Experimental Investigation and Simulation of Magnetic Flux Leakage from Metal Loss Defects

Abstract

Magnetic flux leakage (MFL) principle is widely used in detecting defects in cross-country pipelines. The tools based on the MFL techniques termed as instrumented pipeline inspection gauge (IPIG) are frequently used as per statutory requirement. The tool identifies the location of metal loss and also characterizes the size of metal loss defects in terms of length, width along circumference and depth in terms of percentage loss. Tool velocity in terms of frequency of data acquisition is important parameter whose effect on the MFL signal and on the defect quantification has been studied. Operation of linear pull through rig under various combinations of MFL tool parameters such as velocity, frequency and spatial sampling has been developed. A set of experiments by varying velocity from 0.25 to 2 m/s keeping frequency constant at 450 Hz have been carried out. MFL signals obtained from all known defects have been analyzed for its nature and quantifying the dimension of defect. The effect of velocity on individual dimensions of the defect has been studied in this work. Within the limitation of the experiments carried out, the present work indicates that smaller defects cannot be reported with better accuracy. Also, the velocity is seen to have a significant effect in characterizing the length of the defect using IPIG especially for defects of larger area.