Limitations of Magnetic Fields
What are the Limitations of Magnetic Fields?
Here is a list of explanations of the limitations of magnetic locating.
The main disadvantage is that in most cases the research shows that magnetic locating in buildings doesn't give reliable, consistent results for most situations.
Limited to Ferrous Materials: Cannot detect non-ferrous metals like copper, aluminum and others, which can limit its application in certain utility locating tasks.
Martensitic stainless steels (which have a ferritic microstructure) are magnetic. Austenitic stainless steels contain nickel and are non-magnetic.
Interference: The presence of large ferrous objects or heavily mineralized soils can sometimes cause false signals or make locating more challenging.
Depth Limitation: While effective at locating objects at various depths, locating depths is still limited compared to some other surveying technologies.
Figure 13. Estimated magnetometer response in gammas to objects of different mass at various depths (Benson, et al., 1984).
Figure 11. An example of a contour plot of a crushed buried drum (J. Ursic, EPA Region 5).
Typical locate depths are usually upto about 3 meters deep, and for larger masses like well casings can be detected upto about 6 meters.
Requires Interpretation: The operator must interpret the audio and visual signals to pinpoint the exact location, which can introduce a margin of error based on the operator's experience.