mounting are important factors for the effective operation of these installations. It is possible to use both metallic (steel, titanium-dioxide manganese, and iron-silicon) and nonmetallic (graphite, carbon, etc.) grounding anodes. Steel grounding anodes are used especially extensively. They are made of a various structures both in the as-delivered state and after long-term operation (pipes, rods, channel bars, etc.). As a disadvantage of steel anodes, we can mention their high rate of dissolution equal to 5 kg / A⋅yr in the presence of coke filling and two times higher in the absence of filling. The resistance of the anodes increases with time and it becomes necessary to replace them. The aim of the present work is to study the behavior of the mechanical and electrochemical characteristics of the metal of pipes after operation first as pipelines and later as metallic anodes. Note that these investigations are also of interest from the viewpoint of improvement of the general understanding of the phenomenon of degradation of pipe steels.
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Dal’ East-Ukrainian National University, Severodonets’k, Ukraine. Corresponding author; e-mail: [email protected].
Severodonets’k Linear-Production Administration of Gas
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