Exploration of Physical and Chemical Properties of Steel of Long-Operated Pipelines and Estimation of their Remaining Safe Service Life
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Pavel Revin
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The total length of the linear parts of Russian oil major pipelines is about 46 000 miles and include over 4000 miles circumferential welded seams and approximately 47 000 miles of axial joints. Early 1988, a simple theory of safe operation of “aged” pipelines was developed. The core idea was “the designed pressure should be reduced in proportion to the pipeline’s age”. Practical application of this theory caused reduction of the oil pipelines’ throughput capacity by 30%, so it became a deterrent for the increasing production. Since 2000 Russia is paying the highest attention to performing research and experimental aimed at exploration of actual mechanical and chemical properties of steel of both long-operated and newly constructed oil pipelines. Transneft R&D, LLC is the leading Russian organization in this sphere. Meanwhile Transneft Diascan, JSC is the biggest Russain developer of pipeline non-distructable control and diagnostic technologies. 2000-2002, the research was focused on pipe steel ageing. Starting from 2002, its scope was expanded to include studies on evaluation of service life and durability of the long-operated pipelines. It has been proved that the pipe steel properties change as follows: 1) smaller degree in the course of operation, as the low-cycle loadings have insignificant effect; 2) steel properties degrade: - through the manufacturing cycle; In the age-defect areas mechanical properties degrade significantly; high sulfur steels suffer significant (by 1.5 - 2 times) reduction of impact resilience, ultimate stress limit and yield point.