Clarifying question about chloride ions, water softening & corrosion
A traditional softener has a zeolite resin that "holds" positive ions. When it is charged the Na ions fill the resin. Then in service , the positive ions - Ca , Mg , etc , exchange places with the Na ions, putting Na in the water . In theory the back flush of the softener after charging, removes the Cl ions. So that in service the only Cl present would be what is in your raw water as the Cl is not affected by the softening. Water corrosion results from conductivity ( any ions) and oxygen; Although Cl  ions are especially active. Generally "waters" leave a CaCO3 type scale that forma a protective layer ( scaling ) that  reduces corrosion. Serious evaluation of water corrosion looks at the water "scaling index" to get a initial idea of how corrosive it may be. Softening water reduces the scaling index and promotes corrosion . I removed a softener from one house I owned for that reason; However it was Lake Michigan water which has a very good scale index - enough to be protective but not enough to restrict water flow. I also had to replace a couple sections of copper pipe that had corroded through in the 20+ years the softener had been in service. On the other hand , softeners are useful in very hard natural waters.