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Matco Associates Inc. Specialists in Materials Engineering, Corrosion and Failure Analysis

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The Corrosion Forum: How you determine the presence and extent of graphitization in cast iron water mains?

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    • CommentAuthorzee
    • CommentTimeFeb 8th 2008 edited
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    Matco provides methods for the non-destructive detection of graphitization corrosion in gray cast iron, based on magnetic force sensing and on magnetic flux density measurements.

    In the magnetic force sensing scheme, an external field is applied by a permanent magnet, at the end of a rigid beam. The hand held sensing apparatus is designed so that, when placed against a pipe, the magnet is in close proximity to the test surface. Measuring the deflection of the beam (by, for example, a strain gauge) gives an indication of the force of attraction between the magnet and the metal. The decreased permeability in graphitized regions will result in lower flux density through; and measurably lower magnetic force over; graphitized regions as compared with intact regions.

    Note that such a force-based device will be sensitive to the orientation in which it is used, as the weight of the magnet itself will deflect the beam more or less, depending on the orientation. Electronic compensation for this effect can be provided, for example, by incorporating low-cost MEMS accelerometers into the sensing device.

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