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Iron and steel act differently. Steel objects may take
on a permanent magnetism, which may not line up with the
Earth’s field, and may be much stronger in intensity. Magnetic
survey pins, for example, can be found at a distance of several
yards/ metres. A buried steel rod, orientated vertically may
appear to have only one magnetic pole, either North or South,
as the opposite pole maybe sufficiently deep as not to show
up at all.
Where iron or steel pipe work runs across a site, this may
produce a series of north and south poles along the length
of the pipe. Where iron pipe has flanged joints each section of
pipe may behave as a separate magnet. The joints may show up
on the surface as an abrupt change from North to South. For this
reason the M-Scan has a ‘flange’ symbol which appears
on the display whenever there is a change from North to South
or vice versa. With careful use of the M-Scan, and knowledge of
the pipe-section lengths, it may be possible to locate the flanged
joints. In some industries it can be useful to target excavations
on the pipe joints where leaks may develop.
Steel pipes can also display magnetic reversals along a single
length which do not always appear at joints or junctions.
This is due to the pipes having taken on permanent
magnetism during manufacture or use.
Figure 4 An iron pipe run may appear as a series of long
bar-magnets with abrupt changes from North to South
at the joints or flanges of the pipes.
Application Note 2.
How Objects Appear to a Magnetometer
Summary of Contents for M-SCAN
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