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FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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IDEAL<br />

BEND<br />

FIELDS<br />

MEASURED<br />

BEND<br />

FIELDS<br />

5 ky<br />

Sky<br />

- 85 -<br />

Figure 3: Magnetometer radial and axial magnetic field component profiles above<br />

a real pipeline joint before and after cold bending show almost ideal<br />

field patterns after. The more complex patterns before arise<br />

because this joint consists of two joints factory welded together<br />

and there are small relict poles near the center of the double<br />

joint. The stress induced changes are a significant percentage of<br />

the earth's field itself and much greater than the natural variations<br />

in the earth's field which are normally less than 100 gamma in<br />

a day.

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