Please show me some case study or other document that shows damage to copper water pipes as a result of AC current flow.
As I tried to say before, current on a copper water pipe doesn't cause a problem, but when the current such as a lost neutral raises the copper above Earth potential it will. place any conductive metal in Earth and put a voltage on it, that also has a return though earth and see how long it will last, this is the same problem with stray current/voltage in a Marina that can dissolve a metal boat hull, even a copper one.
Here is one statement on this from copper.org:
Other factors that could promote underground corrosion of copper include:
Oxygen differential concentration cells. Preferential corrosion is sometimes found on the underside of copper tubes because they are in contact with undisturbed soil where the oxygen content is reduced, in contrast to the upper portion of the tube which may be exposed to aerated backfill where oxygen content is high.
Variable aeration characteristics. These depend on particle size and distribution, the degree of compaction, and the drainage characteristics of the soil or backfill material.
Deicing practices. If the chloride content of the soil is elevated because of deicing (thawing salts for roadways and side walks) the metal becomes more anodic than the areas where the chloride content of the backfill material is lower.
Stray currents. Direct current (DC) from impressed cathodic current corrosion protections systems or from the grounding of alternating current (AC) systems to the underground copper service can be detrimental.
From this site:
prevent_corrosion_cu_tube_buried.html
I'm still searching for other info, but I have personally seen this happen many times, but every time there was an elevated voltage on the pipe, I have also see where copper ground rods were almost completely gone from the very same thing.
Passing current through the pipe will not cause this, but elevating the voltage on the pipe above Earth potential will.
I can't answer why its more prominent when the elevated voltage is coming from a bad primary neutral connection, but it seems to be, as in 4 cases 3 of them just had the water company replacing the water pipe with plastic then people started getting shocked so we were called, and the reason they had the water pipe replaced was of holes in it.
in one case I looked at the bad pipe they had left behind, and it looked like it was immersed in acid, had green corrosion all over it, and was eaten almost all the way through.