The pipe on the hot side is what let go. I had a water test done about 20 months ago then I installed a water soften ,we were getting a little bit of white stains on the taps. Now I think the reason for the failure is when I put the sidearm on I had to remove the back flow valve in the outlet line .doing this I removed most of the plastic liner on the top end of the tube,it is there where the line let go . I had the side arm returning to the very top of the tank ,I have now moved it to the pressure relief valve . I also contacted the outfit that does the plumbing at my work they said that on these new tanks if the plastic liner gets compromised the tank will fail in a few years . One more thing not sure it had anything to do with this ,but when I installed the soften the tube had a Crack in it. It filled the heater and all the lines full of the median. I flushed the system but still had some of that crap floating around ,had to install a spin down filter on the hot side of the tank to catch it.
Also reading on line that some are saying that a softener also shortens life of the heater not sure on that one
All my plumbing to and from the heater is pex thinking that should not be electrolysis
Guess the saving on the hydro bill for 5 seasons is now put back into a 400 heater lol
Vernn