Recently information on disasters related to and caused by breakdowns in oil and gas trunk pipelines have been appearing with increasing frequency in the mass media. These occurrences are related to the progressive growth of flaws in operational pipes when the flaw dimensions exceed critical values. If a pipe is free of flaws initially, it can operate for many years until flaws nucleate. If a new as-manufactured pipe contains even insignificant flaws, they continue to develop during operation until the complete breakage of the pipeline caused by dynamic stresses. Because of this, considerable attention has been given to the quality control of pipes. At manufacturing plants 100 % of the produced pipe are inspected by combined techniques of nondestructive quality control. The magnetic fluorescent-penetrant inspection of pipes end faces (machined bevels for subsequent welding) is one of the principal stages of the inspection. The presence of flaws of any orientation at a pipe face is unacceptable. Possible flaws emerging at the faces surface include separations, expanded nonmetallic inclusions, and cracks of any orientation. Usually, a flaw whose extent is 1/8' (3.2 mm) is inadmissible. The use of magnetic fluorescent-penetrant inspection for solving this problem is not accidental since only this method provides sufficiently high sensitivity during high levels of testing with relatively simple equipment. To find flaws by magnetic-powder testing, in general, and by fluorescent-penetrant inspection, in particular, a magnetic field should be induced at the inspected surface. The field should be parallel to the surface (tangential field) and directed transversely to a flaw. Since the orientations of flaws at the pipe-face surface can be different, the magnetic-field direction should be varied in time. This is achieved by inducing a rotary magnetic field at the inspected surface.
Magnetic fluorescent-penetrant inspection of end faces of pipes during in-line production
Magnetische Fluoreszenz-Eindringprüfung der Endflächen von Rohrleitungen zur Betriebsprüfung
Russian Journal of Nondestructive Testing ; 41 , 3 ; 166-169
2005
4 Seiten, 3 Bilder, 6 Quellen
Article (Journal)
English
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