Indian Journal of Science and Technology

Abstract

Background/Objectives: The purpose of this work is to develop a new method of non-destructive inspection for measuring defect parameters during the in-line inspection, without prior preparation of internal surface of the pipe. Methods: The basic principle behind this method is to form a magnetic field inside the pipe. In cases which show mechanical damage on the pipeline inner or outer surface, increased magnetic field amplitudes appear. Measurements of the value of the magnetic field amplitude along the pipeline inner surface enable to detect the defect occurrence and to evaluate the defect transverse dimensions and depth based on the magnetic peak height and width. Findings: The article provides a detailed description of the magnetic field changes in the defect localization area and presents an algorithm for determining the pipeline wall loss. A measuring sensor is selected; the choice of sinusoidal alternating current passing through the pipe body is justified and the principle of the developed method implementation is described. Also, an experiment has been conducted in which it was found that the magnetic field amplitude depends on the defect depth. The smaller pipeline wall loss in the defect zone, the higher the magnetic field variation is. Thus, the experiment confirms the validity of the noncontact magnetic method for pipeline NDT with alternating magnetization of metal. The novelty of the method lies in the possibility to conduct the non-destructive inspection of the pipeline without prior surface preparation, through a layer of corrosion and slime deposits, providing the clearance up to 20 mm between the pipe wall and the measuring sensor, with the probability of defect detection making 0.9. Applications/Improvements: This method provides solution for timely inspection of corrosion damage in subsurface pipelines of small-diameter heating networks (DN200, DN400) of housing and public utilities in places inaccessible for external inspection.

Keywords: Alternate Magnetization, Defect, In-Line Inspection, Magnetic Field, Non-destructive Testing, Pipeline, Slime Deposits, Thickness Measurement