Electrolysis was a bad term for what I was trying to say, but AC voltage between the grounding system and Earth and or water pipes can cause damage as in pitting to copper pipes the same way it does to our copper wires when the insulation is compromised, I don't know how many DB feeds to trailers I have had to repair from damaged insulation on the feeders the copper would be all but dissolved away.
I posted a few years ago about an apartment complex where people were receiving shock's in the basement apartments when they were in the shower standing on tile over concrete and touch the faucet handles, but this was an after effect because this one building had started having problems with the underground water supply lines leaking all copper, I was told it all started about a year before we were called (when the shocks started to happen) the first few times they had plumbers repair the copper main to the building it would last a few months and again they would have leaks, this complex was over 30 years old and never had a problem up till then, the shocks started happening when the plumber replaced all the piping up to the building with plastic.
On the complex property is 12 buildings each fed with there own separate water main, and electric supply from the utility, each building had a pad mounted transformer which was fed from one phase out at the street, the MV cable the utility used was a exposed concentric neutral, the one to this building had a bad C crimp connection that bonded the concentric to the MGN out at the pole, after testing at several points on the grounding system to Earth and the pad mounted transformer to Earth which all had the same voltage level of around 56 volts, we knew we had a bad return path on the concentric neutral, the utility line men can out and dug up the old MV feed and found most of the concentric neutral had dissolved also copper, their ground rod in the transformer pad was also gone and was just laying over with the bond conductor still hanging on to it, they replaced the MV feed with a new one that had a jacket over the concentric neutral, we installed new rods at the building as well as a new rod was installed at the transformer, all was fine for about 4 months then we get another call that they were getting complaints again of shocks, only this time they said the were not as severe, I went back out there and recorded a voltage of about 34 volts at the transformer pad, I called the utility engineer (friend of mine) and told him what these line men did when they connected the new concentric neutral, they had left the old bad C crimp and had just left a tail to which they butt spliced the new MV cables concentric neutral to, I guess they had moved the old C crimp enough that it made a connection for a little while but it went bad again which again put all the return current from the transformer back on the ground rods and since they were still fairly new they didn't have the voltage drop of the older ones that had almost all dissolved away, if they had and since the water pipe had been replaced with plastic, the voltage of the grounding system could had risen to the 7200 volts of the primary after they made a new connection to the MGN (this time they used two C crimps for it) we never got another call.
The first time I was there, the complex maintenance man showed me a few pieces of the old copper pipe that the plumbers had replaced and one piece had a large corroded out hole, it was I think a 1 1/2" copper pipe and beside the large hole the pipe had all kinds of smaller pin holes and pits, then he showed me a piece that was a new piece the plumber had installed to repair it before, and even this newer pipe had pin holes and pits just like the older pipe.
All the damage was on the outside of the pipes well till it went through the wall of the pipe, he even said they dug up some of the pipes at the other buildings to make sure they didn't have any problems at these buildings and said those pipes were like brand new other then discoloration but no pitting at all, only this building was affected.
Also when the plumber dug up the old street main tap the old pipe had a short piece of plastic pipe from the tap to where it connected to the pipe that went to the building so there was no continuity to the city main and is probably why there was a voltage potential difference that cause the damage, if it had been connected the return current from the transformer would probably not had been able to create enough difference of potential to cause this much damage and the bad primary neutral could have gone un-noticed for years.
This is why I always check for the voltage to Earth potential on the system grounding as you can have current on the grounding system but not have a differance of potential to Earth or very little, because the grounding can be just parallel neutral current and might cause 2 or 3 volts differance but when you see 10 volts or higher you have other problems that like in this case could be very dangerous.
It was very lucky no one was hurt or killed as the potential was there.
