13. A coating fault often gives an apparent rise in the conductor signal not fall, beyond the defect location, a result of phase summing of continuing and escaped signal currents. This can result in fault indications where none actually exist.

14. Because subsequent analysis of results is required, cannot investigate problem areas in detail during actual survey. Must in most cases, come back to this using Pearson Technique.

15. High iron ore content in soil affects results.

16. Affected by AC/DC Traction Systems. Cannot be used in congested areas such as under city streets. Current mapping equipment gives poor results in congested areas.

17. In the Pearson technique, the sensitivity of Surveyors ears to distinguish changes in signal level or sensitivity of meter/recording device limits the techniques application.

18. Linking Operators together in the Pearson limits close examination at fences, ditches, hedges, through undergrowth and can be very dangerous at road and rail crossings.

19. Electromagnetic techniques do not work where the soil resistivity is high.

20. Cannot be used satisfactorily to inspect parallel pipelines because the signal is induced onto the other parallel pipelines not subject to the inspection. This could lead to inspecting the wrong pipeline particularly if the lines eventually separate in different directions.

21. All AC techniques are not very good at delineating coating faults such as crown cracking in coal tar, or many small faults in close proximity such as ruffling in Tapes. They appear as high background noise.

22. Cannot be used on bare pipe.

23. Electric shocks are possible due to high voltages sometimes used by the transmitter.

24. Does not distinguish between a coating fault and extraneous metal in the pipeline trench so can indicate faults where none exists.