Cathodic Protection - Stray Current

[hank999]

I have a impressed current cathodic system that includes two protected structures each operated from separate rectifiers. The two systems are not bonded together. The first structure is a series of vaults (approx. 10-ft depth) configured along a straight line. The second structure is a pipeline (approx. 7-ft deep) that runs parallel to the vaults. The two structures are separated by 140-ft. The vaults and the pipeline lie in between the anode strings for each. We are considering de-energizing the CP to the pipeline and want to avoid stray current problems. I am concerned that stray current could travel between the structures.
Question: What test should be used to determine if the pipeline or the vaults will not be adversely affected after the pipeline is de-energized?

 

[brimmer]

Whether there is stray current affecting the pipeline will have nothing to do with that rectifier being on or off, if there is stray current it will be there regardless of whether the pipeline rectifier is on or off, coming from the vault rectifier already. Remember the current will just take the path of least resistance to get back to the source, so current from the vaults could already be using the pipeline to get back to the vault area and vice versa. The way to test is to set up interrupters on the rectifiers. You can set up one interrupter on one rectifier, and take structure to soil readings on the other structure, to see if there is any influence. If there is, there is some current path. You can also set up on both rectifiers, and cycle them so they are on and off at different times, then take soil to structure readings. You could also induce current onto the pipeline, and trace the current with a mapper to see if the current leaves the pipeline anywhere (i.e. somewhere towards the vaults).