There are several reasons why this concept is probably not practical. A few are:

1. Any current flow through the permanent reference electrode above the nanoamp range will damage the electrode and/or cause a shift in the half cell potential.

2. A review of any over-the-line potential survey will demonstrate that the potential of the pipeline can vary significantly (on the order of 0.5V or more) over distances of just a 100 meters or so. Therefore, the installation of this device at one location will only be sensitive to changes in the pipeline condition over a very short distance. How exact length of this distance will depend upon the quality of the pipeline coating, but it will still be very limited.

3. The potential of a pipeline at a given location can vary quite a bit as conditions change. Potentials during a rainy season can be quite different from potentials during the dry season due to changing IR drops in the soil. Telluric currents due to changes in the earth's magnetic field (from solar storms) or local thunderstorms can also cause short term swings on the order of several tenths of volts (or more) over periods of just a few minutes.

Thank you Sir. But I would give following clarifications:

1) After your input on my earlier question on 'use of half cell for providing current' I would rather search for a voltage sensing relay in the range of required 'sensed voltage' so that no current is drawn through the half cell.

2) I am having sufficient data on 'Pipe-to-soil potential(PSP)' that has been collected periodically that suggests that the C.P. system current has been regularly modified keeping in mind that the voltage is not above -0.85V (the minimum voltage being -1.5V near C.P. station) at any point with respect to Cu/CuSO4 half cell.

3) The coating has regularly been refurbished according to requirement as indicated by periodic PSP survey. The survey has also been done prior to rainy season & data is recorded. The scheme suggested in my paper is NOT BASED ON ABSOLUTE VALUE OF PSP, RATHER IT IS BASED ON VALUE OF PSP AT EVERY 2 KMS. AS COMPARED TO THE VALUE RECORDED AT THAT SPECIFIC LOCATION (TLP) RECENTLY(that shall be my reference) so that any abnormal drop in that value would indicate the location of theft/ pilferage within 2 kms.(distance b/w two adjacent TLPs). That would give the Patrolling team AN IDEA OF PROBABLE STRETCH OF PIPELINE TO CONCENTRATE UPON, INSTEAD OF GOING FOR BLIND PATROLLING OF HUNDREDS OF KMS.

Also, in the rare case of highly moist soil the 'Voltage Sensing Relay' at that location shall be set accordingly)

Further, recently we had a Closed Interval Potential Survey(CIPS) that takes PSP of every meter of the entire stretch of hundreds of kms. of underground pipeline. So, I am planning to use the data as reference for future use.

There is a system of Leak detection based on Acoustic signals. But that is too costly & has a drawback that movement of tractors/earth movers or even transport vehicles etc. nearby also generates signals( as the pipeline is just 1 metre below the surface) that has been misleading. So, there is a general practice of manual patrolling that is very time taking & ineffective, if any how rain or watering of the fields was done it is practically impossible to identify the location by visual inspection, thus my paper may be helpful in concentrating at a much smaller stretch of land.

But I agree that my paper has a scope of refinement that can be made after actual field application having a well maintained C.P. system, good upkeep of coatings & regular monitoring of PSP values.

I had also tried to locate the leak by noting the difference in the time taken by 'Pressure Drop Pulse' to reach at nearest upstream & downstream pump stations. Please refer one of my Question regarding that.