Since magnetism is strongly stress dependent, Magnetic Flux Leakage (MFL) inspection tools have the potential to locate and characterize mechanical damage in pipelines. However, MFL application to mechanical damage detection faces hurdles which make signal interpretation problematic: 1) the MFL signal is a superposition of geometrical and stress effects, 2) the stress distribution around a mechanically damaged region is very complex, consisting of plastic deformation and residual (elastic) stresses, 3) the effect of stress on magnetic behaviour is not well understood. This paper summarizes recent results of experimental and modeling studies of MFL signals resulting from mechanical damage. In experimental studies, mechanical damage was simulated using a tool and die press to produce dents of varying depths in plate samples. MFL measurements were made before and after selective stress-relieving heat treatments. These annealing treatments enabled the stress and geometry components of the MFL signal to be separated. In general, geometry effects scale with dent depth and tend to dominate in deep dents, while stress contribution to the MFL signals is relatively constant and is more significant for shallow dents. The influence of other parameters such as flux density and topside/bottomside inspection was also quantified. In the finite element analysis work, stress was incorporated by modifying the magnetic permeability in the residual stress regions of the modeled dent. Both stress and geometry contributions to the MFL signal were examined separately. Despite using a number of simplifying assumptions, the modeled results matched the experimental results very closely, and were used to aid in interpretation of the MFL signals.


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    Title :

    Detection of mechanical damage using the magnetic flux leakage technique


    Additional title:

    Nachweis mechanischer Schädigung mittels magnetischer Streuflusstechnik


    Contributors:
    Clapham, L. (author) / Babbar, V. (author) / Byrne, J. (author)


    Publication date :

    2004


    Size :

    8 Seiten, 9 Bilder, 5 Quellen


    Remarks:

    (Nicht paginiert)


    Type of media :

    Conference paper


    Type of material :

    Storage medium


    Language :

    English




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