The method of in-tube underground magnetic nondestructive testing is based on detecting the magnetic field that leaks from a pipe wall in the vicinity of surface and subsurface flaws. The phenomenon underlying the method is as follows: If the magnetized segment of a pipe contains a discontinuity, some part of the magnetic flux leaks outside the pipe wall and may be detected by a sensor located near the inner surface of that wall. The first attempts to solve the problem of the large number of cases in which pipes of underground trunks were damaged as a result of either general or stress corrosion began in the United States in 1956. These attempts included design and development of in-tube pig flaw detectors for inspection of underground pipelines. On the basis of the experience collected over many years both in Russia and abroad during in-tube testing of gas pipelines [11], some conclusions can be drawn. For example, results of tests conducted from 2000 to 2004 may be generalized for a sample of stress-corrosion flaws. In-tube inspections were conducted in western Siberia and in the northern and central parts of Russia; the total length of the inspected pipelines was 45053 km. A distribution of the in-tube inspections by year is shown in Fig. 9. The in-tube inspections were conducted in 530-, 720-, 820-, 1020-, 1220- and 1420-mm-dia gas pipelines. However, since the sample of flaws in small-diameter gas pipelines is insignificant, statistical analysis has only been performed for large-diameter pipelines (1020, 1220, and 1420 mm) (Fig. 10). Note that the largest number of flaws was detected during the first year of operations of pig flaw detectors with transverse magnetization (Fig. 11). Later, even though the annual amount of testing increased, the number of detected flaws remained at virtually the same level. This observation may be explained by the fact that, during the first year, gas pipelines were inspected in the north, where stress-corrosion is the strongest damage factor. The geography of inspections was later expanded and flaws were detected in pipelines in central Russia, but the number of flaws was significantly smaller. Statistical analysis involved certain factors and their effect on the occurrence of stress-corrosion flaws. The following factors were taken into account: the length of a pipeline segment, the pipe perimeter, the pipe manufacturing method (longitudinal welded one- and two-seam pipes, spiral welded, and seamless pipes), the soil and climatic environment of a pipeline, the pipeline operating life, the pipeline diameter, and the pipeline wall thickness.


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    Title :

    The magnetic method for in-tube nondestructive testing of gas and oil pipelines. The past and the present


    Additional title:

    Die magnetische Methode zur zerstörungsfreien Rohrinnenprüfung von Gas- und Ölpipelines. Die Vergangenheit und die Zukunft


    Contributors:

    Published in:

    Publication date :

    2006


    Size :

    12 Seiten, 19 Bilder, 11 Quellen




    Type of media :

    Article (Journal)


    Type of material :

    Print


    Language :

    English