Mr. Phariss you are the only man I ever heard, outside of Proctor & Gamble, to say soap is corrosive. It sure is. & I thank you for saying so.
I might suggest that it is the hydrochlorid acid and salt (NaCl) that does it.
Back in the Day, when it was OK to have algae blooms in lakes & rivers, the Nice Soap people neutralized the caustic (used to make soap) with phosphoric acid. Phosphoric acid is a rust preventatiive. The phos is a great fertilizer for algae, amongst other plants.
When we all decided to stop killing the fish, the Nice Soap people switched from phosphoric acid to hydrochoric acid. Some of you know it as muriatic acid. At some concentration, it eats the $#*! out of everything.
The Nice Soap people like to pump their product around whilst processing it. So they add salt, as in table salt, to make it flow better. Salt makes soap flow better kinda like it makes garden slugs flow better. All soap, all soap has salt in it. Soap with various orange or lemon additives is slightly more acid & Urban Legend has it, can eat a hold thru a stainless sink in a week or so , if left to its own devices.
My former employer sold a superaustenitic stainless which would tolerate all this salt plus a little acid. It was fine with us that the Nice Soap people like salt & hydrochloric acid. But we, at least I, did marvel at this pracice. I was the tech support guy, a.ka. Director of Technology.