METHOD FOR FLAW DETECTION OF MAIN PIPE-LINES IN SECTIONS PREDISPOSED TO CORROSION CRACKING UNDER VOLTAGE Russian patent published in 2005 - IPC

FIELD: methods for flaw detection of pipe-lines, applicable for inspection of pipe-lines in sections predisposed to corrosion cracking under voltage.

SUBSTANCE: after removal of the insulating coating from the pipe surface and before shooting of stress-corrosion defects of the sections of their surface with visible deposits of corrosion products containing siderite are determined loose corrosion products are removed from these sections. Shooting of stress-corrosion defects is carried out by an edgy-current, or magnetic-field, or magnetic eddy-current flaw detector by detection and separation of zones, in which the values of readings of the used flaw detector exceed the mean values of the given flaw detector in the defectless section of the pipe by more than 2.2 times. The point with the maximum value of readings of the used flaw detector is determined for each separate zone, and the section including this point is scraped bright to metal. The depth of the stress-corrosion defect is determined by a repeated registration of the maximum value of readings of the used flaw detector. The values of readings of the used flaw detector noted before scraping are determined in the points of appearance of stress-corrosion cracks, the lesser of them is selected, which is used as a criterion value for restriction of the zone of the pipe surface, the values of readings of the used flaw detector inside which exceed the found criterion value. The length and width of the stress-corrosion defect are determined by projecting of the restricted zone of the pipe surface onto the longitudinal and circular generating lines of the pipe with a subsequent measurement of the dimensions of the obtained projections.

EFFECT: reduced area of the inspected surface of the pipe-lines and scraped defective sections.

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