Estimating the technical state and safe operational life of pipelines from the results of in-tube nondestructive testing

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Estimating the technical state and safe operational life of pipelines from the results of in-tube nondestructive testing

Miroshnichenko, B.I.

The testing technique for examining the state and safe operational life of pipelines containing corrosion and stress-corrosion flaws is considered. This technique is currently used to examine the state of pipelines of OAO Gazprom. This technique is based on the processing and analysis of the database on the in-tube inspection of gas pipelines. For analysis of corrosion flaws, the first repeated NDT should be performed after four years and the following NDT should be performed after six years to detect nucleation of new corrosion sources and to confirm or correct the previously found values of the corrosion rate. For analysis of stress-corrosion flaws only at the segments of gas pipelines containing previously detected flaws, NDT should be performed after two years. For all other stress-corrosion flaws, NDT should be performed according to a schedule for analysis of corrosion flaws. In conclusion, it is necessary to mention the actual periods of in-tube inspections based on the experience in various countries: In the United States, all main gas pipelines are inspected once per 1-3 years, but the inspections are limited only to corrosion inspection. In Canada, in-tube inspection of all main gas pipelines is performed once per 2-3 years to test corrosion and periodically to test stress-corrosion. In Germany, regular in-tube stress and stress-corrosion inspections are not performed. In Russia, in-tube inspections of all main gas pipelines of large and medium diameters with 100 % corrosion and stress-corrosion testing are performed once per 7-8 years. In Kazakhstan, in-tube inspection with 100 % monitoring of corrosion and selective monitoring of stresscorrosion is performed once per 6 years.