Study of corrosion cracking of the main oil & gas pipelines
The article describes results of researches of stress corrosion cracking (SCC) under operating conditions (Western Siberia, the Urals, the Ufa plateau), and also studying of physicomechanical characteristics, steel microstructures and impurities by sulphidic inclusions of metal of refused oil and gas pipelines. Researches showed that physicomechanical characteristics of metal corresponded to standard requirements to trumpet steels. The X-ray structure analysis of deposits showed that in their structure there are oxides and iron carbonates. Microhardness distribution near a colony of cracks similarly to distribution for single cracks. Computer modeling intense the metal deformed a condition for a single crack and their colony is carried out. It is revealed that the colony of cracks is less dangerous, than a single crack. However the loadings created at carrying out a stress dough, do not influence stable development of SCC for the smallest cracks in colony which at further operation of the gas pipeline can lead to its destruction. Analytical dependences of kinetics of destruction and their parameters, allowing to define a residual resource of the pipeline having single cracks or their colony are found. Examples of such calculation are given. Studying of electrochemical behavior of samples of steel from focal zones typically for SCC showed that at low temperatures for course of SCC it is necessary to break a bigger power barrier, than at high temperatures. Thermodynamic stability of X70 steel in the corrosion environment decreases with increase of mechanical tension or increase in number of cycles of loading. For the quantitative description of this process analytical dependences are found and their parameters are defined. Key words:
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mechanical-chemical activity; polarizing curves; stress corrosion cracking; stress strain behavior; three-electrode electrochemical cell; коррозионное растрескивание под напряжением; механохимическая активность; напряженно-деформированное состояние; поляризационные кривые; стресс-тест; трехэлектродная электрохимическая ячейка References to this article (GOST) A.G. Gareyev, O.A. Nasibyllina, R.G. Rizvanov. Study of corrosion cracking of the main oil & gas pipelines // Electronic scientific journal "Oil and Gas Business". 2012. №6. P.126-146. URL: http://ogbus.ru/authors/Gareev/Gareev_2.pdf